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Mai, Yuan Yen. "Current-mode DC-DC buck converter with current-voltage feedforward control /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20MAI.
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Alsseid, Aleisawee M. "Dynamics and control of high voltage DC grids." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=189675.
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Recently, HVDC based on VSC technology has become an area of growing interest because of its suitability in forming a transmission link for transmitting large amounts of power. M-VSC-HVDC has the possibility of being an attractive alternative to AC transmission in city centres, where underground cable transmission is preferred for safety and environmental reasons. Multi-terminal DC grids based on VSC-HVDC could be a competitive and attractive option, for many applications such as the integration of renewable energy and oil/gas platforms into the onshore grid system for supplying power to large metropolitan areas. Therefore, this thesis focuses on the control of M-VSC-HVDC and DC grids based on VSC. Firstly, a detailed non-linear model on a Power System Computer Aided Design/ElectroMagnetic Transients including Direct Current (PSCAD/EMTDC) simulation software for a 2-terminal HVDC based on VSC is presented in chapter 3. In the context of what is a complicated controller analysis and design task, the detailed analytical linear small signal state-space VSC-HVDC test system is modelled in MATLAB and is presented in chapter 3. The model should have good accuracy within the frequency range for the main HVDC control loop i.e. below 100Hz. Secondly, an eigenvalue stability study for control gains optimization is presented in chapter 4, with the use of the root locus technique. Very good matching accuracy is established in chapter 4 for the linear analytical model when compared with the detailed non-linear PSCAD test system models. A detailed comparison of the outer-loop control performance at the receiving end is presented in chapter 5. PID control (inner-loop) with d-axis current control and the DC voltage droop control (outer-loop) is confirmed to be adequate for advanced control design for an M-VSC-HVDC system and DC grid network. A 121st order MIMO small signal linearized dynamic model of a 5-terminal DC network is presented in chapter 6. The model accuracy is verified using detailed non-linear PSCAD simulation. The model has been used to study the effects of the DC voltage droop control on the dynamic and transient behaviour of the DC network. The work presented in this thesis therefore seeks to make a novel contribution by; presenting a detailed non-linear and linearized dynamic model of a DC grid based on a VSC test system. This model has significantly increased our confidence in the feasibility of DC grid networks. A higher order MIMO small signal linearized dynamic model of a 5-terminal DC network and an M-VSC-HVDC has been developed. They are the most detailed analytical models currently available. These models can be used for larger DC grids of any complexity. This thesis applies modeling knowledge boundaries to the automated building of an analytical model of a DC system and could be adapted for a very complex DC system. Two main issues regarding the implementation of the droop scheme have been investigated systematically by using the developed small signal model. Namely, the impacts and the selections of the DC droop gain and the cutoff frequency of the DC voltage droop filter. A systematic design of DC droop gains for DC grids has been presented. This thesis resolves a number of issues with developing DC grids and increases our confidence in building future complex DC transmission systems.
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Mao, Hong. "Topology and control investigation for low-voltage high-current isolated DC-DC converters." Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/RTD/id/4405.
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University of Central Florida College of Engineering ThesisHigh conversion efficiency and fast transient response at high switching frequency are the two main challenges for low-voltage high-current DC-DC converters, which are the motivations of the dissertation work. To reduce the switching power loss, soft switching is a desirable technique to keep power loss under control at high switching frequencies. A Duty-Cycle-Shift (DCS) concept is proposed for half-bridge DC-DC converters to reduce switching loss. The concept of this new control scheme is shifting one of the two symmetric PWM driving signals close to the other, such that ZVS can be achieved for the lagging switch due to the shortened resonant interval.
Ph.D.
Doctorate;
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical and Computer Engineering
216 p.
xviii, 216 leaves, bound : ill. ; 28 cm.
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Salomonsson, Daniel. "Modeling, Control and Protection of Low-Voltage DC Microgrids." Doctoral thesis, Stockholm : Elektriska energisystem, Electric Power Systems, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4666.
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Jimenez, Carrizosa Miguel. "Hierarchical control scheme for multi-terminal high voltage direct current power networks." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112039/document.
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Cette thèse traite de la commande hiérarchique de réseaux à courant continu multi-terminaux à haute tension (MT-HVDC) intégrant des sources d'énergie renouvelables à grande échelle. Le schéma de contrôle proposé est composé de quatre ‘couches’ : le contrôle local où se trouvent les convertisseurs de puissance, avec une échelle de temps de l’ordre de la milliseconde ; le contrôle primaire qui est décentralisé et appliqué à plusieurs terminaux avec une échelle du temps de l’ordre de la seconde ; un niveau de commande où la communication est prise en compte et où l’approche de Modèle du Commande Prédictive (MPC) assure la planification de la tension et de la puissance à leur état d'équilibre, pour l'ensemble du système; enfin, le contrôleur de niveau supérieur, qui est principalement basé sur les techniques d'optimisation, où les aspects économiques sont pris en compte (il s’agit du réglage dit tertiaire).Au niveau des convertisseurs, un accent particulier est mis sur les convertisseurs bidirectionnels DC/DC. Dans cette thèse, trois topologies différentes sont étudiées en profondeur: deux phases Dual Active Bridge (DAB), trois phases DAB, et l’utilisation de la technologie Modular Multilevel converter (MMC) comme convertisseur DC/DC. Pour chaque topologie, une commande non-linéaire spécifique est discutée. D’autre part une nouvelle fonction pour le convertisseur DC/DC est étudiée. Il s’agit de son utilisation comme disjoncteur à courant continu (DC-CB). En ce qui concerne le contrôle primaire, qui permet de maintenir le niveau de tension continue dans le réseau, nous avons étudié trois philosophies de contrôle: celle de maître/esclave, celui du contrôle « voltage margin control » et celle de la commande du statisme (droop control). Enfin, nous avons choisi d'utiliser le droop control, entre autres, parce que la communication entre les nœuds n’est pas nécessaire. Concernant la commande secondaire, son principal objectif est de planifier le transfert de puissance entre les nœuds du réseau, qui fournissent la tension et la puissance de référence aux contrôleurs locaux et primaires, même lorsque des perturbations apparaissent. Dans cette partie, nous avons proposé une nouvelle approche pour résoudre les problèmes de flux de puissance (équations non-linéaires) basée sur le théorème du point fixe de l’application contractive. Ceci permet d'utiliser plus d'un slack bus, contrairement à l’approche classique basée sur la méthode de Newton-Raphson. Par ailleurs, le réglage secondaire joue un rôle très important dans les applications pratiques, en particulier lorsque les sources d'énergie renouvelables (variables dans le temps). Dans de tels cas, il est intéressant de considérer des dispositifs de stockage afin d'améliorer la stabilité de tout le système. Il est également possible d'envisager différents types de prévisions (météo, charge, ..) basées sur la gestion des réserves de stockage. Toutes ces caractéristiques ont suggéré l'utilisation d'une approche MPC. Dans ce contexte, plusieurs critères d'optimisation ont été considérés, en particulier la minimisation des pertes de transmission ou des congestions dans le réseau.La tâche principale de réglage tertiaire est de d'atteindre l'optimisation économique de l'ensemble du réseau. Dans cette thèse, nous avons pu maximiser le profit économique du système en agissant sur le marché réel, et en optimisant l'utilisation des périphériques de stockage. Dans le but de mettre en œuvre la philosophie de contrôle hiérarchique présentée dans cette thèse, nous avons construit un banc d'essai expérimental. Cette plate-forme dispose de quatre terminaux reliés entre eux par l'intermédiaire d'un réseau à courant continu, et connectés au réseau principal de courant alternatif. Ce réseau DC peut fonctionner à un maximum de 400 V, et avec une courant maximal de 15 AThis thesis focuses on the hierarchical control for a multi-terminal high voltage direct current (MT-HVDC) grid suitable for the integration of large scale renewable energy sources. The proposed control scheme is composed of 4 layers, from the low local control at the power converters in the time scale of units of ms; through distributed droop control (primary control) applied in several terminals in the scale of unit of seconds; and then to communication based Model Predictive Control (MPC) that assures the load flow and the steady state voltage/power plan for the whole system, manage large scale storage and include weather forecast (secondary control); finally reaching the higher level controller that is mostly based on optimization techniques, where economic aspects are considered in the same time as longer timespan weather forecast (tertiary control).Concerning the converters' level, special emphasis is placed on DC/DC bidirectional converters. In this thesis, three different topologies are studied in depth: two phases dual active bridge (DAB), the three phases DAB, and the use of the Modular Multilevel Converter (MMC) technology as DC/DC converter. For each topology a specific non-linear control is presented and discussed. In addition, the DC/DC converter can provide other important services as its use as a direct current circuit breaker (DC-CB). Several operation strategies are studied for these topologies used as DC-CB.With respect to primary control, which is the responsible to maintain the DC voltage control of the grid, we have studied several control philosophies: master/slave, voltage margin control and droop control. Finally we have chosen to use droop control, among other reasons, because the communication between nodes is not required. Relative to the secondary control, its main goal is to schedule power transfer between the network nodes providing voltage and power references to local and primary controllers, providing steady state response to disturbances and managing power reserves. In this part we have proposed a new approach to solve the power flow problem (non-linear equations) based on the contraction mapping theorem, which gives the possibility to use more than one bus for the power balance (slack bus) instead of the classic approach based on the Newton-Raphson method. Secondary control plays a very important role in practical applications, in particular when including time varying power sources, as renewable ones. In such cases, it is interesting to consider storage devices in order to improve the stability and the efficiency of the whole system. Due to the sample time of secondary control is on the order of minutes, it is also possible to consider different kinds of forecast (weather, load,..) and to achieve additional control objectives, based on managing storage reserves. All these characteristics encourage the use of a model predictive control (MPC) approach to design this task. In this context, several possibilities of optimization objective were considered, like to minimize transmission losses or to avoid power network congestions.The main task of tertiary control is to manage the load flow of the whole HVDC grid in order to achieve economical optimization. This control level provides power references to the secondary controller. In this thesis we were able to maximize the economic profit of the system by acting on the spot market, and by optimizing the use of storage devices. In this level it is again used the MPC approach.With the aim of implementing the hierarchical control philosophy explained in this thesis, we have built an experimental test bench. This platform has 4 terminals interconnected via a DC grid, and connected to the main AC grid through VSC power converters. This DC grid can work at a maximum of 400 V, and with a maximum allowed current of 15 A
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Mwaniki, Fredrick Mukundi. "High voltage boost DC-Dc converter suitable for variable voltage sources and high power photovoltaic application." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/37320.
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Important considerations of a photovoltaic (PV) source are achieving a high voltage and drawing currents with very little ripple component from it. Furthermore, the output from such a source is variable depending on irradiation and temperature. In this research, literature review of prior methods employed to boost the output voltage of a PV source is examined and their limitations identified. This research then proposes a multi-phase tapped-coupled inductor boost DC-DC converter that can achieve high voltage boost ratios, without adversely compromising performance, to be used as an interface to a PV source. The proposed converter achieves minimal current and voltage ripple both at the input and output. The suitability of the proposed converter topology for variable input voltage and variable power operation is demonstrated in this dissertation. The proposed converter is also shown to have good performance at high power levels, making it very suitable for high power applications.
Detailed analysis of the proposed converter is done. Advantages of the proposed converter are explained analytically and confirmed through simulations and experimentally. Regulation of the converter output voltage is also explained and implemented using a digital controller. The simulation and experimental results confirm that the proposed converter is suitable for high power as well as variable power, variable voltage applications where high voltage boost ratios are required.Dissertation (MEng)--University of Pretoria, 2013.
gm2014
Electrical, Electronic and Computer Engineering
Unrestricted
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Luo, Feng. "Integrated Switching DC-DC Converters with Hybrid Control Schemes." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193904.
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In the modern world of technology, highly sophisticated electronic systems pave the way for future's information technology breakthroughs. However, rapid growth on complexity and functions in such systems has also been a harbinger for the power increase. Power management techniques have thus been introduced to mitigate this urgent power crisis. Switching power converters are considered to be the best candidate due to their high efficiency and voltage conversion flexibility. Moreover, switching power converter systems are highly nonlinear, discontinuous in time, and variable. This makes it viable over a wide operating range, under various load and line disturbances. However, only one control scheme cannot optimize the whole system in different scenarios. Hybrid control schemes are thus employed in the power converters to operate jointly and seamlessly for performance optimization during start-up, steady state and dynamic voltage/load transient state.In this dissertation, three switching power converter topologies, along with different hybrid control schemes are studied. First, an integrated switching buck converter with a dual-mode control scheme is proposed. A pulse-train (PT) control, employing a combination of four pulse control patterns, is proposed to achieve optimal regulation performance. Meanwhile, a high-frequency pulse-width modulation (PWM) control is adopted to ensure low output ripples and avoid digital limit cycling. Second, an integrated buck-boost converter with a tri-mode digital control is presented. It employs adaptive step-up/down voltage conversion to enable a wide range of output voltage. This is beneficial to ever-increasing dynamic voltage scaling (DVS) enabled, modern power-efficient VLSI systems. DVS adaptively adjusts the supply voltage and operation frequency according to instantaneous power and performance demand, such that a system is constantly operated at the lowest possible power level without compromising its performance. Third, a digital integrated single-inductor multiple-output (SIMO) converter, tailored for DVS-enabled multicore systems is addressed. With a multi-mode control algorithm, DVS tracking speed and line/load regulation are significantly improved, while the converter still retains low cross regulation.All three integrated CMOS DC-DC converters have been designed and fabricated successfully, demonstrating the techniques proposed in this research. The measurements results illustrate superior line and load regulation performances and dynamic response in all these designs.
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Deng, Na. "DC-DC converters for current flow control, voltage conversion and integration of energy storage systems in DC grids." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6326/.
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The advantages of DC transmission over the traditional AC transmission, particularly under medium and high voltage level, are widely recognised in recent years. In order to utilise DC power transmission in a more efficient manner, a construction of multi-terminal DC grids is put forward in previous literature. However, the development of large-scale DC grids faces various technical challenges, such as the power flow management, the voltage conversion and regulation, and the fault current management. One substantial and promising solution against these technical challenges whilst enhancing the controllability and flexibility of DC grids is by the inclusion and control of DC-DC converters. In this thesis, three potential applications of the DC-DC converter in future DC grids are investigated: 1) acting as a DC current/power flow controller for current/power flow management in meshed DC grids; 2) acting as a DC transformer for the interconnection of DC grids; 3) acting as a DC interface for integrating energy storage systems into DC grids.
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Zheng, Chen Pei. "Capacitive-coupling grid-connected inverter with adaptive dc-link voltage control." Thesis, University of Macau, 2015. http://umaclib3.umac.mo/record=b3335728.
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Nazari, Mohammad. "Control of DC voltage in Multi-Terminal HVDC Transmission (MTDC) Systems." Licentiate thesis, KTH, Elektriska energisystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-147551.
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With recent advances in power electronic technology, High-Voltage Direct Current (HVDC) transmission system has become an alternative for transmitting power especially over long distances. Multi-Terminal HVDC (MTDC) systems are proposed as HVDC systems with more than two terminals. These systems can be geographically wide. While in AC grids, frequency is a global variable, in MTDC systems, DC voltage can be considered as its dual. However, unlike frequency, DC voltage can not be equal across the MTDC system. Control of DC voltage in MTDC systems is one of the important challenges in MTDC systems. Since the dynamic of MTDC system is very fast, DC voltage control methods cannot rely only on remote information. Therefore, they can work based on either local information or a combination of local and remote information. In this thesis, first, the MTDC system is modeled. One of the models presented in this thesis considers only the DC grid, and effects of the AC grids are modeled with DC current sources, while in the other one, the connections of the DC grid to the AC grids are also considered. Next, the proposed methods in the literature for controlling the DC voltage are described and in addition to these methods, some control methods are proposed to control the DC voltage in MTDC system. These control methods include two groups. The first group (such as Multi-Agent Control methods) uses remote and local information, while the second group (such as Sliding Mode Control and H¥ control) uses local information.The proposed multi-agent control uses local information for immediate response, while uses remote information for a better fast response. Application of Multi-Agent Control systems leads to equal deviation of DC voltages from their reference values. Using remote information leads to better results comparing to the case only local information is used. Moreover, the proposed methods can also work in the absence of remote information. When AC grid is considered in the modeling, the MTDC system has anon-linear dynamic. Sliding Mode Control, a non-linear control method with high disturbance rejection capability, which is non-sensitive to the parameter variations, is applied to the MTDC system. It controls the DC voltage very fast and with small or without overshoot. Afterward, a static state feedback H¥ control is applied to the system which minimizes the voltage deviation after a disturbance and keeps the injected power of the terminals within the limits. Finally, some case studies are presented and the effectiveness of the proposed methods are shown. All simulations have been done in MATLAB and SIMULINK.QC 20140911
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Spallarossa, Claudia. "Frequency and voltage control in mixed AC and DC transmission networks." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/32154.
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The construction of a European Super Grid, where existing AC systems are connected through High Voltage Direct Current (HVDC) corridors, is one contribution to accommodating a high penetration of renewable energy by diversifying the energy mix and trading surpluses from some regions. This raises questions over the dynamics of mixed AC and DC systems that need to be thoroughly studied. This thesis examines the level of coupling of AC networks interconnected via HVDC and the provision of system services between AC networks via DC links. Since areas such as the North Sea may see interconnected DC links, control of such multi-terminal DC grids (MTDC) in the case of converter outages is also pursued. To form realistic case studies, a number of mixed AC and DC transmission networks were modelled and validated, in particular a dynamic equivalent model of the Great Britain transmission system coupled via voltage source converter (VSC) HVDC to the Scandinavian transmission network. To answer questions over the interaction of the dynamics of modular multi-level converters (MMC) with AC system dynamics, reduced dynamic models of such converters were developed taking an energy balancing approach. The impacts that two-level or modular multi-level VSCs produce on the dynamics of the hosting AC grids were investigated through perturbation studies. The displacement of conventional generation by converter-interfaced sources sees a decrease in frequency response provision and inertia and calls for alternative provision. Several methods for enhancing the frequency recovery (post outage) of AC grids were designed for and applied to VSCs of HVDC interconnectors. Supplementary droop control was found to improve the frequency nadir after a loss of in-feed event at the cost of passing some of that loss to the adjacent AC systems via the HVDC interconnection. Identifying and exploiting the overload capability of MMC enabled the sharing of primary reserves and improvement of the nadir frequency by allowing extra power to be transferred through HVDC links. Proposals to use the internal energy storage capability of MMCs for inertia provisions were investigated but the results show that the scope for this is very limited. It is important that where MTDC grids are envisaged, the power flow control is able to deal with converter station outages and not cause large disturbance to the DC or AC networks. Deficiencies with proposed methods were identified and a new proposal for coordinated control with multiple bus masters was made and control performance improvements demonstrated.
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Arbetter, Barry Steven. "DC-DC converter utilizing hysteretic current-mode control for low-voltage microprocessor systems with power management." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3219222.
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Yao, Liangbin. "HIGH CURRENT DENSITY LOW VOLTAGE ISOLATED DC-DC CONVERTERSWITH FAST TRANSIENT RESPONSE." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3205.
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With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel's roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs.Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD
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Pepa, Elton. "Adaptive Control of a Step-Up Full-Bridge DC-DC Converter for Variable Low Input Voltage Applications." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/9722.
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This thesis shows the implementation of a novel control scheme DC-DC converter. The converter is a phase-shifted full-bridge PWM converter that is designed to operate as a front stage of a power conversion system where the input is a variable low voltage high current source. The converter is designed to step-up the low voltage input to an acceptable level that can be inverted to a 120/240 VAC 60Hz voltage for residential power. A DSP based adaptive control model is developed, taking into account line variations introduced by the input source while providing very good load dynamics for the converter in both discontinuous and continuous conduction modes. The adaptive controller is implemented using two voltage sensors that read the input and the output voltages of the converter. The controller's bandwidth is comparable to current mode control, without the need for an expensive current sensor, yet providing the noise immunity seen in voltage mode controllers. The intended input source was a fuel cell but in its absence a DC supply is utilized instead. The system is simulated for both discontinuous and continuous conduction modes and implemented and demonstrated for the continuous conduction mode. The test results are shown to match the simulation results very closely.Master of Science
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Nergaard, Troy. "Modeling and Control of a Single-Phase, 10 kW Fuel Cell Inverter." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34180.
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As the world's energy use continues to grow, the development of clean distributed generation becomes increasingly important. Fuel cells are an environmentally friendly renewable energy source that can be used in a wide range of applications and are ideal for distributed power applications. In this study, the power conversion element of a dual single-phase, 10 kW stand-alone fuel cell system is analyzed. The modular converter consists of a DC-DC front-end cascaded with a half-bridge inverter. The entire system is accurately modeled, to help determine any interactions that may arise. Control strategies based on simplicity, performance, and cost are evaluated. A simple voltage loop, with careful consideration to avoid transformer saturation, is employed for the phase-shifted DC-DC converter. Several experimental transfer functions were measured to confirm the modeling assumptions and verify the control design of the DC-DC converter. Two control options for the inverter are explored in detail, and experimental results confirm that the modulation index must be controlled to regulate the output voltage during various load conditions. The final system is implemented without the use of current sensors, thus keeping the inverter cost down. Experimental results using a power supply are given for resistive, inductive, and nonlinear loads and the performance is acceptable. Fuel cell test results, including transient response, are also displayed and analyzed.Master of Science
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Chen, Fang. "Control of DC Power Distribution Systems and Low-Voltage Grid-Interface Converter Design." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77532.
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DC power distribution has gained popularity in sustainable buildings, renewable energy utilization, transportation electrification and high-efficiency data centers. This dissertation focuses on two aspects of facilitating the application of dc systems: (a) system-level control to improve load sharing, voltage regulation and efficiency; (b) design of a high-efficiency interface converter to connect dc microgrids with the existing low-voltage ac distributions, with a special focus on common-mode (CM) voltage attenuation.
Droop control has been used in dc microgrids to share loads among multiple sources. However, line resistance and sensor discrepancy deteriorate the performance. The quantitative relation between the droop voltage range and the load sharing accuracy is derived to help create droop design guidelines. DC system designers can use the guidelines to choose the minimum droop voltage range and guarantee that the sharing error is within a defined range even under the worst cases.
A nonlinear droop method is proposed to improve the performance of droop control. The droop resistance is a function of the output current and increases when the output current increases. Experiments demonstrate that the nonlinear droop achieves better load sharing under heavy load and tighter bus voltage regulation. The control needs only local information, so the advantages of droop control are preserved. The output impedances of the droop-controlled power converters are also modeled and measured for the system stability analysis.
Communication-based control is developed to further improve the performance of dc microgrids. A generic dc microgrid is modeled and the static power flow is solved. A secondary control system is presented to achieve the benefits of restored bus voltage, enhanced load sharing and high system efficiency. The considered method only needs the information from its adjacent node; hence system expendability is guaranteed.
A high-efficiency two-stage single-phase ac-dc converter is designed to connect a 380 V bipolar dc microgrid with a 240 V split-phase single-phase ac system. The converter efficiencies using different two-level and three-level topologies with state-of-the-art semiconductor devices are compared, based on which a two-level interleaved topology using silicon carbide (SiC) MOSFETs is chosen. The volt-second applied on each inductive component is analyzed and the interleaving angles are optimized. A 10 kW converter prototype is built and achieves an efficiency higher than 97% for the first time.
An active CM duty cycle injection method is proposed to control the dc and low-frequency CM voltage for grounded systems interconnected with power converters. Experiments with resistive and constant power loads in rectification and regeneration modes validate the performance and stability of the control method. The dc bus voltages are rendered symmetric with respect to ground, and the leakage current is reduced. The control method is generalized to three-phase ac-dc converters for larger power systems.Ph. D.
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Ramasamy, Thaiyal Naayagi. "Bidirectional DC-DC converter for aircraft electric energy storage systems." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/bidirectional-dcdc-converter-for-aircraft-electric-energy-storage-systems(34423ae1-ebfb-48bd-a66d-fd03b45615e7).html.
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Future aircraft are likely to employ electrically powered actuators for adjusting flight control surfaces, and other high power transient loads. To meet the peak power demands of aircraft electric loads and to absorb regenerated power, an ultracapacitor-based energy storage system is examined in which a bidirectional dual active bridge DC-DC converter is used. This Thesis deals with the analysis, design, development and performance evaluation of the dual active bridge (DAB) converter, which can act as an interface between the ultracapacitor energy storage bank and the aircraft electrical power network. A steady-state analysis is performed for the DAB converter producing equations for the device RMS and average currents and the peak and RMS currents in the coupling inductor. This analysis focuses on understanding converter current shapes and identifying the zero-voltage switching (ZVS) boundary condition. A converter prototype was designed and built and its operation verified through SABER simulations confirming the accuracy of the analysis. Experimental results are included to support the analysis for 7kW, 20 kHz operating conditions giving a measured efficiency of 90%. To enhance the performance of the converter under light-loads, a quasi-square-wave mode of operation is proposed in which a dead-time is introduced either on the transformer primary voltage, or on the transformer secondary voltage, or simultaneously on both transformer primary and secondary. A similar detailed analysis as that for square-wave operation has been undertaken for all three cases and the converter performance was analysed focusing on ZVS operating range, impact of the RMS/peak inductor currents and converter efficiency. The theoretical work was validated through SABER simulations and proof of concept experimental measurements at 1kW, 20 kHz, which resulted in converter efficiency well above 91%. A 9%-17% improvement in efficiency and a 12%-17% improvement in ZVS operating range over square-wave operation are observed for similar operating conditions. Furthermore, a novel bidirectional current control technique for the DAB converter is presented. A SABER simulation has been performed and the converter operation is validated for square-wave and quasi-square-wave modes under steady-state and transient conditions.
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Haryani, Nidhi. "Zero Voltage Switching (ZVS) Turn-on Triangular Current Mode (TCM) Control for AC/DC and DC/AC Converters." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96397.
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One of the greatest technological challenges of the world today is reducing the size and weight of the existing products to make them portable. Specifically, in electric vehicles such as electric cars, UAVs and aero planes, the size of battery chargers and inverters needs to be reduced so as to make space for more parts in these vehicles. Electromagnetic Interference (EMI) filters take up a more than 80 % of these power converters, the size of these filters can be reduced by pushing the switching frequency higher. High frequency operation (> 300 kHz) leads to a size in reduction of EMI filters though it also leads to an increase in switching losses thus compromising on efficiency. Thus, soft switching becomes necessary to reduce the losses, adding more electrical components to the converter to achieve soft switching is a common method. However, it increases the physical complexity of the system. Hence, advanced control methods are adopted for today's power converters that enable soft switching for devices specifically ZVS turn-on as the turn-off losses of next generation WBG devices are negligible. Thus, the goal of this research is to discover novel switching algorithms for soft turn-on.
The state-of the-art control methods namely CRM and TCM achieve soft turn-on by enabling bi-directional current such that the anti-parallel body diode starts conducting before the device is turned on. CRM and TCM result in variable switching frequency which leads to asynchronous operation in multi-phase and multi-converter systems. Hence, TCM is modified in this dissertation to achieve constant switching frequency, as the goal of this research is to be able to achieve ZVS turn-on for a three-phase converter. Further, Triangular Current Mode (TCM) to achieve soft switching and phase synchronization for three-phase two-level converters is proposed. It is shown how soft switching and sinusoidal currents can be achieved by operating the phases in a combination of discontinuous conduction mode (DCM), TCM and clamped mode. The proposed scheme can achieve soft switching ZVS turn-on for all the three phases. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kW with a density of 110 W/in3.
The discussion of TCM in current literature is limited to unity power factor assumption, however this limits the algorithm's adoption in real world applications. It is shown how proposed TCM algorithm can be extended to accommodate phase shift with all the three phases operating in a combination of DCM+TCM+Clamped modes of operation. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kVA with a density of 110 W/in3. TCM operation results in 33 % higher rms current which leads to higher conduction losses, as WBG devices have lower on-resistance, these devices are the ideal candidates for TCM operation, hence to accurately obtain the device parameters, a detailed device characterization is performed.
Further, proposed TCM+DCM+Clamped control algorithm is extended to three-level topologies, the control is modified to extract the advantage of reduced Common Mode Voltage (CMV) switching states of the three-level topology, the switching frequency can thus be pushed to 3 times higher as compared to state-of-the-art SVPWM control while maintaining close to 99 % efficiency. Two switching schemes are presented and both of them have a very small switching frequency variation (6%) as compared to state-of-the-art methods with >200% switching frequency variation.Doctor of Philosophy
Power supplies are at the heart of today's advanced technological systems like aero planes, UAVs, electrical cars, uninterruptible power supplies (UPS), smart grids etc. These performance driven systems have high requirements for the power conversion stage in terms of efficiency, density and reliability. With the growing demand of reduction in size for electromechanical and electronic systems, it is highly desirable to reduce the size of the power supplies and power converters while maintaining high efficiency. High density is achieved by pushing the switching frequency higher to reduce the size of the magnetics. High switching frequency leads to higher losses if conventional hard switching methods are used, this drives the need for soft switching methods without adding to the physical complexity of the system. This dissertation proposes novel soft switching techniques to improve the performance and density of AC/DC and DC/AC converters at high switching frequency without increasing the component count. The concept and the features of this new proposed control scheme, along with the comparison of its benefits as compared to conventional control methodologies, have been presented in detail in different chapters of this dissertation.
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Gonzalez-Torres, Juan Carlos. "Transient stability of high voltage AC-DC electric transmission systems." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS041.
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Les nouvelles politiques adoptées par les autorités nationales ont encouragé pendant les dernières années l'intégration à grande échelle des systèmes d'énergie renouvelable (RES). L'intégration à grande échelle des RES aura inévitablement des conséquences sur le réseau de transport d'électricité tel qu'il est conçu aujourd'hui, car le transport de l'électricité massif sur de longues distances pourrait amener les réseaux de transport à fonctionner près de leurs limites, réduisant ainsi leurs marges de sécurité. Des systèmes de transport d’électricité plus complexes seront donc nécessaires.Dans ce scénario, les systèmes de transmission à Courant Continu Haute Tension (HVDC) constituent la solution la plus intéressante pour le renforcement et l'amélioration des réseaux à Courant Alternatif (AC) existants, non seulement en utilisant des configurations point à point, mais aussi dans des configurations multi-terminales. L'introduction des systèmes HVDC aboutira à terme à un réseau électrique hybride haute tension AC/DC, qui doit être analysé comme un système unique afin de mieux comprendre les interactions entre le réseau AC et le réseau DC.Cette thèse porte sur l'analyse de la stabilité transitoire des systèmes de transmission électrique hybrides AC/DC. Plus particulièrement, deux questions ont été abordées: Quel est l'impact d'un défaut du réseau DC sur la stabilité transitoire du réseau AC? Comment est-il possible de se servir des systèmes de transmission DC en tant qu'actionneurs afin d'améliorer la stabilité transitoire AC ?Dans la première partie de ce travail, les modèles mathématiques du réseau hybride AC/DC sont décrits ainsi que les outils nécessaires à l'analyse du système en tenant compte de sa nature non linéaire. Ensuite, une analyse approfondie de la stabilité transitoire du réseau électrique dans le cas particulier d'un court-circuit dans le réseau DC et l'exécution des stratégies de protection correspondantes sont effectuées. En complément, des indicateurs de stabilité et des outils pour dimensionner les futurs réseaux de la MTDC afin de respecter les contraintes des stratégies de protection existantes sont proposés.La deuxième partie de la thèse porte sur les propositions de commande pour la modulation des références de puissance des systèmes de transmission HVDC dans le but d'améliorer la stabilité transitoire du système AC connecté à ce réseau DC. Tout d'abord, nous axons notre étude sur le contrôle non linéaire des liaisons HVDC point à point dans des liaisons hybrides AC/DC. La compensation rapide des perturbations de puissance, l'injection de puissance d'amortissement et l'injection de puissance de synchronisation sont identifiées comme des mécanismes par lesquels les systèmes HVDC peuvent améliorer les marges de stabilité des réseaux AC.Enfin, une stratégie de contrôle pour l'amélioration de la stabilité transitoire par injection de puissance active dans par un réseau MTDC est proposée. Grâce à la communication entre les stations, la commande décentralisée proposée injecte la puissance d'amortissement et de synchronisation entre chaque paire de convertisseurs en utilisant uniquement des mesures au niveau des convertisseurs. L'implémentation proposée permet d'utiliser au maximum la capacité disponible des convertisseurs en gérant les limites de puissance d'une manière décentraliséeThe new policy frameworks adopted by national authorities has encouraged the large scale-integration of Renewable Energy Systems (RES) into bulk power systems. The large-scale integration of RES will have consequences on the electricity transmission system as it is conceived today, since the transmission of bulk power over long distances could lead the existing transmission systems to work close to their limits, thus decreasing their dynamic security margins. Therefore more complex transmissions systems are needed.Under this scenario, HVDC transmission systems raise as the most attractive solution for the reinforcement and improvement of existing AC networks, not only using point-to-point configurations, but also in a Multi-Terminal configuration. The introduction of HVDC transmission systems will eventually result in a hybrid high voltage AC/DC power system, which requires to be analyzed as a unique system in order to understand the interactions between the AC network and the DC grid.This thesis addresses the transient stability analysis of hybrid AC/DC electric transmission systems. More in particular, two questions sought to be investigated: What is the impact of a DC contingency on AC transient stability? How can we take advantage of the of DC transmission systems as control inputs in order to enhance AC transient stability?In the first part of this work, the mathematical models of the hybrid AC/DC grid are described as well as the necessary tools for the analysis of the system taking into account its nonlinear nature. Then, a thorough analysis of transient stability of the power system in the particular case of a DC fault and the execution of the corresponding protection strategies is done. As a complement, stability indicators and tools for sizing future MTDC grids in order to respect the constraints of existing protection strategies are proposed.The second part of the thesis addresses the control proposals for the modulation of power references of the HVDC transmission systems with the purpose of transient stability enhancement of the surrounding AC system. Firstly, we focus our study in the nonlinear control of point-to-point HVDC links in hybrid corridors. Fast power compensation, injection of damping power and injection of synchronizing power are identified as the mechanisms through which HVDC systems can improve stability margins.Finally, a control strategy for transient stability enhancement via active power injections of an MTDC grid is proposed. Using communication between the stations, the proposed decentralized control injects damping and synchronizing power between each pair of converters using only measurements at the converters level. The proposed implementation allows to fully use the available headroom of the converters by dealing with power limits in a decentralized way
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Khaleghi, Kerahroudi Shadi. "Development of novel operational stability control systems for embedded high voltage DC links." Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/12566.
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In order to achieve the ambitious decarbonisation targets of the UK government, up to 30GW of wind generation could be connected to the GB transmission system by 2020. The challenges imposed when incorporating this volume of renewable energy are significant, introducing new technical challenges for National Grid as the system operator for the Great Britain transmission system. The majority of this new renewable generation will be connecting in Scotland and offshore in the UK as a whole. This results in greater uncertainty in the system from significant changes to the direction and volume of power flows across the network. In addition this implies a higher power transfer capacity requirement on the AC transmission lines, which are currently stability-limited, connecting SPT (Scottish Power Transmission) and National Grid networks. The required power transfer capability increases every year because of the large-scale increase in wind generation. Therefore, there is insufficient transmission capacity in the existing network to accommodate the increasing power transfer without constraining output of some generation plants. A range of new state of art technologies such as embedded HVDC link and Thyristor Controlled Series Compensation (TCSC) are planned to be added to the GB system in order to provide additional capacity and consequently facilitate the integration of large-scale renewable generation. It is, therefore essential that National Grid explores new ways of operating the transmission network and new devices to gain additional benefit from the HVDC link and the TCSC capabilities with regard to the system stability enhancement. This thesis investigates the effectiveness of the HVDC link and the TCSC with a view to system stability enhancement. A hierarchical stability control system to enhance the stability limit and achieve the best transient and dynamic performance using the HVDC link and the TCSCs as actuators in the feedback control system is proposed. In addition, a stability control system, using a robust and stabilising Sample Regulator multivariable control design method , to guarantee the system robustness and stability is proposed and designed. The performance and capability of the designed controller in co-ordinated control of the forthcoming power flow control devices are demonstrated on benchmark networks as well as full dynamic models of the GB transmission system using various study cases. Finally, the effectiveness of the West Coast HVDC link in improving the inter-area oscillation damping is presented using the developed model of the future GB transmission system.
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Miao, Dongmin. "Voltage Stabilization Control of Wide-Speed-Range Permanent-Magnet Synchronous Generator Systems." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/246410.
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DC power systems have a constant DC-link voltage, as well as the advantages such as high stability, high efficiency, small size and light weight; therefore, they are widely used in stand-alone power systems, e.g. the power systems in aircrafts and automobiles, isolated wind power generation systems, etc. Permanent-Magnet Synchronous Generators (PMSGs) possess the advantages including high power density, high efficiency, and high control precision, and have obtained great attention and have been widely used in military, inductry, and daily life. Pulse Width Modulation (PWM) rectifier has been one of the main power conversion topologies thanks to its full controllability. The key point in the dissertation is to study the DC power system consisting of a PMSG to be the main power input device and a PWM rectifier to be the main power conversion topology. The objective of control is to output a constant DC-link voltage in a wide PMSG speed range. Since the PM-excited flux linkage is constant, when the PMSG is working at a high speed, field-weakening is needed to stabilize the stator voltage, further to stabilize the DC-link voltage. Hybrid excitation may be used to realize the field-weakening, but it has complex structure; no auxiliary devices are needed in the field regulation with the armature current, and can be easily realized with the PWM recifier and field-regulation control strategies. In this dissertation, the typical applications of the DC power systems are first introduced, with a comprehensive analysis and elaboration on the relevant research throughout the world. The research work is focused on the DC power system and its stabilization control, which is composed of a PMSG and a PWM rectifier. The involved research content in this dissertation includes the following aspects: 1. DC power system design with a wide-speed-range PMSGAs for the common DC power systems, PMSG with high power density, high efficiency is selected to the system power input device, usually with a variable-speed prime mover. The PWM rectifier with fully controlled switches is chosen to be the power conversion topology, which converts the AC power generated by PMSG into DC power, and supplies the DC load after the DC filter. The matching between the system requirements and the generator parameters are determined. Through finite-element analysis (FEA), a PMSG with strong field-weakening ability and suitable for wide-speed-range operation has been designed and manufactured, and the system test bench has been built based on dSPACE. 2. Study, analysis, optimization and experimental verification of the traditional control strategiesAccording to the PMSG designed in part 1, the DC-link model has been built, as well as the control model of the traditional control strategies, e.g. field-oriented control (FOC), direct torque control (DTC), and the effectiveness of the DC-link voltage stabilization control has been verified in a wide speed range. The theory of active damping has been proposed and analyzed, and has been utilized in the DC-link voltage control. When the load on the DC-link changes, the dynamic response of the DC-link voltage has been greatly accelerated, and it recovers quickly to its reference value. In the meantime, the performance influence of the prime mover speed on the actual system test bench should be considered. Finally, the performance of FOC and DTC has been compared and analyzed. 3. Analysis and experimental verification of the direct voltage control (DVC), and the comparative study of all the studied control strategiesThe derivation process of DVC has been theoretically analyzed: the inner current loops in FOC have been eliminated to obtain the direct voltage field-oriented control (DVFOC); the reference value of d-axis voltage in DVFOC has been replaced by the product of the stator voltage calculated by the speed and the load condition, and the sine value of load angle generated by the DC-link voltage PI controller, in order to form the DVC-1. Further, the DC-link voltage PI controller directly outputs the reference value of load angle and it becomes DVC-2. Finally, the comparative study has been carried out among all the studied control strategies.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Soltau, Nils Verfasser], Doncker Rik W. [Akademischer Betreuer] [De, and Antonello [Akademischer Betreuer] Monti. "High-power medium-voltage DC-DC converters : design, control and demonstration / Nils Soltau ; Rik W. de Doncker, Antonello Monti." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1158599544/34.
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Yu, Jianghui. "DC Fault Current Analysis and Control for Modular Multilevel Converters." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/78054.
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Recent research into industrial applications of electric power conversion shows an increase in the use of renewable energy sources and an increase in the need for electric power by the loads. The Medium-Voltage DC (MVDC) concept can be an optimal solution. On the other hand, the Modular Multilevel Converter (MMC) is an attractive converter topology choice, as it has advantages such as excellent harmonic performance, distributed energy storage, and near ideal current and voltage scalability.
The fault response, on the other hand, is a big challenge for the MVDC distribution systems and the traditional MMCs with the Half-Bridge submodule configuration, especially when a DC short circuit fault happens. In this study, the fault current behavior is analyzed. An alternative submodule topology and a fault operation control are explored to achieve the fault current limiting capability of the converter.
A three-phase SiC-based MMC prototype with the Full-Bridge configuration is designed and built. The SiC devices can be readily adopted to take advantage of the wide-bandgap devices in MVDC applications. The Full-Bridge configuration provides additional control and energy storage capabilities. The full in-depth design, controls, and testing of the MMC prototype are presented, including among others: component selection, control algorithms, control hardware implementation, pre-charge and discharge circuits, and protection scheme.
Systematical tests are conducted to verify the function of the converter. The fault current behavior and the performance of the proposed control are verified by both simulation and experiment. Fast fault current clearing and fault ride-through capability are achieved.Master of Science
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Tuffaha, Mutaz, and Dhafer Yahia Saleh. "Control Strategy for a DC/DC Buck Converter based on a Hamiltonian Model to suppress the Ripples at the Input stage." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-12111.
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AC/DC Buck converters have been used widely in many applications from cell phones to vehicle battery chargers. Due to their importance many researchers have been studying their behavior to improve their efficiency and reduce their size and/or cost. One of the most common defects of these converters, whether they are used for high power or low power applications, is the unwanted ripples in the input voltage across the input stage. It is believed that these ripples are caused by the interaction between the converter itself or its controller with the rectifier required to change the AC input into DC followed by an input filter. Many strategies have been suggested to tackle this problem. A new strategy to improve the controller of that converter was suggested by M. Lenells [1] and it was based on a Hamiltonian model for the 3-phase AC/DC converter together with its rectifier. As a first step, we simulated this model for a single-phase DC/DC buck converter only using the so-called S-Functions in MATLAB/SIMULINK. Then we could find a control law that would reduce the ripples in the input voltage and keep the output voltage constant simultaneously. In this report, we present this model and its simulation to pave the way for the control and simulation of the 3-phase AC/DC converter.
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Tang, Lianxiang 1970. "Control and protection of multi-terminal DC transmission systems based on voltage-source converters." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84437.
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This thesis deals with the control and protection of Multi-Terminal DC (MTDC) transmission systems based on Voltage-Source Converters (VSCs). The MTDC system enables several AC systems to be integrated by way of a DC network. Potential applications of the MTDC system are: off-shore wind farms, city center feeds.The complexity of the combined AC/DC circuits and their cross-coupling make it difficult to adjust the VSC control parameters to eliminate sustained oscillations and instability which appear frequently. The control part of the thesis is a systematic investigation which addresses the problems.
Firstly, the mechanism of sustained oscillations is discovered to be cross-converter resonance between the AC and DC circuits of a VSC system. Secondly, the unstable modes have been identified by establishing the small signal perturbation model of the entire MTDC system and applying eigenvalue analysis. The general philosophy adopted in the solution consists of reducing complexity by partitioning the MTDC system into several independent subsystems by applying DC voltage decoupling and AC current-tracking techniques at each VSC station. This eliminates the cross-converter resonance. It is found that the addition of damping filters stabilize the MTDC.
Because AC fault protection is standard know-how, the thesis focuses on protection against faults in the DC network of MTDC system. After gaining knowledge on DC fault characteristics, four protection strategies (which have different costs to be balanced against restoration times) are developed. The location of the faulted DC line and its isolation (so that the remainder of the DC network can resume service) is a most challenging task. The Handshaking Method is invented to handle this problem. Selective fault detection schemes, which ensure, for example, that AC faults are not mistaken for DC faults, are also developed. During a DC fault, the DC capacitors can become unbalanced and a method of balancing the DC capacitors during the restoration stage is developed.
Digital simulations have been used to demonstrate the feasibility of the control and protection strategies.
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Smith, Nathaniel R. "Characterization and Design of Voltage-Mode Controlled Full-Bridge DC/DC Converter with Current Limit." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright152721348332911.
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Ng, Fan. "Operation and DC-link voltage control of three-phase four-wire unified power quality conditioners." Thesis, University of Macau, 2007. http://umaclib3.umac.mo/record=b1677859.
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Nampally, Ashok. "Investigation of modulation dynamics and control of modular multilevel converter for high voltage DC grids." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=235573.
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Energy security concerns and the impact of traditional sources of power generation on the climate have prompted a rise in renewable energy expansion around the world. Power transmission from remote generation sites to consumers over long distance is most efficient using High-Voltage Direct Current (HVDC) transmission lines. Consequently, HVDC and the integration of renewable resources are considered as key perspectives in the improvement of sustainable energy systems capable of secure and stable electric power supply. With the intention of huge energy demand in the future, the multi-terminal DC grid concept is proposed based on various converter topologies like Line Commutated Converter (LCC), Voltage Sourced Converter (VSC), and Modular Multilevel Converter (MMC) HVDC technologies. These converters play a vital role in integrating remotely-located renewable generation and reinforcing existing power systems. The MMC has become increasingly popular in HVDC transmission compared to conventional line commutated converters, two-level and multilevel voltage source converters. Low generation of harmonics, a low switching frequency of semiconductors, sine formed AC voltages and currents, black start capability and higher overall efficiency are a few of the unique features of MMC. The MMC is characterised by a modular arm structure, formed by a cascade connection of a vast number of simple cells with floating DC capacitors. These cells are called Sub-Modules (SMs) and can be easily assembled into a converter for high voltage power conversion systems. Compared with traditional VSCs, the analytical modelling of MMC is more challenging. This is because of technical issues such as higher order system, the discontinuous and non-linear nature of signal transfer through converters, the complexity of the interaction equations between the AC and DC variables, and harmonic frequency conversion through AC side and DC side of the converter. This work intends to resolve these challenges by developing a detailed non-linear model using fundamental switching Selective Harmonic Elimination (SHE) modulation technique, an average MMC model in DQ0 frame and an analytical dynamic MMC model, which can be suitable for small-signal stability studies, and control design. Firstly, the detailed model of MMC using fundamental switching SHE modulation scheme has been developed using PSCAD/EMTDC (Power systems computer aided design Electromagnetic transients for DC) software. The basic terms and equations of the MMC have been presented along control loops. The significance of the switching frequency on the performance of the MMC has been studied as well as the relation between the switching frequency, the Total Harmonic Distortion (THD) and the number of output voltage levels. Detailed representation of MMC systems in PSCAD/EMTDC programs incorporates the modelling of Insulated-Gate Bipolar Transistor (IGBT) valves and should typically utilise small integration time-steps to represent fast switching events precisely. Computational burden introduced by such detailed models make the study of steady-state and transient events more complex, highlighting the need to implement more efficient models that provide comparative behaviour and dynamic response. Secondly, average DQ0 models has been implemented to accurately replicate the steady-state, dynamic and transient behaviour of MMC in PSCAD/EMTDC programs. These simplified models represent the average response of switching devices and converters by using averaging techniques involving controlled sources and switching functions. Developing the MMC average model in DQ0 frame was a challenging task because of the multiplication terms in the MMC average model in ABC frame. The proposed approach to overcome this challenge is considering generic form for the product variables and multiplying them in ABC frame and then transferring only the DC and fundamental frequency components of the results to DQ0 frame. The comparisons between detailed model and the average model validated the effectiveness of the average model in representing the dynamics of MMC. It is at least one hundred times faster than the detailed model for the same simulation time step. Finally, a dynamic analytical MMC model and associated controls have been proposed. To enable the model application to a broad range of system configurations and various dynamic studies, the model is built on a modular modelling approach using four sub-systems; an AC system, Phase Locked Loop (PLL) system, MMC system and a DC arrangement. The developed MMC system model has been linearized and implemented in state-space form. To select the best open-loop controller gains, eigenvalue analysis is performed for each particular test system. The rationality and correctness of the proposed model are verified against non-linear PSCAD/EMTDC simulations, and good accuracy is obtained in the time domain analysis. Further, the model is also verified in the frequency domain, and it is concluded that the developed model can be employed for dynamic analysis below 300 Hz.
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Abouda, Salim. "Contribution à la commande des systèmes photovoltaiques : application aux systèmes de pompages." Thesis, Reims, 2015. http://www.theses.fr/2015REIMS005/document.
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L'objectif des travaux présentés dans cette thèse est d'apporter une contribution à l'étude d'un système photovoltaïque fonctionnant à sa puissance maximale et énergétiquement autonome. Le cas étudié, dans cette thèse, concerne la commande d'une chaine de pompage photovoltaïque dans un site isolé. Dans ce sens, et pour que le système photovoltaïque fonctionne à sa puissance maximale, il doit comporter un étage d'adaptation associé à un algorithme MPPT. Dans notre étude, nous avons utilisé deux algorithmes MPPT, l'algorithme “Perturb and Observe” (P&O) puis l'algorithme “ Increment of Conductance” (IncCond). Dans quelques applications industrielles, il est parfois nécessaire de maintenir la tension délivrée par le système photovoltaïque constante. Pour cela, un système de contrôle de cette tension est présenté. Les méthodes utilisées pour la simulation de ce système sont basées sur l'utilisation d'un régulateur PID, puis sur le contrôle par mode glissant, et enfin sur un contrôleur par logique floue. Ce système est testé pour une charge résistive puis pour le cas d'une pompe centrifuge entrainée par un moteur à courant continu à aimant permanent. Ensuite, nous avons étudié le cas d'une chaine de pompage utilisant un moteur asynchrone triphasé comme moteur d'entrainement. Dans le but d'avoir la possibilité de régler le débit d'eau, et en se basant sur la caractéristique de proportionnalité entre la vitesse et le débit, la méthode de contrôle direct du couple, Direct Torque Control - DTC est utilisée pour la commande de la vitesse du moteur asynchroneThe aim of the work presented in this thesis is to contribute to the study of a photovoltaic system operating at its maximum power and energetically autonomous. The case studied in this thesis relates to the control of a chain of photovoltaic pumping in an isolated site. In this sense and for the PV system operates at its maximum power, it must include a converter associated with a MPPT algorithm. In our study, we used two MPPT algorithms, the algorithm “Perturb and Observe” (P & O), then the algorithm “Increment of Conductance” (IncCond). In some industrial applications, it is sometimes necessary to maintain the voltage delivered by the PV system constant. For this, a control system of this voltage is presented. The methods used for the simulation of this system are based on the use of a PID controller and the sliding mode control, and finally a fuzzy logic controller. This system was tested for a resistive load then for the case of a centrifugal pump driven by a permanent magnetic DC motor. Then we studied the case of a pumping chain using a three-phase induction motor as a drive motor. In order to be able to regulate the flow of water, the Direct Torque Control method “DTC” is used to control the speed of the induction motor because it is proportional with the water flow
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Boulanger, Isabelle. "Lillgrund Wind Farm Modelling and Reactive Power Control." Thesis, KTH, Elektriska energisystem, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119256.
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The installation of wind power plant has significantly increased since several years due to the recent necessity of creating renewable and clean energy sources. Before the accomplishment of a wind power project many pre-studies are required in order to verify the possibility of integrating a wind power plant in the electrical network. The creation of models in different software and their simulation can bring the insurance of a secure operation that meets the numerous requirements imposed by the electrical system. Hence, this Master thesis work consists in the creation of a wind turbine model. This model represents the turbines installed at Lillgrund wind farm, the biggest wind power plant in Sweden. The objectives of this project are to first develop an accurate model of the wind turbines installed at Lillgrund wind farm and further to use it in different kinds of simulations. Those simulations test the wind turbine operating according to different control modes. Also, a power quality analysis is carried out studying in particular two power quality phenomena, namely, the response to voltage sags and the harmonic distortion. The model is created in the software PSCAD that enables the dynamic and static simulations of electromagnetic and electromechanical systems. The model of the wind turbine contains the electrical machine, the power electronics (converters), and the controls of the wind turbine. Especially, three different control modes, e.g., voltage control, reactive power control and power factor control, are implemented, tested and compared. The model is tested according to different cases of voltage sag and the study verifies the fault-ride through capability of the turbine. Moreover, a harmonics analysis is done. Eventually the work concludes about two power quality parameters.
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Keskar, Neeraj. "High bandwidth wide LC-Resr compliant sigma-delta boost DC-DC switching converters." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22530.
Full textAbstract:
In low power, battery-operated, portable applications, like cell phones, PDAs, digital cameras, etc., miniaturization at a low cost is a prominent driving factor behind product development and marketing efforts. As such, power supplies in portable applications must not only conform and adapt to their highly integrated on-chip and in-package environments but also, more intrinsically, respond quickly to fast load dumps to achieve and maintain high accuracy. The frequency-compensation network, however, limits speed and regulation performance because, in catering to all combinations of the output capacitor, its equivalent series resistance Resr, and the power inductor resulting from tolerance and modal design targets, it must compensate the worst-case condition and therefore restrain the performance of all other possible scenarios. Sigma-delta control, which addresses this issue in buck converters by easing its compensation requirements and offering one-cycle transient response, has not been able to simultaneously achieve high bandwidth, high accuracy, and wide LC-Resr compliance in boost (step-up) converters. This thesis investigates and presents techniques to achieve sigma-delta control in boost converters by essentially using explicit current and voltage control loops. The proposed techniques are developed conceptually and analytical expressions for stability range and transient response are derived. The proposed concepts are validated and quantified through PCB and IC prototypes to yield 1.41 to 6 times faster transient response than the state of the art in current-mode boost supplies, and this without any compromise in LC-Resr compliance range.
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Ay, Gokce Mehmet. ""." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605283/index.pdf.
Full textAbstract:
This thesis focuses on the design of an electrical drive system for the purpose of
high precision motion control. A modern electrical drive is usually equipped with a
current regulated voltage source along with powerful motion controller system
utilizing one or more micro-controllers and/or digital signal processors (DSPs).
That is, the motor drive control is mostly performed by a dedicated digital-motion
controller system.
Such a motor drive mostly interfaces with its host processor via various serial
communication protocols such as Profibus, CAN+, RS-485 etc. for the purpose of
receiving commands and sending out important status/control signals. Considering
that the motor drives lie at the heart of every (multi-axis) motion control system, the
aim of this thesis is to explore the design and implementation of a conventional DC
motor drive system suitable for most industrial applications that require precision
and accuracy. To achieve this goal, various underlying control concepts and
important implementation details are rigorously investigated in this study.
A low power DC motor drive system with a power module, a current regulator and
a motion controller is built and tested. Several design revisions on these subsystems
are made so as to improve the overall performance of the drive system itself.
Consequently, important &ldquoknow-how&rdquo
required for building high performance (and high power) DC motor drives is gained in this research.
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Elkhomri, Othman. "DSP IMPLEMENTATION OF DC VOLTAGE REGULATION USING ADAPTIVE CONTROL FOR 200 KW 62000 RPM INDUCTION GENERAT." Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2926.
Full textAbstract:
The thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship has been modeled using adaptive control technique to vary the gains automatically at any load condition. The adaptive control technique has been successfully generalized for real time DSP implementation to regulate the DC voltage for high speed induction generators rated from 5 kW to 200 kW.M.S.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering
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Benahmed, Sif Eddine. "Distributed Cooperative Control for DC Microgrids." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0056.
Full textAbstract:
Au cours des dernières années, le réseau électrique connait une transformation rapide avec la pénétration massive des unités de production renouvelables et distribuées. Le concept de microgrids (micro-réseau électrique) est un élément clés de cette transition énergétique. Ces micro-réseaux sont constitués par un ensemble de plusieurs unités de production distribuées (DGUs), d'unités de stockage (SUs) et de charges interconnectées par des lignes électriques. Un microgrid peut être installé dans plusieurs endroits, par exemple dans des maisons, des hôpitaux, des quartiers, etc. et fonctionne soit en mode connecté au réseau principale, soit en mode isolé (autonome). Les microgrids sont confrontés à plusieurs défis liés à la garantie de la stabilité, la cybersécurité, l'optimisation des coûts énergétiques, la gestion de l'énergie, la qualité de l'énergie, etc. Dans ce travail, nous concentrons notre attention sur le contrôle des microgrids à courant continu en mode de fonctionnement autonome. La principale contribution de cette thèse est l’établissement de lois de commande par retour d’état distribuées assurant un partage de courant proportionnel entre les unités de production, une régulation de la tension moyenne des lignes et un équilibrage simultané des états de charge des éléments de stockage. En partant de l'hypothèse que les agents (DGU ou SU) ont les mêmes paramètres physiques, la preuve de la convergence exponentielle et globale est donnée en l’absence d’une connaissance de la charge présente sur le réseau. La thèse est divisée en trois parties. La première partie présente le concept des microgrids, un état de l’art sur leurs stratégies de contrôle et les préliminaires mathématiques nécessaires tout au long du manuscrit. La deuxième partie constitue la contribution théorique de cette thèse et aborde la synthèse de lois de contrôle distribuées, garantissant les objectifs envisagés en l’absence d’une connaissance de la charge variable sur le réseau et même en cas de perturbation constantes au niveau de l’entrée de commande. Cette garantie est apportée en considérant trois actions intégrales distribuées de type consensus. Dans la troisième partie, les contrôleurs proposés sont évalués dans différents scénarios par le biais de simulation Matlab/Simulink et de tests Hardware-in-the-Loop (HIL) en temps réel. Les résultats montrent que les objectifs de contrôle sont atteints avec succès, ce qui illustre l'efficacité de la méthodologie de contrôle proposéeIn recent years, the power grid has undergone a rapid transformation with the massive penetration of renewable and distributed generation units. The concept of microgrids is a key element of this energy transition. Microgrids are made up of a set of several distributed generation units (DGUs), storage units (SUs) and loads interconnected by power lines. A microgrid can be installed in several locations, for example in houses, hospitals, a neighborhood or village, etc., and operates either in connected mode to the main grid or in isolated (autonomous) mode. Microgrids are facing several challenges related to stability assurance, cyber-security, energy cost optimization, energy management, power quality, etc. In this work, we focus our attention on the control of islanded direct current microgrids. The main contribution is the design of a new distributed control approach to provably achieve current sharing, average voltage regulation and state-of-charge balancing simultaneously with global exponential convergence. The main tools are consensus in multi-agent systems, passivity, Lyapunov stability, linear matrix inequalities, etc. The thesis is divided into three parts. The First part presents the concept of microgrids, a literature review of their control strategies and the mathematical preliminaries required throughout the manuscript. The second part deals with the design of the proposed distributed control approach to achieve the considered objectives. The system is augmented with three distributed consensus-like integral actions, and a distributed-based static state feedback control architecture is proposed. Starting from the assumption that the agents (DGUs or SUs) have the same physical parameters, we provide proof of global exponential convergence. Moreover, the proposed control approach is distributed, i.e., each agent exchange relative information with only its neighbors through sparse communication networks. The proposed controllers do not need any information about the parameters of the power lines neither the topology of the microgrid. The control objectives are reached despite the unknown load variation and constant disturbances. In the third part, the proposed distributed controllers are assessed in different scenarios through Matlab/Simulink simulation and real-time Hardware-in-the-Loop experiment. The results show that the control objectives are successfully achieved, illustrating the effectiveness of the proposed control methodology
35
Rabbani, Ronak. "Developing and deploying enhanced algorithms to enable operational stability control systems with embedded high voltage DC links." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/12293.
Full textAbstract:
The increasing penetration of renewable energy resources within the Great Britain (GB) transmission system has created much greater variability of power flows within the transmission network. Consequently, modern transmission networks are presented with an ever increasing range of operating conditions. As a result, decision making in the Electricity National Control Centre (ENCC) of the GB electrical power transmission system is becoming more complex and control room actions are required for reducing timescales in the future so as to enable optimum operation of the system. To maximise utilisation of the electricity transmission system there is a requirement for fast transient and dynamic stability control. In this regard, GB electrical power transmissions system reinforcement using new technology, such as High Voltage Direct Current (HVDC) links and Thyristor-Controlled Series Compensation (TCSC), is planned to come into operation. The research aim of this PhD thesis is to fully investigate the effects of HVDC lines on power system small-disturbance stability in the presence of operational uncertainties. The main research outcome is the comprehensive probabilistic assessment of the stability improvements that can be achieved through the use of supplementary damping control when applied to HVDC systems. In this thesis, two control schemes for small-signal dynamic stability enhancement of an embedded HVDC link are proposed: Modal Linear Quadratic Gaussian (MLQG) controller and Model Predictive Controller (MPC). Following these studies, probabilistic methodologies are developed in order to test of the robustness of HVDC based damping controllers, which involves using classification techniques to identify possible mitigation options for power system operators. The Monte Carlo (MC) and Point Estimated Method (PEM) are developed in order to identify the statistical distributions of critical modes of a power system in the presence of uncertainties. In addition, eigenvalue sensitivity analysis is devised and demonstrated to ensure accurate results when the PEM is used with test systems. Finally, the concepts and techniques introduced in the thesis are combined to investigate robustness for the widely adopted MLQG controller and the recently introduced MPC, which are designed as the supplementary controls of an embedded HVDC link for damping inter-area oscillations. Power system controllers are designed using a linearised model of the system and tuned for a nominal operating point. The assumption is made that the system will be operating within an acceptable proximity range of its nominal operating condition and that the uncertainty created by changes within each operating point can possibly have an adverse effect on the controller’s performance.
36
Kasap, Onur. "Development Of A Pc Numerical System For High Voltage Sphere Gap Control." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606145/index.pdf.
Full textAbstract:
In this thesis, a high precision motion and position control system has been developed and applied to a high voltage sphere gap control and measurement system. The system is able to support up to 3-axes position and motion control. The control system includes a microcontroller card, three DC servo motor driver cards and a data storage unit. To provide communication between computer and motion control system, the Universal Serial Bus (USB) port is used.
The microcontroller card is equipped with an USB interface and a PIC (Peripheral Interface Controllers) microcontroller. This microcontroller controls the dedicated motion control processors (LM629), on servo motor driver cards and read/write operations of data storage unit, which consists of a Multi Media Card.
37
Chewele, Youngie Klyv. "Model predictive control of AC-to-AC converter voltage regulator." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86339.
Full textAbstract:
Thesis (MEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: The development of fast and efficient processors, programmable devices and high power semiconductors has led to the increased use of semiconductors directly in the power supply path in order to achieve strict power quality standards. New and advanced algorithms are used in the process and calculated on-line to bring about the required fast response to voltage variations. Losses in high voltage semiconductors increase with increased operating frequencies. A balance between semiconductor power losses and power quality is achieved through control of power semiconductor switching frequencies. A predictive control algorithm to achieve high power quality and limit the power losses in the high power semiconductor switches through switching frequency control is discussed for a tap switched voltage regulator. The quality of power, voltage regulator topology and the control algorithm are discussed. Simulation results of output voltage and current are shown when the control algorithm is used to control the regulator. These results are verified by practical measurements on a synchronous buck converter.
AFRIKAANSE OPSOMMING: Die ontwikkeling van vinnige en doeltreffende verwerkers, programmeerbare toestelle en hoëdrywings halfgeleiers het gelei tot 'n groter gebruik van halfgeleiers direk in die kragtoevoer pad om streng elektriese toevoer kwaliteit standaarde te bereik. Nuwe en gevorderde algoritmes word gebruik in die proses en word aan-lyn bereken om die nodige vinnige reaksie tot spanningswisselinge te gee. Verliese in hoë-spannings halfgeleiers verhoog met hoër skakel frekwensies. 'n Balans tussen die halfgeleier drywingsverliese en spanningskwalteit is behaal deur die skakel frekwensie in ag te neem in die beheer. 'n Voorspellinde-beheer algoritme om ‘n hoë toevoerkwaliteit te bereik en die drywingsverliese in die hoëdrywingshalfgeleier te beperk, deur skakel frekwensie te beheer, is bespreek vir 'n tap-geskakelde spanning reguleerder. Die toevoerkwaliteit, spanningsreguleerder topologie en die beheer algoritme word bespreek. Simulasie resultate van die uittree-spanning en stroom word getoon wanneer die beheer algoritme gebruik word om die omsetter te beheer. Hierdie resultate is deur praktiese metings op 'n sinkrone afkapper.
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Ayachit, Agasthya. "Steady-State and Small-Signal Modeling of A-Source Converter." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534187954423628.
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Ditlefsen, Arne Marius. "Wave Energy Conversion : Simulation Verification and Linearization of Direct Drive Wave Energy Converter with Variable DC-link Voltage Control." Thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9912.
Full textAbstract:
Lowering the cost of wave energy conversion is an essential task for it to succeed as a future energy resource. In this work a converter, assumed cheaper than the regular back to back converter setting, have been investigated for a electric direct drive point absorber. Both experimental work and simulations are used in the analysis. In the experimental work, a permanent magnet generator with a 6-pulse diode rectifier, a DC-link and a DC/DC converter equivalent, was used. Steady state, dynamic and transient measurements were preformed and a simulation model was compared to the measurements. Good results were obtained and deviations were in general small, mostly +-3% for voltage and current measurements and +-8% for torque measurements. Based on transient measurements and simulations a general linearization of the system was made in order to obtain useful information about the system. A step up converter was used in the simulation and it demonstrated stable passive loading control. By using the information obtained by the linearization, the performance of the simulation model was improved by decreasing the DC-link capacitance. The modified simulation model had significant less torque ripple than the initial. The linearization model also can been used to identify time delay represented by the power take off unit in a wave energy converter. This will be done for a commercial size wave energy converter summer 2009.
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Alves, Montanari Allan. "Enhanced instantaneous power theory for control of grid connected voltage sourced converters under unbalanced conditions." IEEE Transactions on Power Electronics, 2017. http://hdl.handle.net/1993/32184.
Full textAbstract:
This thesis introduces a new method especially designed to control the instantaneous power in voltage sourced converters operating under unbalanced conditions, including positive, negative and zero sequence content. A transformation technique, labelled mno transformation, was developed to enable the decomposition of the total instantaneous power flowing on three-phase transmission topologies into constant and oscillating terms. It is applied to three-wire and four-wire schemes, especially accommodating zero sequence unlike previous approaches. Classical and modern electric power theories are presented, particularly focusing on their definitions for adverse AC scenarios. The main mathematical transformations conceived to analyze such situations are summarized, showing their respective advantages and disadvantages. An enhanced instantaneous power theory is introduced. The novel proposed power equations, named mno instantaneous power components, expands the application of the p-q theory, which is attached to the αβ0 transformation. The mno instantaneous power theory is applied to develop an innovative power control method for grid connected voltage sourced converters in order to minimize power oscillations during adverse AC scenarios, particularly with zero sequence content. The method permits to sustain constant instantaneous three-phase power during unbalanced conditions by controlling independently the constant and the oscillating terms related to the instantaneous power. The effectiveness of the proposed control approach and the proposed power conditioning scheme was demonstrated using electromagnetic transient simulation of a VSC connected to an AC system.May 2017
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Kotecha, Ramchandra M. "Analysis and Comparison of Popular Models for Current-Mode Control of Switch Mode Power Supplies." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1300211710.
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Hadjikypris, Melios. "Supervisory control scheme for FACTS and HVDC based damping of inter-area power oscillations in hybrid AC-DC power systems." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/supervisory-control-scheme-for-facts-and-hvdc-based-damping-of-interarea-power-oscillations-in-hybrid-acdc-power-systems(cc03b44a-97f9-44ec-839f-5dcbcf2801f1).html.
Full textAbstract:
Modern interconnected power systems are becoming highly complex and sophisticated, while increasing energy penetrations through congested inter-tie lines causing the operating point approaching stability margins. This as a result, exposes the overall system to potential low frequency power oscillation phenomena following disturbances. This in turn can lead to cascading events and blackouts. Recent approaches to counteract this phenomenon are based on utilization of wide area monitoring systems (WAMS) and power electronics based devices, such as flexible AC transmission systems (FACTS) and HVDC links for advanced power oscillation damping provision. The rise of hybrid AC-DC power systems is therefore sought as a viable solution in overcoming this challenge and securing wide-area stability. If multiple FACTS devices and HVDC links are integrated in a scheme with no supervising control actions considered amongst them, the overall system response might not be optimal. Each device might attempt to individually damp power oscillations ignoring the control status of the rest. This introduces an increasing chance of destabilizing interactions taking place between them, leading to under-utilized performance, increased costs and system wide-area stability deterioration. This research investigates the development of a novel supervisory control scheme that optimally coordinates a parallel operation of multiple FACTS devices and an HVDC link distributed across a power system. The control system is based on Linear Quadratic Gaussian (LQG) modern optimal control theory. The proposed new control scheme provides coordinating control signals to WAMS based FACTS devices and HVDC link, to optimally and coherently counteract inter-area modes of low frequency power oscillations inherent in the system. The thesis makes a thorough review of the existing and well-established improved stability practises a power system benefits from through the implementation of a single FACTS device or HVDC link, and compares the case –and hence raises the issue–when all active components are integrated simultaneously and uncoordinatedly. System identification approaches are also in the core of this research, serving as means of reaching a linear state space model representative of the non-linear power system, which is a pre-requisite for LQG control design methodology.
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Shehada, Ahmed. "Novel Multilevel Converter for Variable-Speed Medium Voltage Switched Reluctance Motor Drives." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85111.
Full textAbstract:
A novel multilevel converter that is especially suited for high speed multi-megawatt switched reluctance motor drives operating at the medium voltage level is presented. The drive is capable of variable speed, four-quadrant operation. Each phase leg of the converter contains an arbitrary number of cascaded cells connected in series with the phase winding. Each cell contains a half-bridge chopper connected to a capacitor. The converter is named the cascaded chopper cell converter. The modular nature of the converter with the ability to add redundant cells makes it very reliable, which is a key requirement for medium voltage drive applications. A comprehensive control algorithm that overcomes the challenges of balancing and controlling cell capacitor voltages is also proposed. A suitable startup algorithm to limit startup current and switching losses, as well as ensure that cell capacitor voltages remain controlled at startup, is suggested. Details of the drive design such as component sizing and control parameter selection are also discussed. A detailed simulation model is developed and explained, and simulation results are provided for primary validation. Operation with standard current and speed control is first simulated. Then a scheme that gives way to a controller that operates the drive in single-pulse mode is developed and presented. This single-pulse control scheme controls the turn-on and turn-off angles, as well as the energization voltage level, in order to obtain high efficiency. Practical considerations related to the drive such as reliability, efficiency, and cost considerations are also discussed. Finally, a detailed comparison of the proposed converter to another competing converter is performed. Besides its scalability to high voltages and powers, the reliability and efficiency of the proposed converter makes it also a candidate for sub-megawatt applications requiring minimum downtime, or any application where high efficiency or improved performance is required.
A small part of this work is also dedicated to brushless dc machines. Control methods for a new converter for brushless dc machines are proposed and verified via simulation. The main advantage of this converter with the proposed control is that it allows exact control of torque or speed up to twice the rated speed, without resorting to current phase advancing or other flux-weakening techniques.Ph. D.
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Kaya, Mehmet Can. "Design, Implementation, And Control Of A Two&." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610106/index.pdf.
Full textAbstract:
In this thesis a two-stage AC/DC/DC power converter is designed and implemented. The AC/DC input stage of the converter consists of the two–
phase interleaved boost topology employing the average current mode control principle. The output stage consists of a zero voltage switching phase shifted full bridge (ZVS&
#8211
PS&
#8211
FB) DC/DC converter. For the input stage, main design goals are obtaining high input power factor, low input current distortion, and well regulated output dc voltage, and obtaining these attributes in a power converter with high power density. For the input stage, the interleaved structure has been chosen in order to obtain reduced line current ripple and EMI, reduced power component stresses, and improved power density. The control of the pre&
#8211
regulator is provided by utilizing a new commercial monolithic integrated circuit, which provides interleaved continuous conduction mode power factor correction (PFC). The output stage is formed by utilizing the available prototype hardware of a ZVS&
#8211
PS&
#8211
FB DC/DC converter and mainly the system integration and controller design and implementation studies have been conducted. The converter small signal model is derived and utilizing its transfer function and employing voltage loop control, the output voltage regulator has been designed. The output voltage controller is implemented utilizing a digital signal processor (DSP). Integrating the AC/DC preregulator and DC/DC converter, a laboratory AC/DC/DC converter system with high overall performance has been obtained. The overall system performance has been verified via computer simulations and experimental results obtained from laboratory prototype.
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Lam, Chi Seng. "An adaptive low dc-voltage controlled LC coupling hybrid active power filter in three-phase four-wire power systems." Thesis, University of Macau, 2012. http://umaclib3.umac.mo/record=b2580608.
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Shahin, Ahmed Eid Moussa. "Contribution à l’optimisation des structures de conversion DC/DC non isolées." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL045N/document.
Full textAbstract:
Dans ce mémoire, nous avons étudié les convertisseurs d’interface permettant l’interconnexion d’une source basse tension non linéaire et d’un bus DC moyenne tension. La source choisie, pour l’étude, était une pile à combustible de type PEM. La structure de puissance retenue correspondant à la mise en cascade d’un convertisseur entrelacé en entrée et d’un convertisseur trois niveaux en sortie. Afin de dimensionner au mieux le convertisseur global, nous avons proposé un modèle analytique permettant de connaitre l’ensemble des pertes dans le système en fonction du point de fonctionnement et de ses paramètres. Nous avons montré que l’ensemble des pertes dans le convertisseur peut être modélisé par deux résistances non linéaires dont l’estimation est possible à partir des modèles moyens du convertisseur. Une commande basée sur le concept de platitude des systèmes différentiels a été utilisée pour assurer les différentes contraintes du système tout en obtenant des propriétés dynamiques élevées en asservissement et en régulation. Dans la dernière partie du mémoire, nous nous sommes intéressés aux solutions permettant de satisfaire les contraintes sur le taux d’ondulation de courant en entrée du convertisseur. Nous avons proposé et dimensionné une nouvelle structure de convertisseur permettant de supprimer les ondulations de courant générées par le convertisseur de puissance. Ce filtre actif se connecte en parallèle avec le convertisseur de puissance. Des résultats expérimentaux ont permis de montrer que le taux d’ondulation de courant d’un convertisseur élévateur a été réduit, le taux d’ondulation de courant passant de 23.3% à 1.9%In this thesis, we studied interface converters enabling the interconnection of a low voltage nonlinear source and a medium voltage DC bus. The source selected for the study was a fuel cell PEM. The chosen power architecture corresponds to a cascaded structure constituted with an interleaved Boost converter at input stage and a three-level Boost converter at output stage. To design the converter, we proposed an analytical model to know the total losses in the system according to the operating point and its parameters. We showed that all losses in the converter can be modeled by two nonlinear resistors. An estimation of these resistors, deduced from average model of the converter, is developed. A control based on the concept of differential systems flatness has been used for the proposed converter structure. It allows taking into account the different system constraints. High dynamic properties as regard to external perturbations or parameters variations are achieved. In the last part of the thesis, we investigate solutions to respect the constraints on the rate of input current ripple. We propose a new active filtering converter connected in parallel with the power one. We have shown that the ripple current of a boost converter was reduced, the ripple current being reduced from 23.3% to 1.9%
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Busquets, Monge Sergio. "A novel pulsewidth modulation for the comprehensive neutral-point voltage control in the three-level three-phase neutral-point-clamped dc-ac converte." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6372.
Full textAbstract:
Las topologías de convertidores multinivel han recibido una atención especial durante las dos últimas décadas debido a sus notables ventajas en aplicaciones de alta potencia y media/alta tensión. En estas topologías, y comparadas con el convertidor tradicional de dos niveles, el voltaje que soporta cada dispositivo semiconductor es menor, evitando los problemas asociados con la interconexión serie de dispositivos. La distorsión armónica en la tensión de salida es también menor y la eficiencia mayor. Pero incorporan un número superior de dispositivos semiconductores y la estrategia de modulación resultante es, por tanto, más compleja.Entre estas topologías, el convertidor cc-ca de tres niveles trifásico con conexión al punto neutro del bus de cc es probablemente el más popular. La aplicación a este convertidor de técnicas de modulación convencionales causa una oscilación de la tensión del punto neutro de baja frecuencia (tres veces la frecuencia fundamental de la tensión de salida). Esta oscilación, a su vez, supone un incremento del estrés de tensión de los dispositivos y provoca la aparición de armónicos de baja frecuencia en la tensión de salida.
Esta tesis presenta una nueva técnica de modulación del pulso de conducción de los dispositivos semiconductores para convertidores de tres niveles trifásicos con conexión a punto neutro, capaz de conseguir un control completo de la tensión del punto neutro con una distorsión armónica reducida en la tensión de salida alrededor de la frecuencia de conmutación. Esta nueva técnica de modulación, basada en la definición de unos vectores espaciales virtuales, garantiza el equilibrado de la tensión del punto neutro con cualquier carga (lineal o no, cualquier factor de potencia) y para todo el rango de tensión de salida, con el único requisito de que la suma de corrientes de fase sea nula.
Las características de la técnica de modulación propuesta y sus beneficios con respecto a otras modulaciones se han verificado a través de simulaciones y experimentos tanto en lazo abierto como en lazo cerrado.
Multilevel converter topologies have received special attention during the last two decades due to their significant advantages in high-power medium- and high-voltage applications. In these topologies, and compared to the previous two-level case, the voltage across each semiconductor is reduced, avoiding the problems of the series interconnection of devices. The harmonic distortion of the output voltage is also diminished and the converter efficiency increases. But a larger number of semiconductors is needed and the modulation strategy to control them becomes more complex.
Among these topologies, the three-level three-phase neutral-point-clamped voltage source inverter is probably the most popular. The application of traditional modulation techniques to this converter causes a low frequency (three times the fundamental frequency of the output voltage) oscillation of the neutral-point voltage. This, in turn, increases the voltage stress on the devices and generates low-order harmonics in the output voltage.
This thesis presents a novel pulsewidth modulation for the three-level three-phase neutral-point-clamped converter, able to achieve a complete control of the neutral-point voltage while also having a low output voltage distortion at around the switching frequency. The new modulation, based on a virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear, any load power factor) over the full range of converter output voltage, the only requirement being that the addition of the output three-phase currents equals zero.
The performance of this modulation approach and its benefits over other previously proposed solutions are verified through simulation and experiments in both open- and closed-loop converter configurations.
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Fares, Adnan. "Development of advanced architectures of power controllers dedicated to Ultra High Switching Frequency DC to DC converters." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS195.
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La sophistication grandissante des dispositifs intelligents ultra-portatifs, tels que les smartphones ou les tablettes,crée un besoin d'amélioration des performances des organes de conversion de puissance.La tendance des technologies d'acheminement de puissance évolue progressivement vers une fréquence plus élevée, une meilleure densité d'intégration et une plus grande flexibilité dans les schémas d'asservissement. La modulation dynamique de tension est utilisée dans les circuits intégrés de gestion de puissances(DVS PMICs)des transmetteurs RF alors que la modulation DVFS est utilisée dans les PMICs dédiées au CPUs et GPUs. Des DCDC flexibles et fonctionnant à haute fréquence constituent aujourd'hui la solution principale en conjonction avec des régulateurs à faible marge de tension (LDO).L'évolution vers des solutions à base de HFDCDC de faibles dimensions pose un défi sérieux en matière de 1)stabilité des boucles d'asservissement,2)de complexité des architectures de contrôle imbriquant des machines d'état asynchrones pour gérer une large dynamique de puissance de sortie et 3)de portabilité de la solutions d'une technologie à une autre.Les solutions les plus courantes atteignent aujourd'hui une gamme de 2 à 6 Mhz de fréquence de découpage grâce à l'usage de contrôleurs à hystérésis qui souffrent de la difficulté à contenir la fréquence de découpage lors des variations de la tension ou du courant en charge.Nous avons voulu dans ce travail étendre l'usage des méthodes de conception et de modélisation conventionnelles comme le modèle petit signal moyen, dans une perspective de simplification et de création de modèles paramétriques. L'objectif étant de rendre la technique de compensation flexible et robuste aux variations de procédés de fabrication ou bien aux signaux parasités inhérents à la commutation de puissance.Certes, le modèle moyen petit signal, au demeurant bien traité dans la littérature, réponds amplement à la problématique de compensation des DCDCs notamment quand la stabilité s'appuie sur le zéro naturel à haute fréquence inhérent à la résistance série ESR de la capacité de sortie, mais les HFDCDC actuels utilisent des capacités MLCC ayant une très faible ESR et font appel à des techniques de compensation paramétriques imbriquant le schéma de compensation dans la génération même du rapport cyclique. La littérature existante sur le fonctionnement de la machine d'état, se contente d'une description simpliste de convertisseurs PWM/PFM mais ne donne que très peu d'éléments sur la gestion des opérations synchrones/asynchrones alternant PWM,PFM,écrêtage de courant, démarrage ou détection de défaillance. Dans ce travail, notre études est axée sur les deux aspects suivants:1)La modélisation paramétrique et la compensation de la boucle d'asservissement de HFDCDC et 2)la portabilité de la conception de la machine d'états du contrôleur notamment lorsqu'elle intègre des transitions complexes entre les modes.Dans la première section, nous avons développé un modèle petit signal moyen d'un convertisseur Buck asservi en mode courant-tension et nous l'avons analysé pour faire apparaitre les contributions proportionnelle, intégrale et dérivé dans la boucle. Nous avons démontré la possibilité d'utiliser le retour en courant pour assurer l'amortissement nécessaire et la stabilité de la boucle pour une large dynamique de variations des conditions de charge.Dans la seconde section, nous avons développé une architecture de machine d'états sophistiquée basé sur la méthode d'Huffman avec un effort substantiel d'abstraction que nous a permis de la concevoir en description RTL pour une gestion fiable du fonctionnement asynchrone et temps réel.Notre contribution théorique a fait l'objet d'une réalisation d'un PMIC de test comportant deux convertisseurs Buck cadencés à 12MHz en technologie BiCMOS 0.5um/0.18um. Les performances clefs obtenues sont:une surtension de 50mV pendant 2us suite à l'application d'un échelon de courant de 300mAThe continuous sophistication of smart handheld devices such as smartphones and tablets creates an incremental need for improving the performances of the power conversion devices. The trend in power delivery migrates progressively to higher frequency, higher density of integration and flexibility of the control scheme. Dynamic Voltage Scaling Power Management ICs (DVS PMIC) are now systematically used for powering RF Transmitters and DVFS PMICS using Voltage and Frequency scaling are used for CPUs and GPUs. Flexible High frequency (HF) DC/DC converters in conjunction with low dropout LDOs constitute the main solution largely employed for such purposes. The migration toward high frequency/small size DCDC solutions creates serious challenges which are: 1) the stability of the feedback loop across a wide range of loading voltage and current conditions 2) The complexity of the control and often-non-synchronous state machine managing ultra large dynamics and bridging low power and high power operating modes, 3) The portability of the proposed solution across technology processes.The main stream solutions have so far reached the range of 2 to 6 MHz operation by employing systematically sliding mode or hysteretic converters that suffer from their variable operating frequency which creates EMI interferences and lead to integration problems relative to on-chip cross-talk between converters.In this work we aim at extend the use of traditional design and modeling techniques of power converters especially the average modeling technique by putting a particular care on the simplification of the theory and adjunction of flexible compensation techniques that don't require external components and that are less sensitive to process spread, or to high frequency substrate and supply noise conditions.The Small Signal Average Models, widely treated in the existing literature, might address most needs for system modeling and external compensation snubber design, especially when aiming on the high frequency natural zero of the output capacitor. However, HFDCDC converters today use small size MLCC capacitors with a very low ESR which require using alternative techniques mixing the compensation scheme with the duty cycle generation itself. The literature often provides a simplistic state machine description such as PWM/PFM operations but doesn't cover combined architectures of synchronous / non synchronous mode operations such as PWM, PFM, Current Limit, Boundary Clamp, Start, Transitional and finally Fault or Protection modes.In our work, we have focused our study on two main axes: 1) The parametric modeling and the loop compensation of HFDCDC and 2) the scalability of the control state machine and mode inter-operation. In the first part, we provided a detailed small signal averaged model of the “voltage and current mode buck converter” and we depicted it to emphasize and optimize the contributions of the Proportional, Integral and Derivative feedback loops. We demonstrated the ability to use the current feedback to damp and stabilize the converter with a wide variety of loading conditions (resistive or capacitive). In the second part, we provided architecture of the mode control state machine with different modes like the PWM, PFM, soft-start, current limit,… .The technique we have used is inspired by Huffman machine with a significant effort to make it abstract and scalable. The state machine is implemented using RTL coding based on a generic and scalable approach.The theoretical effort has been implemented inside a real PMIC test-chip carrying two 12MHz buck converters, each employing a voltage and current mode feedback loop. The chip has been realized in a 0.5um / 0.18um BiCMOS technology and tested through a dedicate Silicon validation platform able to test the analog, digital and power sections. The key performance obtained is a 50mV load transient undershoot / overshoot during 2us following a load step of 300mA (slope 0.3A/ns)
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Fox, Ian Micah. "Design and Applications of Hybrid Switches in DC-AC Power Converter Topologies." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1543157006458193.
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Giral, Castillón Roberto. "Síntesis de estructuras multiplicadoras de tensión basadas en células convertidoras continua-continua de tipo conmutado." Doctoral thesis, Universitat Politècnica de Catalunya, 1999. http://hdl.handle.net/10803/6329.
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Uno de los campos más importantes de la Electrónica de Potencia es el de los convertidores de potencia conmutados, que debido a sus características de alto rendimiento energético, reducido tamaño, posibilidades de regulación del factor de potencia y de elevación de tensión, etc., están presentes en un gran número de las etapas de alimentación de los equipos electrónicos actuales.Las mejoras tecnológicas en ámbitos como el de la integración de circuitos han permitido importantes reducciones en el tamaño de los equipos (por ejemplo en los ordenadores). Sin embargo, este proceso de reducción de tamaño que, además, suele venir unido a unas especificaciones más rígidas en cuanto a costes, rendimiento, seguridad y prestaciones en general, no se ha producido en igual medida en las etapas de alimentación. El estudio de los convertidores conmutados es por lo tanto un campo necesitado de esfuerzos de investigación y desarrollo.
Para potencias superiores a 25 W, y especialmente en potencias superiores a 150 W, una de las estrategias utilizadas para mejorar las prestaciones de los convertidores es el uso del denominado "interleaving" o entrelazado , definido como la puesta en paralelo de N convertidores idénticos desfasando sus señales de control de forma uniforme a lo largo del periodo de conmutación.
Con el objetivo principal de reducir al máximo los rizados de la tensión de salida y de la corriente de entrada, en esta tesis se estudian casos particulares de "interleaving" en estructuras convertidoras continua-continua que utilizan el convertidor elevador ("boost") como célula básica y cuyas tensiones de salida son, idealmente y operando en modo de conducción continua, múltiplos enteros positivos de la tensión de entrada, de ahí la denominación de multiplicadores de tensión que aparece en el título de tesis propuesto. Posteriormente se analizan las posibilidades de regulación de tensión que presentan algunos de los casos de estudio, a costa de incrementar los rizados.