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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.
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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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Kuang, Jinbo. "Series and parallel voltage sources SPWM converters." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56794.
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This research work examines how the presently available gate-turn-off thyristors (GTOs), which are still relatively slow, may be used in force-commutated High Voltage Direct Current transmission (HVDC) and Static Var Compensation (SVC) converters by employing series and/or parallel connected multi-converter modules in conjunction with a phase-shifting principle which cancels the undesirable switching harmonics. It points to the advantages of incorporating the well-known Sinusoidal Pulse Width Modulation (SPWM) technique because it enables feedback control, active filtering and regulatory functions to be performed by the converters. This is because a reasonable bandwidth of the modulating signal is transmitted by the multi-converter station in spite of the low switching rates of the GTO valves.
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Xie, Hailian. "Voltage Source Converters with Energy Storage Capability." Licentiate thesis, Stockholm : Division of electrical machines and power electronics, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4191.
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Zhang, Yushu. "Multilevel voltage source converters in high voltage direct current transmission systems." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25814.
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This research focuses on voltage source multilevel converters in high voltage direct current (HVDC) transmission systems. The first Voltage Source Converter based HVDC (VSC-HVDC) systems with series connected IGBTs in a two-level converter represented a solution to meet industrial and economical requirements but is associated with significant drawbacks such as high dv/dt and di/dt, high switching loss, and poor output voltage and current quality. To overcome these issues, the multilevel converter was proposed for HVDC application. The Modular Multilevel Converter (M2C) was the first multilevel converter to be commercially used in the power industry. In this thesis, the M2C is investigated mainly in terms of operating principle, capacitor size and capacitor voltage ripple, capacitor voltage balancing technique and modulation scheme. The results of this investigation show that the M2C offers the following features: improved efficiency, lower supporting voltage and current in the switching devices and low dv/dt. These features make the M2C suitable for HVDC systems. Two new operational principles and modulation strategies for a Hybrid Cascaded Multilevel Converter (HCMC) are proposed in this thesis. Both modulation schemes extend the modulation index linear range and improve the output waveform quality. This gives the HCMC a higher power density than any known multilevel converter topology for the same dc link voltage and switching device rating. Simulations for both types of multilevel converter (M2C and HCMC) are supported by practical results from scaled hardware laboratory converters. Mathematical analysis and calculation of conversion loss for both types of multilevel converter and for the conventional two-level converter are performed. It is shown that both M2C and HCMC provide lower conversion loss compare to the conventional two-level converter. A control strategy for these two multilevel converters in point-to-point and multi-terminal HVDC systems is also studied. Simulation results show that these two converters are able to operate over the entire specified P-Q capability curve and are capable of riding through ac faults without imposing any over-voltage or over-current on the converter switches.
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Raczkowycz, Julian. "Monolithic data converters and integrated voltage reference sources." Thesis, University of Huddersfield, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290740.
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Ormrod, James Ernest. "Harmonic state space modelling of voltage source converters." Thesis, University of Canterbury. Electrical and Computer Engineering, 2013. http://hdl.handle.net/10092/8081.
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The thesis describes the development of a model of the three-phase Voltage Source Converter (VSC) in the Harmonic State Space (HSS) domain, a Linear Time Periodic (LTP) extension to the Linear Time Invariant (LTI) state space. The HSS model of the VSC directly captures harmonic coupling effects using harmonic domain modelling concepts, generalised to dynami- cally varying signals. Constructing the model using a reduced-order three-phase harmonic signal representation achieves conceptual simplification, reduced computational load, and direct inte- gration with a synchronous frame vector control scheme.
The numerical switching model of the VSC is linearised to gain a small-signal controlled model, which is validated against time-domain PSCAD/EMTDC simulations. The controlled model is evaluated as a STATCOM-type system, exercising closed-loop control over the reactive power flow and dc-side capacitor voltage using a simple linear control scheme. The resulting state- space model is analysed using conventional LTI techniques, giving pole-zero and root-locus analyses which predict the dynamic behaviour of the converter system. Through the ability to independently vary the highest simulated harmonic order, the dependence on the closed-loop response to dynamic harmonic coupling is demonstrated, distinguishing the HSS model from fundamental-only Dynamic Phasor models by its ability to accurately model these dynamics.
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Twining, Erika. "Voltage compensation in weak distribution networks using shunt connected voltage source converters." Monash University, Dept. of Electrical and Computer Systems Engineering, 2004. http://arrow.monash.edu.au/hdl/1959.1/9701.
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Kalitjuka, Tatjana. "Control of Voltage Source Converters for Power System Applications." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14370.
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The research work is aimed on the investigation of possible modeling and control schemes for the dc-link of VSC, with the purpose of identifying the impact of such modeling and control on the dynamics of the conversion system. A system consisting of back-to-back converters with equivalent grid interconnection and source representation is designed in the software PSCAD/EMTDC using a detailed switching model of the inverter and rectifier components. The control technique based on the well-established concept of vector control is implemented. The main task of the master thesis is oriented towards the achievement of more reliable dc-link dynamics with smaller required capacitance. The control algorithm is based on balancing the power between inverter and rectifier through the dc-link with the minimum dc voltage variations. Dc-link voltage regulation is achieved by implementing a control based on the energy stored in the dc-link capacitor. Alignment to a dq synchronous reference frame orientation with PI regulators is used in the control philosophy for decoupling purposes.
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Arulampalam, A. "Power quality improvement with battery supported voltage source converters." Thesis, University of Manchester, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488248.
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Borisov, Konstantin A. "Multifunctional voltage source converter for shipboard power systems." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-06042007-142951.
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Hawley, Joshua Christiaan. "Modeling and Simulation of a Cascaded Three-Level Converter-Based SSSC." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/10109.
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This thesis is dedicated to a comprehensive study of static series synchronous compensator (SSSC) systems utilizing cascaded-multilevel converters (CMCs). Among flexible AC transmission system (FACTS) controllers, the SSSC has shown feasibility in terms of cost-effectiveness in a wide range of problem-solving abilities from transmission to distribution levels. Referring to the literature reviews, the CMC with separated DC capacitors is clearly the most feasible topology for use as a power converter in the SSSC applications. The control for the CMC-Based SSSC is complicated. The design of the complicated control strategy was begun with well-defined system transfer functions. The stability of the system was achieved by trial and error processes, which were time-consuming and ineffective.
The goal of this thesis is to achieve a reliable controller design for the CMC-based SSSC. Major contributions are addressed as follows: 1) accurate models of the CMC for reactive power compensations in both ABC and DQ0 coordinates, and 2) an effective decoupling power control technique.
To simplify the control system design, well-defined models of the CMC-Based SSSC in both ABC and DQ0 coordinates are proposed. The proposed models are for the CMC-Based SSSC focus on only three voltage levels but can be expanded for any number of voltage levels. The key system transfer functions are derived and used in the controller design process. To achieve independent power control capability, the control technique, called the decoupling power control used in the design for the CMC-Based STATCOM is applied. This control technique allows both the real and reactive power components to be independently controlled.
With the combination of the decoupling power control and the cascaded PWM, a CMC with any number of voltage levels can be simply modeled as a three-level cascaded converter, which is the simplest topology to deal with. This thesis focuses on the detailed design process needed for a CMC-Based SSSC.Master of Science
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Kazerani, Mehrdad. "Dyadic matrix converter theory : development, and application to voltage-source-converter type matrix converter." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28794.
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For the past twenty years, the theoretical advance of the matrix converters has been impeded by the complexity arising from the time-varying trigonometric functions in their transformation matrix. In addition, the switching difficulties associated with the bidirectional switches have complicated the practical implementation of this class of converters.In this thesis, the dyadic matrix structure and the a-b-c to d-q-0 transformation have been melded together to develop the dyadic matrix converter theory which is a generalized theory for the three-phase to three-phase matrix converters.
The thesis addresses the zero-sequence interaction in the matrix converters and the role of the zero-sequence elements in the Displacement Power Factor (DPF) correction on the utility-side, based on the Static VAR Controller (SVC) principle. Also, it is proved that using all the control degrees of freedom available, the dual condition of Unity Displacement Power Factor (UDPF) on side-1 and Field Vector Control (FVC) on side-2 can be established.
In this thesis, a new matrix converter topology, based on the three-phase voltage-source converters, has been proposed in which the switching difficulties reported in the conventional nine-bidirectional-switch topology have been bypassed. The theoretical expectations have been verified by the simulation as well as experimental tests on a laboratory prototype of the new matrix converter topology composed of three units of voltage-source converters each rated at 1 kVA.
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You, Keping Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "A new bidirectional AC-DC converter using matrix converter and Z-source converter topologies." Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/37450.
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This thesis proposes a new bidirectional three-phase AC-DC power converter using matrix converter and Z-source inverter topologies. Advantages of the AC-DC matrix converter are the inherently controllable power factor, the tight DC voltage regulation, the wide bandwidth with quick response to load variation, the single-stage buck-voltage AC-to-DC power conversion; advantages of the z-source inverter are the increased reliability by allowing the shoot-through between upper and lower power switches of one inverter leg, insensitivity to DC bus voltage due to the extra freedom of controlling DC-link voltage. The proposed Matrix-Z-source converter (MZC) marries up both advantages of AC-DC matrix converter and Z-source inverter. It can achieve voltage-boost DC-AC inversion capable of variable voltage variable frequency (VVVF) AC output; it can achieve voltage-buck AC-DC rectification capable of inherent control over AC current phase angle and DC output regulation with a (VVVF) AC source supply. Both foresaid performance in DC-AC inversion and AC-DC rectification can be implemented in a simple open-loop control manner. Three constraints of VSI, in the bidirectional AC-DC power conversion, are the peak AC voltages are always less than DC-link voltage, closed-loop control has to be employed when DC regulation and/or AC current phase angle control are required, and AC voltage is sensitive to the variation of the DC-link voltage in DC-AC inversion. The voltage-boost inversion and/or voltage-buck rectification of MZC overcomes the first constraint; thus MZC enables the AC machine voltage increased higher than DC-link voltage hence advantages of running AC machine at relatively high voltages are enabled. The direct DC voltage regulation and inherent AC-current-phase-angle control of MZC overcomes the second constraint in an open-loop manner; hence a simplified system design is obtained with sufficient room for the further improvement by closed-loop control schemes. The extra freedom in controlling DC-link voltage of MZC overcomes the third constraint hence a DC source voltage adaptable inverter is obtained. This thesis focuses on the study of the feasibility of the proposed MZC through theoretical analysis and experimental verification. At first, the proposed MZC is conceptually constructed by examining the quadrant operation of AC-DC matrix converter and Z-source inverter. After the examination of the operating principles of both AC-DC matrix converter and Z-source inverter, the configuration of MZC is then proposed. The MZC has two operating modes: DC-AC inversion and AC-DC rectification. Circuit analysis for both operating modes shows that the new topology does not impose critical conflict in circuit design or extra restriction in parameterization. On the contrary, one version of the proposed MZC can make full advantage of Z-source network components in both operating modes, i.e. a pair of Z-source inductor and capacitor can be used as low-pass filter in AC-DC rectification. The modulation strategy, average modeling of system, and features of critical variables for circuit design of the proposed MZC were examined for each operating mode. Simulations of the proposed MZC and its experimental verification have been presented. Analytical models of conduction and switching losses of the power-switch network in different operating mode have shown that the losses in the MZC compare favorably with conventional VSI for a range of power factor and modulation indices.
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Pegueroles, Queralt Jordi. "Control of voltage source converters for distributed generation in microgrids." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/316782.
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Microgrids are the near future candidate to reduce the dependence on the carbon-based generation, towards a more environmentally friendly and sustainable energy paradigm. The popularization of the use of renewable energy sources has fostered the development of better technologies for microgrids, particularly power electronics and storage systems. Following the improvements in microgrid technologies achieved in the last decade, a new challenge is being faced: the control and management of microgrids for its operation in islanded mode, in addition to its large scale integration into the current electrical power system.
The unregulated introduction of distributed generation based on renewable energy sources into the power system could cause as many problems as it would solve. The unpredictability of the generated power would introduce large disturbances into the electric system, making it difficult to control, and eventually resulting in an unstable system. To overcome these issues, the paradigm of microgrids has been proposed: a small power system, able to operate islanded from the main grid, which will permit the large scale introduction of renewable energy sources interfaced with power electronic converters together with energy storage systems into the distribution grids. Microgrids¿ ability to allow their users to operate islanded from the utility grid, brings the potential to offer a high quality of service. It is in the islanded operation mode, particularly in microgrids with a high proportion of renewable based generation, where the major technical challenges are found.
This thesis focuses in three of the main challenges of islanded and weak electrical grids: the power converter control of electrical storage systems, its decentralized control design, and also the improvement of power quality in grids disturbed by renewable generation. These topics are addressed from a control point of view, that is, to tackle the electrical problems, modelling them and proposing advanced control strategies to improve performance of microgrids.
Energy storage system are a vital element to permit the islanded operation of microgrids, either in the long or short term. New control strategies are proposed in this thesis for the improvement of the converters¿ performance. In addition to the control of the converter, the management and control of different energy storage systems for microgrids are also studied. In particular, supercapacitors and batteries have been considered for the short and long term operation, respectively.
Then, the control of islanded microgrids is addressed. Typical controls for islanded microgrids are analysed and new tools for designing stable controllers are proposed. Also, methodologies to analytically obtain the operating point (power flow) of droop controlled grids are studied and proposed.
The high penetration of renewable energy sources in weak low-voltage grids results in undesirable electrical disturbances. This problematic in power quality is tackled and innovative solutions to mitigate it are proposed. In particular, a novel power smoothing scheme with simultaneous state of charge regulation of the ESS and power filtering.
The new power smoothing scheme, along with the proposed control strategies for storage systems have been experimentally validated in a laboratory test bench, using a supercapacitor bank and a high power lithium-ion battery available at IREC's facilities.Les microxarxes són les candidates en un futur a curt termini, a substituir la generació basada en el carbó, de cara a assolir un sistema energètic més respectuós amb el medi ambient i més sostenible. La popularització de l'ús d'energies renovables ha fomentat la millora de les tecnologies per a microxarxes, en particular els sistemes d'emmagatzematge i l'electronica de potència. Desprès de les millores en tecnologies de microxarxes aconseguides durant l'última dècada, hi ha un nou repte al qual fer front: el control i gestió de microxarxes per la seva operació aïllada, a més de la integració a gran escala dins del sistema elèctric actual. La introducció descontrolada de fonts de generació distribuides en el sistema elèctric pot causar tants problemes com els que podria sol·lucionar. La incertesa en la producció elèctrica pot introduir grans pertorbacions al sistema elèctric, fent-lo difícil de controlar, i fins i tot el pot arribar a inestabilitzar. Per tal de fer front a aquestes dificultats, es proposa el paradigma de microxarxa: un petit sistema elèctric capaç d'operar de forma aïlla de la xarxa de distribució elèctrica, el qual hauria de permetre la integració a gran escala d'energies renovables a través de l'electrònica de potència, juntament amb sistemes d'emmagatzematge d'energia, dins de les xarxes de distribució. Les microxarxes permeten als seus usuaris a funcionar aillats de la xarxa elèctrica, donant la possibilitat d'oferir una alta qualitat de servei. És en el mode de funcionament aïllat, particularment en microxarxes amb una altra proporció de generació basada en renovables, on es troben la major part de reptes tecnològics. Aquesta tesi es centra en tres d'aquests reptes de les xarxes aillades i dèbils: el disseny del control per a convertidors de potència per a sistemes d'emmagatzematge elèctric, el control descentralitzat de les microxarxes i també la millora en la qualitat de subministre elèctric en xarxes afectades per generació renovable. Aquestes temes es tracten des d'el punt de vista de la teoria de control de sistemes, aixó significa, abordar el problema elèctric, modelar-lo, i proposar estrategies de control avançades per millorar el funcionament de les microxarxes. Els sistemes d'emmagatzematge són un element vital per permetre l'operació aïllada de les microxarxes, tant a llarg com a curt termini. En aquesta tesi es proposen noves estratègies de control per millorar el funcionament dels convertidors d'electrònica de potència. A més del control del convertidor, també s'estudia la gestió i control de diferents sistemes d'emmagatzematge d'energia per a microxarxes. En particular, supercondensador i bateries s'han considerat per l'operació a curt i llarg termini respectivament. Seguidament, s'enfila el control de microxarxes aïllades. S'analitzen els controls típics per a microxarxes i es proposen noves eines de disseny que permeten garantitzar l'estabilitat. A més a més, metodologies per a obtenir el punt d'operació (el flux de potènica) per a xarxes amb control tipus "droop" també s'estudien i proposen. L'alta penetració de fonts d'energia renovables en xarxes de baixa tensió i febles resulta en pertorbacions elèctriques indesitjables. Aquesta problematica en la qualitat de subministrament s'aborda i es proposen solucions inovadores per mitigar els efectes negatius. En particular, s'ha proposat un nou sistema de suavitzat de potència que regula simltaneament l'estat de càrrega del sistema d'emmagatzematge i filtra la potencia fluctuant. El nou esquema de suavitzat de potència, juntament amb les estrategies proposades per als sistemes d'emmagatzematge elèctric s'han validat experimentalment en un banc de laboratori, emprant superconsadors i una bateria d'alta potència, disponibles a les instal·lacions de l'IREC.
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Mulolani, Francis. "Performance of direct power controlled grid-connected voltage source converters." Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/3754.
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In this thesis the performance of direct power controlled grid-connected voltage source converters (VSCs) is investigated. Of particular interest is the stability of the controller with the third-order LCL filter employed as the grid filter, effect of grid impedance variations and grid voltage distortion, and current limitation during voltage dips. The control scheme implemented is virtual-flux direct power control with space vector modulation (VF-DPC-SVM). By mathematical modelling and stability analysis, it is found that the closed-loop power control system is stable for all values of proportional gain when the current sensors are on the inverter side of the LCL filter. The inverter current together with the estimated grid virtual-flux is used to estimate the active power and the reactive power. The difference between the estimated reactive power and the reactive power on the grid side is compensated for, using a new reactive power error compensation scheme based on the estimated capacitor current. The control system is found to be robust to changes in grid inductance, and remains stable for a range of grid inductance values, and controller proportional gain. It is demonstrated in simulation and experimentally that the total harmonic distortion (THD) of the current injected by the VSC is less than the limit of 5 %, set by standards, for all different values of grid inductance and proportional gain. This is true even in the presence of significant grid voltage distortion. To control the VSC during voltage dips without damaging the semiconductor devices, a new current limiting algorithm is proposed and implemented. The positive-sequence component of the virtual-flux is used for synchronization and power estimation to achieve balanced, undistorted currents during unsymmetrical voltage dips. Experimental results show that the current achieved during unsymmetrical voltage dips is balanced and has a THD of less than 3 %.
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Lu, Bin 1969. "A feedback control algorithm for voltage-source matrix converter /." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28001.
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One application of the voltage-source, matrix converter is as an asynchronous link, joining two AC power systems with different frequencies (50Hz/60Hz), or at the same frequency (60Hz/60Hz) but at different phase angles. This thesis work shows that for this kind of link, there exists an automatic closed-loop feedback strategy to control the real and reactive powers quickly and independently.In this thesis, the new matrix converter topology, based on the three-phase voltage-source converters, has been used.
The thesis mixes the dyadic matrix structure the a-b-c to d-q-o transformation and feedback control theory together to get the results.
Digital simulations are presented.
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Lu, Bin. "A feedback control algorithm for voltage-source matrix converter." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37268.pdf.
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Sirisukprasert, Siriroj. "The Modeling and Control of a Cascaded-Multilevel Converter-Based STATCOM." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11142.
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This dissertation is dedicated to a comprehensive study of static synchronous compensator (STATCOM) systems utilizing cascaded-multilevel converters (CMCs). Among flexible AC transmission system (FACTS) controllers, the STATCOM has shown feasibility in terms of cost-effectiveness in a wide range of problem-solving abilities from transmission to distribution levels. Referring to the literature reviews, the CMC with separated DC capacitors is clearly the most feasible topology for use as a power converter in the STATCOM applications. The controls for the CMC-based STATCOM were, however, very complicated. The intricate control design was begun without well-defined system transfer functions. The control compensators were, therefore, randomly selected. The stability of the system was achieved by trial and error processes, which were time-consuming and ineffective. To be able to operate in a high-voltage application, a large number of DC capacitors are utilized in a CMC-based STATCOM. All DC capacitor voltages must be balanced in order to avoid over-voltages on any particular link. Not only do these uneven DC voltages introduce voltage stress on the semiconductor switches, but they also lower the quality of the synthesized output waveforms of the converter. Previous researches into DC capacitor voltage-balancing techniques were very straightforward, in that individual voltage compensators were added into the main control loop. However, the compensator design for these individual loops is very problematic because of the complexity of the voltage-loop transfer functions. Basically, the trial and error technique again provides the simplest way to achieve acceptable compensators. Moreover, the greater number of voltage levels, the more complex the control design, and the main controller must perform all of the feedback control procedures. As a result, this approach potentially reduces the reliability of the controller.
The goal of this dissertation is to achieve high-performance, reliable, flexible, cost-effective power stages and controllers for the CMC-based STATCOM. Major contributions are addressed as follows: 1) optimized design for the CMC-based STATCOM power stages and passive components, 2) accurate models of the CMC for reactive power compensations in both ABC and DQ0 coordinates, 3) an effective decoupling power control technique, 4) DC-link balancing strategies; and 5) improvements in the CMC topology.
To enhance the modularity and output voltage of the CMC, the high-switching-frequency, high-power H-bridge building block (HBBB) and the optimized design for its power stage and snubber circuits are first proposed. The high-switching-frequency feature is achieved by utilizing the Virginia Tech-patented emitter turn-off (ETO) thyristor. Three high-power HBBB prototypes were implemented, and their performance was experimentally verified.
To simplify the control system design, well-defined models of the CMC in both ABC and DQ0 coordinates are proposed. The proposed models are for the CMC with any number of voltage levels. The key system transfer functions are achieved and used in the control design processes. To achieve independent power control capability, the control technique, called the decoupling power control, is proposed. By applying this control technique, real and reactive power components can be controlled separately.
In order to balance the DC capacitor voltages, a new, effective pulse width modulation (PWM) technique, which is suitable for any number of H-bridge converters, is proposed. The proposed cascaded PWM algorithm can be practically realized into the field programmable gate arrays (FPGA), and its complexity is not affected by the number of voltage levels. In addition, the complexity of the main controller, which is essentially based on the digital signal processor (DSP), is no longer a function of the number of the output voltage levels. The basic structure of the cascaded PWM is modular, which, in general, enhances the modularity of the CMC power stages.
With the combination of the decoupling power control and the cascaded PWM, a CMC with any number of voltage levels can be simply modeled as a three-level cascaded converter, which is the simplest topology to deal with. This significantly simplifies and optimizes the control design process. To verify the accuracy of the proposed models and the performance of the control system for the CMC-based STATCOM, a low-power, seven-level cascaded-based STATCOM hardware prototype is implemented. The key control procedures are performed by a main controller, which consists of a DSP and an FPGA. The simulation and experimental results indicate the superior performance of the proposed control system, as well as the precision of the proposed models.Ph. D.
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Orellana, Barceló Marcos. "Advanced digital resonant control techniques for grid-connected voltage source converters." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/665552.
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It is a fact that the presence of power distributed generation sources in the electrical sector is growing exponentially worldwide. This can mainly be explained by the increase of renewable energy production, which involves principally grid-connected single- and three-phase Voltage Source Converters (VSCs).
Regarding the regulations for medium and high power inverters, it is not enough to generate currents with low harmonic content and a unity-power-factor operation: grid-connected VSCs also have to work properly when the electrical grid presents non-ideal characteristics such as frequency variations, sags, swells or a high impedances, among other disturbances.
In line with the above and to improve the grid currents quality, LCL filters are widely used at the input of VSCs for their attenuation capabilities at high frequencies. However, they present a big resonance that may produce robustness issues. In order to study this problem and to stablish a basis for the controllers design, the grid-connected VSC mathematical models have been obtained, analysed and discretised, including passive and active LCL resonance damping techniques.
Adaptive Feedforward Cancellation (AFC) is the control technique addressed in this research work, leading to robust designs which are able to face all the grid disturbances aforementioned. AFC controllers, formed by resonators, have been considered in continuous- and discrete-time forms, and presenting infinite and finite gain, along with an anti-windup system for limitation purposes.
The development of an AFC control design method (directly in discrete time), and the use of automatic code generation tools, have allowed a fast implementation of the resonant controllers into a Digital Signal Processor (DSP). The experimental results obtained from the VSC prototypes (also developed during this thesis), prove the robustness of this control technique.Es un hecho que la presencia de fuentes de generación de energía distribuida en el sector eléctrico está creciendo exponencialmente a nivel mundial. Esto se debe esencialmente al incremento de la producción de energías renovables, que están estrechamente relacionadas con convertidores estáticos de potencia monofásicos y trifásicos (VSC) conectados a la red eléctrica. Con respecto a la normativa en el ámbito de los inversores de media y alta potencia, ya no es solamente necesario que éstos generen unas corrientes con un bajo contenido en armónicos y un factor de potencia unitario: el funcionamiento de dichos equipos debe ser correcto frente a situaciones no ideales de la red como variaciones de frecuencia, huecos de tensión o redes débiles, entre otros. En consonancia con lo anterior y para mejorar la calidad de las corrientes de red, los filtros LCL son ampliamente utilizados a la entrada de los VSC por su gran atenuación a altas frecuencias. Sin embargo, la gran resonancia que presentan puede generar problemas de robustez. Para estudiar este fenómeno y crear una base para el diseño de los controladores, se han obtenido, analizado y discretizado los modelos matemáticos de los VSC conectados a la red, incluyendo técnicas de amortiguación pasivas y activas para el filtro LCL. La técnica de control abordada en este trabajo de investigación se denomina Adaptive Feedforward Cancellation (AFC), con la que se han conseguido diseños robustos y capaces de hacer frente a las perturbaciones en la red detalladas anteriormente. Los controladores AFC, formados por resonadores, han sido considerados en tiempo continuo y discreto, y con ganancias infinita y finita, junto con un sistema de limitación anti-windup. El desarrollo de un método de diseño de control AFC (directamente en tiempo discreto) y el uso de herramientas de generación automática de código, han permitido una rápida implementación de los controladores resonantes en un procesador digital de señales (DSP). Los resultados experimentales obtenidos con los prototipos de convertidores monofásico y trifásico (también desarrollados durante esta tesis), confirman la robustez de esta técnica de control.
C’est un fait que la présence de sources de génération d’énergie distribuée dans le secteur électrique est en train de croître exponentiallement à niveau mondiale. Ceci est principalement à cause de l’augmentation de la production d’énergies renouvelables, qui est étroitement liée à des convertisseurs statiques de puissance monophasés et triphasés (VSC) connectés au réseau électrique. Par rapport aux régulations dans le domaine des onduleurs de moyenne et forte puissance, il n’est pas seulement nécessaire qu’ils génèrent des courants à bas contenu harmonique avec un facteur de puissance unitaire: le fonctionnement de ces systèmes doit être correct face à des situations non idéales du réseau comme variations de fréquence, creux de tension ou réseaux faibles, parmi d’autres. Dans cet esprit et pour améliorer la qualité des courants du réseau, les filtres LCL sont vastement utilisés à l’entrée des VSC pour leur capacité d’atténuation aux hautes fréquences. Néanmoins, la grande résonance qu’ils présentent peut générer des problèmes de robustesse. Pour l’étude de ce phénomène et créer une base pour la conception des contrôlleurs, les modèles mathématiques des VSC ont été obtenus, analysés et discretisés, y compris techniques d’amortissement passives et actives pour le filtre LCL. La technique de commande abordée dans ce travail de recherche s’appelle Adaptive Feedforward Cancellation (AFC), avec laquel il a été possible d’obtenir des contrôlleurs robustes et capables de faire face aux perturbations du réseau nommées précédemment. Les contrôlleurs AFC, constitués de résonateurs, ont été considerés en temps continu et discret, et avec des gains infinis et finis, ainsi qu’un système de limitation anti-windup. Le développement d’une méthode de conception de commande AFC (directement en temps discret) et l’utilisation d’outils de génération de code automatique, ont permis une implementation rapide des contrôlleurs résonantes dans un processeur de signal numérique (DSP). Les résultats expérimentaux obtenus avec les prototypes des convertisseurs monophasé et triphasé (aussi développés pendant cette thèse), réalerment la robustesse de cette technique de commande.
És un fet que la presència de fonts de generació d’energia distribuïda al sector elèctric està creixent exponencialment a nivell mundial. Això es deu principalment a l’increment de la producció d’energies renovables, directament vinculades a convertidors estàtics de potència monofàsics i trifàsics (VSC) connectats a la xarxa elèctrica. Pel que fa a la normativa en l’àmbit dels inversors de mitjanes i altes potències, ja no és solament necessari que els convertidors generin corrents amb baix contingut harmònic amb un factor de potència unitari, sinó que el funcionament d’aquests equips deu ser correcte enfront de situacions no ideals de la xarxa com ara variacions de freqüència, forats de tensió o xarxes febles, entre altres. D’acord amb l’anterior, i per millorar la qualitat dels corrents de xarxa, els filtres LCL són àmpliament utilitzats a l’entrada dels VSC per la seva capacitat d’atenuació a altes freqüències. No obstant això, la gran ressonància que presenten pot generar problemes de robustesa. Per estudiar aquest fenomen i crear una base per al disseny dels controladors, s’han obtingut, analitzat i discretitzat els models matemàtics dels VSC connectats a la xarxa, incloent tècniques d’esmorteïment passives i actives per al filtre LCL. La tècnica de control abordada en aquest treball de recerca es denomina Adaptive Feedforward Cancellation (AFC), amb la qual s’han aconseguit dissenys robustos i capaços de fer front a les pertorbacions de la xarxa detallades anteriorment. Els controladors AFC, formats per ressonadors, han sigut considerats en temps continu i discret, i amb ganàncies infinita i finita, juntament amb un sistema de limitació anti-windup. El desenvolupament d’un mètode de disseny de control AFC (directament en temps discret) i l’ús d’eines de generació automàtica de codi, han permès una ràpida implementació dels controladors ressonants en un processador digital de senyals (DSP). Els resultats experimentals obtinguts amb els prototips de convertidors monofàsic i trifàsic (també desenvolupats durant aquesta tesi), confirmen la robustesa d’aquesta tècnica de control
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Martin, Fregelius. "Power electronics and controller interface for a Voltage Source Converter." Thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-322903.
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The purpose of the thesis is to develop a system for a split-rotor drive and evaluatecontrollers and their internal components such as processors, communicationprotocols and execution speed for controlling magnetization currents in a hydropower station.The first part of the thesis builds the theory review and provides an introduction tothe most common processors and controllers available. The processors which wasevaluated were microprocessor, DSP and FPGA which have a high capacity andvariety of implementation possibilities. Two controllers, PLC and PAC whereevaluated, which contain some or several of the processors and have a wide variety ofinputs and outputs and support as well several communication protocols.Three different communication protocols; WLAN 802.11, Ethernet 802.3 andBluetooth 802.15.1. Evaluation was made by comparing BER, throughput, speed and implementationcomplexity. The second part of the thesis was to develop and order an interface card forconnecting power-electronics and measurements circuits for the system, based on thetheory and evaluation of the controller and communication protocols.
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Hussain, Essam Khalafalla Ali. "Parallel single phase voltage source converters topologies fed from renewable energy resources." Thesis, University of Sheffield, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.632727.
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Zhang, Di. "Analysis and Design of Paralleled Three-Phase Voltage Source Converters with Interleaving." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27579.
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Three-phase voltage source converters(VSCs) have become the converter of choice in many ac medium and high power applications due to their many advantages, including low harmonics, high power factor, and high efficiency. Modular VSCs have also been a popular choice as building blocks to achieve even higher power, primarily through converter paralleling. In addition to high power ratings, paralleling converters can also provide system redundancy through the so-called (N+1) configuration for improved availability, as well as allow easy implementation of converter power management. Interleaving can further improve the benefit of paralleling VSCs by reducing system harmonic currents, which potentially can increase system power density. There are many challenges to implement interleaving in paralleled VSCs system due to the complicated relationships in a three-phase power converter system. In addition, to maximize the benefit of interleaving, current knowledge of symmetric interleaving is not enough. More insightful understanding of this PWM technology is necessary before implement interleaving in a real paralleled VSCs system.
In this dissertation, a systematic methodology to analyze and design a paralleled three-phase voltage source converters with interleaving is developed. All the analysis and proposed control methods are investigated with the goal of maximizing the benefit of interleaving based on system requirement.
The dissertation is divided into five sections. Firstly, a complete analysis studying the impact of interleaving on harmonic currents in ac and dc side passive components for paralleled VSCs is presented. The analysis performed considers the effects of modulation index, pulse-width-modulation (PWM) schemes, interleaving angle and displacement angle. Based on the analysis the method to optimize interleaving angle is proposed. Secondly, the control methods for the common mode (CM) circulating current of paralleled three-phase VSCs with discontinuous space-vector modulation (DPWM) and interleaving are proposed. With the control methods, DPWM and interleaving, which is a desirable combination, but not considered possible, can be implemented together. In addition, the total flux of integrated inter-phase inductor to limit circulating current can be minimized. Thirdly, a 15 kW three phase ac-dc rectifier is built with SiC devices. With the technologies presented in this dissertation, the specific power density can be pushed more than 2kW/lb. Fourthly, the converter system with low switching frequency is studied. Special issues such as beat phenomenon and system unbalance due to non-triplen carrier ratio is explained and solved by control methods. Other than that, an improved asymmetric space vector modulation is proposed, which can significantly reduce output current total harmonic distortion (THD) for single and interleaved VSCs system. Finally, the method to protect a system with paralleled VSCs under the occurrence of internal faults is studied. After the internal fault is detected and isolated, the paralleled VSCs system can continue work. So system reliability can be increased.Ph. D.
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Terciyanli, Alper. "Design And Implementation Of A Current Source Converter Based Active Power Filter For Medium Voltage Applications." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611767/index.pdf.
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This research work is devoted to the design, development and implementation of a Current Source Converter (CSC) based Active Power Filter (APF) for Medium Voltage (MV) applications. A new approach has been proposed to the design of the CSC based APF for reducing the converter kVA rating considerably. This design approach is called the Selective Harmonic Amplification Method (SHAM), and is based on the amplification of some selected harmoniccurrent components of the CSC by the input filter, and the CSC control system, which is specifically designed for this purpose. The proposed SHAM has been implemented on the first industrial CSC based APF for the elimination of 11th and 13th current harmonics of 12-pulse rectifiers fed from Medium Voltage (MV) underground cables in order to comply with IEEE Std. 519-1992. 450 kVA rated APF with only 205 kVA CSC rating has been connected to the MV bus via a coupling transformer of 600kVA, 34.5/1.1 kV. The power stage of the CSC based APF is composed of water-cooled high voltage IGBT and diode modules. Reference currents to be generated by the CSC are obtained by the use of a selective harmonic extraction method, by mploying synchronously rotating reference frames for each selected harmonic component. An Active damping method is also used to suppress the oscillations around the natural frequency of the input filter, excluding the harmonic components to be eliminated by APF. Simulation and field test results have shown that SHAM can successfully be applied to a CSC based APF for reduction of converter kVA rating, thus making it a cost- competitive alternative to voltage source converter based APFs traditionally used in industry applications.
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Perera, Lasantha Bernard. "Multi Level Reinjection ac/dc Converters for HVDC." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1085.
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A new concept, the multi level voltage/current reinjection ac/dc conversion, is described in this thesis. Novel voltage and current source converter configurations, based on voltage and current reinjection concepts are proposed. These converter configurations are thoroughly analyzed in their ac and dc system sides. The fundamentals of the reinjection concept is discussed briefly, which lead to the derivation of the ideal reinjection waveform for complete harmonic cancellation and approximations for practical implementation. The concept of multi level voltage reinjection VSC is demonstrated through two types of configurations, based on standard 12-pulse parallel and series connected VSC modified with reinjection bridges and transformers. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. The multi level current reinjection CSC is also described using two configurations based on standard 12-pulse parallel and series connected CSC modified with associated reinjection circuitry. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. Taking the advantage of zero current switching in the main bridge valves, achieved through multi level current reinjection, an advanced multi level current reinjection scheme, consisting thyristor main bridges and self-commutated reinjection circuitry is proposed. This hybrid scheme effectively incorporates self-commutated capability into a conventional thyristor converter. The ability of the main bridge valves to commutate without the assistance of a turn-off pulse or line commutating voltage under the zero current condition is explained and verified by EMTDC simulations. Finally, the applications of the MLCR-CSC are discussed in terms of a back to back HVDC link and a long distance HVDC transmission system. The power and control structures and closed loop control strategies are presented. Dynamic simulation is carried out on PSCAD/EMTDC to demonstrate the two systems ability to respond to varying active and reactive power operating conditions.
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Lamont, Lisa Ann. "Modelling and control of a VSC (voltage source converter) tranmission system." Thesis, University of Ulster, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414074.
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Zhao, Xiaodong. "Advanced control of voltage source converter based multi-terminal HVDC systems." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676499.
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This thesis focuses on the advanced control methods for multi-terminal High Voltage Direct Current (HVDC) systems integrating offshore wind farms. Several key issues are investigated in this thesis, including controller design to improve the system dynamic performance, power loss reduction with controller optimization, system stability and dynamics assessment. A DC voltage backstepping control method is designed considering the cable dynamics and controller delay effects. DC cable and converter current loop dynamics are included in the voltage controller design. This control method is applied to a point-to-point and a 4-terminal HVDC system with a conjunction point. Simulation results show that the controller performance can be improved in terms of the disturbance rejection., The relation between Voltage Source Converter (VSC) control action and power losses in the multi-terminal HVDC systems is investigated. For a 4-terminal system, it is shown that the transmission loss can be reduced by properly setting the droop gain ratio between different terminals. For each converter, it is demonstrated by simulation that through a proper controller design, the power loss can be significantly reduced while controller performance can be maintained. A new droop setting design method is proposed. It is shown that due to the existence of droop control, DC voltage deviation will affect the power flow accuracy when the steady state is changed. The impact of DC voltage deviation on the power flow accuracy is studied to tackle this problem, and the DC voltage deviation can be kept unchanged, without affecting the steady state power flow. A droop gain selection procedure is proposed to satisfy the system stability requirement. A state feedback enhanced droop controller is proposed to improve the dynamic performance and stability requirement. With the proposed method, it is shown that the system stability can be guaranteed under both small and large droop gains.
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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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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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Raza, Muhammad. "Offshore grid control of voltage source converters for integrating offshore wind power plants." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461835.
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The offshore grid in North and Baltic Sea can help Europe to achieve 2020 and 2030 renewable energy target to counter climate changes . The formation of offshore grid requires the interconnection between several offshore wind power plants with multiple onshore grids. A voltage source converter based high voltage direct current transmission system is suitable to operate such an integrated offshore network. The offshore grid will enhance the trade between countries, provide better infrastructure for offshore wind power plants integration, and improve the energy market.
This thesis presents the control system design of voltage source converter to operate an offshore grid. The offshore grid is built gradually , starting from the integration of a single offshore wind power plan! till combined offshore AC and OC network in arder to perform the power system analysis associated with the networks such as steady-state power flow, dynamic behavior, network stability, and short circuit response. The research presents the method of determining control parameters with respect of power distribution and network stability requirements.
The research presents the frequency and voltage droop schemes to enhance the grid-forming mode of voltage source converter to operate in parallel in the offshore grid. A multi-objectives optimal power flow algorithm is proposed to determine the frequency and voltage droop gains in order to control the active and reactive power distribution among converters. Later, the impact of these droop gains on network dynamics and stability are analyzed. The study shows that the converter performance influences the offshore AC network stability in conjunction with the droops control loop.
Furthermore, a short circuit and frequency coordinated control schemes are presented for both offshore wind generation units and grid-forming converters . The frequency coordinated control scheme reduces !he wind power up to the maximum available export capacity after the disturbance in the offshore grid. lt is suggested that !he coordination control mus! have both frequency and over voltage control for improved transient response.
In the end, converter control of mullí-terminal OC network and its integration with the offshore AC network has been presentad. The research demonstrate the converter ability to control the distribution of power among the transmission system while ensuring the network stability. The finding of the research can be applied to derive the information and recommendation for the future wind power plants projects.Las redes eléctricas marítimas en el Norte y en el Mar Báltico pueden ayudar a Europa a conseguir los objetivos para 2020 y 2030 de combatir el cambio climático. La formación de la red eléctrica marítima requiere la interconexión entre varios parques eólicos marinos con múltiples redes eléctricas en tierra. Un convertidor de la fuente de voltaje basado en el sistema de transmisión de corriente directa de alto voltaje es el apropiado para poder operar una red marítima integrada. Las redes eléctricas marítimas aumentarán el comercio entre países, proveerán una mejor infraestructura para la integración de los parques eólicos marinos y mejorarán el mercado energético. Esta tesis presenta el diseño del sistema de control del convertidor de las fuentes de voltaje para operar una red eléctrica marítima. La red eléctrica marítima se construye gradualmente, empezando por la integración de un solo parque eólico marino hasta la combinación de redes eléctricas marítima en CA y CD, esto para mejorar el análisis del sistema de potencia asociado con las redes, tales como el flujo de potencia en estado estacionario, el comportamiento dinámico, la estabilidad de la red y la respuesta en corto circuito. La investigación presenta el método de determinación de parámetros de control con respecto a la distribución de potencia y los requerimientos de estabilidad de la red. La investigación presenta los esquemas de frecuencia y la caída de voltaje para mejorar el método de formación de red del convertidor de la fuente de voltaje y operar en paralelo con la red eléctrica marítima. Se propone un algoritmo de múltiples objetivos para lograr un flujo de potencia óptimo, determinar las ganancias en la frecuencia y en la caída de voltaje y así lograr controlar la distribución de potencia activa y reactiva entre los convertidores. Después, se analiza el impacto de estas ganancias en la dinámica y estabilidad de la red. El estudio nos muestra que el desempeño del convertidor influencia la estabilidad de la red eléctrica marítima en CA en conjunto con el lazo de control de la caída. Así mismo, se presentan los esquemas de control coordinado de frecuencia y corto circuito, aplicados para las unidades de generación eólica marítima y los convertidores en red. El esquema de control coordinado de frecuencia reduce la potencia eólica hasta la máxima capacidad de exportación disponible después de las perturbaciones en la red eléctrica marítima. Se sugiere que la coordinación del control debe de tener control sobre la frecuencia y el sobre voltaje para mejorar la respuesta en transitorios. Por último, se presenta el control del convertidor de las multiterminales en la red CD y su integración con la red eléctrica marítima en CA. La investigación demuestra la habilidad que posee el convertidor para controlar la distribución de potencia, junto con el sistema de transmisión, mientras se asegura la estabilidad de la red. Los hallazgos de esta investigación pueden ser aplicados para obtener información y recomendaciones en los futuros proyectos de parques eólicos.
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Mohan, Sumitha. "Stability and disturbance compensation using digital control for grid connected voltage source converters /." Dresden : TUDpress, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016239313&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Li, Peng. "New types of voltage source converters applied in flexible AC transmission system devices." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25774.
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The uses of flexible alternating current transmission system (FACTS) controllers in next generation smart grids are encouraged by the increased uses of decentralized and highly meshed grid structures that may affect the stability of power systems. Voltage source converter (VSC) based FACTS devices have reduced footprint and offer increased control flexibility, extended range and faster reaction time than line commutated thyristor based equivalent solutions. The performance of commonly used FACTS devices that employ a two-level converter is summarized. Then, multilevel converters and direct AC-AC converters which are viable for FACTS applications are reviewed. The outcomes of the literature surveys are refined to identify new features that may be critical for future centralised and decentralized smart grids such as: control range extension, improved efficiency and power density at reduced hardware cost. To pursue these features, three novel VSC topologies are proposed and analysed: An AC voltage-doubled (ACVD) topology with an internal inverting buck-boost cell in each phase-leg, is able to synthesize twice the output voltage of a conventional two-level VSC for the same dc link voltage, is proposed. A number of new modulation and control strategies that aim to further increase DC utilization of the ACVD converter and to manage its internal dynamic interaction to prevent the appearance of low-order harmonics in the output currents, are presented. With its high DC-rail utilization and sophisticated control strategies, the ACVD converter offers an extended power control range, which is increasingly important for shunt and series type FACTS devices. The controlled transition full-bridge hybrid multilevel converter (CTFB-HMC) with chain-links of full-bridge cells is proposed to combine the advantages of improved wave-shaping ability, reduced footprint and high efficiency, which promote its applications in medium and high voltage FACTS devices. An AC hexagonal chopper using heterodyne modulation to decouple the control of AC voltage amplitude from that of the phase-angle is proposed. For scalability to medium and high voltage, a modular multilevel AC hexagonal chopper (M2AHC) is developed. With adoption of a quasi-two-level transitional mode for reduced cell number and minimized footprint, dv/dt is limited and reliability is improved. Simulation and experimentation are used to validate the modulation, control and FACTS implementation of the three proposed converters.
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Lu, Weixing 1966. "Control and application of multi-terminal HVDC based on voltage-source converter." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82921.
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A Multi-Terminal Direct Current (MTDC) system consists of several Voltage-Source Converters (VSCs) whose dc terminals are connected in shunt across the buses of a dc network. The dc voltages are determined by the electric charges stored across the dc capacitor of every Voltage-Source Converter (VSC). As dc over-voltage leads to failure in the solid-state switches and dc under-voltage leads to waveform distortion, the target of safe, economic design is a narrow voltage margin of about 5% around a nominal dc voltage rating. The worst case scenario consists of an accidental loss of a Voltage-Source Converter because the sudden large change in dc power causes the dc capacitors to charge up or down, exceeding the voltage margin before power balance can be re-established by local feedbacks of the Voltage-Source Converters (VSCs).Part I of the thesis shows how the target can be achieved by: (1) planning the dc voltage reference setting and the power reference settings of the Voltage-Source Converters (VSCs) which satisfy the voltage margins in steady-state for both the pre-fault and post-fault conditions; (2) incorporating an Advanced DC Voltage Control (ADCVC) which enables the dc voltage margins to be satisfied during the transient periods.
Part II of the thesis is concerned with finding innovative applications for Multi-Terminal Direct Current (MTDC) systems. It shows that the high degree of controllability of the Multi-Terminal Direct Current (MTDC) system can be exploited in: (1) optimal acquistion of wind power in offshore wind-farms; (2) providing premium quality power in underground cable in-feeds of city centers; (3) providing simultaneous inter-area decoupling and local area damping in interconnections.
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AL, Jowder Fawzi A. Rahman. "Embedded SSSC in series capacitor compensation and in voltage source converter station." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84869.
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This thesis shows that series capacitive compensation of transmission lines by a combination of Static Synchronous Series Compensator (SSSC) and dielectric capacitors lowers the cost of series compensation. The SSSC has two functions: (1) to provide some series capacitive reactance compensation; (2) to damp out incipient unstable Subsynchronous Resonance (SSR) modes. Digital simulation using HYPERSIM shows that for an overall capacitive depth of compensation of 0.7 pu, the SSSC component is only about 1/3 of the capacitive Mvar. Based on the transient stability limit, the transmissibility of the line is increased by a factor of 2.23 for a depth of compensation of 0.7.A second objective of this thesis is to extend the application of the SSSC concept. This application is found in HVDC, where there is no synchronizing power. In the family of Voltage-Source Converter (VSC) HVDC, it is possible to embed the control of the SSSC in the converter station so that there is enhanced synchronizing power. The effectiveness of the synchronizing power (together with damping power) is demonstrated through digital simulations of a turbine-generator system which is connected to a VSC-HVDC Station.
The thesis shows that the SSSC has two modes of operation: (1) the constant reactance mode, in which the SSSC voltage is proportional to the line current, and (2) the constant quadrature voltage mode, in which the SSSC voltage is a constant quadrature voltage independent of the line current. A comparison between the two modes shows that the constant reactance mode provides higher synchronizing power and has a higher transient stability limit.
Eigenvalue analysis and digital simulations are the methodologies used.
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Meier, Stephan. "Novel voltage source converter based HVDC transmission system for offshore wind farms." Licentiate thesis, KTH, School of Electrical Engineering (EES), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-568.
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Offshore wind farms have recently emerged as promising renewable energy sources. For increasing distances between offshore generation and onshore distribution grid, HVDC transmission systems based on voltage source converters can be a feasible and competitive solution. This thesis presents a comprehensive evaluation of a novel integrated wind farm topology that includes the generator drive system, the turbine interconnection and the HVDC transmission.
In the proposed concept, every wind turbine is connected to a single-phase medium-frequency collection grid via a distribution transformer and a cycloconverter, which allows the wind turbines to operate at variable speed. The collection grid is connected to an HVDC cable via a transmission transformer and a single-phase voltage source converter. This thesis evaluates in detail the principle of operation, which is also verified with system simulations in PSCAD.
The proposed concept promises several potential benefits. Converter switching losses and stress on the semiconductors for example can be considerably reduced by applying a soft-switched commutation scheme in all points of operation. Single-phase medium-frequency transformers have comparably low losses and their compact size and low weight implies an important benefit in an offshore environment. In addition, the voltage source converter is considerably simplified by the reduction to one phase leg, which implies a substantial cost saving.
Several technical challenges are identified and critically evaluated in order to guarantee the feasibility of the proposed concept. Especially the design of the medium-frequency collection grid is crucial as unwanted system resonances can cause dangerous overvoltages. Most of the technical challenges concern the specific characteristics of the proposed concept. The insulation of the single-phase medium-frequency transformers for example needs to withstand the high voltage derivatives. This thesis contains also considerations regarding the dimensioning and optimization of different system components.
A survey of different transmission systems for the grid connection of wind farms shows the potential of the proposed concept, which addresses several problems associated with electrical systems of wind farms. Both the requirements for variable-speed operation of the wind turbines and an interface for HVDC transmission are fulfilled in a cost-effective way. Compared to conventional voltage source converter based HVDC transmission systems, the initial costs are reduced and the expected annual energy production is increased. In addition, the proposed voltage source converter based HVDC transmission system can fully comply with recent requirements regarding the grid connection of wind farms.
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Xu, Ling. "Modeling, Analysis and Control of Voltage-Source Converter in Microgrids and HVDC." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4967.
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The objective of this dissertation is to carry out dynamic modeling, analysis and control for Voltage-Source Converters (VSC). Two major applications of VSC will be investigated in this dissertation: microgrid application and High Voltage Direct Current (HVDC) application.
In microgrid applications, VSC is used to integrate distributed energy sources such as battery and provide system functions: such as real and reactive power regulation, voltage and frequency support during islanding condition, and abnormal system condition mitigation. In HVDC applications, VSC is used to interconnect dc systems with ac systems. The functions supplied by VSC are similar to that in microgrids. However, the transfer capability and stability in such kind of system are of major interests.
Therefore, Part I of this dissertation focuses on VSC's applications in microgrids. A battery's inverter can be operated in both grid-connected PQ regulation mode and voltage and frequency support mode during islanding condition. Transition scheme between these two control modes is firstly investigated to guarantee a smooth dynamic performance. Secondly, a coordinated control strategy between battery's and PV station's VSCs is developed to improve microgrid's power flow. Thirdly, power quality improvement through the battery's inverter is investigated. VSC's control and capability for microgrid operation at normal, transient, and abnormal conditions will be modeled and analyzed.
Part II of this dissertation focuses on VSC's applications in HVDC. The following topics are investigated in this dissertation: (i) how to design VSC-HVDC's controller using system identification method? (ii) How to coordinate VSCs in multi-terminal HVDC scenarios? And (iii) how to determine VSC-HVDC system's transfer capability based on stability limits? High-fidelity simulation technology is employed to tackle control validation while frequency domain impedance modeling technique is employed to develop analytical models for the systems. With linear system analysis tools such as Nyquist plots and Bode plots, stability limits and impacting factors of VSC-HVDC systems can be identified.
This dissertation led to four journal papers (two accepted, one request of revision, one to submit) and five conference papers. The major contributions of this dissertation include:
1) Developed VSC and microgrid models in high-fidelity simulation environment. Developed and validated VSC control schemes for variety of microgrid operations: normal, abnormal, and transient. The developed technologies can facilitate a battery to make up solar power, improve system dynamic performance during transients, and improve power quality.
2) Developed VSC-HVDC simulation models, including two-terminal HVDC and multi-terminal HVDC. Developed VSC-HVDC control schemes for two-terminal and multi-terminal systems. Developed analytical impedance models for VSC-HVDC systems and successfully carried out stability limit identification.
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Sen, Gokhan. "Voltage and Current Programmed Modes in Control of the Z-Source Converter." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1226508637.
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Cwikowski, Oliver. "Synthetic testing of high voltage direct current circuit breakers." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/synthetic-testing-of-high-voltage-direct-current-circuit-breakers(2f15e62f-8b2c-4e29-884e-323b90af2d11).html.
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The UK is facing two major challenges in the development of its electricity network. First, two thirds of the existing power stations are expected to close by 2030. Second, is the requirement to reduce its CO2 emissions by 80% by 2050. Both of these challenges are significant in their own right. The fact that they are occurring at the same time, generates a significant amount of threats to the existing power system, but also provides many new opportunities. In order to meet both these challenges, significant amounts of offshore wind generation has been installed in the UK. For the wind generation with the longest connections to land, Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) transmission has to be used. Due to the high power rating of the offshore wind farms, compared to the limited transmission capacity of the links, a large number of point-to-point connections are required. This has lead to the concept of HVDC grids being proposed, in order to reduce the amount of installed assets required. HVDC grids are a new transmission environment and the fundamental question of how they will protect themselves must be answered. Several new technologies are under consideration to provide this protection, one of which is the HVDC circuit breaker. As HVDC circuit breakers are a new technology, they must be tested in a laboratory environment to prove their operation and improve their Technology Readiness Level (TRL). This thesis is concerned with how such HVDC circuit breakers are operated, rated, and tested in a laboratory environment. A review of the existing circuit breaker technologies is given, along with descriptions of several novel circuit breakers developed in this thesis. A standardized method of rating DC circuit breaker and their associated test circuit is developed. Mathematical analysis of several circuit breakers is derived from first principles and low power prototypes are developed to validate these design concepts. A high power test circuit is then constructed and a semiconductor circuit breaker is tested. The key learning outcomes from this testing are provided.
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Paterakis, Fotis Konstantinos. "Development of alternative pulse width modulation methods for conventional and multilevel voltage source inverters." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/13856.
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Multilevel inverters have attracted wide interest in both the academic community and the industry for the past decades. Therefore, the investigation and development of modulation strategies in multilevel inverters emerges as a necessity for the industry and researchers. In this doctoral thesis, alternative modulation methods suitable for three-level conventional single-phase inverters and especially for cascade H-bridge multilevel inverters are discussed and proposed. The theory of Equal Areas is reformed and presented and its modifications are proposed. These modifications are compared with other well-known modulation schemes, such as carrier-based modulation schemes and programmed pulse width modulation techniques. The advantage of the modified Equal Areas Pulse Width Modulation (EAPWM) is its algorithmic simplicity due to simple algebraic relationships, which results in less computational effort. A fully mathematical formulation for the Equal Areas modulation is proposed for both conventional and multilevel inverters. The EAPWM is shown to produce well-formed switched output voltages that have low total harmonic distortion at even low switching frequencies. The importance of this thesis is complimented by the results, produced after the implementation of EAPWM in multilevel inverters, which can be used as a more accurate reference when compared with other modulation strategies. Moreover, this direct modulation strategy has been extended to work on higher amplitude modulation ratios, in a linear manner, while entering the over modulation region. In this context, modified algorithms have been developed using different criteria for the calculation of the pulses’ width and their placement inside the time interval. The equal areas method, implemented in conventional single-phase inverters, uses odd pulse numbers per half cycle, holding integer frequency ratios in contrast to its implementation in multilevel inverters, where non-integer frequency ratios occur due to the level-by-level application. The application of the method is verified by simulations together with experimental work using a full-scale prototype inverter.
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Høvik, Kristin Malene. "Control of Offshore Passive Platform System Voltage and Frequency through Control of Onshore Back-to-Back Voltage Source Converters." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14137.
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This thesis work shows implementation and testing of existing control strategies in a novel offshore passive platform configuration. Control of the platform voltage and frequency is done through control of a shore-based B2B-VSC configuration, when the frequency on shore differs from the frequency on the platform. An 80 km HVAC-cable and transformers separates the shore-based B2B-VSCs from the platform installation. The system is modeled and simulated in MATLAB® Simulink™ SimPowerSystems™. The grid-side VSC is applied conventional cascaded controllers, with an inner current control loop and outer loops controlling the DC-link voltage and the flow of reactive power from the grid. Two different control strategies were implemented for the platform-side VSC, denoted as control strategy 1 and 2. Control strategy 1 controls the platform voltage magnitude, while keeping the frequency fixed, and is implemented with a simple PI-controller. Control strategy 2 controls both platform voltage magnitude and frequency, and was based on a cascaded control configuration, similar to that of a weak-grid system, implemented for the passive platform system. Both control strategies were implemented for the platform system and tested for three worst-case changes of platform load: loss of all loads, increase of passive load and large induction motor starting. The platform steady-state and transient voltages and frequency were evaluated based on the requirements for voltage and frequency defined in IEC 61892: standard for mobile and fixed offshore units, electrical installations. Control strategy 1 was tested for both normal and autonomous operation, when a constant DC-link voltage was applied. It was also tested for full B2B-VSC configuration, with the grid-side system VSC controlling the DC-link voltage and flow of reactive current from the grid. In all the three configurations, control strategy 1 failed to meet the system requirements set by the IEC 61892 standard for allowable voltage magnitude transients during loss-of-all-load and large-induction-motor-start. Control strategy 2 was tested with constant DC-link voltage when platform voltage measurements were available. The simulation results show no visible voltage or frequency transients for any of the three load change tests applied, and the system operation satisfies the IEC 61892 requirements for all the worst-case load change tests. The platform voltage and frequency are independent of the load dynamics, which is a desirable quality when controlling the voltage on a complex platform configuration. Control strategy 2 shows promising potential for controlling the platform voltage and frequency from shore. However, further research and testing must be done before this control strategy can be utilized in a real platform system. The proposed system controlled by control strategy 2 would allow removal of the low efficiency, high emission gas turbine driven synchronous generator that are the standard power source on oil platforms today. Eliminating the need for, or usage of the gas turbine, for power production on offshore oil and gas platforms, could reduce the total CO2 and NOx emissions of the petroleum sector considerably.
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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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Namburi, Krishna Mohan Pavan Kumar. "A Novel Dithering Algorithm to Reduce Electro Magnetic Interference in Voltage Source Inverters." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1342106230.
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Ucak, Onur. "Design And Implementation Of A Voltage Source Converter Based Hybrid Active Power Filter." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611095/index.pdf.
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This research work is devoted to the analysis, design and implementation of a shunt connected Hybrid Active Power Filter by the use of a lower rated voltage source PWM converter, and a series connected LC passive filter. In recent years, voltage and current harmonics have become a serious problem both in transmission and distribution systems, due to the widespread usage of non-linear loads such as diode/thyristor rectifiers, electric arc furnaces and motor drives. In order to obtain a better performance than those of the conventional passive filter solutions, active power filters (APF) have been worked on and developed. Among various
configurations listed in the literature, conventional shunt connected voltage source active power filter is widely used in industrial applications. Unfortunately, for large power applications, the losses and the rating of the APF increase considerably. As a result, various hybrid filter topologies have been developed which combine the advantages of both passive and active filters.
In this thesis, a shunt connected hybrid active power filter is developed by combining a 4.7 kVA voltage source converter and a 30kVAR 7th harmonic passive filter. The developed system has been implemented to eliminate the most dominant 5th, 7th and 11th current harmonic components existing at 400V low voltage bus of TUBITAK SPACE Technologies Institute. The theoretical and experimental results have shown
that the DC link voltage of the converter and the rating of APF are minimized while keeping the filtering performance satisfactory.
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Bicer, Nazan. "A Current Source Converter Based Statcom For Reactive Power Compensation At Low Voltage." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12612007/index.pdf.
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This research work is devoted to the analysis, design and development of the Current-Source Converter (CSC) based distribution-type Static Synchronous Compensator (D-STATCOM) for low-voltage applications in reactive-power control in order to achieve i) faster transient response in reactive-power control, ii) lower current harmonic distortion, iii) lower power losses and iv) minimum storage elements in comparison with conventional solutions. The developed CSC-D-STATCOM includes a low-pass input filter and a three phase forced-commutated CSC which is composed of six insulated gate bipolar transistors (IGBT) with built-in series diodes. The analysis and the control of the CSC-D-STATCOM are carried out in dq-synchronous reference frame in order to obtain the reference current waveform which is to be generated by switching the IGBTs at 3kHz with the use of space vector modulation.
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Hamad, Mostafa Saad Abdallah. "Performance improvement of a medium-voltage series-connected twelve-pulse current source converter." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607443.
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This thesis investigates the performance of a medium-voltage (MV) 12-pulse controlled rectifier in conjunction with a tapped front-end transformer used with a shunt active power filter (APF) for ac-side compensation. A series APF based on a magnetic amplifier is used for dc-side compensation. The series APF is coupled with the shunt APF to a common controlled dc-bus. forming an ac/dc unified power controller. An operating power locus is introduced that combines symmetrical and asymmetrical firing of the two constituent 6-pulse converters. It provides the ' lowest' total harmonic distortion (THO) with a maximum reactive power of 0.5 pu. Even with the proposed power locus, a harmonic compensation technique is mandatory. Hence a shunt APF is connected to the secondary taps of the front-end, star/star/delta, transformer to improve the input current THD and power factor. The APF with predictive current control and synchronous d-q frame base control arc used. To avoid time delay effects, the actual APF inverter transfer function is u.sed to formulate an open loop control strategy, used to achieve better harmonic cancellation than previously investigated techniques. To reduce the active filter current, a fixed shunt capacitor bank is connected to the transformer secondary taps to offset the proposed power locus and consequently, to minimize VAr compensation required of the APF. A series APF with a magnetic amplifier is used as a voltage harmonic compensator on the deside. It improves the output voltage ripple factor (RF) and reduces the de-link smoothing inductance requirement. Coupling both compensation techniques improves the supply current TI-ID, produces a near unity power factor, and the output voltage RF is reduced. An auxiliary dc-voltage source for the series APF is avoided by coupling the two compensators back-to-back. MATLAi3 simulation results for the MY system are experimental1y verified with a scaled low-voltage prototype system.
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Brinsfield, Jason. "Modeling and Simulation of Parallel D-STATCOMs with Full-Wave Rectifiers." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1209.
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In recent years, both a significant increase in electrical demand and a large influx of intermittent renewable energy sources have put a considerable stress on the nation’s electrical grid. Conventional power flow control techniques such as capacitor banks and tap-changing transformers are incapable of adequately handling the rapid fluctuations in power supply and demand that today’s grid experiences. Flexible AC Transmission System (FACTS) controllers are a practical way to compensate for such rapid power fluctuations. One type of shunt FACTS controller is the Static Synchronous Compensator (STATCOM), which uses fully controllable switches to source or sink reactive power to a point on the grid, thus reducing voltage fluctuations due to load changes. The purpose of this thesis is to model and simulate the operation of two Distribution STATCOMs (D-STATCOMs) operating on the same point on the grid. These D-STATCOMs also utilize parallel full-wave rectifiers that directly connect the ac grid to the dc capacitor of the D-STATCOMs. Parameters such as power loss, reaction time, stability, and THD are measured for several test scenarios. Results from this thesis show that two D-STATCOMs operating on the same point can be stable and effective under a wide range of conditions. This thesis also concludes that the inclusion of parallel rectifiers with the D-STATCOMs results in no performance improvement of the D-STATCOMs.
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Cha, Han Ju. "Analysis and design of matrix converters for adjustable speed drives and distributed power sources." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/1048.
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Recently, matrix converter has received considerable interest as a viable alternative to the conventional back-to-back PWM (Pulse Width Modulation) converter in the ac/ac conversion. This direct ac/ac converter provides some attractive characteristics such as: inherent four-quadrant operation; absence of bulky dc-link electrolytic capacitors; clean input power characteristics and increased power density. However, industrial application of the converter is still limited because of some practical issues such as common mode voltage effects, high susceptibility to input power disturbances and low voltage transfer ratio. This dissertation proposes several new matrix converter topologies together with control strategies to provide a solution about the above issues.
In this dissertation, a new modulation method which reduces the common mode voltage at the matrix converter is first proposed. The new method utilizes the proper zero vector selection and placement within a sampling period and results in the reduction of the common mode voltage, square rms of ripple components of input current and switching losses.
Due to the absence of a dc-link, matrix converter powered ac drivers suffer from input voltage disturbances. This dissertation proposes a new ride-through approach to improve robustness for input voltage disturbances. The conventional matrix converter is modified with the addition of ride-through module and the add-on module provides ride-through capability for matrix converter fed adjustable speed drivers.
In order to increase the inherent low voltage transfer ratio of the matrix converter, a new three-phase high-frequency link matrix converter is proposed, where a dual bridge matrix converter is modified by adding a high-frequency transformer into dc-link. The new converter provides flexible voltage transfer ratio and galvanic isolation between input and output ac sources.
Finally, the matrix converter concept is extended to dc/ac conversion from ac/ac conversion. The new dc/ac direct converter consists of soft switching full bridge dc/dc converter and three phase voltage source inverter without dc link capacitors. Both converters are synchronized for zero current/voltage switching and result in higher efficiency and lower EMI (Electro Magnetic Interference) throughout the whole load range. Analysis, design example and experimental results are detailed for each proposed topology.
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Shah, Shahil. "Small and Large Signal Impedance Modeling for Stability Analysis of Grid-connected Voltage Source Converters." Thesis, Rensselaer Polytechnic Institute, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10786614.
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Interactions between grid-connected converters and the networks at their terminals have resulted in stability and resonance problems in converter-based power systems, particularly in applications ranging from wind and PV farms to electric traction and HVDC transmission networks. Impedance-based modeling and analysis methods have found wide acceptance for the evaluation of these resonance problems.
This thesis presents small and large signal impedance modeling of grid-connected single and three phase voltage source converters (VSC) to enable the analysis of resonance conditions involving multiple frequency components, and both the ac and dc power systems at the VSC terminals. A modular impedance modeling approach is proposed by defining the VSC impedance as transfer matrix, which captures the frequency cross-coupling effects and also the coupling between the ac and dc power systems interfaced by the VSC. Ac and dc impedance models are developed for a VSC including the reflection of the network on the other side of the VSC. Signal-flow graphs for linear time-periodic (LTP) systems are proposed to streamline and visually describe the linearization of grid-connected converters including the frequency cross-coupling effects. Relationships between the impedance modeling in dq, sequence, and phasor domains are also developed. The phasor-domain impedance formulation links the impedance methods with the phasor-based state-space modeling approach generally used for bulk power systems. A large-signal impedance based method is developed for predicting the amplitude or severity of resonance under different grid conditions. The small-signal harmonic linearization method is extended for the large-signal impedance modeling of grid-connected converters. It is shown that the large-signal impedance of a converter is predominantly shaped by hard nonlinearities in the converter control system such as PWM saturation and limiters.
This thesis also deals with the problem of synchronizing a generator or microgrid with another power system. A VSC-based synchronizer is proposed for active phase synchronization and a distributed synchronization method is developed for microgrids.
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Joseph, Tibin. "Operation and control of voltage source converters in transmission networks for AC system stability enhancement." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/111498/.
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The rapid expansion in power transmission for the integration of large-scale renewables is foreseen in the future. This will be complemented by infrastructure reinforcements in the form of series compensation and high-voltage direct current (HVDC) links. These changes will bring forth new operability challenges to grid operators. The stability issues pertained to such reinforcements: potential threat of subsynchronous resonance (SSR) and frequency regulation will be investigated in this thesis. Utilising the existing and future voltage source converters (VSC) based HVDC links to support the AC system by proving ancillary services will be of significant importance in the coming decades. The research work presented in this thesis is aimed to address these challenges, in particular, the technical barriers associated with AC/DC interaction and to propose measures to avoid any potential instability. The main contributions of this research work comprise of four parts, namely, (1) analysis of interactions in-terms of SSR in AC/DC grids, (2) design of SSR damping (SSRD) controllers, (3) experimental demonstration of SSRD schemes, and (4) assessment and improvement of frequency regulation in a wind-thermal bundled AC/DC grid. An VSC-HVDC connected series-compensated AC system resembling the Great Britain (GB) power system has been used as the test network to evaluate the operability challenges pertained to the reinforcements. A state-space representation has been formulated and an eigenvalue analysis has been performed to assess the impact of VSC-HVDC on the torsional modes of nearby connected thermal generation plants. This is followed by damping torque investigation for SSR screening with the results compared against time-domain simulations for testing the accuracy of the small-signal models for SSR studies. A series of SSRD schemes is presented which have been integrated with the VSC-HVDC to damp SSR in the series-compensated GB power system. In addition, this thesis proposes an adaptive SSRD method based on the real-time estimation of the subsynchronous frequency v Abstract component present in series-compensated transmission lines–key information for the optimal design of HVDC subsynchronous damping controllers. Furthermore, the combined AC/DC GB network has been implemented in a real-time digital simulator and connected to a VSCHVDC scaled-down test-rig to performhardware-in-the-loop tests. The efficacy and operational performance of the AC/DC network while providing SSR damping is tested through a series of experiments. In order to provide frequency support in a wind-thermal bundled AC/DC system a dualdroop controlmethod is presented. The scheme binds the system frequency with the DC voltage of an HVDC network. For completeness, the performance of the proposed method is compared to conventional frequency regulation schemes. Sensitivity studies and eigenvalue analyses are conducted to assess the impact that wind penetration and changes in the dual-droop coefficient have on grid stability. Experimental validation is performed using a real-time hardware-inthe- loop test-rig, with simulation and experimental results showing a good agreement and evidencing the superior performance of the proposed frequency support scheme.
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Cvetkovic, Igor. "Modeling and Control of Voltage-Controlling Converters for Enhanced Operation of Multi-Source Power Systems." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85850.
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The unconventional improvements in the power electronics field have been the primary reason for massive deployment of renewable energy sources in the electrical power grid over the past several decades. This needed trend, together with the increasing penetration of micro-, and nano- grids, is bringing significant improvements in system controllability, performance, and energy availability, but is fundamentally changing the nature of electronically-interfaced sources and loads, altering their conventionally mild aggregate dynamics, and inflicting low- and high- frequency dynamic interactions that never before existed at this magnitude. This problem is not restricted only to the grid; modern electronic power distribution systems built for airplanes, ships, electric vehicles, data-centers, and homes, comprise dozens, even hundreds of power electronics converters, produced by different manufacturers, who provide very limited details on converters' dynamic behavior - distinctiveness that has the highest impact on how two converters, or converter and a system interact. Consequently, substantial dispersion of power electronics into the future grid will significantly depend on engineers' capability to understand how to model and dynamically control power flow and subsystem interactions. It is therefore essential to continue developing innovative methods that allow easier system-level modeling, continuous monitoring of dynamic interactions, and advanced control concepts of power electronics converters and systems.
The dissertation will start with a "black box" approach to modeling of three-phase power electronics converters, introducing a method to remove source and load dynamics from in-situ measured terminated frequency responses. It will be then shown how converter, itself, can perform an online stability assessment knowing its own unterminated dynamics, and being able to measure all terminal immittances. The dissertation will further advance into an approach to control power electronics converters based on the electro-mechanical duality with synchronous machines, and end with selected examples of system-level operation, where small-signal instability in multi-source power systems can be mitigated using this concept.Ph. D.
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Spahić, Ervin. "Voltage source converter HVDC connection of offshore wind farms and the application of batteries." Aachen Shaker, 2008. http://d-nb.info/992480779/04.
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