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1
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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Badawy, Ahmed Darwish. "Current source dc-dc and dc-ac converters with continuous energy flow." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25915.
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This work considers current sourced powerelectronic converters. The thesis classifies and presents several new single-phase and three-phase differential-mode current source inverters that evolve from the basic dc-dc converter topologies. The switched, large-signal, and small-signal models of these converters are presented, and used to develop control strategies for the proposed differential-mode inverters, considering their inversion and rectification modes. The viability of each differential mode inverter/rectifier is validated using simulations and experimentation. The performances of different proposed buck, boost, and buck-boost current source inverters are discussed and compared in terms of efficiency, total harmonic distortion, input current ripple, capacitor stresses, and control complexity. Some of the proposed current source inverters offer buck-boost capability (can operate with output voltage less or greater than the input dc voltage), which is suited for grid-connected operation of single-stage three-phase buck-boost inverters. Phase variables and synchronous frame controllers are used to provide satisfactory inverter operation in inversion and rectification modes. The inherent low-order harmonic currents in the input and output of the proposed converters (predominantly, negative sequence 2nd order harmonic) are supressed using PI and PR controllers. Also, interleaved carriers are used to reduce the input current ripple of the three-phase inverters. The proposed converters can operate over a full control range from 0 to unity power factor, with power flow in both directions (unlike the conventional six-pulse current inverter). Additionally, a nonlinear control strategy, sliding mode control, is implemented with to achieve faster dynamic inverter response during faults as well as elimination of dccurrent injection into ac grid. This is necessary during unbalanced operation. Operation of single-phase differential-mode buck-boost inverters is presented, including suppression of the 2nd order harmonic in the input dc current by two methods. In the first, active suppression of the 2nd harmonic uses a power electronic circuit. The second method manipulates the modulating signal in combination with a relatively large capacitor to trap the oscillating power that causes the 2nd order harmonic to appear input dc link current. The two single-phase harmonic suppression approaches are compared.
3
Jassim, Bassim M. H. "Active current sharing control schemes for parallel connected AC/DC/AC converters." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/3086.
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The parallel operation of voltage fed converters can be used in many applications, such as aircraft, aerospace, and wind turbines, to increase the current handling capability, system efficiency, flexibility, and reliability through providing redundancy. Also, the maintenance of low power parallel connected units is lower than one high power unit. Significant performance improvement can be attained with parallel converters employing interleaving techniques where small passive components can be used due to harmonic cancellation. In spite of the advantages offered by parallel connected converters, the circulating current problem is still a major concern. The term circulating current describes the uneven current sharing between the units. This circulating current leads to: current distortion, unbalanced operation, which possibly damages the converters, and a reduction in overall system performance. Therefore, current sharing control methods become necessary to limit the circulating current in a parallel connected converter system. The work in this thesis proposes four active current sharing control schemes for two equally rated, directly paralleled, AC/DC/AC converters. The first scheme is referred to as a “time sharing approach,” and it divides the operation time between the converters. Accordingly, in the scheme inter-module reactors become unnecessary, as these are normally employed at the output of each converter. However, this approach can only be used with a limited number of parallel connected units. To avoid this limitation, three other current sharing control schemes are proposed. Moreover, these three schemes can be adopted with any pulse width modulation (PWM) strategy and can be easily extended to three or more parallel connected units since they employ a modular architecture. The proposed current sharing control methods are employed in two applications: a current controller for three-phase RL load and an open loop V/f speed control for a three-phase induction motor. The performance of the proposed methods is verified in both transient and steady state conditions using numerical simulation and experimental testing.
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Santiago-González, Juan Antonio. "Miniaturization of Ac-Dc power converters for grid interface." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120371.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 185-189).<br>In this thesis we present a two-stage ac/dc grid-connected converter for computer applications. Also known as off-line power supplies, these converters have to meet various demanding specifications such as a wide input voltage range (typically 0-376 V), large voltage step down (typical output voltages range from 12-48 V), harmonic current limits and galvanic isolation. The focus of this work is in the reduction in volume of ac/dc converters while keeping efficiency constant or improving it, which is challenging to achieve while meeting all the specifications. The thesis breaks down the converter in subsystems and explores architectural and topological trade-offs, modeling, component selection and control methods. The performance of each individual subsystem is experimentally verified. The first stage of the converter is a step-down power factor correction (PFC) converter. This stage interacts with the grid and draws the necessary ac power from the line and rectifies it. Following the PFC is a capacitor bank, which is used to both buffer the ac power from the line and to provide hold-up energy to the output. The capacitor selection process is detailed in the thesis. The second stage of the converter provides isolation and regulation to the output. Two different approaches to the second stage converter are presented: using commercially available, "plug and play" converters and developing a custom converter. The full system is evaluated with both solutions and is compared to other state of the art converters. The final prototype achieves an efficiency of 95.33% at full power (250 W) and 230 Vac input, and a power density of 35 W/in3.<br>by Juan Antonio Santiago-González.<br>Ph. D.
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Shen, Jian. "GTO Pulsed Width Modulated (PWM) converter for railway traction applications." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308484.
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Anderson, Glenn Warwick Jan. "Hybrid simulation of AC-DC power systems." Thesis, University of Canterbury. Electrical and Computer Engineering, 1995. http://hdl.handle.net/10092/1176.
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Transient stability studies are primarily concerned with the generator response of ac power systems and use only steady state type equations to model HVdc converter terminals. These equations are adequate for small disturbances at the converter terminals but cannot accurately represent a converters behaviour during, and through its recovery of, a significant transient disturbance. A detailed three phase electromagnetic analysis is necessary to describe the converters correct behaviour. This thesis describes an accurate and effective hybrid method combining these two types of studies, for analyzing dynamically fast devices such as HVdc converters within ac power systems. Firstly, conventional techniques are reviewed for both a transient stability analysis of power systems and for an electromagnetic transient analysis of HVdc converters. This review deals in particular with the two programs that constitute the hybrid developed in this thesis. Various techniques are then examined to efficiently and accurately pass the dynamic effects of an HVdc link to an ac system stability study, and the dynamic effects of an ac system to a detailed HVdc link study. An optimal solution is derived to maximise the inherent advantages of a hybrid. Finally, the hybrid is applied to a test system and its effectiveness in performing its task is shown.
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Haryani, Nidhi. "Zero Voltage Switching (ZVS) Turn-on Triangular Current Mode (TCM) Control for AC/DC and DC/AC Converters." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96397.
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One of the greatest technological challenges of the world today is reducing the size and weight of the existing products to make them portable. Specifically, in electric vehicles such as electric cars, UAVs and aero planes, the size of battery chargers and inverters needs to be reduced so as to make space for more parts in these vehicles. Electromagnetic Interference (EMI) filters take up a more than 80 % of these power converters, the size of these filters can be reduced by pushing the switching frequency higher. High frequency operation (> 300 kHz) leads to a size in reduction of EMI filters though it also leads to an increase in switching losses thus compromising on efficiency. Thus, soft switching becomes necessary to reduce the losses, adding more electrical components to the converter to achieve soft switching is a common method. However, it increases the physical complexity of the system. Hence, advanced control methods are adopted for today's power converters that enable soft switching for devices specifically ZVS turn-on as the turn-off losses of next generation WBG devices are negligible. Thus, the goal of this research is to discover novel switching algorithms for soft turn-on.
The state-of the-art control methods namely CRM and TCM achieve soft turn-on by enabling bi-directional current such that the anti-parallel body diode starts conducting before the device is turned on. CRM and TCM result in variable switching frequency which leads to asynchronous operation in multi-phase and multi-converter systems. Hence, TCM is modified in this dissertation to achieve constant switching frequency, as the goal of this research is to be able to achieve ZVS turn-on for a three-phase converter. Further, Triangular Current Mode (TCM) to achieve soft switching and phase synchronization for three-phase two-level converters is proposed. It is shown how soft switching and sinusoidal currents can be achieved by operating the phases in a combination of discontinuous conduction mode (DCM), TCM and clamped mode. The proposed scheme can achieve soft switching ZVS turn-on for all the three phases. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kW with a density of 110 W/in3.
The discussion of TCM in current literature is limited to unity power factor assumption, however this limits the algorithm's adoption in real world applications. It is shown how proposed TCM algorithm can be extended to accommodate phase shift with all the three phases operating in a combination of DCM+TCM+Clamped modes of operation. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kVA with a density of 110 W/in3. TCM operation results in 33 % higher rms current which leads to higher conduction losses, as WBG devices have lower on-resistance, these devices are the ideal candidates for TCM operation, hence to accurately obtain the device parameters, a detailed device characterization is performed.
Further, proposed TCM+DCM+Clamped control algorithm is extended to three-level topologies, the control is modified to extract the advantage of reduced Common Mode Voltage (CMV) switching states of the three-level topology, the switching frequency can thus be pushed to 3 times higher as compared to state-of-the-art SVPWM control while maintaining close to 99 % efficiency. Two switching schemes are presented and both of them have a very small switching frequency variation (6%) as compared to state-of-the-art methods with >200% switching frequency variation.<br>Doctor of Philosophy<br>Power supplies are at the heart of today's advanced technological systems like aero planes, UAVs, electrical cars, uninterruptible power supplies (UPS), smart grids etc. These performance driven systems have high requirements for the power conversion stage in terms of efficiency, density and reliability. With the growing demand of reduction in size for electromechanical and electronic systems, it is highly desirable to reduce the size of the power supplies and power converters while maintaining high efficiency. High density is achieved by pushing the switching frequency higher to reduce the size of the magnetics. High switching frequency leads to higher losses if conventional hard switching methods are used, this drives the need for soft switching methods without adding to the physical complexity of the system. This dissertation proposes novel soft switching techniques to improve the performance and density of AC/DC and DC/AC converters at high switching frequency without increasing the component count. The concept and the features of this new proposed control scheme, along with the comparison of its benefits as compared to conventional control methodologies, have been presented in detail in different chapters of this dissertation.
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Babayan-Aghan, Vahik. "Investigation into different types of single-phase AC/DC convertors." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/7063.
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The work detailed in the thesis compares the performance of single-phase thyristor bridge converters under different control strategies; considering in particular the efficiency, ac side power factor and harmonic content of the current and voltage waveforms. Extensive practical investigations were performed, in which, analogue and digital control circuits were developed to provide the drive signals necessary for a converter to operate in the different control modes for: a) A series -connected fully-controlled double thyristor bridge (used mainly in traction applications) operating under sequence control and; b) A fully controlled single-bridge operating under sequence and conventional control. A novel pulse-width modulation control strategy was developed for the single-bridge converter, using gate turn-off thyristors as the switching elements, whereby output voltage control is obtained by variation of the modulation index. Turn-on and turn-off signals for the power devices were obtained using an analogue control circuit. The advantages and disadvantages of this switching strategy compared with conventional and sequence control were studied, and results clearly showed that an improved input power factor and lower supply current and load voltage harmonics were all obtained. Mathematical models for single and double bridge converters operating under sequence and conventional control were developed using tensor techniques. Using these models, computer programmes were written in Fortran 77 on the University mainframe computer, to assemble automatically and solve the network equations as the converter topology changes. In addition, analytical models were also developed on the assumption that the load current is completely smooth. However, such an assumption is not justifiable with ac-to-dc converters and consequently a novel technique was developed to include the load current ripple in calculating the supply current harmonics. The results obtained are compared with both the computed and experimental ones.
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Norrga, Staffan. "On soft-switching isolated AC/DC converters without auxiliary circuit /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256.
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Gitau, Michael N. "Optimal PWM switching strategy for single-phase AC-DC converters." Thesis, Loughborough University, 1994. https://dspace.lboro.ac.uk/2134/7205.
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The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase AC-DC converter-fed traction drives. The objective is to eliminate low-order supply current harmonics, including those injected into the supply due to load-side current ripple. Other advantages that the switching strategy has to offer over phase-control include improved supply power factor, reduced VA consumption for a given demand speed and load, reduced torque and speed ripple and smaller armature circuit smoothing inductance. The effect of field current boost on the dynamic response of the drive is also described. It is shown that field boost helps to reduce the speed rise-time by increasing the electromagnetic torque available during acceleration periods. Closed-loop control of a 4-quadrant DC drive is described and a comparison made between the performance of PID-control and pseudo-derivative feedback control. It is shown that pseudo-derivative feedback control has several advantages to offer, amongst which are ease of tuning of the controller gains and a superior performance following load torque disturbances. A laboratory size drive system was designed and built, and used to validate simulation predictions for both the switching strategy and pseudo-derivative feedback control. A microcontroller based hardware implementation of both the switching strategy and a digital pseudo-derivative feedback controller was adopted, with the switching strategy being implemented using an off-line approach of precalculating the switching angles and storing these in look-up tables. The armature voltage controller comprises a dual-converter employing IGBTs as switching devices. The use of IGBTs allows higher switching frequencies at significant power levels than would be possible if GTOs were used. It also simplifies the gate drive circuit design and minimises the need to use snubber circuits.
11
Chen, Weilun Warren. "Bidirectional Three-Phase AC-DC Power Conversion Using DC-DC Converters and a Three-Phase Unfolder." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6905.
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Strategic use of energy storage systems alleviates imbalance between energy generation and consumption. Battery storage of various chemistries is favorable for its relatively high energy density and high charge and discharge rates. Battery voltage is in dc, while the distribution of electricity is still predominantly in ac. To effectively harness the battery energy, a dc-ac inverter is required.
A conventional inverter contains two high-frequency switching stages. The battery-interfacing stage provides galvanic isolation and switches at high frequency to minimize the isolation transformer size. The grid-interfacing stage also operates at high frequency to obtain sinusoidal grid currents and the desired power. Negative consequences of high-frequency switching include increased switching loss and the generation of large voltage harmonics that require filtering.
This dissertation proposes an alternative two-stage inverter topology aimed at reducing converter size and weight. This is achieved by reducing the number of high-frequency switching stages and associated filter requirements. The grid-interfacing stage is operated at the line frequency, while only the battery-interfacing stage operates at high frequency to shape the line currents and control power flow. The line-frequency operation generates negligible switching loss and minimal current harmonics in the grid-interfacing stage. As a result, the required filter is reduced in size. Hardware designs are performed and compared between the conventional and proposed converters to quantify expected size reduction. Control methods are developed and verified in simulation and experiment to obtain high-quality line currents at all power factors.
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Hamed, Ibrahim. "Comparison between Active and Passive AC-DC Converters For Low Power Electromagnetic Self-Powering Systems : A theoretical and experimental study of low power AC-DC converters." Thesis, Mittuniversitetet, Institutionen för elektronikkonstruktion, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-39600.
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Electromagnetic based energy harvesting systems such as Variable reluctance energy harvesting systems (VREH) have shown to be an effective way of extracting the energy of rotating parts. The transducer can provide enough power to run an electronic sensing system, but the problem arises in finding an efficient way of rectifying that power to generate a stable energy supply to run a system, which this report will investigate. Active and passive voltage doublers have proven to be a suitable candidate in solving this issue due to the simplicity and the small footprint. This thesis will aim to compare active and passive voltage doublers under various scenarios in order to understand under which circumstances are active or passive voltage doublers to be preferred. From the conducted experimental measurements, this thesis concluded that active voltage doublers are recommended during high RPMs (>10 RPM) while passive voltage doublers (especially fullwave voltage doubler) is recommended at lower RPMs. Quality of power also plays a significant role in this study. Therefore, measurements have also been done for ripple and rise time. From the measurements, this thesis can conclude that the overall power quality was the best in Full-wave voltage doublers, while Active-voltage doublers had lower ripple than FWVDs at higher current loads.
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Woods, Joseph. "The parallel connection of single phase DC to AC power converters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39102.pdf.
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Dong, Dong. "Ac-dc Bus-interface Bi-directional Converters in Renewable Energy Systems." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28495.
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This dissertation covers several issues related to the ac-dc bus-interface bi-directional converters in renewable energy systems.
The dissertation explores a dc-electronic distribution system for residential and commercial applications with a focus on the design of an ac-dc bi-directional converter for such application. This converter is named as the â Energy Control Centerâ due to its unique role in the system. First, the impact of the unbalanced power from the ac grid, especially the single-phase grid, on the dc system operation is analyzed. Then, a simple ac-dc two-stage topology and an advanced digital control system is proposed with a detailed design procedure. The proposed converter system significantly reduces the dc-link capacitor volume and achieves a dynamics-decoupling operation between the interfaced systems. The total volume of the two-stage topology can be reduced by upto three times compared with the typical design of a full-bridge converter. In addition, film capacitors can be used instead of electrolytic capacitors in the system, and thus the whole system reliability is improved.
A set of ac passive plus active filter solutions is proposed for the ac-dc bus-interface converter which significantly reduces the total power filter volume but still eliminate the total leakage current and the common-mode conducted EMI noises by more than 90%. The dc-side low-frequency CM voltage ripple generated by the unbalanced ac voltages can be eliminated as well. The proposed solution features a high reliability and fits three types of the prevalent low-voltage ac distribution systems.
Grid synchronization, a critical interface control in ac-dc bus-interface converters, is discussed in detail. First, a novel single-phase grid synchronization solution is proposed to achieve the rejection of multiple noises as well as the capability to track the ac voltage amplitude. Then, a comprehensive modeling methodology of the grid synchronization for three-phase system is proposed to explain the output frequency behaviors of grid-interface power converters at the weak grid, at the islanded condition, and at the multi-converter condition. The proposed models provide a strong tool to predict the grid synchronization instabilities raised from industries under many operating conditions, which is critical in future more-distributed-generation power systems.
Islanding detection issues in ac-dc bus-interface converters are discussed in detail. More than five frequency-based islanding detection algorithms are proposed. These solutions achieve different performances and are suitable for different applications, which are advantageous over existing solutions. More importantly, the detailed modeling, trade-off analysis, and design procedures are given to help completely understand the principles. In the end, the effectiveness of the proposed solutions in a multiple-converter system are analyzed. The results drawn from the discussion can help engineers to evaluate other existing solutions as well.<br>Ph. D.
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Dey, Sourav. "Large-Signal Analysis of Buck and Interleaved Buck DC-AC Converters." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1409578634.
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Borle, Lawrence J. "Zero average current error control methods for bidirectional AC-DC converters." Thesis, Curtin University, 1999. http://hdl.handle.net/20.500.11937/539.
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This thesis is concerned primarily with the optimization of the current regulation in bi-directional ac-dc power converters through the use of appropriate current control methods. Following a review into prior current control technology, current control methods which attempt to achieve Zero Average Current Error (ZACE) in each switching period are presented. A ZACE controlled converter offers independent real and reactive power flow control with negligible low order current harmonics, a relatively narrow switching frequency band, and relative immunity to power circuit parameter variations, including DC link or AC line voltage harmonics. ZACE and other desirable characteristics in a current control method are discussed. The single phase ac and dc ripple current is characterized.Two new types of ZACE current control techniques for directly controlling the inductor current in switched power converters are introduced in this thesis together with variations for certain applications. Slope-generated hysteresis (SGH), the first to be developed, is a hysteresis method which uses the slopes of the current error signal alone to generate a hysteresis band which will result in a fixed switching frequency. Slope-generated hysteresis-clock (SGHC) is presented as an alternative with a dual clock to force a narrow switching frequency band.Ramptime current control is the second type of ZACE current control presented. Developed as an improvement over SGH, ramptime produces ZACE in each switching period by using the timing of a previous switching instant relative to the coincident previous current error signal excursion time to determine each switching instant. The digital current error polarity signal is the only variable input required to produce a pwm output.Variations of ramptime current control are also presented. Polarized ramptime is a subset of ramptime which maintains a narrow switching frequency band despite switching delays. Dual ramptime is the final enhancement of ramptime where two polarized ramptime regulators are used together to provide the appropriate choice between full-bridge and half-bridge switching in a single phase current controlled full-bridge voltage source inverter with the ac ripple current minimized without compromising the transient response. Using this technique, excellent fidelity and a narrow switching frequency band are demonstrated.The ZACE current control techniques are applied to a three phase voltage source inverter. A "standing phase" system of control for a three wire, three phase inverter is chosen over individual phase control since only two current regulators are required to control two decoupled current error signals, and the effective switching frequency is reduced by one third.The new ZACE methods are found to compare favourably in simulation to existing linear and hysteresis type current control techniques. SGH current control has equivalent fidelity to any other hysteresis control in delivering the reference current waveform, but is prone to noise in the hysteresis band determination requiring filtering. This, combined with the effect of switching delays compromises the narrowness of the switching frequency band. SGHC current control is also prone to noise in the generation of the hysteresis band, and results in a decrease in the fidelity of reproduction of the reference waveform. Ramptime current control is a robust technique, largely immune to power circuit parameter and voltage variances, with good fidelity and a relatively narrow switching frequency band. Polarized ramptime current control is shown to produce excellent fidelity with a narrow switching frequency band.The operation of the ZACE methods in single and three phase prototype converters is demonstrated. A field installation of a grid-connected ramptime current controlled converter is shown to source 20 kW of real power onto the grid from a photovoltaic array with a maximum power point tracking control, while independently providing grid voltage support through reactive power control.The effect of the synchronization of the current regulators on the ac and dc current ripple are presented. Synchronized polarized ramptime regulators are shown to produce the minimum ripple current in simulation and in the prototype operation.ZACE current control techniques, and ramptime and polarized ramptime in particular, are presented as a significant contribution to the control of current in power electronic converters.
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Borle, Lawrence J. "Zero average current error control methods for bidirectional AC-DC converters." Curtin University of Technology, School of Electrical and Computer Engineering, 1999. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10467.
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This thesis is concerned primarily with the optimization of the current regulation in bi-directional ac-dc power converters through the use of appropriate current control methods. Following a review into prior current control technology, current control methods which attempt to achieve Zero Average Current Error (ZACE) in each switching period are presented. A ZACE controlled converter offers independent real and reactive power flow control with negligible low order current harmonics, a relatively narrow switching frequency band, and relative immunity to power circuit parameter variations, including DC link or AC line voltage harmonics. ZACE and other desirable characteristics in a current control method are discussed. The single phase ac and dc ripple current is characterized.Two new types of ZACE current control techniques for directly controlling the inductor current in switched power converters are introduced in this thesis together with variations for certain applications. Slope-generated hysteresis (SGH), the first to be developed, is a hysteresis method which uses the slopes of the current error signal alone to generate a hysteresis band which will result in a fixed switching frequency. Slope-generated hysteresis-clock (SGHC) is presented as an alternative with a dual clock to force a narrow switching frequency band.Ramptime current control is the second type of ZACE current control presented. Developed as an improvement over SGH, ramptime produces ZACE in each switching period by using the timing of a previous switching instant relative to the coincident previous current error signal excursion time to determine each switching instant. The digital current error polarity signal is the only variable input required to produce a pwm output.Variations of ramptime current control are also presented. Polarized ramptime is a subset of ramptime which maintains a narrow ++<br>switching frequency band despite switching delays. Dual ramptime is the final enhancement of ramptime where two polarized ramptime regulators are used together to provide the appropriate choice between full-bridge and half-bridge switching in a single phase current controlled full-bridge voltage source inverter with the ac ripple current minimized without compromising the transient response. Using this technique, excellent fidelity and a narrow switching frequency band are demonstrated.The ZACE current control techniques are applied to a three phase voltage source inverter. A "standing phase" system of control for a three wire, three phase inverter is chosen over individual phase control since only two current regulators are required to control two decoupled current error signals, and the effective switching frequency is reduced by one third.The new ZACE methods are found to compare favourably in simulation to existing linear and hysteresis type current control techniques. SGH current control has equivalent fidelity to any other hysteresis control in delivering the reference current waveform, but is prone to noise in the hysteresis band determination requiring filtering. This, combined with the effect of switching delays compromises the narrowness of the switching frequency band. SGHC current control is also prone to noise in the generation of the hysteresis band, and results in a decrease in the fidelity of reproduction of the reference waveform. Ramptime current control is a robust technique, largely immune to power circuit parameter and voltage variances, with good fidelity and a relatively narrow switching frequency band. Polarized ramptime current control is shown to produce excellent fidelity with a narrow switching frequency band.The operation of the ZACE methods in single and three phase prototype converters is demonstrated. A field installation of a ++<br>grid-connected ramptime current controlled converter is shown to source 20 kW of real power onto the grid from a photovoltaic array with a maximum power point tracking control, while independently providing grid voltage support through reactive power control.The effect of the synchronization of the current regulators on the ac and dc current ripple are presented. Synchronized polarized ramptime regulators are shown to produce the minimum ripple current in simulation and in the prototype operation.ZACE current control techniques, and ramptime and polarized ramptime in particular, are presented as a significant contribution to the control of current in power electronic converters.
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Rizzoli, Gabriele <1987>. "Development of DC/AC power converters for applications requiring high efficiency." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7292/1/Rizzoli_Gabriele_Tesi.pdf.
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Silicon-based power devices have dominated power electronics applications over the last decades. Research and development in microelectronics have pushed the performance of power devices to face some fundamental limitations of silicon material. Wide band-gap semiconductors, such as silicon carbide, offer a solution to the pressing energy efficiency performance requirements of power electronic systems. Silicon carbide power devices can operate at higher temperatures, higher frequencies, and generate less power losses as compared to traditional silicon-based technologies. The use of wide band-gap transistors, however, is not the only way to increase the efficiency of the converters. Special DC to AC topologies, named soft switching converters, can be adopted as well in order to reduce the switching losses of transistors. The development of DC to AC power converters for applications requiring high efficiency is presented in this thesis. Silicon and silicon carbide based inverters, as well as soft switching inverters, have been analyzed and fabricated for performance comparison.
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Rizzoli, Gabriele <1987>. "Development of DC/AC power converters for applications requiring high efficiency." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7292/.
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Silicon-based power devices have dominated power electronics applications over the last decades. Research and development in microelectronics have pushed the performance of power devices to face some fundamental limitations of silicon material. Wide band-gap semiconductors, such as silicon carbide, offer a solution to the pressing energy efficiency performance requirements of power electronic systems. Silicon carbide power devices can operate at higher temperatures, higher frequencies, and generate less power losses as compared to traditional silicon-based technologies. The use of wide band-gap transistors, however, is not the only way to increase the efficiency of the converters. Special DC to AC topologies, named soft switching converters, can be adopted as well in order to reduce the switching losses of transistors. The development of DC to AC power converters for applications requiring high efficiency is presented in this thesis. Silicon and silicon carbide based inverters, as well as soft switching inverters, have been analyzed and fabricated for performance comparison.
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Santos, Heron Alves dos. "Design of a controlled single-phase ac-dc converter for interconnection of DC and AC buses of a microgrid." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12977.
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The recent growth expectation of the participation of solar-photovoltaic energy sources in the power generation matrix has significantly increased the number of grid-connected systems. For connection to power grid, it is essential to use a dc-ac converter, which is able to suit the characteristics of the power provided by the photovoltaic modules to grid parameters. This dissertation presents a project proposal of a 2 kW single phase dc-ac converter for connecting a 311 V dc bus to a 220 Vrms ac bus of a microgrid. The proposed converter is bidirectional and allows, when necessary, the power flow from ac to dc bus. The study shows, through simulation and prototype implementation in the laboratory, that with the application of an appropriate control strategy it is possible to control the direction of power flow, as well as properly modulating the current flowing between two buses, dc, powered by photovoltaic panels and the battery bank, and the ac, at grid side. The prototype had a yield of about 91% and has injected electric current with low harmonic content (THDi less than 5%).<br>A recente expectativa de crescimento da participaÃÃo da energia solar-fotovoltaica na matriz de geraÃÃo de energia elÃtrica aumentou significativamente o nÃmero de conexÃes desses sistemas à rede elÃtrica. Para que a interligaÃÃo com a rede elÃtrica convencional seja possÃvel, à indispensÃvel a utilizaÃÃo de conversores CC/CA, capazes de adequar as caracterÃsticas da energia disponibilizada pelos mÃdulos fotovoltaicos aos padrÃes da rede. Esta dissertaÃÃo apresenta uma proposta de projeto de conversor CC/CA de 2 kW para conexÃo de dois barramentos de uma microrrede, um CC em 311 V e outro CA em 220 Vrms. O conversor proposto à bidirecional e permite, quando necessÃrio, o fluxo de energia elÃtrica do barramento CA para o CC. O estudo realizado mostra, atravÃs de simulaÃÃes e de implementaÃÃo de protÃtipo em laboratÃrio, que com a aplicaÃÃo de uma estratÃgia de controle adequada à possÃvel controlar o sentido do fluxo de potÃncia do conversor, assim como modular apropriadamente a corrente que flui entre dois barramentos, o CC, alimentado por painÃis fotovoltaicos e por banco de baterias, e o barramento CA, do lado da rede elÃtrica. O protÃtipo desenvolvido apresentou rendimento de cerca de 91% e forneceu corrente elÃtrica de baixo conteÃdo harmÃnico (THDi menor que 5%).
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Bulhosa, João Paulo Rodrigues. "Controlo de um conversor AC-DC-AC para turbinas eólicas baseadas no PMSG." Master's thesis, Instituto Politécnico de Bragança, Escola Superior de Tecnologia e de Gestão, 2009. http://hdl.handle.net/10198/2062.
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A dissertação teve como objectivo o estudo e implementação do controlo de um conversor AC-DC-AC, constituído por um conversor DC/DC elevador e um inversor de tensão monofásico, para efectuar a ligação à rede de turbinas eólicas baseadas no gerador síncrono de ímanes permanentes.
O controlo global do conversor AC-DC-AC seguiu uma estratégia na qual o controlo do conversor elevador e do inversor de tensão monofásico é implementado de modo independente. O primeiro visa maximizar a potência extraída da turbina através da implementação de um algoritmo de seguimento do ponto de potência máxima (MPPT), enquanto o segundo tem a função de extrair toda a energia proveniente do primeiro fornecendo-a à rede eléctrica com factor de potência unitário. Isto é conseguido com controlo em corrente através do qual se procura garantir que a corrente gerada pelo inversor está em fase com a tensão da rede.
O desenvolvimento do controlo foi realizado no programa Simulink. Os controladores foram dimensionados, implementados, testados e validados progressivamente, de modo a minimizar o número de parâmetros a ajustar ao mesmo tempo.
Foi desenvolvida uma interface gráfica, utilizando o programa ControlDesk, para permitir os ajustes necessários dos controladores e visualização de diversas variáveis do sistema. Esta fase do trabalho foi desenvolvida no Instituto Politécnico de Bragança, com vista à implementação prática.
Os trabalhos continuaram com a realização de um estágio, no âmbito do programa Erasmus, no CIEMAT – Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas e posteriormente no CEDEX - Centro de Estudios y Experimentación de Obras Públicas, em Madrid.
No CIEMAT foi apresentado o estado de desenvolvimento dos realizados no IPB, tendo em vista a implementação laboratorial. Os primeiros resultados experimentais foram obtidos no CEDEX com o controlo do conversor elevador. The goal of this dissertation was the analysis, implementation and control of an AC-DC-AC power converter built with a DC/DC step-up converter and a single phase inverter for grid-tied wind turbines based on permanent magnet synchronous generator.
The overall control of the converter AC-DC-AC followed a strategy in which the control of the step-up converter and the single phase inverter was implemented independently. The first is used to maximize the power available in the wind turbine through the implementation of an algorithm for the maximum power point tracking (MPPT), while the second is used to capture all the energy provided by the first and send it to the grid with unit power factor. This is achieved with current control of the inverter in order to ensure that the current generated by the inverter is in phase with the mains voltage.
The development of the monitoring program was carried out with the software Simulink. The PI controllers were designed, implemented, tested and validated step-by-step to minimize the number of parameters to adjust the same time.
A graphical interface was developed using the software ControlDesk to allow suitable adjustments of the control, and display several variables of the system. This stage of work was developed at the Instituto Politécnico de Bragança, in view of the practical implementation.
The work continued during an internship within the framework of Erasmus in CIEMAT - Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas and later in CEDEX - Centro de Estudios y Experimentación de Obras Públicas, in Madrid.
In CIEMAT, the state of development of the work developed in IPB was presented, and continued in view of the implementation in laboratory. The first experimental results were obtained in CEDEX with the control of the step-up converter.
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Wang, Wenfei. "Analysis, design and applications of digitally controlled bridgeless AC/DC buck converter." Thesis, The University of Sydney, 2012. https://hdl.handle.net/2123/29157.
Full textAbstract:
Power factor correction (PFC) is now mandatory in modern power
electronic systems due to the awareness of ‘pollution’ to the grid by the
current harmonics resulting in the adoption of standards and regulations such
as IEC 61000-3-2 to limit the current harmonics in the electricity networlm.
To improve the input power factor of power converters, normally a PFC
circuit is placed between the grid and the switching converters. In universalline
(90V-264V) applications, it is vital to maintain high efficiency across the
entire input voltage range for the AC/DC rectifier with a high power factor
and low line current distortion. The configuration consisting of a bridge
rectifier and a boost converter has been regarded as the most commonly used
structure due to its simple circuitry and good power factor performance.
However, its relatively high output voltage causes high switching losses of the
power semiconductors.
In this thesis, a generalised power converter structure using bridgeless and
voltage-doubler configurations is developed. A new family of bridgeless PFC
converters is derived to improve conversion efficiency, followed by a new
digitally controlled bridgeless buck converter operating in discontinuous input
voltage mode (DIVM) operation which is analysed in detail. The converter
inherits PFC property by adding an input LC filter and operating the converter
at a constant duty cycle thereby improving power factor, and achieving high
efficiency.
In modern power systems, power converters with varying power factor
are becoming popular. They could contribute to system power factor (PF)
when a large number of converters and non-renewable and renewable energy
sources and different types of loads are connected. It would be ideal if all
power converters in the power system are able to adjust its PF to provide
voltage support of the power system. In addition, integrating varying power
factor feature into electronic loads would be a desirable feature for system
power quality testing purposes. Furthermore, varying power factor could be
applied to dimming fluorescent lamps for daily use and even intermittent or
fluctuating loads in manufacturing plants. In this thesis, a buck converter
working in DIVM with an adjustable power factor is proposed. Experimental
results of a laboratory prototype to verify the analysis and design of the
proposed topologies are given. Comparative results based on calculation,
simulation and experiment are also given to validate the feasibility of the
proposed circuits.
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Lopez, Santos Oswaldo. "Contribution to the DC-AC conversion in photovoltaic systems : Module oriented converters." Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0001/document.
Full textAbstract:
Ces dernières années, un intérêt croissant pour les systèmes électroniques de puissance a été motivé par l'émergence de sources d'énergie distribuées et renouvelables raccordées aux réseaux électriques. Dans ce contexte, la nécessité de topologies de faibles puissances alimentées par quelques modules photovoltaïques, en évitant l'utilisation de transformateurs, a ouvert l'étude de convertisseurs spéciaux et l’étude des stratégies de commande associées afin d’assurer la stabilité, la fiabilité et un rendement élevé du dispositif. Une possible solution est d’utiliser un dispositif générique connu dans la littérature scientifique et commerciale comme « micro-onduleur » ou «convertisseur intégré au module » qui avec le module photovoltaïque définit un produit « plug and play » appelé "module AC".Ce travail est consacré à l'étude d'un micro-onduleur monophasé avec deux étapes sans transformateur raccordée au réseau. La topologie proposée est composé d’un convertisseur DC-DC non isolé élévateur avec un gain quadratique et un onduleur réducteur lié au réseau connectés en cascade. Le convertisseur DC-DC extrait en permanence la puissance maximale du module photovoltaïque malgré les changements dans les conditions environnementales. L'étape DC-AC injecte la puissance extraite par l'étape DC-DC dans le réseau et assure un niveau élevé de qualité de l’énergie. Les efforts de recherche de ce travail sont concentrés sur la mise au point de commandes utilisant comment base, la théorie de contrôle par mode de glissement, qui conduit à une mise en œuvre simple avec une description théorique complète validée á partir de simulations et expérimentations.Après avoir décrit l'état de l’art dans le premier chapitre, le manuscrit est divisé en quatre chapitres, qui sont dédiés respectivement à l’algorithme de recherche du point de puissance maximale (MPPT), á l’étape de conversion DC-DC, á l'étape de conversion DC-AC et finalement au micro-onduleur complet. Un nouvel algorithme de recherche extrémal du point de puissance maximale est développé (SM-ESC). Pour la étape DC-DC, le convertisseur élévateur quadratique avec seulement un interrupteur contrôlé est étudié utilisant le concept de résistance sans perte par mode de glissement (de l’acronyme anglais : Sliding-Mode Loss-Free-Resistor – SM-LFR) afin d’obtenir un gain de tension élevé avec un fonctionnement sûr et compatible avec l’algorithme MPPT. Pour la étape DC-AC, le convertisseur de pont complet est contrôlé comme un onduleur de source de puissance (de l’acronyme anglais : Power Source Inverter - PSI) en utilisant une commande par mode de glissement qui poursuit une référence sinusoïdale de courant de sortie. Cette commande est complétée par une boucle de régulation de la tension du bus DC qui assure une haute qualité d’énergie injectée dans le réseau. Enfin, les trois étapes constitutives sont fusionnées pour obtenir un micro-onduleur complètement contrôlé par la technique de mode de glissement, ce qui constitue le principal résultat et contribution de cette thèse<br>These last years, a growing interest in power electronic systems has been motivated by the emergence of distributed renewable energy resources and their interconnection with the grid. In this context, the need of low power topologies fed by a few photovoltaic modules avoiding the use of transformers opens the study of special converters and the associated control strategies ensuring stability, reliability and high efficiency. A resulted generic device known in the commercial and scientific literature as “microinverter” or “module integrated converter” performs a plug and play product together with the PV module called an “AC module”.This work is devoted to the study of a transformer-less single-phase double-stage grid-connected microinverter. The proposed topology has a non-isolated high-gain boost type DC-DC converter and a non-isolated buck type DC-AC converter connected in cascade through a DC bus. The DC-DC converter permanently extracts the maximum power of the PV module ensuring at the same time a good performance coping with power changes introduced by the change in the environmental conditions. The DC-AC stage injects the power extracted by the DC-DC stage into the grid ensuring a high level of power quality. The research efforts focus on the involved control functions based on the sliding mode control theory, which leads to a simple implementation with a comprehensive theoretical description validated through simulation and experimental results.After giving the state-of-the-art in the first chapter, the manuscript is divided into four chapters, which are dedicated to the Maximum Power Point Tracking (MPPT), the DC-DC stage and its control, the DC-AC stage and its control and the complete microinverter. A new Extremum Seeking Control (ESC) MPPT algorithm is proposed. The single-switch quadratic boost converter is studied operating as a Loss-Free-Resistor (LFR) obtaining a high DC output voltage level with a safe operation. The full-bridge converter is controlled as a Power Source Inverter (PSI) using a simple sliding-mode based tracking law, regulating the voltage of the DC bus and then ensuring a high power quality level in the grid connection. Finally, the three building blocks are merged to obtain a sliding mode controlled microinverter constituting the main result and contribution of the work
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Malan, Wynand Louis. "Design, modelling and control of CLC Tee-Resonant Dual Active Bridge Converters." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/200329/1/Wynand_Malan_Thesis.pdf.
Full textAbstract:
Tee-Resonant Dual Active Bridges are isolated, bidirectional, DC-DC converters that behave as voltage-controlled current sources, which makes them especially useful for battery charging applications. In this work, three new phase-shift modulation strategies are proposed that can improve the converter efficiency at high switching frequencies and enable loss-shifting between the primary and secondary sides. To model the converter, a large signal state-space model is derived and it is demonstrated to be useful for controller design. Lastly, a converter topology is proposed that enables direct integration of the converter with the grid, including power factor correction capability.
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Natsheh, Ammar Nimer. "Analysis, simulation and control of chaotic behaviour and power electronic converters." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/5739.
Full textAbstract:
The thesis describes theoretical and experimental studies on the chaotic behaviour of a peak current-mode controlled boost converter, a parallel two-module peak current-mode controlled DC-DC boost converter, and a peak current-mode controlled power factor correction (PFC) boost converter. The research concentrates on converters which do not have voltage control loops, since the main interest is in the intrinsic mechanism of chaotic behaviour. These converters produce sub-harmonics of the clock frequency at certain values of the reference current I[ref] and input voltage V[in], and may behave in a chaotic manner, whereby the frequency spectrum of the inductor becomes continuous. Non-linear maps for each of the converters are derived using discrete time modelling and numerical iteration of the maps produce bifurcation diagrams which indicate the presence of subharmonics and chaotic operation. In order to check the validity of the analysis, MATLAB/SIMULINK models for the converters are developed. A comparison is made between waveforms obtained from experimental converters, with those produced by the MATLAB/SIMULINK models of the converters. The experimental and theoretical results are also compared with the bifurcation points predicted by the bifurcation diagrams. The simulated waveforms show excellent agreement, with both the experimental waveforms and the transitions predicted by the bifurcation diagrams. The thesis presents the first application of a delayed feedback control scheme for eliminating chaotic behaviour in both the DC-DC boost converter and the PFC boost converter. Experimental results and FORTRAN simulations show the effectiveness and robustness of the scheme. FORTRAN simulations are found to be in close agreement with experimental results and the bifurcation diagrams. A theoretical comparison is made between the above converters controlled using delayed feedback control and the popular slope compensation method. It is shown that delayed feedback control is a simpler scheme and has a better performance than that for slope compensation.
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White, Terence H. "A three-phase hybrid dc-ac inverter system utilizing hysteresis control." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FWhite%5FTerence.pdf.
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Alam, Md Muntasir Ul. "Investigation of bridgeless single-phase solutions for ac-dc power factor corrected converters." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62355.
Full textAbstract:
In modern power supplies and battery chargers, a front-end power factor correction (PFC) AC-DC converter is used to comply with regulatory requirements for input current harmonics. The prevalence of standards and recommended practices to meet harmonic current limits has gained, and continues to gain, momentum over recent years. Additionally, the improvement of overall converter efficiency is critical for the emergence and acceptance of these converter technologies, to meet the standard of efficiency and power factor requirements.
This dissertation presents some innovative solutions for bridgeless non-isolated and isolated PFC AC-DC converters. All proposed converter solutions realize bridgeless converter operation to reduce conduction losses and operate in hybrid resonant pulse-width-modulation (HRPWM) mode. The PWM switches share the same gating signal, so the converter does not need extra circuitry to sense the positive and negative ac input line-cycle operation.
The first contribution is a non-isolated bridgeless AC-DC converter, which has inherent inrush current-limiting capabilities. The converter architecture also enables simple implementation of lightning and surge protection systems. Moreover, this converter can survive sustained over-voltage events and can limit the voltage stress on the converter and downstream components.
The second contribution is a non-isolated bridgeless AC-DC converter, which realizes soft-switching operation to reduce switching losses. This converter can operate at high switching frequency to increase power density.
The third contribution is a three-level non-isolated bridgeless AC-DC converter, which has high voltage gain. This converter also provides soft-switching operation of all the power devices. Due to the three level architecture, all commutations occur with a voltage level equivalent to half the output voltage, which further reduces switching losses. This converter can utilize lower voltage rated devices, which reduces system cost.
The final contribution is a single-stage bridgeless isolated AC-DC converter. This converter shows low conduction loss due to bridgeless operation and low voltage stress of the secondary diodes, low switching loss due to soft-switching operation, and a transformer that has no dc magnetizing current and does not store energy. These characteristics minimize the transformer size and increases transformer efficiency.<br>Applied Science, Faculty of<br>Engineering, School of (Okanagan)<br>Graduate
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Atighechi, Hamid. "Dynamic average-value model of high power ac-dc converters and HVDC systems." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44578.
Full textAbstract:
High power switching converters such as line-commutated converters (LCC) and high voltage direct current (HVDC) systems are widely used in modern energy grids for interconnection of industrial loads, large motor drives, as well as electronically-interfaced renewable/alternative/distributed energy resources (DER) and storage systems. For design and analysis of systems with power-electronic-based DERs and loads, accurate and efficient computer models are essential. This thesis is focused on dynamic average-value models (AVM) that neglect switching of converter circuits and are established by averaging the variables (currents and voltages) over a prototypical switching interval. The AVMs are continuous (free of switching), allow using larger integration time steps, and typically run much faster than the conventional detailed switching models, which makes them particularly useful for the system-level studies. This thesis considers the parametric AVM framework, and extends this approach to the thyristor-controlled LCCs operating in inverter mode with current source or voltage source control. The proposed modeling methodology is demonstrated on various topologies including the HVDC CIGRE benchmark system. The research is further extended to incorporate the ac side harmonics into the AVM using the multiple reference frame theory. Traditionally, the AVMs are developed using state-variable-based approach. This thesis also presents a new parametric AVM for direct interfacing in nodal-analysis-based electromagnetic transient programs (EMTP), e.g., PSCAD/EMTDC, EMTP-RV, and MicroTran. It is expected that the proposed models and interfacing approaches will find their application in widely used transient simulation tools and will be appreciated by many researchers and practicing engineers worldwide.
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Wang, Xinxin. "Design and implementation of internal model based controllers for DC/AC power converters." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7628.
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The aim of this thesis is to design and implement an advanced control system for a working three-phase DC to AC power converter. Compared to the traditional PI controller used widely in industry, the new voltage controller can track the reference voltage with improved accuracy and efficiency in the presence of different kind of local loads, and also works well in the single phase voltage control. This voltage controller is combined with a power controller to yield a complete controller. An important aspect of this work is the hardware implementation of the whole system. Main parts of this thesis are: 1. Review of H-infinity and repetitive control techniques and their applications in power converters. 2. Design of a new voltage controller to eliminate the DC component in the output voltages, and taking into account the practical issues such as the processing delay due to the digital signal processor (DSP) implementation. 3. Modelling and simulation of the converter system incorporating different control techniques and with different kinds of loads. 4. Hardware implementation and the two-processor controller. The parallel communication between the DSPs. 5. The main problems encountered in hardware implementation and programming. The software used to initialize DSPs, implement the discrete time voltage controller and other functions such as generations of space vector pulse width modulation (SVPWM) signals, circuit protections, analog to digital (AD) cOl)versions, data transmission, etc. 6. Experimental results under circumstances of no load connected to the converter, pure three-phase resistive loads, three-phase unbalanced resistive loads and the series resistor-inductor loads.
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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.
Full textAbstract:
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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Green, Simon Richard. "Permanent magnet drives in the more-electric aircraft." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327196.
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Odnegård, Joakim. "Fault Impact Mitigation in Grid Connected Converters." Thesis, KTH, Elektrisk energiomvandling, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-107494.
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The present thesis deals with fault impact mitigation in grid connected converters used for High Voltage Direct Current transmission. Certain critical fault cases require additional obstructing protection actions to ease the impact on the converter valves. DC sided faults drives high fault currents through the converters. Single phase to ground faults at the converter AC bus results in overvoltages across the converter valve arms. The phenomenon of these faults are described both for symmetric and asymmetric configurations. Different available solutions are explained and evaluated. Simulations in PSCAD/EMTDC show the impact of the protection measures. A three phase short circuit introduced on the tertiary winding of the transformer is an effective temporary measure against the destructive fault cases. It is shown in this report that a tertiary shortcircuit will greatly reduce the overvoltages after converter bus faults and redirect a large part of the fault currents after DC faults. With the lower voltage on the tertiary winding, it is a suitable connection point for short circuit devices.
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Shahbazi, Mahmoud. "Contribution à l'étude des convertisseurs statiques AC-DC-AC tolérants aux défauts." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0074/document.
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Les convertisseurs statiques triphasés AC/DC/AC à structure tension sont largement utilisés dans de nombreuses applications de puissance. La continuité de service de ces systèmes ainsi que leur sécurité, leur fiabilité et leurs performances sont aujourd'hui des préoccupations majeures de ce domaine lié à l'énergie. En effet, la défaillance du convertisseur peut conduire à la perte totale ou partielle du contrôle des courants de phase et peut donc provoquer de graves dysfonctionnements du système, voire son arrêt complet. Afin d'empêcher la propagation du défaut aux autres composants du système et assurer la continuité de service en toute circonstance lors d'une défaillance du convertisseur, des topologies de convertisseur "fault tolerant" associées à des méthodes efficaces et rapides de détection et de compensation de défaut doivent être mises en oeuvre. Dans ce mémoire, nous étudions la continuité de service de trois topologies de convertisseurs AC/DC/AC avec ou sans redondance, lors de la défaillance d'un de leurs interrupteurs. Deux applications sont ciblées : l'alimentation d'une charge RL triphasée et un système éolien de conversion de l'énergie basé sur une MADA. Un composant FPGA est utilisé pour la détection du défaut, afin de réduire autant que possible son temps de détection. Des variantes permettant d'optimiser la méthode de détection de défaut sont également proposées et évaluées. Les trois topologies de convertisseurs proposées, associées à leurs contrôleurs, ont été validées de la modélisation/ simulation à la validation sur banc de test expérimental, en passant par le prototypage "FPGA in the Loop" du FPGA, destiné plus spécifiquement à la détection du défaut<br>AC/DC/AC converters are widely being used in a variety of power applications. Continuity of service of these systems as well as their reliability and performances are now of the major concerns. Indeed, the failure of the converter can lead to the total or partial loss of the control of the phase currents and can cause serious system malfunction or shutdown. Thus, uncompensated faults can quickly endanger the system. Therefore, to prevent the spread of the fault to the other system components and to ensure continuity of service, fault tolerant converter topologies associated to quick and effective fault detection and compensation methods must be implemented. In this thesis, we present the continuity of service of three AC/DC/AC fault tolerant converters with or without redundancy, in the presence of a fault in one of their switches. Two types of applications are studied: the supply off a three-phase charge and a wind energy conversion system based on a DFIG. An FPGA based implementation is used for fault detection, in order to reduce the detection time as much as possible. Three optimizations in the fault detection method are also presented. During these researches, the three proposed converter topologies and their controllers are validated in simulations and also experimentally, while being validated in a "FPGA in the Loop" prototyping
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LI, QUAN, and q. li@cqu edu au. "HIGH FREQUENCY TRANSFORMER LINKED CONVERTERS FOR PHOTOVOLTAIC APPLICATIONS." Central Queensland University. N/A, 2006. http://library-resources.cqu.edu.au./thesis/adt-QCQU/public/adt-QCQU20060830.110106.
Full textAbstract:
This thesis examines converter topologies suitable for Module Integrated Converters
(MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to
the development of the MIC topologies based on the two-inductor boost converter,
which has received less research interest than other well known converters.
The thesis provides a detailed analysis of the resonant two-inductor boost converter
in the MIC implementations with intermediate constant DC links. Under variable
frequency control, this converter is able to operate with a variable DC gain while
maintaining the resonant condition. A similar study is also provided for the resonant
two-inductor boost converter with the voltage clamp, which aims to increase the
output voltage range while reducing the switch voltage stress. An operating point
with minimized power loss can be also established under the fixed load condition.
Both the hard-switched and the soft-switched current fed two-inductor boost
converters are developed for the MIC implementations with unfolding stages. Nondissipative
snubbers and a resonant transition gate drive circuit are respectively
employed in the two converters to minimize the power loss.
The simulation study of a frequency-changer-based two-inductor boost converter is
also provided. This converter features a small non-polarised capacitor in a second
phase output to provide the power balance in single phase inverter applications.
Four magnetic integration solutions for the two-inductor boost converter have also
been presented and they are promising in reducing the converter size and power loss.
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Lessing, Marlon Henrique. "Analysis, design and implementation of single-stage high-frequency-isolated DC-AC flyback converters." Universidade Tecnológica Federal do Paraná, 2016. http://repositorio.utfpr.edu.br/jspui/handle/1/2410.
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Esta dissertação propõe a análise de dois conversores de estágio único, isolados em alta frequência e adequados para aplicações de conexão à rede elétrica. Inicialmente, é introduzida uma nova estratégia de modulação para o conversor flyback bidirecional com conexão diferencial. Esta modulação melhorada proporciona melhor desempenho, reduzindo os valores de corrente RMS para cada componente do circuito, contribuindo assim para a redução das perdas por condução. As análises estáticas do conversor operando em ambas estratégias de modulação alternativa e original são apresentadas. A análise dinâmica também é realizada, fornecendo a função de transferência da corrente de saída pela razão cíclica do conversor ligado à uma carga resistiva e acoplado a uma fonte de tensão. Um protótipo com potência de saída de 500 W, 20 kHz, com tensão de entrada de 70 V e 127 VRMS na tensão de saída é apresentado e os resultados experimentais que comparam a nova estratégia de modulação confirmam a análise teórica e desempenho superior. Uma tensão de saída com baixa THD é alcançada para ambas estratégias de modulação, operando em malha aberta em no modo de condução contínua. O segundo conversor é um flyback com grampeamento ativo adequado para ser utilizado como um micro-inversor em aplicações de energias renováveis. As principais características da topologia são o relativo baixo número de componentes, o isolamento em alta frequência, possibilidade de ser utilizado como elevador de tensão de saída e operação em ZVS. O grampeamento ativo permite recuperar a maior parte da energia armazenada na indutância de dispersão dos indutores flyback e, assim, uma melhoria na eficiência do conversor é atingida. A análise estática é fornecida para o conversor operando em CCM. Além disso, uma função de transferência da corrente de saída pela razão cíclica é apresentada para uma carga resistiva na saída. Para este conversor duas frequências de comutação de 100 kHz e 50 kHz foram testadas num protótipo construído para 500 W, com tensão de entrada de 70 V e tensão de saída de 127 VRMS.<br>This thesis proposes the analysis of two single-stage high-frequency isolated converters suited for grid-tied applications. Firstly, a new modulation strategy to the bidirectional flyback converter with differential output connection is introduced. This improved modulation provides better performance by reducing the RMS current values for every circuit element, thereby contributing to reduced conduction losses. The static analyses of the converter operating in both the original and the alternative switching strategies are presented. Dynamic analysis is also performed, providing the output-current-to-duty-cycle transfer function of the converter connected to a resistive load and coupled to an output voltage source. A 500 W, 20 kHz, 70 V input voltage and 127 VRMS output voltage prototype is presented and experimental results comparing the new modulation strategy to the original confirm the theoretical analyses and superior performance of the alternative switching strategy. A low THD output voltage is achieved for both switching strategies, operating in open loop and in continuous conduction mode. The second converter is an active-clamping flyback converter suitable to be used as a microinverter in renewable energy applications. The main features of the topology are the relatively low component count, high-frequency isolation, voltage step-up capability and zero voltage switching. The active clamping allows to recover most of the energy stored in the flyback inductors’ leakage inductance and thus an improvement on the system efficiency is achieved. The static analysis for CCM operation is provided. In addition, an output-current-to-duty-cycle transfer function for a resistive load connected to the output of the converter is presented. Two switching frequencies of 100 kHz and 50 kHz were tested in a prototype built for 500 W, 70 V input voltage and 127 VRMS output voltage.
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Lamb, Jacob. "Corrective schemes for internal and external abnormalities in cascaded multilevel inverters." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/35803.
Full textAbstract:
Doctor of Philosophy<br>Department of Electrical and Computer Engineering<br>Behrooz Mirafzal<br>Corrective schemes for facilitating continued operation of dc-ac converters during internal and external abnormalities are presented in this dissertation. While some of the developed techniques are suited for any dc-ac converter topology, most of the presented methodologies are designed specifically for cascaded H-bridge (CHB) multilevel converters. While CHB provide increased scalability and efficiency compared to traditional topologies, these converters are more likely to experience internal faults due to the additional components required. Realizing the full potential of CHB converters requires fault tolerant techniques, such as those demonstrated in this dissertation. Adaptive sinusoidal pulse width modulation (ASPWM) is introduced in this dissertation as a method which enables CHB to directly utilize time-variant dc sources, increasing CHB flexibility when compared to traditional pulse width modulation (PWM) methods which require dc sources with equal magnitudes or with magnitudes existing in specific ratios. Two alternative algorithms are presented to enable ASPWM implementation, providing a trade off between system performance and required sensor circuitry. This dissertation also introduces a load independent analytical approach for identifying discordant operating points, i.e. operating points where some cells in an asymmetric CHB leg regenerate power while the overall leg delivers power, or vice-versa. Identification of these points is essential due to the deleterious effects which can result from extended discordant operation, for instance overcharging of batteries leading to lifespan degradation or even catastrophic failures such as fires or explosions. Additionally, a method for rapidly identifying, isolating, and verifying internal IGBT open-circuit and gate-driver faults is presented in this dissertation to address the increased probability of switch failures occurring within CHB. The proposed approach enables converter operation to continue in the event of gate-driver or open-circuit faults, but avoids unnecessary converter reconfiguration due to gate-misfiring faults. For a CHB leg with M cells, the proposed technique identifies and isolates open-circuit switch faults in less than 2M measurement (sampling) cycles, and verification is completed in less than one full fundamental cycle. Furthermore, this dissertation introduces a real-time implementable atypical PWM technique which enables increased dc bus utilization under a wide range of non-ideal operating conditions. While this approach is suitable for a wide range of converters operating under external abnormalities, for instance maximizing dc bus utilization for converters providing auxiliary services such as negative-sequence compensation, this approach also facilitates operation of CHB with faulty cells. The proposed method can be used with any control technique and any carrier-based PWM method, enabling its implementation in both symmetric and asymmetric CHB. In addition to these fault tolerant techniques, a novel approach for analyzing the active- and reactive-power deliverable by grid-interactive converters is proposed. This method facilitates performance comparisons for various converter configurations, simplifying the process for selecting filter components, dc bus voltages, and other system parameters. This analytical approach also enables converter performance to be analyzed during internal and external fault events, allowing assessment of converter robustness. The efficacy of the developed techniques are supported by MATLAB/Simulink simulations as well as experimental data obtained using a laboratory-scale cascaded H-bridge multilevel converter.
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Musavi, Fariborz. "Investigation of high performance single-phase solutions for AC-DC power factor corrected boost converters." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/35082.
Full textAbstract:
Plug-in Hybrid Electric Vehicles (PHEVs) and Electric Vehicles (EVs) are an emerging trend in automotive circles, and consumer’s interest is growing rapidly. With the development of PHEVs, battery chargers for automotive applications are becoming a large market for the power supply industries. The improvement of overall charger efficiency is critical for the emergence and acceptance of these vehicular technologies, as the charger efficiency increases, the charge time and utility cost decreases. Additionally, to meet the efficiency and power factor requirements and regulatory standards for the AC supply mains, power factor correction is essential.
Due to limited space in vehicle and increasing power consumption, chargers are required to deliver more power with smaller volume. As a key component of a charger system, the frontend
AC-DC converter must achieve high efficiency and high power density. In this dissertation, several conventional plug in hybrid electric vehicle charger front end AC-DC converter topologies are investigated and a new bridgeless interleaved and a phase shifted semi-bridgeless power factor corrected converter are proposed to improve the efficiency and performance, which is critical to minimize the charger size, charging time, and the amount and cost of electricity drawn from the utility. A detailed analytical model for these topologies is developed, enabling the calculation of power losses and efficiency. Experimental and simulation results of several prototype boost converter converting universal AC input voltage to 400 V DC at 3.4 kW are given to verify the proof of concept, and analytical work reported in this thesis. The results show a power factor greater than 0.99 from 750 W to 3.4 kW, THD less than 5% from half load to full load and a peak efficiency of 98.94% at 265 V input and 1200 W load.
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Louganski, Konstantin. "Generalized Average-Current-Mode Control of Single-Phase AC-DC Boost Converters with Power Factor Correction." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/27331.
Full textAbstract:
The dissertation presents a generalized average-current-mode control technique (GACMC), which is an extension of the average-current-mode control (ACMC) for single-phase ac-dc boost converters with power factor correction (PFC). Traditional ACMC is generalized in a sense that it offers improved performance in the form of significant reduction of the current control loop bandwidth requirement for a given line frequency in unidirectional and bidirectional boost PFC converters, and additional functionality in the form of reactive power control capability in bidirectional converters. These features allow using a relatively low switching frequency and slow-switching power devices such as insulated-gate bipolar transistors (IGBTs) in boost PFC converters, including those designed for higher ac line frequencies such as in aircraft power systems (360â 800 Hz). In bidirectional boost PFC converters, including multilevel topologies, the GACMC offers a capability to supply a prescribed amount of reactive power (with leading or lagging current) independently of the dc load power, which allows the converter to be used as a static reactive power compensator in the power system.
<BR><BR>
A closed-loop dynamic model for the current control loop of the boost PFC converter with the ACMC has been developed. The model explains the structure of the converter input admittance, the current phase lead phenomenon, and lays the groundwork for development of the GACMC. The leading phase admittance cancellation (LPAC) principle has been proposed to completely eliminate the current phase lead phenomenon and, consequently, the zero-crossing distortion in unidirectional converters. The LPAC technique has been adapted for active compensation of the input filter capacitor current in bidirectional boost PFC converters.
<BR><BR>
The dynamic model of the current control loop for bidirectional boost PFC converters was augmented to include a reactive power controller. The proposed control strategy enables the converter to process reactive power and, thus, be used as a reactive power compensator, independently of the converter operation as an ac-dc converter.
<BR><BR>
Multiple realizations of the reactive power controller have been identified and examined in a systematic way, along with their merits and limitations, including susceptibility to the ac line noise. Frequency response characteristics of reactive elements emulated by means of these realizations have been described.
<BR><BR>
Theoretical principles and practical solutions developed in this dissertation have been experimentally verified using unidirectional and bidirectional converter prototypes. Experimental results demonstrated validity of the theory and proposed practical implementations of the GACMC.<br>Ph. D.
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Singh, Gunjan. "Computer control of a pulse width modulated AC/DC converter under a variable frequency power supply." Ohio : Ohio University, 1993. http://www.ohiolink.edu/etd/view.cgi?ohiou1175884455.
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Dalvi, Mahesh. "Computer controlled generation of PWM waveform using harmonic distortion minimization scheme." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177442328.
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Rustom, Khalid. "STEADY STATE AND DYNAMIC ANALYSIS AND OPTIMIZATION OF SINGLE-STAGE POWER FACTOR CORRECTION CONVERTERS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2216.
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With the increased interest in applying Power Factor Correction (PFC) to off-line AC-DC converters, the field of integrated, single-stage PFC converter development has attracted wide attention. Considering the tens of millions of low-to-medium power supplies manufactured each year for today's rechargeable equipment, the expected reduction in cost by utilizing advanced technologies is significant. To date, only a few single-stage topologies have made it to the market due to the inherit limitations in this structure. The high voltage and current stresses on the components led to reduced efficiency and an increased failure rate. In addition, the component prices tend to increase with increased electrical and thermal requirements, jeopardizing the overarching goal of price reduction. The absence of dedicated control circuitry for each stage complicates the power balance in these converters, often resulting in an oversized bus capacitance. These factors have impeded widespread acceptance of these new techniques by manufacturers, and as such single stage PFC has remained largely a drawing board concept. This dissertation will present an in-depth study of innovative solutions that address these problems directly, rather than proposing more topologies with the same type of issues. The direct energy transfer concept is analyzed and presented as a promising solution for the majority of the single-stage PFC converter limitations. Three topologies are presented and analyzed based on this innovative structure. To complete the picture, the dynamics of a variety of single-stage converters can be analyzed using a proposed switched transformer model.<br>Ph.D.<br>School of Electrical Engineering and Computer Science<br>Engineering and Computer Science<br>Electrical Engineering PhD
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Luo, You Gang, and 羅有綱. "High-performance AC/DC converters." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/85254283529982708794.
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Jan, CHih-Chiang, and 詹智強. "Study of Directly-Converted-Type DC/AC and AC/AC converters for UPS." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/66199330272462907879.
Full textAbstract:
碩士<br>國立成功大學<br>電機工程研究所<br>84<br>In this thesis, a directly-converted-type dc/ac and ac/ac
converter topology for UPS is proposed. Using the technique of
the Buck-Boost circuit, a reliable sinusoidal ac output is
presented at load end for the case of ac or dc input. Voltage-
mode and current-mode control methods are investigated to deal
with various loads and sources. Good output characteristics are
achieved in the voltage-mode control for dc input. However,
when ac input is applied, the output will distort. In order to
solve this problem , the current- mode control is addressed. In
the current mode control, by way of additional current feedback
loop is used, the proposed system can obtain the better output
profile. To verify the proposed scheme, the prototype is
implemented. The experiment results are agreed with the
theoretical analysis.
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Mallik, Dhara I. "Design of isolated DC-DC and DC-DC-AC converters with reduced number of power switches." Thesis, 2017. https://doi.org/10.7912/C2H652.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)<br>There are various types of power electronic converters available in recent days. In
some applications (e.g. PC power supply), it is required to supply more than one load
from a single power supply. One of the main challenges while designing a power converter
is to increase its e ciency especially when the number of power switches employed is
relatively large. While several loads are supplied from a single source, if the power loss in
the switches cannot be reduced, then the expected utilization of using a single source is not
very feasible. To reduce the loss and increase e ciency, the thesis presents a novel design
with reduced number of switches.
The scope of this thesis is not limited to the dc-dc converter only, the converter to supply
three phase ac loads from a single dc source is also presented. This discussion includes an
improved fault tolerant configuration of the inverter part. The generated waveforms from
the simulations are included as a demonstration of satisfactory results.
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Yeh, Ding-Hau, and 葉丁豪. "Study of Feedforward Controlled DC-AC Converters." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/62461881976939097008.
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碩士<br>國立成功大學<br>電機工程學系<br>85<br>In this thesis, a DC-AC converter controlled with feedforward pulsewidth modulation (FF-PWM) is proposed. It is mainly consisted of a two-output-ports flyback transformer and a commutator. Because the output voltage magnitude of a transformer is proportional to the number of its turns, the output voltage can be controlled simply be varying the other slave output. At low frequency, the converter behaves as a linear power amplifier with constant gain. In addition, the seitching frequency of the power switches in the commutator is as low as 120Hz and each switch changes its status as the voltage across it is nearly zero, so the swicthing loss is very little and the dead time effect is no longer a concern. An experimental prototype is set up to verify the hypothesis and discuss the practicability.
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Darabi, Mostafa. "A new family of dc-dc-ac power electronics converters." Thesis, 2014. http://hdl.handle.net/1805/5851.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)<br>This thesis proposes a family of non-isolated bidirectional converter in order to
interface dc and ac variables. Such power electronics solutions guarantee: (i) bidirectional
power flow between dc and ac converter sides, (ii) independent control in both
converter sides, (iii) high level of integration with a reduction of one power switch
and its drive circuits, (iv) implementation of two functions by using a unique power
conversion stage and (v) reduction of the capacitor losses. Despite proposing new
power converter solutions, this thesis presents an analysis of the converters in terms
of pulse-width-modulation (PWM) strategy, dc-link capacitor variables, and suitable
a control approach.
Solutions for single-phase, three-phase and three-phase four-wire systems are proposed
by employing a converter leg with three switches. A possible application of
this converter is in Vehicle-to-Grid (V2G) systems and interfacing dc microgrid with
a utility grid.
In addition to the new power electronics converters proposed in this thesis, an
experimental setup has been developed for validation of the simulated outcomes. The
proof-of-concept experimental setup is constituted by: DSP, Drivers & Integrating
Board, Power Supply and, Power Converter & Heat-Sink .
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Hwang, Jae-Won George. "Control of AC-DC-AC converters with minimized DC link capacitance under grid harmonic distortion." 2007. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=452840&T=F.
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Luo, Ye-Sing, and 羅業興. "Adaptive AC-DC Converters for Wireless Power Transmission." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/rj6w2w.
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博士<br>國立臺灣大學<br>電子工程學研究所<br>105<br>For the development of the Internet of Things (IoT), wearable devices, and implantable medical devices, the wireless power transmission is receiving significant attention. In these applications, the external power from a transmitter is transmitted by the coils / antennas, and an AC voltage will be received in a wireless device. To convert the AC voltage into a DC one for the device working, an AC-DC converter is widely adopted. The cores of the AC-DC converters usually use a diode-connected MOS transistor or a comparator-based active diode. However, the diode-connected MOS transistor and the active diode suffer from the threshold voltage of a transistor and the turn on/off delay time of the comparator, respectively. Both of them reduce the output voltage and the power conversion efficiency (PCE) of the AC-DC converters. Hence, increasing the output voltage and the PCE are the crucial topics for the AC-DC converters.
This thesis presents two AC-DC converters to increase their output voltages and PCEs. In chapter 2, an AC-DC converter with adaptive threshold voltage compensation is presented. A compensation voltage is adjusted in the background to compensate the threshold voltage of the transistors. The output voltage and the PCE of the AC-DC converter are increased. In chapter 3, an AC-DC converter using an adaptive pulse controller is presented to receive the low input amplitude. The adaptive pulse controller adjusts the delay time and pulse-width of the pulses in the background to turn on/off the power switches. The output voltage is kept as high as possible, and the PCE of this AC-DC converter is enhanced. Finally, the conclusions are given in chapter 4.
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Huang, Yi-Shuo, and 黃怡碩. "ERROR BOUNDED CURRENT CONTROLLERS FOR AC/DC BOOST CONVERTERS." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/34871543156193705145.
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博士<br>國立清華大學<br>電機工程學系<br>90<br>Due to rapid progress of power electronics technology and power semiconductor devices, it is now possible to achieve a much better performance for various power converters. In this dissertation, the research topic is focused on the AC/DC boost converters with bi-directional power flow and with variable power factor. Owing to the fast response, easy implementation and with bounded errors for achieving a specified power quality, the conventional hysteresis current controller has been developed and widely used for long time. However, there still exists some drawbacks for further improvement and some theoretical analysis about certain peculiar phenomenon remains to be clarified. Hence this dissertation, starting from satisfying the basic characteristics of the conventional hysteresis current controller, tries to provide a unified methodology for analyzing the controllers considered in this dissertation. In fact, while applying this methodology to the three-phase case, some peculiar phenomenon about various error-bound-violation cases are now clarified and fully understood for the first time. As a result, an improved three-phase error bounded current controller is proposed to guarantee the satisfaction of a specified error bound
Another important contribution of the dissertation lies in the application of zero mode control at the proper time to further reduce the switching numbers of the converters to achieve better efficiency and reliability. Sound theoretical basis is presented and detailed analysis is also made by using the unified methodology. Totally, four current controllers are proposed. Among them, two single-phase controllers with constant sampling period are inherently suitable for digital implementation. One is more suitable for lower output voltage applications and the other is more suitable for higher output voltage applications. The third single-phase hysteresis controller, instead of using constant sampling period, is however proposed to achieve the minimum switching frequency by using the unified methodology. Finally a three-phase controller is also proposed by extending the previous single-phase result. Due to the two dimensional considerations, this extension process is not a trivial one at all. It is worth pointing out here that, instead of using only the information of the current errors, the proposed controller uses also the information of the sign of the current error derivatives without incurring extra calculations. Hence, better controller performance can be achieved without requiring too much extra efforts. Some simulation and experimental results are also given for verifying the feasibility of the proposed controllers.
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謝振中. "High performance three-phase switching mode AC/DC converters." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/74845760984331046856.
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