This thesis aims to design and build a power electronics system for the rectification and control of magnetization currents in synchronous generators with rotating exciters.The rotating exciter provides three-phase AC while the generator rotor needs DC with a high degree of control. The system needs to be able to rectify the three-phase AC to a stable DC without unwanted harmonic content, neither on the DC or the AC side. For control purposes it is also important that the current in the rotor can be changed very swiftly, preferably by several amperes during a single revolution ofthe machine.The system of choice is a synchronous rectifier bridge consisting of six MOSFET switches operated using the Space vector pulse width modulation (SVPWM) algorithm. This method gives a stable and controllable DC voltage while it keeps the harmonic content of the input currents at a minimum. However the DC voltage will always be higher than the peak line-to-line voltage from the exciter. To be able to lower the voltage below this value a Buck-converter is placed after the rectifier bridge.To gain a higher degree of control of the current density in the rotor windings the windings have been subdivided into three parts. To provide individual control of the current in the three rotor parts each part have been outfitted with a Push and Pull H-bridge.The proposed system has been both simulated using MATLAB Simulink and built and tested in the laboratory with satisfactory results. / I detta examensarbete presenteras ett kraftelektroniksystem för förbättrad kontroll av magnetiseringsstömmar i vattenkraftsgeneratorer som är utrustade med roterande matare.Generatorer används för att konvertera energi från rörelseenergi till elektrisk energi. Detta görs genom att man utsätter spolar för varierande magnetfält; då induceras spänning i spolarna. I vattenkraftsgeneratorer används oftast stora elektromagneter placerade i en rotor för att skapa dessa magnetfält. För att magnetisera elektromagneterna behövs ström som på något sätt måste överföras mellan den statiska och den roterande sidan i generatorn. Traditionellt görs detta med hjälp av släpringar och kolborstar som genom mekanisk kontakt överför elektriciteten. En roterande matare kan beskrivas som en liten generator som har sina elektriska utgångar på den roterande sidan istället för på den statiska sidan. Genom att placera en roterande matare på samma axel som den stora generatorn kan man istället alstra den elektricitet som behövs för att magnetisera generatorn direkt på den roterande sidan. Däregenom undviks många problem som är associerade med lösningen med släpringar.Den roterande mataren ger dock växelström medan magnetiseringsströmmen måste vara likström. Det är här kraftelektroniken kommer in i bilden. Det finns flera sätt att åstadkomma likriktning av ström. I det här projektet har ett fullständigt aktivt system byggts. Systemet är uppbyggt av transistorer av MOSFET typ och kan kontrolleras trådlöst med hjälp av Bluetoothteknik. Systemet ger full kontroll över strömmar och spänningar både på växelströmssidan och på likströmssidan och ska användas till en testgenerator på avdelningen för ellära vid Uppsala Universitet. Där ska den utökade kontroll som systemet ger förutsättningar till användas för att undersöka hur den här typen av system kan optimera de magnetiska krafterna inuti generatorn. En sådan optimering kan minska vibrationerna i generatorn och därigenom minska slitaget på lager och andra delar i maskinen.

In this paper, the development and control of a switched reluctance motor (SRM) applied to the intelligent electric vehicle are presented. In the SRM control policy, speed control and constant torque/constant power control are implemented with modified PI(RISC) control and a chopped current control(CCC). The control policy can restrain torque ripple effectively, and the vibration and acoustic noise are reduced involuntarily. Simultaneously, The speed response to sudden load change becomes less dramatic. Simulate results suggest that modified PI is more powerful than fuzzy control and PI. In the experiment, this paper compares the advantages and disadvantages of PI, fuzzy control and modified PI under no load, fixed load and unfixed load condition. Finally, a Digital Signal Processor(DSP)is adopted to verify the accuracy of simulation, which contributes to the planning of the program composition flow.

The grid voltage is normally required to avoid transient current of the inverter due to asynchronously grid-paralleling connection. This paper presents a seamless transition method to allow the inverter to connect to the grid at any time with no requirement of the grid voltage. The control of the inverter consists of the droop control and the riding-through control. In the droop-controlled mode, the inverter can connect to the utility and supply power according to its rated capacity. On the other hand, the riding-through mode is proposed to suppress the transient current due to asynchronous paralleling. In this mode, the zero-current control is realized to reduce transient current and a phase-locked loop is designed to correct the angle of the inverter output voltage. In addition, the virtual inductance is implemented to improve transient current resulting from the mode transition back to the droop control mode. Design considerations of the seamless transition method are provided and test results are conducted to verify its effectiveness.

In this thesis, position and current control systems for a brushless DC (Direct Current) motor are designed and integrated into one FPGA (Field Programmable Gate Array) chip. Experimental results are obtained by driving the brushless DC motors of Control Actuation System of a guided missile. Because of their high performance, brushless DC motors are widely used in Control Actuation Systems of guided missiles. In order to control the motor torque, current controller is designed and implemented in the FPGA. Position controller is designed to fulfill the position commands. A soft processor in the FPGA is used to connect and configure the current controller, position sensor interfaces and communication modules such as UART (Universal Asynchronous Receiver Transmitter) and Spacewire. In addition / position controller is implemented in the soft processor in the FPGA. An FPGA based electronic board is designed and manufactured to implement control algorithms, power converter circuitry and to perform other tasks such as communication with PC (Personal Computer). In order to monitor the behavior of the controllers in real time and to achieve performance tests, a graphical user interface is provided.

Multifrequency averaging is one of the widely used modeling and simulation techniques today for the analysis and design of power electronic systems. This technique is capable of providing the average behavior as well as the ripple behavior of power electronic systems. Hysteresis current control has fast response and internal current stability through controlling switches to maintain the current within a given hysteresis band of a given current command. However the state space variables in a hysteresis controlled system cannot be directly approached by multifrequency averaging method because of time varing switching frequency. In this thesis, a method of applying multifrequency averaging to hysteresis current controlled dc-dc converters is proposed. A dc-dc converter model with the application of this method has been successfully developed and validated both in simulation and experiment.

Financiadora de Estudos e Projetos / FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Este trabalho apresenta o desenvolvimento de um conversor CA-CC flyback trifÃsico, sem capacitor eletrolÃtico, com correÃÃo do fator de potÃncia, aplicado à iluminaÃÃo pÃblica utilizando LEDs de potÃncia. à realizada uma revisÃo sobre algumas das principais topologias presentes na literatura aplicadas em iluminaÃÃo com LEDs. TambÃm, à proposta a utilizaÃÃo de um conversor CA-CC com alimentaÃÃo trifÃsica, visando a retirada dos capacitores eletrolÃticos do conversor. A confiabilidade dos reatores eletrÃnicos pode ser aumentada com a retirada dos capacitores eletrolÃticos, tendo em vista que a vida Ãtil destes sofre forte influÃncia da temperatura de operaÃÃo. Um estudo acerca de conversores CA-CC trifÃsicos derivados da topologia buck-boost tambÃm à realizado, e uma topologia trifÃsica com um interruptor serà analisada. Um protÃtipo desta topologia à desenvolvido, e os resultados de simulaÃÃo e experimentais comprovam a viabilidade da utilizaÃÃo da mesma em reatores eletrÃnicos para LEDs. O protÃtipo apresenta potÃncia de saÃda de 54 W, com fator de potÃncia de atà 0,99 e rendimento de atà 77%, utilizando nÃcleos de ferrite comerciais de baixo custo e dependendo das condiÃÃes de operaÃÃo. Este protÃtipo pode operar em ampla faixa de tensÃes de entrada, alÃm de possuir uma estratÃgia de controle por modo corrente de pico, o que reduz os custos do projeto graÃas à utilizaÃÃo de um controlador de custo reduzido. / This paper presents the development of a three-phase AC-DC flyback converter with power factor correction without electrolytic capacitor, applied in street lighting using power LEDs. A review of some of the main topologies in the literature applied on LED lighting is performed. Furthermore, the using of an AC-DC converter with three-phase power supply, in order to withdrawal the electrolytic capacitors of the converter, is also proposed. The lifetime and reliability of AC-DC converters may be increased removing the electrolytic capacitors, considering that its lifetime has strong influence of the operating temperature. A study about three-phase AC-DC converters derived from the buck-boost topology is also performed, and a three-phase topology with one switch is analyzed. A prototype of this topology is developed, and the simulation and experimental results evidence the feasibility of using this technology in AC-DC converter LEDs. The prototype has an output power of 54 W, with power factor up to 0.99 and efficiency up to 77%, using low cost commercial ferrite core, and depending on the operating conditions. This prototype can operate in full-range of input voltages and also has a peak current control strategy, which reduces design costs due the using of a low cost controller.

This thesis deals with the description of artificial light sources, that use light-emitting diodes for their operation. Further down, the parameters of LEDs and their emissions are detailed. The work follows with the characterization of principles of LED power regulation. In the practical section, an example of one of the possible LED light source topologies, is designed. The offered solution includes the options to manually and automatically regulate the chromaticity of emitted light. Functionality of the solution was verified experimentally.

Model predictive control (MPC) for switched reluctance machine (SRM) drives is studied in this thesis. The objective is to highlight the benefits of implementing MPC to overcome the main drawbacks of SRMs and position them as an attractive alternative among electrical drives. A comprehensive literature review of MPC for SRM is presented, detailing its current trends as an application still at an early stage. The different features of MPC are highlighted and paired with the most challenging and promising control objectives of SRMs. A vision of future research trends and applications of MPC-driven SRMs is proposed, thus drawing a road-map of future projects, barriers to overcome and potential developments. Several important applications can take advantage of the improved features that SRM can get with MPC, especially from the possibility of defining a unified control technique with the flexibility to adapt to different system requirements. The most important cluster for SRM drives is the high- and ultrahigh-speed operative regions where conventional machines cannot work efficiently. SRMs with MPC can complement then the existing demand for electrical drives with high performance under challenging conditions. Three techniques based on the finite control set model predictive control (FCS-MPC) approach are developed out of the proposed road-map. The first one defines a virtual-flux current tracking technique that improves the existing ones in operating at different speeds and more than one quadrant operation. The method is validated for low- and high- power SRMs in simulations and diverse types of current waveform, making it easy to adapt to existing current shaping techniques. It is also validated experimentally for different operating conditions and robustness against parameter variation. The second technique proposed a predictive torque control that bases its model on static-maps, thus avoiding complex analytical expressions. It improves its estimation through a Kalman filter. The third technique uses a virtual-flux predictive torque control, similar to the first technique for current tracking. The techniques are validated at a wide speed range, thus evidencing superiority in performance without modification on the control structure. / Thesis / Doctor of Philosophy (PhD)

No description available.

A novel torque control algorithm, which adopts a two-phase excitation, is proposed to improve the performance of the Switched Reluctance Motor (SRM) drive. By exciting two adjacent phases instead of single phase, the changing rate and the magnitude of the phase currents are much reduced. Therefore the existing problems caused by the single-phase excitation such as large torque ripple during commutation, increased audible noise and fatigue of the rotor shaft are mitigated. The electromagnetic torque is efficiently distributed to each phase by the proposed Torque Distribution Function (TDF) that also compensates the effects of mutual coupling. To describe the effects of mutual coupling between phases, a set of voltage and torque equations is newly derived for the two-phase excitation. Parameters of the SRM are obtained by Finite Element Analysis (FEA) and verified by measurements. It is shown that the mutual inductance of two adjacent phases partly contributes to generate the electromagnetic torque and introduces coupling between two adjacent phases in the current or flux linkage control loop, which has been neglected in the single-phase excitation. The dynamics of the current or flux linkage loop are coupled and nonlinear due to the mutual inductance between two adjacent phases and the time varying nature of inductance. Each phase current or flux linkage needs to be controlled precisely to achieve the required performance. A feedback linearizing current controller is proposed to linearize and decouple current control loop along with a gain scheduling scheme to maintain performance of the current control loop regardless of rotor position as well as a feedback linearizing flux linkage controller. Finally, to reduce current or flux linkage ripple, a unipolar switching strategy is proposed. The unipolar switching strategy effectively doubles the switching frequency without increasing the actual switching frequency of the switches. This contributes to the mitigation of current or flux linkage ripple and hence to the reduction of the torque ripple. / Ph. D.