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Thesis
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Three port converters used as interface in photovoltaic energy systems
Al-Chlaihawi, Sarab Jwaid Mousa
2017-01-18
Abstract: Abstract In this thesis, three port converters used as power flow control interfaces among two sources and a load were developed and analyzed. In the first chapter, in order to highlight the advantages of three port converters, its structural performances were compared with those of three port interfaces realized with a group of two port converters. After that, a brief survey of three port converters used in stand-alone energy sources like photovoltaic energy sources or hybrid electric vehicles energy sources are given; half-bridge, full-bridge, with or out transformer have been discussed. For stand-alone photovoltaic energy systems, the appropriate power flow control algorithms which include maximum power point tracking were analyzed. In the second chapter, the specific operation modes of three-port dc-dc converter were analyzed; operating principle and mathematical models of switch-mode dc-dc basic converters (buck, boost and buck-boost) have been presented systematically. Also, the topologies of full-bridge and half-bridge dc-dc converters which contain transformers were explained. The operating modes of a three-port converter with transformer, used as interfaces for a stand-alone photovoltaic system which were analyzed in detail. In the third chapter, the power flow management in full-bridge and half-bridge are described. After that, three three-port converters have been simulated: a half-bridge converter with three-winding transformer, a full-bridge converter with three-winding transformer and a Dual Input Single Output converter without transformer. As a result, the output voltage at all three ports were obtained. In the fourth chapter, a comparative study of different multiport converter topologies is done which include non-isolated Dual Input Single Output converter, isolated three-port full-bridge converter and half-bridge converters for interfacing the PV panels with the output load and battery bank. The topology of each of the converter, input and output voltage waveforms, duty cycles and advantages/disadvantages are discussed. In the fifth chapter, a comparative study was done between the original topologies of full-bridge three-port converter against the modified topology. The modification was done to make the converter suitable for use with renewable energy systems especially PV panels. The comparison was done on port voltages and current between the simulated results of our modified converter with experimental results of different existing topologies. In the sixth chapter, the PV cells and their interfacing with load and battery storage with transformer isolation is the focus. A three-port full-bridge converter is used as an interface between input and output ports. A controller is also integrated with the converter which manages the flow of power between different ports as the conditions changes and generates the most optimal PWM signal for all the switches. Different aspects of PV panels are studied along with the mathematical modeling. The irradiance intensity of the PV panels is varied and its effect on the waveforms is noted. Three Port Converters Used as Interface in Photovoltaic Energy Systems 9 In the seventh chapter, a three-port full-bridge converter is modelled, which is based on full-bridge two-port topology. Different modes of operation of the derived converter are discussed along with the key waveforms. Furthermore, we have derived volt-second balance and capacitor charge balance equations of all energy storing passive elements in the converter. In the end, we shift our focus to the design of controller for driving the switches used in the converter and the modelling of PV panels and their controller. In the eighth chapter, a fuzzy logic controller scheme is proposed and tested on a three-port full-bridge converter, which is derived from a full-bridge converter by assuming it into two cells, each one designating a different cell. The fuzzy logic controller is designed in MATLAB/Simulink which takes the difference of powers at PV panel and load as input and generates two signals for each set of switches in each cell. Three Port Converters Used as Interface in Photovoltaic Energy Systems 10 1 Introduction This chapter is dedicated to a survey of different multiport converters and their role in different applications. 1.1 Introduction of multiport converter A schematic of a power system can be seen in Figure 1-1, which consists of an input source, power converter, controller and a load. Thus, a power converter can be seen as an interface that acts between the source and the load, by controlling certain aspects using the controller. The controller measures the output that is fed to the load and compares it with the desirable output called reference and feeds the difference between the two, to the converter. Figure 1-1- Power Electronics Interface [1] The input source and load usually differ in terms of their voltage frequency, magnitude and phases. The job of converter is to facilitate the transformation of input power by converting the desired parameters such as currents and voltages. The controller is the brain of the converter, which assists the converters in power transformation while ensuring the high efficiency and high-power density.
Keyword(s): Energie fotovoltaică -- Teză de doctorat ; Sistem fotovoltaic -- Teză de doctorat ; Convertoare electrice -- Teză de doctorat ; Surse regenerabile de energie -- Teză de doctorat
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Record created 2018-01-15, last modified 2018-01-15
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