Design And Implementation Of DC-DC Converter In Solid State Transformer

Traditional power transformer with good stability and high efficiency has been widely used in modern power system, but there are some defects in traditional power transformesr, such as a big volume, heavy quality, high power consumption, especially, there gradually appears some problems of dealing with power quality issue in recent years; Meanwhile, a mass of power electronics equipments has realized practical successful application in power system represented by Flexible AC Transmission System (FACTS) technique. Therefore, the application of power electronic technology in the field of power transformer has improved the shortcomings of traditional transformer, has become a research focus. So, the concept of solid state transformer appears. Solid State Transformer(also known as power electronic transformer), has the potential to solve many new problems appeared in power system and more extensive applications, for this reason, the study to SST has important theoretical significance and practical value. DC-DC converter is main parts of SST, which has functions of power transfer, voltage transformation and electrical isolation, which have important influences on its volume, weight and efficiency, it is very necessary to research DC-DC converte used in SST.The structure and working principle of SST and DC-DC converter are analyzed, and the function and significance of the DC-DC converter, which is used in the SST, are introduced. Combined with the research situation of SST at home and abroad, the technical status of SST research are expounded, the technical indicators of the DC-DC converter which is applied to SST are proposed in this paper, meanwhile, a detailed design scheme is drew up, at last, the overall scheme of the DC-DC converter is designed. It has been shown by the experiment that the scheme design scheme is reasonable, and the index is clear, finally the expected function can be realized.The hardware circuit of the DC-DC converter applied in SST has been designed, which is including the main power circuit and the control circuit. The full bridge inverter, high frequency transformer, rectifier bridge, output filter circuit, hardware protection circuit, sampling circuit, control circuit and the DSP core plate and its peripheral circuit are the modules of the hardware circuit.Considering the existed problem above, the DC-DC converter applied in SST has been conducted the thorough research in this paper. A series of experiments has been done through the laboratory prototype which is developed by the function of the DC-DC converter. Based on the experiment result, every performance index has reached the expected requirements of the converter. Main contests of the thesis are as follows.Small signal model of the DC-DC converter applied to the SST is established. Double-closed-loop PID control strategy based on outervoltage loop and inner current loop is used. The PI parameters needed to control system was determined. The software program of the DC-DC converter based on TMS320F28335 chip mainly including the main program, A/Dsampling subroutine, interrupt subroutine, phase shifting pulse processing procedures, the phase-shifting angle computing closed loop subroutines and so on was writed which have readable and transplantable characters.A laboratory prototype was designed and developed, the hardware and software are tested. The test results show that the laboratory prototype has the reasonable hardware design, the simple circuit structure and the stably system, achieved power transmission, voltage transformation, electrical isolation expected function of the DC-DC converterin the SST.