Study Of Parallel Voltage Source Converter Based On Advanced Traction Power Supply System

Problems of current traction power supply system in crossing neutral section, power quality and overloading ability are becoming more and more serious as the fast develop of high speed and heavy haul railway. Advanced traction power supply system, using power electronic converters replace transformer, based on three-phase to single-phase converter, is a new type of smart traction power supply system which is able to backout the neutral sections totally and solve the problem of power quality and realize the comprehension of the railway. With the development of modern power electronic devices and technology, the advantages of the system are increasingly prominent.Therefore, it is necessary to study advanced traction power supply system deeply. In this paper, the properties of parallel system and control strategy of advanced traction power supply system based on voltage source type inverter are studied for providing theoretical support for the system of the engineering.This paper discusses the topology of single phase inverter and studies the voltage source inverter control methods firstly. Then, voltage amplitude feedback and feed forward current double closed loop control strategy is used to make the inverter output as a voltage source. Based on the construction of Carson traction network model and proposing of CRH multi-mass mode, the characteristic of circulating current of parallel inverters in traction substation and the parallel traction substation is studied. The cause of active, reactive and dc circulating current are analyzed by using single variable controlled strategy. The simulation verifies the correctness of the analysis of circulation.Through the designing of the single phase lock loop and the current decomposing algorithm, the distributed logic control method is used to control the parallel system in the traction substation and the substation model of parallel inverters is built. A parallel strategy is designed to suit the parallel power substation in this paper. An improved droop control based double closed loop control is proposed, which has overcome shortcoming steady-state error of the traditional droop control. The traction substation in parallel/grid connected simulation model is established.To further verify the correctness of theory analysis and the feasibility of the control strategy, a small power FPGA experimental platform is set up. The FPGA control circuit and IGBT driver circuit are debugged in this paper. The PI control module, single phase lock loop module and current detection module are programmed by Verilog HDL language. Using this experimental platform, the experiment of the double close loop single-phase voltage source inverter, the distributed logic control parallel strategy of and the improved droop control strategy based double closed loop control have been completed. It is certified by the experiment that the system capacity can be expanded by the parallel system studied in this paper, and the designed control system can effectively inhibit parallel circulating current and enhance the reliability of the system.