Study On Parallel Control Method Of Auxiliary Converter For Metro Vehicles

As the most important part of subway vehicle,auxiliary power supply system plays an important role in the normal operation of the vehicle.In order to ensure the stable output capacity and operation reliability of the auxiliary power supply system,the thesis focuses on the control technology of single auxiliary inverter and the parallel control technology of multiple inverters without interconnection.The stable operation ability and output waveform quality of the single auxiliary inverter are the foundation of the parallel system,therefore,the control technology of single inverter is studied in this thesis.By introducing the topology of subway auxiliary inverter,the mathematical models in different coordinate systems are established,and the voltage and current double closed-loop decoupling control method under balanced load is designed.By analysing the harmonic of battery charger,inverter air conditioner and other three-phase rectifier type nonlinear load of auxiliary power supply system,the PIR controller is designed.Among the PIR controller,the PI controller guarantees the output of positive sequence fundamental voltage can track the reference voltage and makes the system have good dynamic performance,the quasi resonant controller is designed to eliminate the voltage distortion caused by nonlinear load.The sequence component analysis of three-phase unbalanced loads in the auxiliary power supply system is also carried out,and a negative sequence component controller is designed to eliminate the influence of negative sequence component and reduce the imbalance degree of inverter output voltage.In the parallel control technology of auxiliary inverters,the basic algorithm of traditional droop control is obtained by analysing the circulation characteristics and power characteristics of the parallel equivalent model of two auxiliary inverters,and the definition of circulation in parallel of n auxiliary inverters is proposed.By analysing the load power distribution characteristics of auxiliary power supply system and line impedance characteristic,it is considered that the resistive droop control method is more suitable for the auxiliary power supply system,and the virtual impedance is added in the droop control to improve the flow characteristics of inverter parallel system,the voltage adjustment strategy is added to compensate the voltage drop caused by the droop control,so as to ensure the parallel AC bus voltage meets the requirement.Finally,a matlab simulation model is built and the voltage output capability of the single auxiliary inverter,the current sharing and stable operation capability of the auxiliary inverter parallel connection system are analysed to verify the feasibility of the proposed control strategy.