Current-sharing performance of an advanced co-phase traction power substation system based on cascade-parallel converter

An advanced co-phase traction power substation system based on the cascade- parallel converter was proposed in this paper, for addressing the power capacity problems of traction power substation and the problems of electrification phase, reactive power, negative sequence and harmonic in railway. The 3-level neutral point clamped (NPC) converter was used in power substation, while the converter was cascaded and paralleled to approve the capacity of system. The system can transfer active power directly between power gird and traction network, the power factor of which is 1, and the neutral-section passing device is canceled completely, which is an ideal co-phase traction power supply system. In this paper, current sharing performance of traction network based on this system is analyzed. The impedance performance of traction network and circulating current characteristic of the system are presented in detail. And then the circulating-current restraining strategy is analyzed, the droop control is proved to achieve a system of parallel. The system is proved having droop characteristic and can parallel operate with multiple converters by using drooping control, achieving current sharing. The simulation results verified the theoretical analysis and that the system achieves current sharing. The control strategy and modulation strategy is verified by experiment.