Study Of Advanced Co-Phase Traction Power Supply System Based On Three-Phase To Single-Phase Converter

Traditional traction power supply system adopts three-phase to two-phase separation mode of power supply. This system is facing pool quality of power supply such as:reactive, harmonics, and negative sequence. And the phase splitting limits the capability of speed and load. With the development of high-speed, heavy--load railway, the system is facing severe tests.This paper introduces a advanced co-phase power supply system based on three level three-phase to single-phase converter, which uses power electronic technology to cancel the neutral-section passing device completely, to achieve the symmetrical of three-phase load and the traction network side flexible controllable.This system improves the quality of electric energy, raises the efficiency of the system and is a new type of smart traction power supply system.The control scheme of advanced co-phase traction power supply system is analyzed in this paper. First of all, the topology of three-phase to single-phase converter is discussed. Then the control of three-phase converter and single-phase converter are studied, the three-phase part adopts dual-loop PI control and the DC capacitor voltage balance while the single-phase part adopts voltage feed-forward control. The mathematical model of the converter is established, the control parameters are set and the bode figures of the system are depicting to prove the stability of the system.For the multi-substations model, Carson model of the system is established to analyze the impedance distribution and the circulation distribution to verify the droop characteristic of the system. Using droop control based on direct power control to achieve current decoupling, the control parameters are set and the bode figures of the system are depicting to prove the stability of the system, current sharing of substations parallel operation are achieved.As harmonic source, the locomotives inject huge harmonic current to the system, the traction power supply system becomes the direct encouraging object, which may cause the damage of equipments. So, it’s necessarily to analyze the harmonic impedance of the system based on distributed capacitance and inductance reduction, the locomotive model of CRH2is set up to simulate the locomotive network coupling, the harmonic of load, substations and grid power are analyzed, the results meet the national standard, the extreme case of injection high harmonic current is also taken into consideration, the simulation results shows that the harmonic performance of the system is better than the existing system and provides theoretical reference for avoiding harmonic resonance.To verify the performance and characteristics of the system, three-phase to single-phase converter operation, single substation and multi-substations grid-connected simulation model and harmonic analysis model are built in Matlab/Simulink environment. The simulation of locomotive network coupling is carried out. The simulation results show that the advanced co-phase traction power supply system can solve the problem of power quality, harmonic, reactive and three-phase unbalance current better, has the obvious superiority.