DC micro-grid based on DC traction power supply system and electric vehicle batteries charging & discharging system

In view of the existing problems in DC traction power supply system and electric vehicle (EV) batteries charging system, a DC micro-grid is proposed: EV batteries are connected to DC traction power supply system via off-board bidirectional chargers, forming a ring DC micro-grid in a sub-region, in which EV batteries can be charged by DC traction power supply system and voltage of overhead contact system can be stabilized by the EV batteries charging and discharging system. A method that place ultra-capacitors in parallel with EV batteries is designed to improve system performance. Voltage droop control is adopted by parallel bidirectional chargers, which can achieve double-quadrant operation and avoid the circulating current as well. In the end, simulation results are presented to demonstrate the feasibility of this system.