YN/VD connected balance transformer based electrical railway negative sequence current compensation system with passive control scheme
A new negative sequence current compensation system (NSCCS) is proposed to improve the power quality in electrical railway power system. The NSCCS consists of a balance transformer in YN/VD connection and a three phase converter. The balance transformer used here can supply both two phase voltages with 27.5 kV for electrical locomotives and three phase voltages for low or medium voltage converter. So, a large capacity step down transformer used to match the voltage of converter is not necessary, which can significantly reduce not only the total cost of the equipment, but also the area of the substation. The system topology is introduced and the compensation principle, mathematical model, detection method, and control strategy are expounded. The non linear passive control method for the converter is adopted to design the controller to get a good compensation performance. The simulation and experimental results verify the effectiveness of the compensation system.