Topology study of the active power filter for balanced electrified railway power supply system

The topology of an active power filter is proposed for the electrified railway power supply system, which can compensate the load's negative, reactive and harmonic current, and is suitable for the system adopting asymmetrical transformer. The filter is consisted of two single-phase 4-quadrant converters connected back to back through the dc-link capacitor. Decoupled by the capacitor, the converters can be controlled separately, which simplified the control process and improve the switching efficiency. Viewed from the system's input side, the single-phase inductive load acts as a symmetrical pure resistant. The structure and control principle of the proposed system is discussed in detail. Software simulation of the system is done, and the result of the system with a full load locomotive has verified the feasibility of the proposed topology and control strategy.