DC Bias Suppression in Static Power Converter During Catenary Fault Handling for Railway Flexible AC Traction Power System

Abstract

Flexible AC traction power supply system (FTPSS) has been a potential candidate for high-speed and heavy-haul railways. The catenary fault is a crucial issue in the FTPSS. Since the static power converters (SPCs) become the main source, SPC is required to switch between the voltage-frequency and the fault-current control modes, in order to achieve fault detection and rapid system recovery. However, inappropriate switching method may lead to violent change of instantaneous voltage. Therefore, serious DC bias of SPC output transformer may occur and excite severe overcurrent. It results in the tripping of SPCs and the failure of system recovery, and severely undermine the reliability of FTPSS. To address this issue, this paper analyzes and reveals the mechanism of this DC bias phenomenon. The voltage-time product imbalance during the mode switching process is the main cause of DC bias, and it is related to the voltage phase at the switching instants. Accordingly, a combined method of voltage waveform splicing and DC bias elimination control is proposed. Overcurrent can be avoided, and smooth control-mode switching and rapid system recovery can be achieved. Simulation and experimental results verify the validation of the proposed method.