Analysis of a railway power system based on four quadrant converters operating under faulty conditions

Long distance European trains are usually powered by a single-phase AC line of 25 kV at 50 Hz. Traditionally a traction drive mainly consists of a single-phase AC/DC converter, a DC-link bus and a three-phase DC/AC PWM converter. In the past, the DC-link bus was obtained through diode rectifiers, which generate line currents with high harmonic distortion and low power factor. In order to reduce these problems, the DC/AC converter is based nowadays on four-quadrant interlaced converters. Taking into account the power involved in electric drive trains, rectifier semiconductors are exposed to high stresses that can lead to failures. However, some types of failures such as power switch open-circuit faults may not be immediately detected and lead to more failures in other power switches. The goal of this work is to investigate the operation of a four quadrant interlaced converter, under normal and faulty conditions. For fault detection purposes, the average rectifier line current will be used. Experimental results are presented.