A fault detection procedure for single phase bridge converters

The use of multiple single phase bridges has fault tolerant benefits in high reliability permanent magnet motor drives for use in safety critical applications. This paper describes a technique which continuously monitors the conduction of a single phase bridge, using a single additional current sensor positioned to pick up only the flywheeling currents around the bridge. Correlation of the device firing signals, phase current direction and flywheeling currents enable a fault to be detected. The system identifies the faulted device and its mode of failure, within the short circuit withstand time of the power devices. Accurate knowledge of the nature of the failure allows the bridge controller to take appropriate action to avoid propagation of the fault, which may lead to catastrophic failure of the bridge, affecting the power rails and associated systems. Results of an experimental bridge, incorporating the fault detection system, demonstrate the effectiveness of the technique when the bridge devices have severe open or short circuit faults