Fully Integrated Fault-tolerance for PMSMs in Aviation Applications

An open-circuit fault-tolerant system implementation is presented for sensorless three-phase PMSM drives. The fault-tolerant system uses a fourth inverter leg connected to the motor neutral point, allowing for post-fault two-phase operation. Since the control is sensorless and fault detection is performed by the controller, no additional sensors are required beyond three phase current sensors. Hence, the fault-tolerant system is particularly suitable for highly integrated or compact drive systems. Whilst fault detection and sensorless two-phase control are well documented in existing literature, often little attention is given to the transitional behavior between a fault occurring and post-fault operation. Hence we focus on experimentally testing the fault-tolerant system in its entirety. An open-circuit fault is created during sensorless three-phase operation, causing a transient in the motor torque and speed. The controller rapidly detects the fault, and switches to post-fault control with the faulty leg disabled and the 4th leg connected to the motor neutral. In the test system the fault caused only a 5% dip in motor speed before the speed was smoothly regulated back to the commanded pre-fault speed under the post-fault two-phase control scheme. This fast recovery from a fault condition is particularly beneficial to aviation applications, where even a brief loss of the motor drive may be unacceptable.