High frequency voltage injection based stator inter-turn fault detection in permanent magnet machines

An inter-turn short-circuit fault in the stator winding of an electric machine, denoted as turn fault, has been recognized as one of the most severe faults in permanent magnet machines which requires swift and reliable detection, in order to implement appropriate mitigations. The asymmetry brought by a turn fault is widely used for the fault detection. However, similar features also emerges in a less severe high resistance connection (HRC) fault, which may led to incorrect fault identification. In this paper, a more exclusive turn fault detection method with the ability to differentiate from the HRC fault is proposed. It injects high frequency square wave voltage signals and makes use of the difference in high frequency impedance under the two fault conditions. The sensitivity to HRC fault is largely reduced. The proposed turn fault indicator is independent of operating conditions and robust with respect to state transients. This method is validated in a fault tolerant permanent magnet assisted synchronous reluctance machine drive.