A turn fault mitigation strategy based on current injection technique for a triple 3-phase PMA SynRM

A turn-to-turn short circuit fault usually causes excessive fault current because of very low impedance associated with a few fault turns. It should be dealt with promptly to avoid further damages to the machine, especially for a permanent magnet (PM) machine. In order to limit the turn fault current, a novel turn fault mitigation strategy based on current injection technique is investigated for a triple redundant 3x3-phase PM synchronous reluctance machine (PMA SynRM). First, the flux linkage of the faulty phase where the fault turns are located is estimated considering the influence of PM and currents in the healthy and faulty 3-phase sets. This flux linkage, including that of the fault turns, is subsequently reduced by injecting specific currents to the faulty 3-phase set, leading to much smaller fault current. The proposed current injection method does not affect the operation of the healthy 3-phase sets which continue to produce torque. The effectiveness of the proposed method is validated by extensive finite element (FE) simulation and experimental tests on a prototype 3x3-phase fault tolerant PMA SynRM drive.