Three-phase current injection method for mitigating turn-to-turn short-circuit fault in concentrated-winding permanent magnet aircraft starter generator

Fractional-slot concentrated-winding (FSCW) permanent magnet synchronous machines, which are characterised with high power density, fault tolerance and wide constant-power speed range, are gaining more and more attention in the aircraft starter generator (SG) systems. Nevertheless, the short-circuit (SC) fault, especially the turn-to-turn SC fault, is the obstruct crux in aviation applications. This study is aimed to demonstrate the feasibility of FSCW permanent magnet SG (PMSG) in dealing with turn-to-turn SC fault. The law of FSCW-PMSG SC fault is analysed and verified by finite-element analysis (FEA), including the influence on turn-to-turn SC current by the number of the shorted turns and the coil position in the slot. The three-phase current injection control is employed to mitigate the SC fault in PMSG when a turn-to-turn SC fault occurs. A 24-slot, 16-pole FSCW-PMSG with spoke-type rotor topology is designed to confirm the ability of inhibiting turn-to-turn SC current without the risk of irreversible demagnetisation. Both FEA and experimental results are presented, verifying the effectiveness of the three-phase current injection control in restraining the turn-to-turn SC current for FSCW PMSG in an acceptable range.