A Fault Tolerant Electric Drive based on Bifilar Coils Wound Machine

A novel fault-tolerant electric drive system concept based on a permanent magnet synchronous machine employing two three-phase systems is introduced. The stator winding uses bifilar tooth coils physically separating serial turns of each coil. Each bifilar coil is supplied by separate inverter module while ensuring the same current direction in the slots and, thus, an additive current linkage. With the aim of fault tolerance, this design prevents the risks of inter-turn short circuits within the same coil. Such faults can cause the most severe local fault currents in a stator winding in case of a single-turn short circuit. The paper investigates effects of short circuits between the neighboring turns of the bifilar coils for two system configurations as well as different detection methods by means of finite element analysis in conjunction with field oriented control. Evaluations of the three-phase sum currents, the phase leakage currents, and the phase current spectrum during turn-to-turn faults enable early-stage detection when the fault resistance is still high.