Mitigation of turn-to-turn faults in fault tolerant permanent magnet synchronous motors

This study presents a method to mitigate and alleviate the effects produced by a turn-to-turn short in a fault tolerant permanent magnet synchronous motor with single-layer concentrated windings. The rotor magnets are capable of inducing a high voltage across the fault contact point; this voltage has the potential to generate a high circulating current that promotes the rapid propagation of the fault due to the thermal stress created by the increased localized fault power losses. The scope of this study is for applications where postfault operation is desired, even if it means operating at reduced power capacity and lower speeds. Upon quick detection of a fault, the proposed technique can be used to decelerate the propagation of the fault and extend the machine's postfault life span. The technique consists of a magnetic field-weakening strategy at speeds below nominal, to reduce the voltage induced in the faulted portion. The concept is validated through finite element analysis, modeling, and experimental data. It is demonstrated that the proposed technique reduces the fault current magnitude and winding temperature.