Investigation of fault-tolerant IPM motors for critical applications

Abstract— This paper deals with the design of permanent magnet (PM) motors for mechatronic systems requiring an imperative fault-tolerant capability. The PM motors are more and more used in many applications for their high torque density. However, for critical applications, the motor geometry has to be suitably designed to limit the maximum short–circuit currents and brake torque. In case of short–circuit, the PMs on the rotor induce an e.m.f. on the faulty phases. Thus, even redundant solutions with two motors placed on the same shaft can not be enough when PM motors are used. As a consequence, the PM quantity has to be reduced. In addition, some winding arrangements can be adopted to improve the fault–tolerant capability. Fractional–slot motors yield a high leakage inductance and allow both a physical and magnetic separation among the phases.