Determining the operating region for demagnetization-free fault tolerant control of multiphase PMa-SynRM

This paper presents the process of determining demagnetization-free operating region of multi-phase permanent magnet assisted synchronous reluctance motor (PMa-SynRM) under fault tolerant operating condition using finite element analysis (FEA) tool. The five-phase PMa-SynRM has been considered as a suitable candidate for many critical service applications such as aircraft, electric vehicles, and electric ships due to low cost and high fault-tolerance capability. These machines can generate required torque under single or two-phase fault using only the unaffected phases. However, under the fault condition, the air-gap magnetomotive force (MMF) will be distorted and cause additional harmonics loss and torque ripple. Although the adoption of fault tolerant control (FTC) scheme can improve the performance, there will be large rise and fall in the air-gap MMF which can be threatening to the permanent magnet (PM) for irreversible demagnetization. Therefore, multiphase PMa-SynRM should be carefully operated under FTC to avoid the irreversible demagnetization of its PMs. This study determines the demagnetization-free operating region of a 3 kW five-phase rare-earth (NdFeB35) PM based PMa-SynRM under single and two-phase open fault conditions. Finite element analysis (FEA) has been performed for different thermal levels of the PMs to evaluate the operating range of the motor without demagnetization.