Finite Element Analysis of Fault-Tolerant PM Motors with Independent Phases

This paper presents the finite element (FE) analysis of a multiphase permanent-magnet motor designed to have independent phases structure according to the principles of fault tolerance. The goal of the study is to verify and quantify the independence of the phases from the electromagnetic point of view, one of the key requirements of fault-tolerant machines. The case study refers to a five-phase permanent-magnet motor designed for aircraft flap application. The typical operating conditions of motors designed to operate in fault tolerant environments are considered, such as the opening of one or more phases after the occurrence of a failure. The actual performance of the multiphase motor is compared to that achieved by the superposition of the effects of each phase fed independently, which is the straightforward approach in usual modeling. The results demonstrate that modeling by independent phases leads to a negligible error in term of average torque in all the operating conditions, while the torque ripple and the flux linkages present a certain discrepancy in one or two open-phases operations, as in these cases a deeper saturation of the magnetic paths is reached.