FEA-assisted steady-state modelling of a spoke type IPM machine with enhanced flux weakening capability

Abstract

Interior permanent magnet (IPM) machines with spoke-type design are possible candidates for various applications, including vehicle traction. One of their drawback is the high demagnetizing current required in the flux weakening region to let the motor achieve high speeds. This problem can be mitigated by equipping the motor with a mechanical devices consisting of mobile rotor yokes. These move radially by centrifugal force so as to reduce the air-gap flux at high speed with no need for demagnetizing current injection. This paper addresses the problem of modeling such IPM motor to study its steady-state behavior under different operating conditions, both in the full-flux and in the flux-weakening region of the speed range. The approach uses a limited set of non-linear finite element analysis to characterize the dependency of motor flux linkages on the stator currents and rotor position. Interpolating functions are then obtained to mathematically capture this dependency and plug it into the steady-state electromechanical equations of the motor. The effectiveness and accuracy of the method are assessed through on-load measurements taken on the modelled motor both in low and high speed operation.