Optimization of an Electric Vehicle Traction Motor with a PM Flux Intensifying Stator and a Reluctance Outer Rotor

This paper proposes a novel electric motor concept using stator-embedded phase coils and permanent magnets (PM). A unique pattern of phase coil placement in separate slots using concentrated windings is employed. High flux intensification is achieved using low remanence and non-rare-earth permanent magnets in a spoke-type field arrangement. The exterior rotor has no active electromagnetic component thereby achieving a simple reluctance type configuration. The principle of operation is based on the concept of virtual work with closed-form analytical airgap flux density distributions. Preliminary parametric design studies followed by large scale multi-objective optimization were carried out using electromagnetic FEA to study the geometric impacts of the proposed design as well as the best trade-off between torque, total loss, torque ripple and power factor. Comparative metrics including indices for flux concentration, goodness of excitation, machine goodness, and torque per weight (TRW) indicate competitive performance with PM synchronous designs employing expensive and critical supply rare-earth PMs as well as other state-of-the art high power density traction motors. The proposed novel design considers a 10in outer rotor diameter with a target torque of 370Nm at a base speed of 3,000rpm. The efficiency map of the proposed design also provides insight into its performance at constant torque and constant power regions within the considered torque-speed envelope.