A New Optimized IPMSM for EVs With Reduced Magnet Loss for Over-Modulation Operation

In the traction motor drives of electric vehicle applications, the over-modulation strategy is usually implemented to enhance the output torque capability of the interior permanent magnet synchronous motor (IPMSM), so that the dc input voltage of the inverters can be fully utilized by operating the inverter up to the six-step mode. However, it will inevitably introduce rich harmonic components into phase current, leading to the worsening issue of magnet eddy-current loss (MECL). Therefore, a new hybrid magnet rotor structure for fractional-slot concentrated-winding IPMSM with optimum design for magnet loss reduction is employed with the vital improvement measures concluded as follows: first, high-resistivity ferrite magnets are introduced in the rotor flux paths of the $d$ -axis and $q$ -axis, respectively, to form a hybrid magnets rotor structure together with Nd–Fe–B magnets; second, a rotor structure is proposed by employing a V-type placement of Nd–Fe–B magnets in the $d$ -axis path with the angle of V-type as one of the critical optimization parameters. An optimized design is finally obtained by employing the multi-objective genetic algorithm optimizer in JMAG finite element analysis tools, which is tested to show that the MECL produced in the over-modulation operation can be significantly suppressed by the optimized design.