Design and rotor shape modification of a multiphase high speed permanent magnet assisted synchronous reluctance motor for stress reduction

This paper presents the design and a novel rotor shape of a 3 kW, 25000 rpm permanent magnet assisted synchronous reluctance motor (PMa-SynRM) based on a low speed benchmark model. Multiphase PMa-SynRM can operate with low torque ripple, reduced magnet volume and extended field weakening region which makes it a potential candidate for high speed motor design. However, the challenge of high speed PMa-SynRM design lies in the mechanical stress developed in the rotor which makes it completely different from operating it at low speed region. To manage the stress in high speed design, stress equation has been developed for PMa-SynRM and included in the objective function (OF) along with other parameters. For high speed design, a low speed benchmark model of 3 kW, 1800 rpm, 5 phase PMa-SynRM has been considered as a benchmark model. With lumped parameter model (LPM) and differential evolution strategy (DES), initial design of high speed PMa-SynRM was developed. High speed design showed reduced torque ripple and cogging torque compared with low speed model in finite element analysis (FEA). To understand the impact of including stress in the design objective function, stress analysis has been done for two high speed PMa-SynRM models; one with stress included in OF and another without stress in OF. From simulation, it was observed that, in the design including stress in objective function, stress has been reduced by 30.14%. To reduce stress further, mini flux barrier (FB) has been added in the rotor without affecting reluctance torque. Again, with DES, dimension of min FB has been optimized. Simulation results showed 15.73% improvement in stress by adding the optimized mini flux barrier.