Investigation of Rotor Topologies for Reducing Torque Ripple in Double-Layer IPMSMs for Automotive Applications

Interior permanent magnet synchronous motors (IPMSMs) are currently widely used for traction applications. However, the torque ripple in these motors needs to be reduced because it causes vibration and acoustic noise. Accordingly, this study first determines the guidelines for reducing the torque ripple of multilayer IPMSMs and then proposes a double-layer IPMSM with holes drilled in the rotor core. The torque ripple reduction for the proposed rotor structure is examined using 2-D finite element analysis and experiments with prototypes. The analytical results show that, under maximum torque-per-ampere control, the torque ripple using the proposed model was suppressed by 54.8% compared with the reference model while limiting the average torque reduction to 3.6%. Moreover, multiobjective optimization based on the guidelines is performed. With the proposed structure, the torque characteristics at high and low currents are highly correlated, and a similar torque ripple reduction effect is obtained even at low current, which is frequently used in traction motors for automotive applications. Finally, optimization is performed for an IPMSM with other topologies, resulting in verification of the generalizability of the proposed method.