Characteristic Analysis and Improved Design of IPMSM for Automotive Compressor Through Tapering of Rotor Surface

This study investigates the tapering rotor surface technique in an interior permanent magnet synchronous motor (IPMSM) for electric vehicle compressors. To achieve this, this article proposes a novel tapered rotor design with a nonuniform air gap, created by applying asymmetric shaping to the bridge region along the rotor radius. A conventional IPMSM with a uniform air gap produces a trapezoidal-shaped flux density, introducing high-order harmonics and causing certain drawbacks for the motor. This study selected the offset height of the eccentric center and the distance between the rotor radius and the magnet as improvement design variables. The proposed tapered rotor model, characterized by a nonuniform air gap, demonstrated better performance than the initial model. Subsequently, a stress analysis of the thinned barrier was conducted to validate the structural integrity of the proposed model. The key parameters, such as air-gap flux density, cogging torque, inductance, flux linkage, and efficiency maps, were compared between the initial and improved models using finite element method (FEM) and MATLAB simulations. The proposed tapering motor achieved a 36.36% reduction in cogging torque error rate and a 0.6% improvement in efficiency deviation at the primary operating point. A prototype of the conventional rotor model was manufactured, and its efficiency curve was verified, which showed good agreement with the FEM analysis results.