Hierarchical Optimization Combining Parameter and Topology for Outer Rotor in-Wheel Motors

In-wheel motor (IWM) optimization is critical for its vehicle integration. However, standard algorithms are frequently ineffective when applied to the complex IWM optimization problem, resulting in suboptimal performance and excessive computational costs. This problem arises from the diverse and conflicting objectives, namely peak torque, torque ripple, efficiency, and weight. Thus, this paper introduces a hierarchical optimization method that integrates parameter and topology optimization according to different objectives sequentially. The upper layer employed a computationally fast surrogate model to explore the parameter spaces extensively and select the working point for torque ripple reduction. Then, the lower layer utilizes the best parameter optimization results as constraints, enabling further refinement of the permanent magnet (PM) topology via accurate finite element analysis (FEA). As a result, a radial outer rotor IWM was optimized using this method. Convergence and prototype analyses demonstrate the reliability of the hierarchical optimization with a 10.6% and 1.6% increase in peak torque and efficiency, respectively, and a 43.2% reduction in the torque ripple rate compared with a traditionally engineered counterpart. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.