Design exploration of variable leakage flux interior permanent magnet synchronous motors through parameter and topology optimization using covariance matrix adaptation evolution strategy

Purpose The purpose of this study is to explore novel rotor shapes of variable leakage flux interior permanent magnet synchronous motors (VLF-IPMSMs) via parameter and topology optimization (PTO) to enhance the variable flux characteristics, which are crucial for achieving high torque at low speeds and high efficiency at high speeds in electric vehicle drives. Design/methodology/approach The PTO method combines the normalized Gaussian network ON/OFF method with covariance matrix adaptation evolution strategy, using an objective function that maximizes flux linkage variation and suppresses harmonic components under torque constraints, which are evaluated using the finite element method. Findings For an arc-shaped magnet model identical to the reference model, optimization limited to the end of the magnet region yielded a rotor shape that increased the flux linkage variation by 32.7% and reduced the harmonic index of the radial air gap flux density by 75.2% compared to those of the reference while maintaining the maximum torque. Following the shape sensitivity analysis, low contribution regions were retained in the optimal shape. Upon optimization of the magnet shape parameters, the number of high order harmonic components increased, suggesting convergence to local optima. Originality/value This study demonstrates the application of PTO to VLF-IPMSMs using a newly defined objective function. The results demonstrate the potential of the PTO to identify rotor shapes with enhanced flux variations while clarifying the challenges of low sensitivity regions and local optima.