Diverse Slot-Opening Designs for Cogging Torque and Performance Optimization in PM Machines

The slot-opening structure in permanent magnet (PM) machines plays a crucial role in optimizing torque, electromotive force, and electromagnetic vibration metrics. Consequently, significant attention has been devoted to optimizing its design, particularly focused on reducing cogging torque through methods such as tooth shape optimization and dummy slots. However, current slot-opening design techniques face challenges, particularly in compromising average torque and inadequately suppressing cogging torque due to simplistic modifications of slot reluctance harmonics. In contrast, this study introduces a comprehensive slot harmonics configuration method alongside diverse slot-opening design schemes, showcasing enhanced effectiveness in mitigating cogging torque in various PM machine structures with different pole-slot combinations. The key of this approach involves adjusting the airgap magnetic reluctance harmonics to amplify the least common multiple of interacting harmonics responsible for cogging torque generation. Through extensive validation via finite-element method and experimental test, the proposed method emerges as a promising solution for effectively reducing cogging torque and enhancing the overall performance of PM machines.