PM Magnetization Direction and Arrangement to Maximize Outer Rotor SPMSM Performance

Abstract

The outer rotor surface-mounted permanent magnet synchronous motor (OR-SPMSM) is advantageous for designing high torque due to its ability to achieve a large effective air-gap radius. If the magnetization direction and structural arrangement of the permanent magnets (PM) are optimized to maintain air-gap flux density while reducing PM thickness, the split ratio (SR) can be increased. Increasing SR allows for a larger effective air-gap radius even under limited outer diameter conditions, which can lead to increased torque or reduced current density. In this study, to validate this concept, comparative models are designed through optimization techniques, and their results are analyzed. To solve the optimization problem, a kriging surrogate model is employed as the metamodel, and a genetic algorithm (GA) is used to search for optimal solutions. The obtained results are subsequently analyzed using finite element analysis (FEA) to assess their validity and performance. As a result, the model employing the Halbach array without the rotor yoke exhibited the best performance.