Split ratio optimisation of high‐speed permanent magnet synchronous motor with multi‐physics constraints

Abstract

Split ratio is one of the most crucial parameters in a permanent magnet synchronous machine (PMSM), which has great impact on both machine torque or power, and efficiency. Extensive studies have been carried out on the split ratio optimisation. Compared with the regular-speed machines, the high-speed PMSM has more types of power loss playing dominant roles, and has deeper coupling of multi-physics fields. Therefore, special concerns need be made. More comprehensive and accurate power loss estimation should be implemented; both of the critical mechanical stress constraint of the rotor and the critical thermal constraint, which in turn are associated with the machine electromagnetic performance, should be analysed and must be satisfied during optimal design. All these concerns will be presented in this study. Based on these, a procedure of the split ratio optimisation is proposed. It solely uses analytical equations which are derived in this study, hence it is simple and fast. A 250 kW, 25 krpm high-speed PMSM is taken as a study case, and its optimisation results using the proposed procedure are validated with finite-element analysis. Moreover, influence of the split ratio on various machine performances is discussed.