Estimation Method for Rotor Eddy Current Loss in Ultrahigh-Speed Surface-Mounted Permanent Magnet Synchronous Motor

Surface-mounted permanent magnet synchronous motors (SPMSMs) usually adopt a retaining sleeve for ultrahigh-speed (UHS) applications. The retaining sleeve usually has high electrical conductivity and cannot be segmented. Accordingly, the rotor eddy current loss is high. Moreover, the higher the eddy current loss, the higher is the rotor temperature. Therefore, the rotor eddy current loss should be considered in the design stage. However, the eddy current loss is generally calculated through three-dimensional finite-element analysis (3-D FEA) and considered cumbersome because of the high computation time. This article proposes a simple estimation method for the rotor eddy current loss of a UHS SPMSM according to the motor size. In this study, the mechanically stable cross-sectional structure of the rotor was fixed, and a formula for predicting the eddy current loss of the rotor based on motor size was devised. In this method, the basic electromagnetic formula for eddy current and the frozen permeability method were utilized. The proposed method was validated via comparisons with the results of 3-D FEA.