Magnet Shape Design and Verification for SPMSM of EPS System Using Cycloid Curve

Abstract

A low cogging torque and torque ripple are the most important qualities for electric power steering (EPS) motors. Therefore, various design methods are employed to obtain EPS motors with these qualities. In this study, a novel design method for the pole shape was developed by adopting a cycloid curve to realize the desired qualities of EPS motors without reducing the torque. An evaluation index (δq) was used to design the pole shape of the magnet and to compare the pole shape between the proposed method and the conventional method. The proposed and conventional methods were applied to existing machine designs, and their performances were compared using a finite-element analysis (FEA). The results of the FEA and prototype tests indicated an improved motor performance for the proposed method. INDEX TERMS Electric power steering (EPS), surface permanent magnet synchronous machine (SPMSM), cycloid curve, cogging torque, torque ripple.

Tolerance-Insensitive Design of the Magnet Shape for a Surface Permanent Magnet Synchronous Motor

“…In the case of CET, Rf and Rr are expressed by considering the geometrical relationship in terms of the known variables δq, Rrotor, and n (the number of poles) (8)~(10). In the case of PET, the values of Rf and Rr can be calculated by geometrical relationship [13]. In order to define the shape profiles of CET and PET, the values of R f and R r in Equations 5 and 7 should be defined.…”

“…The epicycloid curve, which is a previously proposed curve, is a rotor surface design method. There also exists an eccentricity curve that is a commonly used rotor surface design method [13]. Therefore, the characteristics of the epicycloid curve were analyzed by comparing the motor performance after applying the eccentricity and epicycloid curves to the same motor.…”

“…In past studies, cycloid curves have been widely applied in mechanical fields (e.g., in speed reducers and oil pumps) [11,12]. However, in the study by Park, Lim, and Lee [13], the cycloid curve was applied to the rotor of a motor. In their study, it was also verified that cogging torque was improved for a motor to which a cycloid curve was applied.…”

Optimal Design of Permanent Magnet Structure to Reduce Unbalanced Magnetic Pull in Surface-Mounted Permanent-Magnet Motors

“…SPMSM has the advantages of simple structure, low manufacturing cost, and convenient installation, which is widely used in practical projects [1], [2]. The use of fractional slot windings can reduce cogging torque and torque fluctuation, increase the operation stationarity.…”

“…The torque fluctuation of motors has an impact on the stationarity under operation and the accuracy of control, especially in the light load and low-speed state. In recent years, many scholars have studied how to reduce the torque fluctuation of PMSM [15], [2], such as optimizing the pole slot matching and the rotor parameters [16]. In [17], it is pointed out that the cogging torque can be reduced by skew pole, and the skew pole angle and the axial segments number to minimize the cogging torque are determined.…”