Novel Rotor Structure Using an Asymmetric Magnet Shape for Surface Permanent Magnet Synchronous Motors

Abstract

Electric motors have long been the most commonly used actuators in industry, with surface permanent magnet synchronous motors (SPMSMs) being particularly popular due to their quick response time and precise control. Research has been conducted to improve the electromagnetic performance of SPMSMs; however, this has resulted in more complex SPMSM structures that cause increases in manufacturing cost and time. The anticipated rapid increase in demand for motors in Industry 4.0 makes it crucial for research to focus not only on improving motor performance but also on reducing structural complexity. To address these challenges, this study proposes asymmetric surface permanent magnet synchronous motor (A-SPMSM) structure that features asymmetric magnets attached to the rotor surface. This novel design aims to reduce structural complexity while minimizing degradation of electromagnetic performance. The proposed A-SPMSM was tested to assess both its structural complexity and electromagnetic performance. To evaluate the structural complexity, we compared the ring type SPMSM (R-SPMSM) and step-skew type SPMSM (T-SPMSM) with A-SPMSM in terms of shape and manufacturing complexity. Additionally, numerical and experimental analyses were conducted to evaluate A-SPMSM's electromagnetic performance by using the cogging-mutual torque ratio and back-EMF values as performance indicators. Comparisons were made between A-SPMSM, R-SPMSM, and T-SPMSM. Two specifications were selected and denoted as Ⅰ and Ⅱ. The analysis results of this study were as follows. First, the study confirmed that A-SPMSM had lower shape complexity than T-SPMSM. A-SPMSM’s shape complexity was 4, and T-SPMSM’s shape complexity was 8. Second, the manufacturing complexity of A-SPMSM was found to be lower than that of both R-SPMSM and T-SPMSM. A-SPMSM’s manufacturing complexity was 4 and T-SPMSM’s shape complexity was 8. Third, through numerical and experimental analysis, the cogging-mutual torque ratio and the measured cogging-mutual torque ratio performance of A-SPMSM was found to be similar to that of both R-SPMSM and T-SPMSM. From numerical analysis, A-SPMSM-Ⅰ, R-SPMSM-Ⅰ, and T-SPMSM-Ⅰ’s cogging-mutual torque ratios were 0.010%, 0.003%, and 0.051%, respectively. A-SPMSM-Ⅱ, R-SPMSM-Ⅱ, and T-SPMSM-Ⅱ’s cogging-mutual torque ratios were 0.038%, 0.002%, and 0.077%, respectively. From the experimental analysis, A-SPMSM-Ⅰ, R-SPMSM-Ⅰ, and T-SPMSM-Ⅰ’s measured cogging-mutual torque ratio were 0.96%, 0.77%, and 0.89%, respectively. A-SPMSM-Ⅱ, R-SPMSM-Ⅱ, and T-SPMSM-Ⅱ’s cogging-mutual torque ratio were 0.83%, 0.78%, and 0.71%, respectively. Fourth, numerical and experimental analysis also confirmed that the back-EMF performance of A-SPMSM was similar to that of both R-SPMSM and T-SPMSM. From numerical analysis, A-SPMSM-Ⅰ, R-SPMSM-Ⅰ, and T-SPMSM-Ⅰ’s back EMF were 5.05 Vrms, 4.40 Vrms, and 5.05 Vrms, respectively. A-SPMSM-Ⅱ, R-SPMSM-Ⅱ, and T-SPMSM-Ⅱ’s back EMF were 7.20 Vrms, 6.25 Vrms, and 7.22 Vrms, respectively. From experimental analysis, A-SPMSM-Ⅰ, R-SPMSM-Ⅰ, and T-SPMSM-Ⅰ’s back EMF were 5.29 Vrms, 4.32 Vrms, and 5.19 Vrms, respectively. A-SPMSM-Ⅱ, R-SPMSM-Ⅱ, and T-SPMSM-Ⅱ’s cogging-mutual torque ratio were 7.63 Vrms, 6.72 Vrms, and 7.41 Vrms, respectively. The results of this study are intended to be used as basic data that can be used for structural changes in SPMSMs in the future. Since only one asymmetric shape of the permanent magnet was studied on this research, optimiztion research about the asymmetric shape is needed in the future. In addition, A-SPMSM was analyzed based on experiments in this study, but it is recommended that future research be conducted based on electromagnetic theory. The theoretical approach will provide a general analytical method for predicting the interactions between the electromagnetic peformances and asymmetric shape of permanent magnets.

Keywords: Asymmetric magnet shape, Back-EMF, Cogging torque, Ring type SPMSM, Step-skew type SPMSM.