Electromagnetic and Thermal Analysis of a Surface-Mounted Permanent-Magnet Motor with Overhang Structure

Abstract

Recently, overhang structures are increasingly used for various applications requiring high torque and power densities in a limited space such as traction motors of electric vehicles and servo motors of robot arms. In the design stage, overhang effects should be taken into account to predict the performances and the temperature rise of a motor with overhang. However, little research has been conducted on the thermal characteristics and analysis methods for a surface-mounted permanent-magnet (SPM) motor with overhang. To address this problem, the electromagnetic and thermal characteristics of the SPM motors with and without overhang are invested in this paper. Specifically, 3-D finite-element method is used in electromagnetic analysis to accurately calculate electromagnetic losses which are heat sources in thermal analysis. Moreover, the lumped-parameter thermal network (LPTN) which can consider overhang effects rapidly and precisely is proposed as an analytical method. Through the proposed LPTN, the computation time for thermal analysis is reduced considerably in comparison with a computational fluid dynamics method, and the temperature rise of the motors are precisely predicted. The results calculated in electromagnetic and thermal analysis are verified experimentally with 0.3 Nm, 20-pole/24-slot SPM motors adopting natural cooling.