Simulation of the effect of segmented axial direction magnets on the efficiency of in-wheel permanent magnet brushless DC motors used in light electric vehicles based on finite element method

Energy efficiency is primary target for electric motor designers. The Eddy current losses can cause deterioration of permanent magnet machines magnetic properties and increase rotor temperature. Therefore the rotor eddy current loses can decrease efficiency of permanent magnet brushless DC (PM BLDC) motors. Permanent magnets when designed with axial segmentation help reduce the eddy current losses. This paper presents an investigative study on calculating eddy current losses of in-wheel permanent magnet brushless direct current motors and the effect of segmented axial direction magnets on the efficiency of these motors used in light electric vehicle. In this study in-wheel PM BLDC motor has been designed and analyzed on with slot/pole combinations 24/20, 36/30, and 42/36, that the motor is rated power of 4 kW at rated speed of 1500 rpm. Finite Element Method (FEM) is used to carry out numerical analysis for an accurate result. The magnet losses and efficiency are calculated for segmented magnets with different quantity of magnets in the axial direction. Changing the number of axial magnet segment from 1 to 20 causes approximately 1% increase in the efficiency. Following the change in number of axial magnet segment, the shaft power values increment is about 40 W, while shaft torque is between 0.25 and 0.30%.