Influence of ratio of external diameter to stack length on torque and efficiency in outer rotor SPMSMs

The miniaturization and high efficiency of permanent magnet synchronous motors (PMSMs) are desired in numerous applications. PMSMs have a number of design parameters in order to enable miniaturization and high efficiency. One such parameter is the ratio of the external diameter to the stack length (D/L). In this paper, we examine the effect of D/L on torque and efficiency in outer rotor surface permanent magnet synchronous motors (SPMSMs). In outer rotor SPMSMs, in which the motor volume, magnet volume, and electric loading are equal regardless of D/L, the model has high torque at D/L = 3.05. Moreover, when the motor is used in HEV applications, the efficiency of the model at D/L = 4.00 is high. In inner rotor SPMSMs, the model has high torque at D/L = 1.98-2.41. Therefore, outer rotor SPMSMs are more suitable for thin structures than inner rotor SPMSMs.