Selecting a Pole and Slot Combination for Main Frequency Vibration Reduction of Permanent Magnet Synchronous Motor

Abstract

In general, a motor using a permanent magnet tends to have a high output density. In addition, high-speed operation is possible by using flux weakening control which can reduce the magnetic flux of the permanent magnet. For this reason, permanent magnet motors are used in a wide range of fields such as industrial, home appliances, and environmentally friendly vehicles. Therefore, interest in permanent magnet motors has increased, and efforts have been made to improve performance such as power density and torque ripple. In particular, selecting a pole and slot combination is the most fundamental of the motor design and determines the large frame of the performance. So, the winding factor and cogging torque according to a pole and slot combination have been considered for a long time. In addition to electrical performance such as torque, vibration and noise of permanent magnet motors become issues, and analysis of the electromagnetic force that is the source of motor vibration is needed. Previous studies have focused on the non-uniformity of electromagnetic force by comparing the electromagnetic force, which is a function of time and space, from a specific time to a spatial distribution. However, in this paper, the air-gap magnetic flux density, which is the cause of the electromagnetic force density, is expressed by the field’s MMF, armature’s MMF, and slot effects. Also, the cause of vibration order, which is the spatial distribution of electromagnetic force density, was analyzed. Based on this, a method of selecting a pole and slot combination considering the vibration reduction in the 2 times power line frequency, which is the fundamental component of electromagnetic force density, and carrier frequency band is proposed. First, the spatial harmonics of the electromagnetic force density are calculated according to a pole and slot combination. Next, the rotation direction of the armature’s MMF generated by the current harmonic of the carrier frequency band is determined. Then, the time and spatial harmonic orders of the air-gap magnetic flux density are calculated by considering the field’s MMF and slot effects. Also the vibration order of the electromagnetic force density is derived by using the Maxwell stress tensor. A pole and slot combination is selected in such a way that the lowest vibration order of the carrier frequency band and the 2 times power line frequency component increases. Finally, the lowest vibration order and the vibration reduction effect of the PMSM applying the proposed pole and slot combination is verified using the FEM and the test.