No-Load Torque Weakening of Dual-Parallel Rotor Permanent Magnet Motor Based on Torque Harmonic Analysis and Auxiliary Slots

Due to the absence of partial stator core and windings, the dual-parallel rotor permanent magnet synchronous motor (DR-PMSM) has a large no-load torque, which limits its application in parallel drive machinery. This paper analyzes the no-load torque based on torque harmonic and realizes the weakening of no-load torque by stator auxiliary slots. The topological structure of double parallel rotor permanent magnet motor is introduced. According to different influencing factors, the composition of no-load torque is analyzed, which includes cogging torque, end effect torque and permanent magnet gears transmission torque. The analytical expression of each torque component is constructed, the relationship between the harmonic frequency of no-load torque and each component is established, and the correctness of theoretical analysis is verified by finite element model. It is proposed to add auxiliary slots in the stator coupling area and on the stator teeth to weaken different no-load torque components. The weakening effect of the number, position and size of auxiliary slots on each component is studied. The performance of the motor before and after optimization is compared and analyzed, and the prototype test platform is built to verify the accuracy of the analysis model. The results show that the proposed method can effectively reduce the no-load torque of DR-PMSM.

1. Introduction

In extruder, two-roll mill, twin-screw pump and other parallel driving mechanical equipment, the current driving mode is the master-slave drive. An induction motor drives the master shaft, and the master shaft transmits the torque to the slave shaft through the synchronous mechanical gear, so as to realize the reverse synchronous rotation of the two shafts. This transmission mode has some problems, such as large system volume, low system efficiency, difficult sealing, and regular maintenance [1], [2]. In addition, due to the strict distance limit of the two shafts, it cannot be directly driven by two independent motors. Therefore, DR-PMSM is getting more and more attention. The mechanical gear between the motor and the equipment is removed. It has the advantages of compact structure, high system efficiency, less maintenance, strict synchronization of master-slave shaft, etc., and can be used to directly drive the load.