L-Type Modular Outer-Rotor Consequent-Pole Motor With Low Torque Ripple and High Permanent Magnet Utilization Ratio

Abstract

Consequent-pole Permanent Magnet (CPM) motors have been widely proposed due to the inherent merit of saving Permanent Magnet (PM) material, although asymmetrical air-gap flux density caused the high torque ripple and asymmetrical back Electro Motive Force (EMF) voltage. So, this paper proposed a new L-type Modular Outer-rotor Consequent-pole PM (LMOCPM) motor as updating candidate to improve the electromagnetic performance of CPMs. Combining the modular rotor with the CPM concept is a new structure for the PM machine to reduce the PM and rotor core volume simultaneously, resulting in a high PM utilization ratio and low rotor loss. Firstly, the operation mechanisms of LMOCPM, conventional surface-mounted PM (SPM) motor, and modular surface-mounted PM (MSPM) motor are introduced based on the MMF-permeance model, and no-load air-gap flux density is investigated to show positive effects of modular structure with unipolar PMs. Then, their electromagnetic performances have been analyzed by the Finite Element Method (FEM), e.g., the air-gap flux density, cogging torque, on-load torque, and the material volume are compared. Finally, the results show that the proposed LMOCPM motor uses 39% less PM material than MSPM and SPM motors, although its average torque is respectively reduced by 2.3% and 6.2% compared to MSPM and SPM motors, resulting in a 61% improvement in PM utilization ratio. Also, the torque ripple of the proposed motor is dramatically fallen to 15.7%, while the torque ripple for MSPM and SPM motors are respectively 28.1% and 22.3% because of the modular rotor structure and PMs with the same magnetization direction.