Improving Efficiency of a Pole-Changing Vernier Machine Considering Residual Magnetic Flux Density

Abstract

This paper presents the efficiency improvement of a pole-changing vernier machine (PCVM) by considering the residual magnetic flux density ( (Formula presented.) ) of low coercivity force (LCF) permanent magnets (PMs). The PCVM operates in two modes: vernier machine (VM) mode and permanent magnet synchronous machine (PMSM) mode, achieved through pole-changing. Pole-changing involves reversing the magnetic flux direction of LCF PM to alter the number of rotor pole pairs. By changing the number of rotor pole pairs, the PCVM operates as a VM mode at low speeds, providing high torque, and as a PMSM mode at high speeds, offering high efficiency. To achieve this, a combination of high coercivity force (HCF) PM and LCF PM is utilized in a single structure. The magnetic flux direction in the LCF PM is determined by (Formula presented.), and the highest efficiency is achieved when (Formula presented.) reaches its maximum value | (Formula presented.) |. This paper focuses on improving efficiency by obtaining (Formula presented.) in VM mode and − (Formula presented.) in PMSM mode through the design process. Additionally, finite element analysis (FEA) is employed to compare the performance of the improved model, which considers (Formula presented.), with that of the conventional model, designed without considering (Formula presented.). The improved model achieves higher (Formula presented.) values in each mode compared to the conventional model, resulting in increased torque density. Consequently, this leads to improved efficiency. © 2023 by the authors.