This article investigates the application of star-delta hybrid concentrated-winding (CW) in permanent magnet vernier machines (PMVMs), with main focus on power factor and field-weakening capability. The analysis results show that the hybrid CW exhibits low-coupling property, namely both the mutual inductances between the comprising coils of each single phase and that among three-phase windings are eliminated. As a result, the q-axis flux linkage and required terminal voltage are reduced substantially, which contributes to improving power factor and field-weakening property. When operating below base speed, higher voltage margins are obtained, thus the proposed PMVM exhibits a higher power factor and wider constant torque region. With speed over base speed, the field-weakening control strategy is adopted, allowing the proposed PMVM to employ a higher q-axis current to generate torque. As a consequence, the output capability and power factor under high-speed field-weakening region are improved. In particular, the maximum achievable output power is improved by 19%, and the constant power speed range (CPSR) ratio is improved from 2 to almost 10.

Permanent magnet vernier machines (PMVMs) are recognized as the most promising candidates for high-torque direct-drive applications. However, their market penetration is hindered by the low power factor. This paper aims to address the low-power-factor challenge, by employing the concept of low-coupling winding. As compared with two conventional PMVMs, the proposed PMVM with low-coupling winding exhibits a substantially improved power factor. To objectively evaluate the potential of the proposed PMVM, a comprehensive comparison between the proposed PMVM and the conventional permanent magnet synchronous machine (PMSM) is conducted. The no-load back-EMF, output torque, power factor, core losses, and efficiency are compared under various operating conditions, encompassing the entire torque-speed range. The strengths and weaknesses of the PMVM are analyzed, and the most promising application scenarios are suggested. Finally, a prototype of the proposed PMVM is fabricated to validate the analysis and comparison results.

Axial-flux permanent magnet synchronous motor (AFPMSM) is a promising solution for in-wheel direct-drive electric bikes (e-bikes) due to its disc-type topology, structural compactness, and high torque density. However, the large electric loading of conventional AFPMSMs for high torque output can lead to severe thermal rise and potential fault risk, which is unbearable for long-running operation and security requirement in e-bike scenario. To address this issue, a comparative study is conducted on the performance of AFPMSM with conventional surface-mounted PM array (S-AFPMSM) and Halbach PM array (H-AFPMSM). The design and optimization procedure for both AFPMSMs is conducted. The investigation result shows that S-AFPMSM features over 30% higher torque density than that of a radial-flux PMSM, but the thermal raise is too much for air-cooling condition. By utilizing Halbach PM array with self-shielding magnetization effect, H-AFPMSM has higher magnetic loading and much less heat loading when it outputs the same torque density as that of S-AFPMSM. As a result, the copper loss is reduced by over 30%, and accordingly the efficiency increases to 94%. A prototype of the motor is manufactured and tested, with results that agree well with the theoretical analysis.

This paper proposes a new double-stator flux-switching permanent-magnet rotary-linear (FSPM-RL) motor, in which both linear and rotary motions can be achieved individually and simultaneously. The proposed motor contains two decoupled structures for achieving two degree-of-freedom motions separately by adopting two sets of orthogonally arrayed PMs. Firstly, the topology and flux path for each motion are introduced. Then, the operating principle and analytical equations related to the performance of each motion are presented. Afterwards, the effect of leading parameters on end-effect and force/torque performance are investigated based on 2D finite-element method (FEM). Moreover, the simulation results of optimized design under 2D FEM are verified by 3D FEM. Meanwhile, by using 3D FEM, the performances under helical motion are investigated. Besides, the performances under helical motion are compared with that under the condition of only linear or rotary motion separately. It is indicated that the output force/torque under the helical motion are nearly the same to that with only linear or rotary motion. In such way, the proposed motor shows good ability in decoupling the rotary and linear motion, which is the common issue in RL motors.