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.

The inverter nonlinearity induces current harmonics and mismatches between permanent magnet synchronous machine reference voltages and terminal voltages, which will degrade the sensorless drive system performance, especially at the low-speed range. In this paper, a radial basis function neural network (RBFNN)-based voltage compensator is proposed to suppress the current ripple. Without the requirement of any additional hardware or complex signal analysis procedure and processing algorithm, the RBFNN is self-tuned to directly generate the compensation voltage with the objective to minimize the current tracking error, so as to improve the active flux modeling accuracy and reduce position and speed estimation fluctuation.

In this paper, the influence of full-pitch and shortpitch windings on the torque and power factor of permanentmagnet vernier (PMV) machines is studied.It is well known that the short-pitch (SP) winding has shorter end windings but with a lower winding factor.Thus, to achieve the largest torque, the full-pitch (FP) winding is preferred in PMV machines.However, it is found in this study that the SP winding, rather than the FP winding, is a better choice to achieve higher output torque of PMV machine at a high power factor level under the same PM consumption.The advantages of SP winding are even more obvious at higher electric loading and higher power factor levels.The theoretical analysis indicates that both torque and power factors are influenced by the winding factor, providing the possibility of better performance of the SP winding than the FP winding.This is further confirmed by the optimization results after performing the multi-objective optimization considering torque, power factor, and PM consumption.Finally, a prototype is manufactured and tested to validate the analysis.

This paper presents a high power-factor permanent magnet vernier machine (PMVM) employing hybrid concentrated-winding (CW). The hybrid winding, carrying both delta- and star-winding sets, allows for low harmonic tooth-wound coil and satisfied winding factor for PMVM with high gear ratio. Therefore, the torque density of the PMVM can be enhanced with reduced end-winding length and more compact structure. More importantly, the mutual inductances between the three phases and the coils that comprise each phase are reduced to a large extent in the hybrid winding, without deteriorating the output torque capability. As a result, the presented PMVM possesses a lower ratio of inductance to PM flux linkage due to the low-harmonic and low-coupling winding, and hence, improved power factor. Two benchmark PMVMs with identical gear ratio have been optimized for comparison. Further finite element results verify that the proposed CW PMVM presents superior performance in terms of end-winding length, torque density, power factor, and efficiency. It is revealed the proposed hybrid CW PMVM can improve the torque density to 23Nm/L from 21Nm/L and 14Nm/L, with the consideration of end-winding volume, and power factor to 0.86 from 0.72.

This paper investigates the two-slot pitch winding vernier machine by stator shifting technique (SST). It shows that the conventional two-slot pitch winding vernier machine can be generated by SST with a special stator shift angle. This paper contributes to exploring other shift angles and their influences on machine performances. Analysis results indicate that different shift angles have a great effect on the armature winding magnetomotive force (MMF) harmonic contents and the flux modulation effect. Consequently, the phase inductance, power factor, core losses, and torque capability will be affected. A single-layer 24-slot/10-pole vernier machine is investigated for verification, and the results show that with an appropriate shift angle, the power factor is improved from 0.6 to 0.7, the iron losses are reduced by 24.5%, and the efficiency is improved by 0.7%, with a slight torque drop of 2.9%.