Rare earth magnets have long been the cornerstone of high-performance electrical machines owing to their exceptional magnetic properties. However, their utilization presents challenges, notably in terms of cost and limited availability of resources. In response, ferrite magnets have emerged as a promising alternative due to their cost-effectiveness and abundant supply. Vernier permanent-magnet (VPM) machines typically exhibit low power factors due to high winding reactance. Given the weaker magnetic properties of ferrite magnets compared to rare earth counterparts, ferrite-based machines inherently suffer from poorer power factors. Short pitch winding is a known strategy to mitigate this issue and enhance power factor. This paper investigates the impact of employing short pitch winding in ferrite VPM machines, alongside an exploration of different gear ratios. The research findings indicate that when a high-power factor is desired, employing short pitch winding can lead to higher torque/power and efficiency compared to full pitch winding in ferrite VPM machines. Moreover, the advantages of short pitch winding are more prominent with higher gear ratios. Finite element analysis is employed to optimize both the machine's topology and performance, providing insights into the intricate interplay between winding configurations, gear ratios, and magnetic materials.

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.

This paper proposes a variable-topology motor drive with soft-shifting method for PMSM operating range extension. To satisfy both heavy-load and high-speed requirement, smooth online conversion between half-bridge topology and series-winding topology is achieved by considering shift transient control. The shift circuit is special designed and the step-by-step shifting method is proposed to avoid the output torque interrupt during the shifting process. By actively controlling and injecting the 0-axis current, the proposed zero-current shifting method solves the reliability issues of shift switches, avoiding the overvoltage and electric spark in electromagnetic relay. The experimental results have verified that the proposed variable-topology motor drive can significantly extend the speed range and achieve high efficiency and high torque capability in the global operating region, while the online topology conversion process using the soft-shifting technology has little effect on the motor operations.

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.

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%.