Ring winding axial flux permanent magnet (PM) machine (RWAFPM) has recently been introduced, which is beneficial in terms of manufacturability and fault tolerability. This study aims to examine the use of RWAFPM for a small‐scale direct‐drive wind generator. The structural features of the RWAFPM make it subjected to remarkable cogging torque. Accordingly, the main efforts of this study are focused on finding a proper solution for its torque profile challenges. In this regard, extensive investigations are carried out on rotor design improvements. First, several schemes are analysed, separately, including pole skewing, pole arc ratio modifying, pole grouping and rotor disks shifting. Then an optimum combination of selected schemes is calculated by the Taguchi method and considering the mean torque value as well as the PM usage. It is demonstrated that significantly improved results could be achieved mainly through cost‐effective modified fabrication. The 3D finite element models are employed throughout the study along with some experimental measurements to verify the results.
The recently introduced Ring Winding Axial Flux Permanent magnet Motor (RW‐AFPM) is inspired by the yokeless structure of Yokeless and Segmented Armature (YASA) AFPMs and the partitioned‐phases configuration of transverse flux motors. Its potential application for rim‐driven electric ships propulsion has been examined in the previous studies and, here, it will be studied for ultra‐light direct‐drive electric boats. Owing to their specific structural features, the relatively large cogging torque of RW‐AFPMs seems to be a significant challenge for such applications. On the other hand, as investigated in previous studies, cogging torque reduction methods, such as conventional skewing, seem unsuitable for this type of machine. Thus, this paper will address the cogging torque issue via a comprehensive pole shape analysis. The results will be useful for all kinds of partitioned‐phases topologies that have high specific torque capability but suffer from large cogging effects. All analyses are performed via 3D‐FE models, the accuracy of which is pre‐verified through experiments.
Purpose Pulsating torques cause a number of problems in electrical machines, including mechanical vibrations, acoustic noise and the depreciation of mechanical equipment. In induction motors, the slot skewing method is an effective way to solve these issues; however, it has some drawbacks such as output torque drop, stray loss intensification due to inter-bar currents and iron loss increment. Besides, slot skewing may not be practical in higher-rated induction motors. In this regard, this paper introduces a modified non-skewed rotor (MNSR) structure as a possible alternative to the skewed designs. Design/methodology/approach The proposed structure includes a two-segmented rotor with an intermediate ring between the rotor parts that are mounted on the shaft with a relative shift angle. Detailed information about the idea and structure of the MNSR as well as its manufacturing aspects will be presented in the second section of the paper. First, the working principle of the proposed design is described via analytical equations to provide an insight into the concept. The shifting angle will then be calculated by analyzing the harmonic contents of the electromagnetic torque. Finally, the validity of the analytical method will be verified by developing three-dimensional finite element models. Findings It is demonstrated that by using the proposed rotor structure, the torque ripple has been reduced to a satisfactory level without significantly affecting the mean torque, unlike the skewing method. Furthermore, the new method could avoid the disadvantages of the skewing method while enhancing other motor characteristics such as iron loss. Also, the total volume of the MNSR is equal to the initial design, and the mass and material differences are also negligible. Originality/value In this paper, a MNSR is introduced as a possible alternative to the skewed patterns. The study mainly focused on electromagnetic torque profile characteristics, i.e. the mean torque enhancement and the ripple reduction. The MNSR structure can be used for general purposes and high-performance applications, especially where excellent torque characteristics are required.
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