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.
Using a dual air-gap structure in a disc-type motor is an effective solution to eliminate undesirable axial force between stator and rotor, by which higher power density can be achieved, too. Furthermore, some of the performance characteristics such as pulsating torque may be improved greatly by adjusting the existing extra selective design parameters in a dual air-gap motor. Accordingly, in this study, a widespread design consideration is carried out on rotor skewing arrangements of a dual rotor (DR) axial flux induction motor with the aim of pulsating torque reduction. The studied scenarios include when the slots of both rotors are skewed exactly similar with different skew angles, the slots of both rotors are skewed similarly but in the opposite directions and the slots of both rotors are not skewed but one rotor is mounted on the shaft by some shift angle relative to the other. The last one is introduced as an alternative to skewed rotors, which is easily executable in small and large size motors with DR topology. Moreover, an algorithm is proposed to determine the appropriate shift angle. Three-dimensional time stepping finite element analysis is employed in all cases for verification. Fig. 12 Torque waveforms at 20% slip for the initial design, skewed rotors and non-skewed shifted rotors
Permanent magnet flux switching machines (FSPMs) have attracted considerable attention in recent years, due to their outstanding characteristics to operate as brushless AC drives. Since they are relatively new, there are particular challenges not only for their design procedure but also for their operating principle comprehension. This study highlights several issues on FSPMs from the basic operation description to their key design points. After a comprehensive description of FSPMs working principles, a detailed discussion is presented on their armature winding design. In addition, this study reviews various methods for their performance modification, including torque profile, electromotive force, and loss characteristics. This study also surveys field regulation technologies, modelling and design optimisation methods applied to FSPMs along with their fabrication and cost issues.
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