Rare-Earth Permanent Magnets (RE-PMs) are widely used in high efficiency and high torque density electrical machines. However, in recent years the exclusive and unstable supply of Rare-Earth Elements (REEs) is a major concern to substitute RE-based electrical machines by less or even no RE alternatives. Ferrite (Fe) PMs as the least expensive PMs show promising opportunities for designing low-cost non-RE electrical machines. This paper reviews some relevant works on Fe-based machines which generally have been conducted to replace RE-based machines. The Fe-based machines including PM brushless, PM-assisted synchronous reluctance, PM flux switching, and PM Vernier machines are introduced and their main design challenges, such as low PM energy product and vulnerability to irreversible demagnetization are addressed. In addition, a comparison of RE-based and Fe-based machines reveals that when both cost and efficiency are the major concerns, Fe-based machines can be a good successor to RE-based machines.

Hysteresis motors are among the main choices for high-speed applications. However, a lack of knowledge exists about the differences among various types of these motors. This paper comparatively examines the operational characteristics of several disc-type hysteresis motors with slotless stators. For this purpose, a disc-type motor with two stator cores and three hysteresis discs has been built as the prototype motor. A new method is presented for appropriate design of this motor. A total of ten different motors have been derived from this motor by changing the position of hysteresis discs along with switching the polarity of specified windings or disconnecting their connection to the supply. Starting and synchronous performance characteristics of these motors have been obtained through various experiments. How those characteristics change and why there are differences between them are extensively analyzed. Accordingly, the motors are compared based on four key criteria, including main flux path in hysteresis discs, thickness of hysteresis discs, number of hysteresis discs adjacent to each stator and the number of stator cores. The results of this comparison are considerably helpful in identification of the impact of various factors on the performance of these motors and selection of the suitable motor for each application.

Hysteresis motors are widely employed for a variety of high speed applications, thanks to their unique features. Usual design methods could not be used for these motors since the operation mechanism of hysteresis motors is also unique. However, an appropriately developed design method has not been provided by the few relevant published works. This study presents a new iterative design method, which is capable of being used for almost all hysteresis motor structures. Also, it is almost independent of the approach of obtaining the design equations. Multi‐stack disc‐type slotless structure has been selected as the case study, because of its interesting capabilities. Its design equations are derived by combining the fundamental laws of electromagnetism with the elliptical model of hysteresis loops. Some new techniques are introduced to increase the accuracy of these equations. A sample motor has been designed by applying the direct search optimisation to the proposed design method. The prototyped sample motor has been subjected to various tests. The measured operating characteristics show a great agreement with the design requirements.

This paper presents a new method to achieve an almost sinusoidal back EMF for a claw pole transverse flux permanent magnet synchronous machine (TFPM) using some appropriate geometrical modifications. To fulfill this goal, instead of using a constant length for the air gap, a rotor position dependent air gap is suggested. Air gap facing surfaces of the stator teeth and rotor flux concentrators are modified to build this variable air gap. It will be shown that in addition to proper shaping of the rotor poles, the air gap facing surface of the stator teeth should be curved to achieve a sinusoidal back EMF. Based on the obtained results from finite element analysis of the machine under no load condition, the proper shape of these surfaces is determined.