Abstract

This work analyzes cogging torque in special electrical permanent magnet (PM) machines. Cogging torque is the no load reluctance torque. Cogging torque arises due to the magnetic attraction between the slotted stator and permanent magnet at no load. Cogging torque causes acoustic noise and vibration in PM machines. Therefore, it is important to analyze the cogging torque in permanent magnet machines.
The cogging torque is analyzed in a variable flux interior permanent magnet synchronous machine (VF IPMSM). Cogging is computed at different magnetization levels. It is observed that cogging torque is proportional to the magnetic flux density. The effect of optimum skewing angles to minimize the cogging torque is analytically calculated and verified by Finite Element Analysis (FEA). The effect of skewing on back EMF and torque ripple is also investigated in detail. Effect of skewing on the magnetization and demagnetization levels is also analyzed.
One of the major problems of variable flux machines (VFMs) is that PMs are susceptible to unintentional demagnetization by armature reaction. Therefore, a rare earth magnet can be added in series with the Alnico magnet to avoid unintentional demagnetization. But cogging torque is higher in the series hybrid variable flux machine (SVFM). This work computes cogging torque in the SVFM using a lumped magnetic circuit model.
Due to the growing demand for rare-earth magnets and the high variation in its price, the current trend in the research focuses on the design of alternative electric machines technologies that either do not use rare-earth magnets or reduces the required magnet volume. This work computes cogging torque in an asymmetrical interior permanent magnet machine where magnet volume is reduced by 30% to achieve the desired performance.
This research work also investigates the performance of axial flux machines and computes cogging torque with different soft magnetic composite materials.