I. Introduction
Flux-switching permanent-magnet (FSPM) machine has been received much attention due to its advantages of high torque density and easy heat management, etc. 1. In order to enhance the torque/power capability, FSPM machine with multi-tooth structure (MFSPM) has been proposed 2. However, not only high power density but also high reliability and good fault-tolerance capability are required for PM machine and hence three novel fault-tolerant MFSPM (FT-MFSPM) machines are proposed in this paper based on the MFSPM machine in 2. The topologies of proposed machines are shown in Fig. 1. To increase the torque density, a new outer rotor FT-MFSPM (Model I) shown in Fig. 1 (a) is proposed based on 2. To further increase the output torque, a middle PM is added in each dummy slot (Model II) as shown in Fig. 1 (b). Employing more PMs is an effective method to improve the toque without consuming the operating energy and thus the dual PM modulated FT-MFSPM machine (Model III) is proposed and shown in Fig. 1 (c).
II. Performance comparisons
The electromagnetic performances of three FT-MFSPM machines are presented in Fig. 2. It can be seen that though Model III exhibits the highest value of flux linkage, back-EMF and electromagnetic torque, it also exhibits the highest value of cogging torque and torque ripple and the most distorted back-EMF. In terms of the fault-tolerant capability, it can be observed from Fig. 2 (e) that the self-inductance of Model I and Model II is almost the same, which is higher than that of Model III.
Overall, Model II is superior to Model I and Model III since Model II has greater output torque and smaller torque ripple than Model I with a few increase of PMs and has greater short-circuit current restrained capability due to higher self-inductance and smaller torque ripple with less PMs. The machine optimization and more detailed comparisons including the losses and efficiency will be further discussed in the full paper.