Study On Structure And Control Of Permanent Magnet Flux-Switching Motors

Early literatures on permanent magnet flux-switching (PMFS) machines can be dated back to the 1950s. Nowadays, the strong request for high-performance electric drives and the advantages in high-energy rare-earth permanent magnet (PM) materials, have opened up new realms for novel topologies of PM machines. And, PMFS machine is reemerging as a PM brushless machine with doubly-salient structure, having both magnets and concentrated windings on the stator. In general, the PMFS machines have distinctive merits such as high power/torque density, high flux-weakening capability and mechanical robustness. It is favorable for high-speed operation. Meanwhile, PMFS machines with different configurations have been proposed for a wide range of applications.This dissertation will firstly introduce the development of the doubly salient permanent magnet (DSPM) machines to reveal the emergence procedure of PMFS machine, and then review systematically the related literatures. Based on these researches on the PMFS machines will be reported, with some innovation results being proposed.Due to the high air gap flux density, severe magnetic saturation and especially doubly-salient structure, cogging torque and torque pulsation, which are of particular importance for machines performance, are rather higher in the PMFS machine than in other PM machines. Therefore, this dissertation mainly focuses on optimizations of machines' geometric and parameters to reduce the cogging torque and torque pulsation. A 6/5-pole and a 12/10-pole PMFS machine are taken as examples to investigate the influence of rotor structure on the cogging torque and torque pulsation. Numerous methods are proposed to reduce the cogging torque. Meanwhile, three different rotor pole configurations, including uniform, step skewed and axial pairing, are presented to decrease the torque pulsation. Moreover, both FEA results and experimental tests confirm that the effectiveness of all these techniques.Furthermore, a PMFS machine with an outer-rotor configuration is proposed for traction applications. In the dissertation, sizing equations are derived to determine the machine dimensions and then FEA models are developed to optimize the machine performance. Moreover, PM segmentation is introduced to improve the machine's flux-weakening capability. Similarly, the machine performance predictions by FEA models are validated by tests on the prototype. On the other hand, thanks to the high flux-weakening capability, the PMFS machines are also quit suitable for wide speed-range generators. However, if the generator speed is high, its output voltage is also high and may damage the power electronics devices of the power converter after the generator. Therefore, in this dissertation, a novel stator-flux orientation strategy based on vector control is proposed to regulate the PMFS generator output voltage with field strengthening or weakening. Compared the conventional generator-AC/DC rectification system, the proposed control algorithm can not only achieve constant DC voltage delivering, but also maintain the generator output voltage in a wide range of speed variation. Both steady-state and dynamic results from simulation and experimental tests are given to verify the effectiveness of the proposed algorithm.