Switched Flux Permanent Magnet Brushless Machines for Electric Vehicles

This thesis investigates different topologies of switched flux permanent magnet (SFPM) machines and variable flux (VF) methods for high speed applications. Although several novel topologies of SFPM machines have been proposed and investigated recently, their torque-speed capability has not been studied systematically. Therefore, the torque-speed capability as well as the open circuit and electromagnetic performance of conventional SFPM machines with three different stator/rotor pole combinations, i.e. 12/10, 12/13 and 12/14, and three novel SFPM machine topologies, i.e. multi-tooth, E-core and C-core are analysed and investigated by the finite element (FE) method and experiments. Moreover, in order to improve the flux-weakening capability of these machines a variable flux method using flux adjusters (FAs) is employed and the corresponding electromagnetic performance of the machines are investigated, analysed and compared. Both FE and measured results show when the FAs are used the torque-speed capability of the three conventional machines can be improved significantly, while no improvement is shown in the three novel topologies primarily due to the large winding inductances. The technique of using flux adjusters has been improved by reducing the number of FAs. Thus, a new mechanical variable-flux machine topology, which uses only half of FAs outside the stator at alternative stator poles, is proposed, developed and analysed. Open circuit results, electromagnetic performance and torque- and power-speed curves of the 12/10, 12/13 and 12/14 stator/rotor pole SFPM machines with alternative FAs are predicted and compared by 2D and 3D-FE, and experimentally validated. Furthermore, a novel SFPM machine topology with radial and circumferential PMs is proposed, investigated and optimized. This topology reduces the stator flux leakage and offers high magnetic utilization. Moreover, this topology can also be developed as a mechanical variable flux machine. Finally, three SFPM machines with variable flux techniques, i.e. mechanically movable flux adjusters (MMFA), mechanically rotatable permanent magnet set (MRMS) and hybrid excitation with backside DC coils (HEBC) are analysed. Their open circuit results and electromagnetic performance with emphasis on torque-speed characteristic are investigated and compared. Additionally, the required power to switch between flux weakening and strengthening states, flux weakening capability and permanent magnet demagnetization withstand capability are predicted, analysed and compared. The influence of end-effect on the torque-speed capability in the conventional, multi-tooth, E-core and C-core SFPM machines is investigated. Measurements and 3D-FE are performed to obtain the torque-speed curve in order to validate the findings of the research. The 3D-FE predicted results match well with the measured results, while the 2D-FE predicted results are lower due to the high end-effect in the SFPM machines.