Investigation of Halbach permanent magnet synchronous machines

Halbach PM machines have many attractive features due to additional transition PMs between main PMs, i.e., N and S poles. This thesis focuses on the investigation of torque capability improvement, demagnetization, and rotor tolerances in Halbach PM machines.
To improve torque capabilities, optimal Halbach PM machines with air- and iron-cored rotors are analyzed. The optimal main and transition PM widths and magnetization angle shifts between adjacent PMs in air-cored machines are both almost equal, while main PMs are much wider than transition PMs and magnetization angle shifts between main and transition PMs are lower than equal values in optimal iron-cored machines. Torque contributions of main and transition PMs are evaluated. The iron-cored rotor can enhance the main PM torque production, while each PM is almost identical in torque production in air-cored machines. Therefore, a mixed NdFeB and ferrite Halbach PM machine with iron-cored rotor is proposed to save the NdFeB volume. Besides, flux focusing effects in Halbach and spoke machines are analyzed, and a mixed Halbach and spoke machine is proposed to further improve the torque capability.
Demagnetization in Halbach PM machines is investigated. For air-cored Halbach PM machines, the higher the segment number, the better the demagnetization withstand capability. However, when segment number > 3, further improvement becomes less significant. Air-cored machines suffer from more severe demagnetization under no- and low-load, while iron-cored machines suffer from more severe demagnetization under high-load. Besides, a notched iron-cored rotor is proposed to improve demagnetization withstand capability.
Finally, single and combined rotor tolerances, including PM thickness, width, and position, in Halbach PM machines are investigated. It is revealed that PM thickness tolerance should be controlled strictly, especially when it exists in main PMs and in Halbach machines with high PM segment number.