This thesis focuses on the development of novel PM machine alternatives to achieve high torque/power density, high efficiency, low cogging torque and torque ripple, as well as remarkable fault-tolerant capabilities even utilizing low-energy ferrite magnets, for various direct-drive applications. In particular, the proposed PM machine alternatives are examined by both types of dual-airgap spoke-type rotor- and stator-PM machines to demonstrate the effectiveness and increase the applied scope.
The proposed PM machine alternatives are designated as dual-airgap, spoke-type PM machines with phase-group concentrated-coil windings, which incorporate the benefits of a phase-group concentrated-coil winding together with the use of a spoke-type array and an unaligned arrangement of two stators/rotors. The adoption of the phase-group concentrated-coil windings is to obtain a unity displacement winding factor, and enhance the flux focusing effects together with the use of spoke-type PM configuration. The unaligned arrangement of two stators/rotors will help to not only achieve a further flux magnification by alternating the PM flux from one air gap to the other but keeping the flux relatively constant in the magnet, but also suppress the cogging torque and torque ripple. The dual-airgap configuration contributes to enhanced torque density from the integration of two PM machines. Finally, the alternate operating principle for the PM flux concentration results in a dual three-phase channel. Together with the electromagnetic isolation of the phases that result from the modular phase-group concentrated-coil windings, it helps to obtain highly improved fault-tolerant capabilities.
To examine the effectiveness of the proposed machine alternatives, the dual-airgap, spoke-type, rotor- and stator-PM machines with the proposed design concept have been investigated. The proposed rotor-PM machines are developed for high electromagnetic performance, while the proposed stator-PM machines exhibit excellent robustness. Both of the proposed PM machines are demonstrated to have higher performance than their conventional PM machines, respectively.
Firstly, the design concept including the basic design criteria and operating principle of the proposed machine alternatives is introduced which based on the rotor- and stator-PM machine topologies, respectively. Then the design procedure including the design, analysis and optimization method for the proposed machines are discussed in detail.
Secondly, the three-phase, axial flux, dual-stator, spoke-type, rotor-PM machine with PGCC windings is first to be designed by D2L method and then verified by 3-D FEM with the aim of demonstrating the design concept and operating principle. Then two types of two-phase, radial flux, dual-stator, spoke-type PM machine with PGCC windings, which conform to the same design concept, are proposed and compared with conventional dual-stator, three-phase and two-phase PM machines to highlight the advantages of the proposed PM machine alternatives. In particular, one of the proposed two-phase PM machines is selected for purposes of optimization to minimize cogging torque and torque ripple, in which the Latin hypercube sampling is applied in a design of experiments process in order to select the sampling points, and the Kriging method is performed for approximation modeling, while a genetic algorithm (GA) is carried out for obtaining the optimal points for the design variables. Then two traction motors with ferrite magnets are designed with the proposed design concept for hybrid electric vehicles (HEVs), which have competitive torque density and efficiency as well as operating range with respect to a referenced rare earth magnet motor employed in the third-generation Toyota Prius, a commercialized HEV.
Thirdly, the axial and radial flux, dual-stator, spoke-type, stator-PM machines with PGCC windings are developed and analyzed by FEM. Through a comparison with the conventional stator-PM machines, the proposed dual-stator, spoke-type, stator-PM machines with PGCC windings also exhibit better performance including high torque/power density, high efficiency, low cogging torque and torque ripple.
Finally, to determine the manufacturing prototype, a quantitative comparison between both types of the proposed radial flux, dual-airgap, spoke-type, rotor- and stator-PM machines with PGCC windings are first to be performed to provide insights into each of their characteristics. Based on the comparison results, the proposed rotor-PM machine topology is selected to be redesigned and manufactured for washing machine applications which is competitive to the requirements of a LG washer motor. Then the experiment is carried out to verify the design and simulation results.