Analysis And Design Of Stator-Excitation Flux-Switching Brushless Machines

Flux-switching machine is a kind of brushless machine with doubly-salient structure, which has excitation sources, e.g., permanent magnets (PMs) or/and field-excited windings, and armature windings on the stator, and no magnets nor windings on the rotor. The flux-switching machines exhibit the advantages of high torque and power density, higher efficiency, strong irreversible demagnetization withstand capability, better thermal dissipation and liquid cooling conditions, and favorable high-speed operation. These advantages are particularly important for applications such as electric vehicles, more/all electric aircraft, wind power technologies, and flywheel system, et al. According to the excitation modes, there are three types of flux-switching machines, namely, permanent magnet flux-switching (PMFS) machines, hybrid-excited flux-switching (HEFS) machines, and wound-excited flux-switching (WEFS) machines. Based on the applications in electric vehicles and wind power technologies, this paper covers the investigation of PMFS and HEFS machines. Specifically, in regard of the design theory, the design method of three-phase PMFS machines considering manufacturing details is proposed. Then, in order to achieve large torque-speed region, the flux-regulation theories and control strategies of HEFS machines are analyzed. Finally, the design method and control strategies of six-phase HEFS machines are studied to improve the stabilities. The corresponding prototypes are manufactured and experiments measurements are carried out, which validate the investigations, and further lay a foundation for further research and development of these machines.The fruits of this work are as follows:1. The analysis model for parameter sensitivities of the PMFS machine is proposed. Combing the simplified equivalent magnetic circuit and finite element analysis (FEA), this new model enables the sensitivities of electromagnetic performances to the design parameters to be evaluated quantitatively during the initial design stage.2. The design methods and modular manufacturing process of a three-phase PMFS machine are studied. The influences of temperature, electromagnetic frequency, different lamination materials, as well as 3D end effect on electromagnetic performances are investigated. A machine prototype is further produced and experimental measurements are carried out to validate the predictions. In order to reduce the cost and difficulties of mass production, special attention is paid to the modular manufacturing method. Furthermore, the FEA-based 3D thermal model of the PMFS machine employing water cooling is proposed. This model enables the thermal behaviors, e.g., temperature distributions to be predicted. And the predictions are further validated by experiments measurements.3. Above studies on PMFS machines lead to the investigations of HEFS machines. In regard of the HEFS machines adopting U-shaped (also called U-core) stator laminations, the flux-regulation principles are discovered by dividing the field winding coils into two groups, namely those located radially outside the PMs and inside the PMs. Then an improved HEFS machine is proposed to enhance the flux-regulation capability.4. To evaluate the thermal behaviors of the HEFS machines, the corresponding 3D thermal FEA models are proposed. Then focused on the electromagnetic and thermal-dissipations performances, a comprehensive comparison of the HEFS machines with different PM locations are given. The analysis is further validated by experimental measurements on corresponding machine prototypes.5. Along with the mathematical model, the drive and control systems of the three-phase HEFS machines are built. Firstly, the mathematical models in both stator reference frame and rotor reference frame, respectively, are built. Then the drive and control system is built and implemented using MATLAB/Simulink, based on which, the dynamic performances under both PM and hybrid-excitations, respectively, are studied. Focused on the top speed and maximum torque output capabilities, the basic design principles and best proportion of PM excitation to field excitation in HEFS machines are proposed. Practically, two typical design requirements are considered.6. Based on the investigations of the three-phase HEFS machine, two six-phase fault-tolerant HEFS machines with E-shaped and U-shaped stator laminations, respectively, are designed, and the fault-tolerant control strategies when open-circuit faults happen to armature coils are studied. Based on FEA, the performances under healthy and fault-tolerant operations, respectively, are analyzed, and the influences of field excitations are also covered. Furthermore, the FEA-based predictions are validated by experimental measurements on the corresponding machine prototypes.7. The mathematical models in both stator reference and rotor reference frames, and the MATLAB/Simulink-based drive and control system of the six-phase HEFS machines are built. The analysis under healthy and fault-tolerant operations shows that, these two HEFS machines exhibit satisfied dynamic characteristic and fault-tolerant capabilities.