Analysis, Design And Control Of Flux-Modulation Permanent-magnet Fault-Tolerant Motor

The adoption of direct-drive technology can eliminate mechanical speed change device such as mechanical gearbox and enable the load to be connected with motor directly, thus offering high efficiency, high reliability, free maintenance and smooth operation. Owing to these advantages of the direct-drive technology, it has received ever increasing attention in recent years. Permanent-magnet motor has the merits of high torque and high efficiency, but it suffers from poor fault tolerant capability generally. Moreover, its torque density needs to be further improved so as to meet the requirements of high torque density and strong fault tolerant capability in the direct-drive motor system. In this thesis, based on flux modulation principle of magnetic gear and theory of fractional slot concentrated winding,a new class of flux-modulation permanent-magnet (FMPM) fault-tolerant motors with high torque density and strong fault-tolerant capability are proposed. A general approach for design of the FMPM fault-tolerant motor with high torque density and strong fault-tolerant capability is also proposed. The major research content of this thesis involve analysis of flux modulation mechanism and operation principle of fractional slot concentrated winding FMPM motor,selection and design of winding layout of the FMPM motor, design and analysis of the proposed FMPM motor, magnetic equivalent network modeling method for the proposed FMPM motor, fault-tolerant control strategy and experimental validation.The fruits of this thesis are as follows:1. The basic operation principle of the fractional slot concentrated winding FMPM motor is introduced by using the magnetomotive force/permanence model. Also, the mechanism of flux modulation and torque enhancement in the FMPM motor is revealed. The power equation and key design parameters significantly influencing electromagnetic torque of FMPM motor are derived and determined, respectively, so as to lay a theoretical basis for the design optimization.2. A comprehensive comparison including operation principle, back electromagnetic force,torque, loss and efficiency between fractional slot concentrated winding and integral slot distributed winding FMPM motors are conducted. The maximum power strategy at high speed for two FMPM motors is proposed, and their speed ranges are extended. The mechanism of winding layout influencing the performances of FMPM motor is revealed,thus providing a reference for designing the winding layout to meet various requirements.3. A new type of hybrid stator structure for the FMPM fault-tolerant motor is proposed. By utilizing the new hybrid stator structure, the number of PM pole-pair, iron core loss, PM eddy-current loss of the FMPM motor can be reduced and the efficiency can be improved,while without sacrificing torque density. The flux modulation effect producing by the new hybrid stator structure is clarified. A general approach for the design of the FMPM fault-tolerant motor with hybrid stator structure is proposed.4. A new FMPM fault tolerant motor with hybrid stator and spoke-array PM is proposed,which solve the problems of conventional FMPM fault-tolerant motor, i.e., low torque density and power factor. On the promise of ensuring strong fault-tolerant capability, the toque density and power factor of the proposed FMPM fault-tolerant motor are significantly enhanced. Also, its efficiency at high speed region is improved.5. The mesh-based reluctance network method is adopted for the modeling of flux-modulation pole. Also, this method is employed together with the conventional magnetic equivalent network method to establish the magnetic equivalent network model of the FMPM motor. In this way, the speed and accuracy of calculation by magnetic equivalent network method can be ensured, thus significantly enhancing the efficiency of design and optimization at early stage.6. The control strategies for normal and fault-tolerant operation of the motor are studied,respectively. The space vector pulse width modulation methods for normal operation and fault-tolerant operation with one phase loss are analyzed, respectively. A conventional and a proposed FMPM fault-tolerant motor are manufactured,respectively. The software and hardware experimental platforms are built. Also, the electromagnetic performances of the two motors are tested and compared. The effectiveness of motor design and control strategy are verified by experimental results.