| With energy crisis and environmental pollution becoming more and more prominent, hybrid electric vehicles (HEVs) and electric vehicles (EVs) as an effective solution have been payed comprehensive attention by home and abroad universities or research institutions. Motor and drive system are core components and common key technologies for EVs. Because of the advantages of high torque density, high efficiency and wide speed range, the interior permanent magnet (IPM) motor has been used in commercial HEVs successfully. However, considering the reduction of the failure rate of the motor and drive system to ensure the safety of occupants, this paper introduces multi-phase, the fractional-slot concentrated winding and fault tolerant tooth structure to the design of IPM motor, formatting a five-phase V-type fault-tolerant IPM motor and a five-phase Spoke-type fault-tolerant IPM motor. Moreover, the proposed motors can not only ensure the advantages of IPM motor but also enhance their reliability. At the same time, the use of hub arrangement can directly drive the wheels, which omit the traditional gear, differential, drive shafts and other mechanical drive components, improving the efficiency of the vehicle. In order to ensure the motors can adapt both the brushless AC (BLAC) control and brushless DC (BLDC) control, unequal tooth width method is applied in Spoke-type motor to have a 144° trapezoidal flattened back-EMF, while the asymmetric air gap method is used in V-type motor to have a highly sinusoidal back-EMF.In terms of motor analysis, finite element software is used to compare and analyze electromagnetic performances of the two motors, and the flux weakening and fault-tolerant performances are the key points. According to magnetic circuit features of the stator and rotor for Spoke-type motor, lumped parameter magnetic circuit (LPMC) model of the stator and rotor for this kind of motor is proposed. And based on the existing branch construction method, the LPMC model for the whole motor is built, which is employed to predict parameters as the back-EMF, inductances, and torque, especially the short-circuit current.In terms of improving the reliability of drive system, the rotation magnetomotive force (MMF) is kept constant before and after the fault for one phase open. Base on this principle, BLAC fault-tolerant control method for V-type motor with a sinusoidal back-EMF is derived; meanwhile, BLDC and equivalent torque BLAC fault-tolerant control methods for Spoke-type motor with a trapezoidal back-EMF are derived. Taking into account the above control strategies are based on the hysteresis PWM, the disadvantages of this method are introduced. Thus, an asymmetrical space vector pulse width modulation (SVPWM) fault-tolerant control strategy is proposed, which can reduce the loss of inverter switches and improve the utilization of the inverter voltage.The fruits of this thesis are as follows:1. The fault-tolerant design and hub structure are introduced into the IPM motor, then, a fault-tolerant IPM motor is proposed, which keep the advantage of IPM motor and enhance the reliability further. Power size equation for the in-wheel motor is derived, and the preliminary design parameters for the two motors are calculated. Moreover, a 144° trapezoidal flattened back-EMF for Spoke-type motor and a highly sinusoidal back-EMF for V-type motor are realized by optimizing the key parameters having impact on back-EMF.2. The characteristics of the fractional-slot concentrated windings are studied, and the relationship between distributed position of different windings and displacement of winding back-EMF is summed up in one phase. Meanwhile, according to the derived low harmonic design equations, different windings are placed in the proper position to achieve low harmonic design of back-EMF for Spoke-type motor.3. The feasibility and necessity of the frozen permeability method applied in the separation of the armature and the permanent magnet affect are verified. Meanwhile, this method can be used in the accurate calculation of the inductance in dq axis and the separation of permanent magnet torque and reluctance torque in electromagnetic torque. Curve fitting is applied to obtain the expressions of torque and flux with current angle, forming a general method for quick calculation of the motor flux weakening region.4. The criteria to evaluating the fault tolerance performance of fault-tolerant motor is given, including the ratio of static mutual-inductance and self-inductance, the influence of dynamic short-circuit current to back-EMF of adjacent phases, the comparison of torque performance before and after the fault under fault-tolerant control strategy.5. LPMC model for Spoke-type motor is proposed, and the method to build reluctance model for each part and the calculation flow for full LPMC model are given. The electromagnetic characteristics of the motor are predicted, especially the short-circuit current.6. The fault-tolerant control strategies under BLDC and BLAC states are derived and the equivalent torque BLAC fault-tolerant control strategy for BLDC motor is given according to the back-EMF characteristics of the two motors. On the basis of hysteresis PWM to realize fault-tolerant control, an asymmetry SVPWM fault-tolerant control method is derived.7. Prototypes for the two fault-tolerant IPM motors are manufactured. Moreover, Static characteristics test experimental platform and fault-tolerant control strategy experimental platform are built. This thesis verifies the correctness of motor simulation and the effectiveness of a variety of fault-tolerant control strategies, and provides an experimental basis for developing high-reliability, high efficiency motor and drive system. |
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