Study On Dynamic Performance Of Hub Permanent Magnet Direct-drive Motor

The automobiles makes people’s travel and transportation of goods more convenient,and makes the world more closely connected.However,it also brings the problems of energy shortage and environmental pollution.Facing this problem,people began to pay attention to electric vehicles because of its energy conservation and environmental protection.vehicle hub permanent magnet(PM)direct-drive motor is directly placed in the hub,which takes up less space and has high efficiency.The direct-drive mode cancels the reduction devices such as planetary gears,which has the advantages of simple structure and convenient control.Because the vehicle hub PM direct-drive motor has these advantages,many electric vehicles are using it to drive.PM synchronous motor for electric vehicle is different from the traditional motor which only works at the rated point.It operates in the whole speed range.The research on the basic performance,loss,endurance mileage and other key issues of the motor needs to be extended to the whole operation range.Reducing the loss of PM synchronous motor for electric vehicles and improving the efficiency of the motor under operating conditions is an important technical means to improve the vehicle endurance mileage.Based on the wheel hub PM direct-drive motor,the no-load characteristics,load characteristics and dynamic performance of the motor under three different cycle conditions are studied in this thesis.The changes of speed,torque and power with time of vehicle hub PM direct-drive motor under three cycle conditions: New European Driving Cycle,World Light Vehicle Test Procedure and China Light-duty Vehicle Test Cycle-passenger are discussed.The loss and efficiency characteristics of vehicle hub PM direct-drive motor under these three cycle conditions are studied.Based on the cycle condition of electric vehicle,the calculation method of total motor loss and electric vehicle driving range under a cycle condition is introduced.The effects of stator tooth width,permanent magnet thickness,pole arc coefficient and stator yoke height on motor energy consumption and electric vehicle range are discussed.Using Taguchi orthogonal test and taking the above four motor structural parameters as optimization factors,the driving range of electric vehicle is compared and optimized.Considering that the actual operating conditions of vehicle permanent hub PM direct drive motor are complex and changeable,vehicle hub PM direct-drive motor is prone to loss of excitation fault.Five loss of excitation fault schemes are adopted to simulate the severity of local loss of excitation fault in motor operation.The distribution of magnetic density of stator teeth and yoke in different loss of excitation fault schemes is discussed.The corresponding relationship between different fractional harmonic content in air gap flux density and different loss of excitation faults is studied.The variation of no-load back EMF and current with the severity of loss of excitation fault is analyzed.