| The energy and environment problems caused by the traditional fuel vehicles are increasingly serious, and the development of new energy electric vehicle is an effective way to solve the problem of energy shortage and environmental pollution. In addition to the main drive system, electric vehicles still have a lot of support systems, including air conditioning system which is the second energy consumption system of electric vehicle, and the core problem of the air conditioning system is the compressor drive motor control. The reasonable selection and optimal control of the compressor drive motor can improve the control performance of the whole vehicle and satisfy the demand of the passenger ride comfort. Permanent magnet brushless DC motor (BLDCM) has the advantages of simple structure, reliable operation, high power density and good performance of speed regulation, which is widely used in the field of variable speed drive. BLDCM is generally driven by square wave current, because the motor winding current can not be changed immediately, so there is a large torque ripple. In this thesis, the BLDCM is used as the compressor drive motor, and the low cost holzer position sensor is used to obtain the information of the rotor position and speed. By using the sine wave current direct drive control strategy, the commutation torque ripple is reduced effectively.First, this thesis analyzes the structure and working principle of BLDCM system. On this basis, the mathematical model of BLDCM is deduced, and the principle of BLDCM speed regulation is analyzed. According to the above analysis results, the BLDCM simulation model is built in Matlab/Simulink. Then, under the square wave current drive, this thesis deeply studies the cause of the BLDCM torque ripple. Non commutation current fluctuation is the main reason of commutation torque ripple, and the change law of commutation torque ripple at different speed is obtained. Based on the torque ripple formula, the effect of the non-ideal back EMF on the commutation torque ripple of square wave current is studied. The smaller counter electromotive force width the bigger torque ripple is caused. Thirdly, the back EMF width is non-ideal due to the manufacturing process of actual motor and other factors, the smaller the width, the closer to the sine wave. In this thesis, the control strategy of BLDCM is directly driven by the sine wave current. The algorithm is simple and easy to implement, and it can effectively restrain the torque ripple. Holzer position signal is discrete state, in order to get high resolution rotor position and speed information, to meet the BLDCM sine wave drive control requirements, the improved mixed order rotor position estimation algorithm is proposed. In order to ensure the reliable operation of the motor, the fault tolerance of the holzer position signal is processed. Finally, taking TMS320F28035 as the control core, the hardware circuit design and software design of BLDCM controller are carried out. The hardware circuit platform is built, and the control strategy is verified by experiments.In this thesis, the BLDCM sine wave current drive scheme using the improved mixed order rotor position estimation algorithm, which can satisfy the requirement of fast start and low noise of air conditioning system, and improve the control performance of the whole vehicle. |
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