Research And Design On Current Hysteresis Loop Control System Of BLDCM

With the development of the permanent magnet material manufacturing technology and the motor control technology,the advantages of brushless DC motor gradually highlighted by its good speed regulation performance,high running efficiency and essy mainernance.At present,it has been widely used in the field of industrial servo,household appliances,medical devices and automobile industry.Traditional fuel vehicles bring more serious pollution to the air today,so the people's demand for electric cars more urgent than ever before.Brushless DC motor met with the requirements of the drive motor of electic cars with its high running efficiency,wide range of speed regulation,high power density and large output torque,so it becoming a research focus in the current.In this thesis,the basic struture of brushless DC motor is introduced;the working principle of brushless DC motor is analysed combining the subject used three-phase octupole motor;several kinds of commonly used brushless DC motor drive circuit,rotor position sensor and the way of modulation are analysed and compared;mathematical model of the brushless DC motor in the form of differential equation is derived,including phase voltage equation,back EMF equation,electromagnetic torque equation and motion equation.All of this provide theoretical basis for the mathematical analysis of the control strategy and the construction of the simulation model.The torque ripple problem of brushless DC motor limits its application in high performance occasion.In this thesis,the relationship of the electromagnetic and the non-commutation phase current is analysed,a strategy of control non-commutation derectly using hysteresis loop control is proposed.In order to avoid the power transistor chopper frequency cuncontrollable phenomenon of the traditional curent hysteresis loop control,a method of through changing the width of the hysteresis loop to achieve power transistor chopper ferquency under control is proposed in this thesis.According to the torque ripple during the commutation when the motor in high speed,a descriminator circuit to check whether in commutation is proposed,combining with overlapping commutation control strategy to suppress the torque ripple during the commutation.The simulation model of the current hytersis loop control system of brushless DC motor is built in the simulation environment of PLECS.Through simulation,the correctness and effectiveness of the currrent hystersis loop control strategy is verified.On the basis of the above theoretical analysis and simulation research,a brushless DC motor controller design based on DSP&CPLD is presented finally in this thesis,including specific hardware circuit and software program diagram.Some certain experiment test is done on this platform,and the experimental results verify the correctness and feasibility of the current hysteresis loop control system of brushless DC motor.