Research And Implementation Of Continuous Current Control System For Brushless DC Motor

Because of the defects in brushed DC motors,they are gradually being replaced by brushless DC motors in applications such as automatic sweepers,power tools,washing machines,and disabled vehicles.Due to the rapid development of integrated circuit theory and motor control theory,the excellent performances of brushless DC motors are gradually approved,and the researches of brushless DC motors,which are full of development potential,have gained very rapid progress and popularity.However,the torque ripple problem is inevitable because of the unique structure and control characteristics of the brushless DC motor,which limits the practical application of the brushless DC motor in high precision and high stability fields.In this article,the main reasons for the commutation torque ripple generated by brushless DC motor is analyzed and a continuous current control method based on positive hexagonal current vector is offered.The method stems from the positive hexagonal current vector by analyzing the cause of the commutation torque ripple,and on this basis,the continuously varying current waveform combined with the space vector control to the commutation torque ripple is obtained.And the technology has been successfully applied to the motor drive of automated guided transport vehicle(AGV).The main contents of this paper are as follows:(1)Describing the basic knowledge of brushless DC motors based on mathematical models briefly,and on this basis,introducing the motor control strategies of the commonly used two-two conduction and three-three conduction.The experimental research method obtains the required continuous current waveform by improving the space vector pulse width modulation(SVPWM)method of the three-three conduction control strategy;(2)Analyzing the reason of the commutation torque ripple generated by the brushless DC motor.According to this reason,the phase current waveform controlled by the rectangular current waveform is improved,and then deduce the continuously variable trapezoidal wave current to get the regular positive hexagonal current vector.The regular positive hexagon current vector is combined with the space vector control method to complete the design of the regular positive hexagonal current vector continuous current control method,and modulated the continuously changing trapezoidal wave current to weaken the torque commutation ripple problem of brushless DC motors;(3)Using STM32F103C8T6 as the main control chip to complete the hardware design of servo controller,it includes three-phase inverter bridge circuit,drive circuit,sampling circuit of DC bus current,overcurrent protection circuit and so on;(4)Under the IAR development environment,a series of software programs designs were implemented with STM32F103C8T6 as the main control chip.Firstly,the main program of the system and the interrupt service program is analyzed,then explain the design of each called secondary program.Finally,the continuous current control method proposed in this paper has obvious suppression effect on commutation torque ripple of brushless DC motors by comparing the difference between the traditional rectangular current waveform control,the direct SVPWM control and the regular positive hexagonal continuous current control in the PWM waveform,the phase current and the DC bus current at different speeds.The system has been actually applied to automated guided transport vehicle(AGV)to keep trolley operate according to the driving trajectory when turning and going straight.