Key Technology Research Of High Power Brushless DC Motor For Electric Vehicle

Electric vehicle(EV)is a renewable and sustainable transport vehicle.Compared to the traditional vehicle,EV has many advantages,including clean,green,energy-efficient,renewable and sustainable.The key technology of EV driving system includes energy technology and drive technology.Energy technology development is currently experiencing a bottleneck,so the development of high performance motor drive system is particularly important.Brushless DC motor(BLDCM)drive system has been widely used and widespread concerned.BLDCM drive system has the advantages of simple mechanical structure,high transmission efficiency,flexible control,etc.,it is suitable for EV control system.The research and analysis of BLDCM drive system in EV are focused in this paper.The purpose of this paper is to solve some problems in the control strategy of BLDCM for EV and develop a suitable drive control system.For this purpose,aimed at the characteristics of BLDCM structure and parameters,some key techniques in the control of BLDCM are analyzed and researched detailedly:A current predictive control strategy is adopted to suppress the commutation torque ripple in BLDCM.Based on the analysis of the principle of the motor commutation torque ripple,the current predictive control strategy combined with improved PWM mode is proposed in this paper.The PWM modulation is performed during commutation period,the PWM ratio is calculated according to the current predictive control strategy.The switching devices of ingoing phase and outgoing phase are modulated with PWM mode during commutation period.The rising slope of ingoing phase current and descending slope of outgoing phase current are controlled to be equal during commutation period,the current of non-commutation phase is kept to be constant.Thereby commutation torque ripple is suppressed.Experimental results validated the effectiveness of the proposed control strategy,it can significantly reduce the commutation torque ripple in the whole speed range.The global fast terminal sliding mode observer(GFTSMO)is adopted to realize the sensorless control of BLDCM.Global fast terminal sliding mode control strategy combines the advantages of linear sliding mode and non-singular terminal sliding mode.The convergence speed of the system state is enhanced.The commutation point is obtained with the zero crossing point of back EMF,The instantaneous torque of the motor is calculated.Compared with the conventional sliding mode observer,the proposed control strategy can enhance the convergence speed,reduce the delay of commutation point,improve the dynamic performance and robustness of the system.Constant current control of regenerative braking system in BLDCM is adopted to extend the driving range of electric vehicle.The single modulation feedback braking mechanism of BLDCM is studied and the mathematical formula of the braking feedback is deduced.The constant current control strategy of regenerative braking is proposed.The closed-loop control system of the braking current is established.In the control system,the reference current and the feedback current are set as the input,the PWM duty ratio is set as the output.Experimental results show that the proposed method can regenerate the braking energy,keep the brake current to be constant,improve the reliability of BLDCM control system.