Research On Brushless DC Motor Driver And Control Strategy For Electric Training Vehicle

Compared with traditional fuel training vehicle,electric training vehicle is powered by batteries,which reduces the consumption of fossil fuels and atmospheric pollution caused by burning gasoline in fuel vehicle,and is environmentally friendly and energy-saving.At present,fuel vehicle still occupies a large proportion in the Chinese market.In order to achieve the connection between ordinary training and examination,the electric training vehicle studied must have the operating characteristics of fuel vehicle.The electric training vehicle keeps a low-speed running state when it is used subject two training in driving school.In this state,it often starts and stops frequently,climbs a hill,and has the characteristics of "idle speed" and "fire out".In order to ensure that the electric training vehicle has good operating characteristics at low speed,its driving motor must output a large torque at low speed.The brushless DC motor retains the good speed regulation,control characteristics and operation characteristics of the DC motor.And its has a series of advantages such as small size,high efficiency,large starting torque,high power density,and maintenance-free,which are suitable for requirements of the electric training vehicle for the driving motor.The torque ripple of brushless DC motor is large when the electric training vehicle is "idle speed",which affects the performance of the electric training vehicle.In this thesis,the direct torque control strategy with duty cycle adjustment is used to suppress the low-speed torque ripple of brushless DC motor.The hardware circuit and software program of driver are designed for the running state of the electric training vehicle in driving school,and the feasibility of designing the hardware and software are verified through experiments.The research content of this thesis is as follows:(1)The development status of electric vehicle,electric training vehicle,brushless DC motor and driver are introduced,the background and purpose of the research topics are pointed out.The driving control system of the electric training vehicle is analyzed.Through the force analysis of the electric training vehicle when climbing the hill,the motor speed,torque and power are calculated.By analyzing the law of training duration of subject two,the batterv capacity is calculated from the perspective of energy.Finally,a 72V,5KW brushless DC motor and six 105 Ah lead-acid batteries are connected in series to form a power battery pack.According to the operating characteristics of the fuel training vehicle engine,the method for the driver to realize "idle speed" and"fire out" control of the motor is given.(2)In order to ensure that the electric training vehicle has good dynamic and static characteristics during "idle speed" operation,the double closed loop control strategy and direct torque control strategy are analyzed and the system design are given.From the dynamic process of commutation of brushless DC motor,the mechanism of direct torque control strategy to suppress low-speed torque ripple is analyzed,and the corresponding simulation model is built in MATLAB/Simulink.The simulation results show that the direct torque control strategy based on duty cycle adjustment reduces the torque ripple of the brushless DC motor by about 20%compared with the double closed-loop control.(3)Accor-ding to the existing motor in the laboratory,the driver hardware circuit is designed with the IPM module as the main power circuit and the STM32 as the main control chip.And the software program is designed in Keil uVision5 development environment.An experimental platform was built to simulate the working process of brushless DC motor for electric training vehicle.Experiments on motor no-load,on-load and "idle speed" were made,and related waveforms and data were measured.The experimental results show that the brushless DC motor driver and control strategy for electric training vehicle designed are suitable for electric training vehicle and have good performance in this thesis.And when using direct torque control,the phase current waveform is close to the ideal square wave,indicating that the direct torque control strategy can effectively reduce the low-speed torque ripple of the brushless DC motor and improve the low-speed performance of the brushless DC motor.