Research Of Brushless DC Motor Control System For Electric Vehicle Drive

As the increasing shortage of energy problems and the pollution caused by fuel vehicle emissions are becoming more and more serious,green and energy-saving vehicles have been an important issue.For electric vehicles have advantages of no pollution,low noise,high efficiency and simple structure,they will become the mainstream of future transportation.Brushless DC motors as the drive motors of electric vehicles,have advantages such as simple structure,reliable operation,good regulation-speed performance,high efficiency,long lifespan and so on.Therefore,this thesis designed a brushless DC motor control system for electric vehicles with the characteristics such as simple structure,strong stability,good starting characteristic,accurate speed control and low cost.In this thesis,basic structure and working principle of the brushless DC motor for electric vehicles were described in detail and the mechanism of rotating magnetic field was analyzed in depth.Based on the distribution law of air-gap magnetic field,a mathematical model of brushless DC motors was established.According to the control technology of brushless DC motors and the performance index of electric vehicles,an overall design scheme with TMS320F28335 as the control core was determined.Through analyzing the traditional PID algorithm,this research proposed an optimization method of variable speed integral and proportional link correction,and applied improved PID control algorithm to double closed-loop control system.In accordance with this control scheme,hardware circuits and software programs of the control system were designed.The hardware circuits consisted of DSP control and motor drive,including power supply circuit,driving circuit,position detection circuit,protection circuit and so on.Meanwhile,hardware circuits of the design were tested and analyzed to verify the feasibility and rationality of them.As for software programs,the modular design method was adopted and the designs of main program and each subroutine including the main program,A/D interrupt subroutine,serial communication subroutine,closed-loop subroutine were accomplished.Finally,a debugging and an experiment of the brushless DC motor control system for electric vehicles were completed by virtue of the designed controller,and speed and current data during the experiment were collected.Through analyzing experimental data,the effects of open-loop control and closed-loop control,traditional PID control algorithm and improved PID control algorithm,single closed-loop control and double closed-loop control on the performances of the control system were compared to verify the feasibility of the control algorithm proposed in the thesis.Compared with traditional PID control algorithm,this control system was more ideal.Load experiment results showed that the brushless DC motor control system for electric vehicles in this thesis has reasonable design,stable operation and good performance index.