Study On Brushless DC Motor Control System In Electric Vehicles

As the energy crisis and the environmental pollution worsening,new energy vehicles gradually come into people's vision.There are many kinds of new energy vehicles,electric vehicles act as a kind of new energy vehicles,which are widely used and developed.Brushless DC Motor(BLDCM)has many characteristics as wide range of speed regulation?low price?simple structure?and it is easy to achieve by square wave drive,so BLDCM has been widely used in many fields.However,when the square wave drive BLDCM,commutation current can not sudden change,it may produce large torque ripple,meanwhile,the existence of the position sensors may make the structures of motor complicated,and if the sensor accuracy could not meet the requirements,it would lead to lower reliability of the system,these shortcomings greatly limit the application of BLDCM in the electric vehicle field.This paper mainly designs and researches the drive and control system of BLDCM.Firstly,this paper compares the differences of structures between BLDCM and Permanent Magnet Synchronous Motor(PMSM),aiming at the problem of large torque ripple in BLDCM under square wave driving mode,deeply analyses the reasons of torque ripple,and try to use the sine wave driving method which is suitable for PMSM into the drive and control system of BLDCM,this paper uses vector control strategy on Space Voltage Vector Pulse Width Modulation(SVPWM)to realize the sine wave drive and control of BLDCM,and builds the vector control system of BLDCM,by comparing with square wave drive and control method in simulation,it verifies that vector control can effectively weaken the torque ripple,achieves the operative effect of low torque ripple?small noises and high efficiency.Secondly,to improve the vector control performance of BLDCM,this paper uses fuzzy PID controller in place of traditional speed PID controller in vector control system,by comparing with the two controllers in simulation,knows that when the system uses fuzzy PID controller,the anti-interference characteristic is stronger,phase current more closes to the ideal state,and torque ripple is further weakened.Finally,this paper uses back electromotive force Sliding Mode Observer(SMO)to realize the position-sensorless vector control of BLDCM,and a novel controlling function is proposed to improve the conventional SMO.By comparing with conventional SMO in simulation,it verifies that the improved SMO could precisely estimate back electromotive force of BLDCM,effectively weaken the chattering without the additional low-pass filter,and simplify the structure of the system.In addition,this paper uses TMS320F28035 of TI company as the control core of the system in hardware design,meanwhile,it designs that DSP minimum system?USB to serial circuit?communication interface circuit of CAN?D/A conversion accuracy? driving circuit?inverter circuit?sampling circuit?digital isolation circuit?fault indication circuit and other peripheral circuits.In software design,it uses CCS5.1 to complete program writing and debugging,and designs that main program?interrupt program?SMO program?SCI program and so on,and realizes position-sensorless vector control of BLDCM.