Research On Low Cost Vector Control System Of BLDCM For Electric Vehicles

Relying on the lower price,convenient usage and environment-friendly,electric vehicles occupies the market of short-distance transport rapidly,it also showing a good economic prospects and the rapid development momentum.Brushless DC motor is widely used in electric vehicles because of its’ small size,wide speed range,light weight and high efficiency.In recent years,in order to improve the user experience from the operating efficiency and stability,decrease operating noise,the market gradually improve its’ requirement to the driver of electric vehicles.The traditional six-step control method obviously can not meet the demand,therefore,the new generation driver with excellent performance is needed desperately.This paper mainly studies the vector control system for brushless DC motor based on single current sensor.Firstly,the brushless DC motor is analyzed from stator and rotor structure and position sensor.On this basis,the basic working principle of BLDCM is analyzed by taking the traditional six-step commutation control as an example.Finally,analyze the Voltage Equation and Torque Formula of Brushless DC Motor in Two-phase Rotating Coordinate.Then,the basic principle of space vector pulse width modulation technology is emphatically introduced,and its implementation method is described in detail from the judgment of the reference voltage vector sector,the calculation of the nonzero basic voltage vector time and the limiting processing in over-modulation region,Which provides a theoretical basis for the follow-up simulation module construction and programming.The simulation model of brushless motor vector control system is built on the platform named Simulink from matlab,and the construction of each sub-module is introduced in detail.Then,two key problems in the design of the system are introduced: phase current reconstruction in non-observable region and motor rotor position estimation based on linear interpolation algorithm.The cause of the error in non-observable region is analyzed,and a solution based on PWM phase shift is proposed.In the matter of rotor position estimation,the basic principle of the linear interpolation algorithm is introduced,the implementation of the method for rotor position estimation is furtherly analyzed based on this basis.Then,based on the above theoretical analysis and simulation model,the system experimental platform is designed from two aspects of hardware and software.In the hardware part,the whole frame is introduced firstly,then the power circuit,the current sampling circuit,the over-current protection circuit and the MOS driving circuit are analyzed in detail.In the software respect,the self-checking for MOSFET,the motor start-up and the implementation and function of hall and ADC interrupt service program are introduced following main program introduction.The SVPWM modulation and phase current reconstruction subroutines in the ADC interrupt service routine are analyzed emphatically.Finally,the system designed by this paper is applied to the hub-type brushless DC motor.The phase current waveform,Hall signal and SVPWM three-phase modulation waveforms are measured when the motor is started and stably operated.The waveforms of the bus current from vector control driver is compared to six-step commutation control driver,And the dynamometer was used to test the motor load characteristic curve under the two drive modes.The test results show that the vector control system designed in this paper can effectively reduce the motor running noise,bus current and torque ripple,and improve the motor running efficiency compared with the traditional six-step commutation control method.