Research And Design Of SVPWM Without Position Sensor Brushless DC Motor

Due to its simple structure,low cost and reliable operation,sensorless brushless DC(direct current)motor has been widely used in many fields.However,there are many problems for the sensorless brushless DC motor in starting commutation torque ripple and control of commutation time,etc.Space vector pulse width modulation(SVPWM)is proposed to deal with those kind of trouble.The main contents of research are as follows:Firstly,it introduces current research status for detection method of brushless DC motor with position sensorless.The detection method of conventional electromotive force about zero crossing for detection voltage is compared with phase voltage.The detection method of rotor position for three phase electromotive force superposition is analyzed deeply,hence this paper releases an optimized back electromotive force superposition algorithm.Secondly,for the issue involved in torque ripple which is caused by the fluctuation of current during commutation,the SPWM technology is compared with SVPWM technology.The basic principle of SVPWM is analyzed.The mathematical model of the motor based on the id = 0 motion mode is established on the rotating coordinate system.Meanwhile three steps of SVPWM algorithm are described,namely,vector position,time of action and order of action.Finally,the simulation model of SVPWM control system for sensorless brushless DC motor is built.The result of simulation is shown that the superposition method for optimized back electromotive force can combine with SVPWM algorithm.Meanwhile it can correctly detect the commutation signal,track the rotor angle and control switching of the space vector sector.In addition,the three-phase current waveform is similar to the sine wave,and also the flux trajectory is round.The capacity for system with load is enhanced,and dynamic response accelerates quickly.In a word,the expected control effect has achieved with certain practical value.