Research On Vector Control System For Position Sensorless Brushless DC Motor

With the development of semiconductor and power electronics technology,brushless DC motors using electronic commutation instead of mechanical commutation have been invented.Compared with the traditional DC motor,the brushless DC motor avoids the defects caused by the brush and the commutator,and has many advantages such as simple control,high torque density,convenient maintenance and low cost.Used in many fields such as precision instruments,home appliances,vehicles,medical equipment,etc.However,in the brushless DC motor control,the rotor position signal is needed to provide the basis for the commutation,and the presence of the position sensor will increase volume of the motor;reduce the reliability under the harsh conditions of high temperature and humidity;high installation accuracy requirements,sensor installation error will adversely affect commutation.Therefore,the position sensorless control technology of brushless DC motors has become an important research direction.In this thesis,the following researches are carried out on the brushless DC motor vector control system.Firstly,a rotor position detection method based on single-phase inductance detection is proposed.This method is suitable for the motor start acceleration stage,which avoids the phenomenon of out-of-step or even reversal that may occur when the motor is started.Secondly,a cyclic freewheeling method in driving phase is proposed,which replaces the energy stored in the winding inductance in the driving phase,instead of the method of returning the inductor energy to the source through the freewheeling diode in the traditional freewheeling,which increased motor torque and reduced start-up time.Thirdly,the rotor position detection method based on sliding mode back EMF observer is used in the steady stage of the motor.With the improvement of the switching function and the rational design of the low-pass filter,the design and simulation of the position sensorless vector control system of the brushless DC motor is realized.Finally,according to the theoretical analysis and design scheme of this thesis,the software and hardware design and experiment of the control system are carried out.The experimental results show that the acceleration capability of the proposed method is significantly improved compared with the traditional method of detecting the rotor position in the acceleration stage based on the induction method.The rotor position detection method based on the sliding mode back EMF observer can accurately detect the rotor position and provide accurate position information for vector control.And the i_d=0 vector control method can reduce torque ripple and operational noise compared to the conventional square wave control.