Design Of Sensorless Control System For A Brushless DC Motor

Brushless DC(BLDC)motors are widely used in industrial control fields,because they have many advantages such as simple structure,high efficiency and easy control.For traditional brushless DC motors,the rotor position signal can be obtained through mechanical position sensor,but the mechanical position sensor not only increases the cost of the motor but also limits the application of the motor in some situations.Therefore,the research of sensorless brushless DC motor control has become the research direction and hotspot of brushless DC motor control.Firstly,in this paper the mathematical model of the brushless DC motor is established based on the analysis of the voltage,back-EMF and electromagnetic torque equations,then the working principle of the motor is analyzed in order to provide theoretical basis for the study of motor starting and commutation.And then the traditional three-step start is studied and carried on the simulation analysis.A closed loop three stage start strategy is proposed on the basis of the traditional three-step start.It can effectively overcome the defects of the traditional three stage startup.Sliding mode observer is a kind of nonlinear observer with simple algorithm and good robustness.To a certain extent,it can reduce the influence of parameter variation and external disturbance on the system,so it is widely used in the field of motor control.But the traditional sliding mode observer has chattering problem,which not only reduces the control precision of the system,but also increases the energy consumption of the system.Secondly,based on the traditional sliding mode observer,the quasi sliding mode observer is constructed by introducing the saturation function.It can effectively restrain the chattering problem of traditional sliding mode observer.The average voltage of the motor is calculated as the input of the observer,to further reduce the motor torque ripple.The line back EMF is obtained through the observer as commutation signal,and it can eliminate the defect that the back EMF is used as the commutation signal.Finally,the simulation model of the motor control system is built to analyze the proposed strategy by MATLB/Simulink.DSP TMS320F2812 chip of TI company is used as control core.A platform of motor control has been set up for test analysis.The simulation and experimental results show that the proposed control strategy is feasible and effective.