Direct Torque Control Of Sensorless Brushless DC Motor

Sensorless Brushless DC Motor with many advantages becomes an excellentchoice for electric vehicle drive motor. However, due to electromagnetic interference,inconsistent commutation current rate of change, armature reaction and mechanicaltechnology and other relevant factors, the motor will have a greater torque ripple atrun time, affecting the speed adjusting performance, and create louder noise. DirectTorque Control Technology has fast response and powerful regulating ability. it caneffectively reduce the torque ripple by the direct control of the instantaneous torque.Therefore, the paper focuses on the research of technologies of rotor positiondetection, torque estimation and three-start in sensorless brushless DC motor directtorque control.Based on the establishment of the back EMF method of Sensorless BrushlessDC Motor, and combined with the features of Brushless DC motor and direct torquecontrol, the paper proposes a new Sensorless Brushless DC motor direct torquecontrol method. Detection of rotor position information for the method using backEMF method, the realization of the motor commutation control, at the same time theapplication of back electromotive force shape function method to estimate the motortorque, flux observation part omitted in DTC, realize direct torque SensorlessBrushless DC motor controlthe method can realize the motor commutation control by using back EMFmethod to detect rotor position information, at the same time, it can realize directtorque Sensorless Brushless DC motor control by applying the back EMF shapefunction method to estimate the motor torque, omitting flux observation part in DTC.This method avoided the complicated flux calculation, simplified the structure ofcontrol system, and can restrain the torque ripple effectively.And then, aiming at the problem of the speed fluctuation in three-step startingof Sensorless Brushless DC Motor, this paper presents a constant current controlmethod of starting. When the motor starts, it applies the current closed-loopfeedback control to keep the motor starting current constant, and according to thedynamics equation of motor rotor,it infers calculation formula of commutation timein the constant current start control. This method can avoid the motor speedfluctuation effectively when starting, having good starting effect. Also, it can ensure the starting current is not too large when starting to protect the motor.based on the above control strategy, the paper established the control system ofSensorless Brushless DC motor, and conducted the numerical simulation research inMATLAB/Simulink environment which show that the control strategy proposed inthis paper has good efficacy and feasibility.Finally, based on F2812DSP processor, this paper developed the hardwaresystem of direct torque control in Sensorless brush DC motor, compiled controlprocedures of the whole control system, and established a complete SensorlessBrushless DC motor controller.