Closed-loop Starting Method Of The Senorless Of The Brushless DC Motor

Currently brushless DC motors(BLDCM)are ever-increasingly utilized in many fields,including industrial controllers and household appliances,the traditional sensor control method can not satisfy the needs of the development of the BLDCM control technology in future.Therefore sensorless control method becomes a major research focus.However the senorless starting method becomes a difficult problem owing to that the rotor position can't be gotten with the sensorless control method during the startup of the motor.In the present the traditional "three-step" starting method,consisted of pre-positioning of the rotor,starting up with boosting and upscalling and driven by testing the zero-crossing points of back-EMF,is widely used in the sensorless control method.Based on this method and combined with advanced research results home and abroad,a new "three-step" closed-loop starting method is proposed.The method can complete the initial rotor's position detection without rotation of the rotor,so that the maximum angle of rotation of the rotor for pre-positioning is reduced to the range within 30 degrees.Meanwhile the information of the rotor's position is able to be fed back at any time during the startup of the motor,which makes the closed-loop starting method realize and compensates for the lack of traditional starting method.Based on the function of BLDCM stator inductance,stator current and rotor position,the initial rotor position detection method is established with the deduced function of the equivalent inductance of stator and the bus current when the rotor position is not changed.In this method,the deviation of determine the initial position of the rotor is reduced to the range within ±15 degrees and the maximum angle of rotation of the rotor for pre-positioning is reduced to the range within 30 degrees,so that the positioning time is reduced.Compared with other PWM motor control methods,Hpwm_Lpwm control methods can avoid the actual zero-crossing points of back-EMF offsets caused by the high frequency PWM signal effectively by analysis,due to that detected back-EMF zero-crossing and the actual zero-crossing are the same in this method.With this method,the filter circuit and the zero-crossing compensation circuit can be eliminating.the cost of the motor driver is reduced but the stability of the motor driver is improved.With the principle of the induced voltage at the vacant phase caused by the two phases of the energized stators and the back-EMF have the same zero-crossing points during the startup of the BLDCM and the amplitude of the former one is bigger than the latter,due to the changing rate of the starting current is much faster and the speed of motor is lowest in the start-up level,a new starting method is established by testing the zero-crossing points of the induced voltage at the vacant phase instead of the zero-crossing points the back-EMF.The new method achieve the closed-loop start-up of the motor with the real-time feedback of the position of the rotor.