Study On Back-EMF Method And Starting Technique Of BLDCM

Brushless DC motor(BLDCM) is a kind of electromechanical integration machinery, and it has been rapidly developing in recent years with the help of the development of power electronic technique and the appearance of new type of permanent magnet material. With it's widely used in many fields, sensorless control especially back-EMF method is more useful than sensor control in many applications.In this paper the common methods of sensorless control of BLDCM are introduced, and the principle of back-EMF method is illustrated in detail. The control system adopts high capability chip dsPIC30f2010. In this paper every circuit is introduced, the AD sampling circuit and hardware filter are carefully introduced. Based on the hard circuit the design of software is explained.The back-EMF amplitude is direct ratio with the speed of motor, so we can not get the position of rotor when the motor is still. Because of this we have to use special starting method. After discuss "three-step" starting procedure which is locating, accelerating and switching, we discuss a new starting method which is locating, switching. We clearly explain this method and the conditions whether this method can be used. The test proved that this method is resultful. We discuss the effect to the phase which turned off when use different PWM modulating way. We design software filters to induce the disturb and the impulse cased by the diode.The results of the experiment show that this system , which is made on the base of the theory above, can control the sensorless BLDC motor to complete the exact commutation. The system presents good static and dynamic performance.