Sensorless brushless dc motor in the control of the positioning in the brushless dc motor, induction electromotive force in stator winding and rotor position maintained a certain relationship, according to & quot; Method of back emf & quot; Commutation of the brushless dc motor based on the principle of work. And amplitude of induction electromotive force is proportional to the speed of the motor. Static or rotating speed when the motor is very low, induction electromotive force amplitude is zero or very small, not used to determine the position of the rotor pole current, so the starting of the brushless dc motor can't converter according to counter electromotive force. in order to ensure the normal order of the brushless dc motor can start, you first need to determine the current position of the rotor, under the condition of light load, with the day of the trapezoidal bemf waveform brushless dc motor is generally USES the magnetic brake motor rotor position. System began to electricity, any given a set of trigger pulse, formed in the air gap a constant amplitude, direction of constant flux, brushless motor, just make sure its amplitude is large enough, so the magnetic flux can be in a certain period of time the motor rotor forcibly positioning in this direction. but, because of the uncertainty of the resting motor rotor position, if before locate its position, the position just in conduction VT1 and VT6, model aircraft, motor stator winding composite magnetic flux d of Fa and rotor shaft Angle is 180 degrees, the motor rotor will not rotate to the position, orientation failure. To solve this problem, can use & quot; Two consecutive & quot; Positioning method. As shown in the above, on the basis of the first position, then conducting the next state, such as conduction VT1 and VT2, it success or failure, no matter for the first time the second positioning must be successful. brushless motor
