Sensorless brushless dc motor control - fly-wheel diode

 Fly-wheel diode method is also called the "third phase conduction method", it is through the parallel inverter bridge on the power switch tube fly-wheel diode conduction and shut off state testing to determine the rotor position. This method applies to 120 ° conduction, three-phase six-step square wave permanent magnet brushless dc motor drive, the implementation scheme of main circuit and power required by the device PWM timing, respectively, as shown in figure 3 (a), (b). Below to T in the chopper, a T b - in the stage of conduction as an example to illustrate its working principle. When T a + from opening to shut off, if the winding self inductance, mutual generator set spare parts inductance are constant, the terminal voltage phase C can be expressed When ec = 0, ea + 4 = 0, V CE, V F is very small, can be ignored.

so the stream diode conduction approximation for the conditions of ec < 0, as long as the detection of D C - conducting state, can detect the C instead of electric potential zero; Appropriate delay, conduction T C - again, and again, can correctly commutation sequence, in turn trigger different power tube, drive motor rotation. wholesalemotor.blogspot.com Fly-wheel diode method the ac motor essence or the potential laws, only in the "disconnect" back emf zero detection have some change. This change in a certain extent, to broaden the motor lamination speed range, especially can widen the lower limit of motor speed, because the fly-wheel diode conduction voltage drop is small, as long as the sensorless brushless dc motor control - liuyunqian @ yeah - embedded learning can, CE and V F and V are usually small. In some applications, the minimum speed of the motor can even less than 100 r/min.