How to achieve the commutation principle of a Hall free brushless motor?

In the past few years, most manufacturers have chosen Hall brushless motors, but Hall DC brushless motors need to be matched with more complex Hall effect sensors, which have adverse factors on the reliability and manufacturing process of the motor. In addition, there are installation issues, which can cause motor performance problems if not installed accurately. The Hall brushless motor runs smoothly and starts reliably. It does not directly use rotor Hall effect sensors, but requires rotor position signals to control motor commutation. The detection of rotor position signals mainly uses detection of stator voltage, current, etc. to estimate rotor position. The commonly used method is back electromotive force (EMF), which is used to detect the back electromotive force (EMF) of the motor to obtain the rotor position signal.

The following is a brief introduction to the back electromotive force detection method for brushless motors:

1. Detection method for zero crossing of back electromotive force

By detecting the zero crossing point of the reverse electromotive force, several key positions of the rotor can be obtained, thereby achieving commutation control of the Hall effect sensor brushless motor.

2. Third harmonic method of back electromotive force

The filtered third harmonic is directly fed into the I/O port of the DSP through a square wave, which reflects the phase information of the third harmonic through a voltage zero crossing comparator.

3. Flyback diode

The position of the rotor is determined by detecting the on and off states of the flyback diode, which is in reverse parallel with the inverter bridge power switch.