Brushless DC motor, due to the brushless, the motor itself can not complete their own current commutation, relying on the external control circuit to achieve commutation. So there is no conventional DC control method, the external control circuit to complete the commutation is realized by the switching tube, due to the flexibility of the switching circuit, it can be convenient to realize more functions than just commutation, so the chopper DC control method is used to control the motor.

First of all, to make the brushless motor rotate, the control department according to the sensed current location of the motor rotor, and then in accordance with the stator winding to determine the order of turning on (or off) the power transistors in the converter, the upper arm power transistors and the lower arm power transistors, so that the current flows through the motor coils to produce a clockwise (or counterclockwise) rotating magnetic field in order, and interact with the magnets of the rotor, so as to make the motor rotate clockwise/counterclockwise This causes the motor to rotate clockwise/counterclockwise. When the motor rotor rotates to the position where another set of signals is sensed, the control department turns on the next set of power transistors, and so on, the motor can continue to rotate in the same direction until the control department decides that the motor rotor should be stopped, then turn off the power transistors (or only turn on the lower arm of the power transistors); motor rotor reversal, then turn on the power transistors in the reverse order.

Phase change control according to the stator winding phase change mode, first find out the three rotor magnet position sensor signal H1, H2, H3 state, and the relationship between the six power tubes, in the form of a table in the microcontroller's EEPROM. 8751 according to the state of the H1, H2, H3 from the state of the power tubes can be found to correspond to the conductive, and through the P1 port to send, you can realize the DC brushless motor phase change. The phase change of the motor can be realized.

Speed control In the process of normal operation of DC brushless motor, as long as the output voltage U0 of digital-to-analog converter is controlled, the current of DC brushless motor can be controlled, and then the current of motor can be controlled. That is, 8751 microcontroller through the cycle of the sensor signal, calculate the motor speed, and compare it with the given speed, such as higher than the given speed, then reduce the output value of the P2 port, reduce the motor current, to achieve the purpose of reducing its speed. If it is higher than the given speed, the output value of the P2 port will be reduced to lower the motor current to reduce its speed.