Control principle of brushless DC motor

To make the motor rotate, the control unit must first determine the current position of the motor rotor according to the current position of the motor rotor sensed by the hall-sensor, and then determine the order of turning on (or turning off) the power transistors in the inverter according to the stator winding. AH, BH, CH (these are called upper arm power transistors) and AL, BL, CL (these are called lower arm power transistors), make current flow through the motor coils in sequence to generate a forward (or reverse) rotating magnetic field, and interact with the rotor. The magnets interact so that the motor rotates clockwise/counterclockwise.

When the motor rotor rotates to the position where the hall-sensor senses another set of signals, the control unit turns on the next group of power transistors, so that the circulating motor can continue to rotate in the same direction until the control unit decides to turn off the power if the motor rotor stops. transistor (or only turn on the lower arm power transistor); if the motor rotor is to be reversed, the power transistor turn-on sequence is reversed.

When the motor rotates, the control part will compare the command (Command) composed of the speed set by the driver and the acceleration/deceleration rate with the speed of the hall-sensor signal change (or calculated by software), and then decide the next group ( AH, BL or AH, CL or BH, CL or ...) switches are turned on, and how long they are on. If the speed is not enough, it will be long, and if the speed is too high, it will be shortened. This part of the work is done by PWM. PWM is the way to determine whether the motor speed is fast or slow. How to generate such PWM is the core of achieving more precise speed control.