Three control methods of brushless motor

1. Square wave control

Square wave control uses brushless motor hall effect sensors or a sensorless estimation algorithm to obtain the motor rotor position and then performs 6 times (every 60°) in an electrical cycle of 360° based on the rotor position. Each commutation position of the motor outputs a force in a specific direction, so the electrical accuracy of the square wave control position can be said to be 60°. Because the phase current waveform of the motor under this control is close to a square wave, it is called square wave control. The advantage is that the control algorithm is simple, the hardware cost is low, and a higher motor speed can be obtained by using an ordinary performance controller; the disadvantage is that the torque fluctuates, there is a certain current noise, and the efficiency cannot reach the maximum value. Square wave control is suitable for brushless motors with low rotational performance requirements.

2. Sine wave control

The sine wave control method adopts an SVPWM wave, the output is a three-phase sine wave voltage, and the corresponding current is also a sine wave current. Thus, there is no concept of square wave-controlled commutation, nor of an electrical cycle being executed an infinite number of times. Obviously, sine wave control has less torque ripple and less current harmonics than square wave control, which makes the control feel more "refined", but the performance of the controller is slightly higher than square wave control, and brushless Motor efficiency cannot reach its peak.

3.FOC control

The sine wave control indirectly realizes the control of the voltage vector and the control of the current, but it cannot control the direction of the current. The FOC control method realizes the current vector control, that is, the stator magnetic field vector control of the brushless motor.