How to adjust the speed of brushless motor?

It is different from the speed regulation of stepper motors (the principle of speed regulation is to rotate a step angle every time a signal is received, so the speed regulation method of stepper motors is frequency speed regulation, that is, the speed of the motor is controlled by changing the frequency of the pulse signal. Adjusting the pulse signal voltage will not change the motor speed.) The brushless motor (bldc motor) has three speed adjustment methods:
 
1. Voltage speed regulation: Generally, a brushless motor is matched with a driver. By changing the output voltage of the driver, the input voltage of the brushless motor can be controlled to adjust the motor speed.
 

2. PWM speed regulation: PWM speed regulation uses pulse width modulation to modulate the constant DC power supply voltage into a pulse voltage sequence with a constant frequency and variable width, so that the average output voltage can be changed to adjust the motor speed. The speed can be adjusted by changing the voltage. Its essence is to adjust the duty cycle. Simply put, the duty cycle is the time ratio between high level and low level in the pulse signal. For example, assuming that the high level is 5V, the low level is 0V, and the duty cycle is 50%, that is half the high level time and half the low level time. At a certain frequency, you can get a simulated 2.5V Output voltage, then with a duty cycle of 75%, the resulting voltage is 3.75V.

The larger the duty cycle, the higher the output pulse amplitude, the larger the voltage, and the higher the rotational speed. On the contrary, the rotational speed will decrease. Therefore, when using PWM speed regulation, if the high-level amplitude is 5V and the amplitude is 3.3V, the motor's speed will only be 66% of the full speed. At this time, if a higher speed is needed, the maximum speed of the motor can be increased. Corresponding ratio to achieve the required speed.
 
3. Series resistor speed control: A potentiometer can be connected in series, but the method is inefficient and only small-power motors can be used. It is generally not recommended to use a potentiometer to regulate the speed of high-power motors.