PWM speed control principle of AC motor and DC motor speed control principle is different, it is not through frequency modulation to adjust the motor speed, but by adjusting the driving voltage of the pulse width, and the circuit of some energy storage elements, change the delivery to the amplitude of the armature voltage, so as to achieve the purpose of changing the speed of DC motor. Its modulation mode is amplitude modulation.
PWM speed control principle of AC motor, mainly through the AC signal of a variable frequency modulation, a high frequency square wave driving voltage, resulting in a change with the frequency modulation signal driving current in the motor armature. Thus, the AC motor armature is driven by this current to produce a rotating magnetic field in accordance with the frequency of the modulation signal, so that the rotation speed of the motor rotor is changed. It is modulated by fm.
This question is not clearly stated in this space. To be brief, AC motor speed control has PWM drive mode of AC motor, DC motor speed control has PWM drive mode of DC motor.
