Question

what is principal of pulse width modulation?​

Answer 1

As its name suggests, pulse width modulation speed control works by driving the motor with a series of “ON-OFF” pulses and varying the duty cycle, the fraction of time that the output voltage is “ON” compared to when it is “OFF”, of the pulses while keeping the frequency constant.

Answer 2

Answer:

Pulse Width Modulation (PWM) is the name of a technique to generate low frequency output signals from high frequency pulses. Rapidly switching the output voltage of an inverter leg between the upper and lower DC rail voltages, the low frequency output can be though of as the average of voltage over a switching period.