Q1Electric Drives
Question
Q.1. Explain the principle of PWM control in a DC chopper circuit.
Answer
PWM control in a DC chopper varies the duty cycle (on-time fraction) of a fixed-frequency switching signal to control the average output voltage delivered to the load, while keeping the switching frequency constant.
Pulse Width Modulation (PWM) control in a DC chopper works by keeping the switching frequency (and hence the total switching period T) constant, while varying the fraction of that period during which the switch is turned on (the on-time Ton, and correspondingly the duty cycle D=Ton/T). Since the average output voltage of a step-down chopper is Vavg=D×Vd, varying D directly and continuously controls the average voltage delivered to the load, allowing smooth, efficient control of motor speed (or any other load requiring variable DC voltage) purely by adjusting the width of the switching pulse within each fixed-length period, hence the name 'pulse width modulation.'