Q6Electric Drives
Question
Q.6. What is the role of a chopper in a DC drive?
Answer
A chopper (DC-DC converter) in a DC drive controls the average DC voltage/current supplied to the motor armature by rapidly switching a fixed DC input on and off at a controlled duty cycle, providing efficient, continuously variable speed and torque control without the losses of a resistive/rheostatic control method.
A chopper is a power-electronic DC-DC converter that regulates the average voltage delivered to a DC motor's armature by rapidly switching the fixed DC supply voltage on and off at a high switching frequency, with the ratio of on-time to total switching period (the duty cycle) determining the resulting average output voltage — for a simple step-down (buck) chopper, Vavg = D×Vsupply, where D is the duty cycle (0 to 1). By varying the duty cycle, the chopper provides smooth, continuously variable control of the motor's armature voltage (and hence its speed, since DC motor speed is approximately proportional to armature voltage), achieving efficient speed control with minimal power loss in the control device itself (since an ideal switch dissipates negligible power either fully on or fully off), unlike the older technique of rheostatic (resistor-based) armature voltage control, which wastes significant power as heat in the series control resistor — this efficiency advantage is the primary reason chopper-based control has become the standard modern approach for DC drive speed control.