Speed control of DC motor based on chopper converter

Chopper-based speed control of a DC motor is a widely used method, especially for series, shunt, or permanent magnet (PMDC) motors.

Control Loop

Open-loop:

• Vary duty cycle manually or via pre-programmed steps.

Closed-loop (more accurate):

1. Measure motor speed using an encoder or tachometer.
2. Compare to reference speed.
3. Use a PI controller to adjust duty cycle.
4. Apply updated duty cycle to chopper via PWM.

Typical Chopper Circuit for DC Motor

For a unidirectional drive (single quadrant):

• The switch is controlled by a PWM signal.
• A freewheeling diode is placed across the motor to allow current flow during switch OFF time.