Q4Advanced Electric Drives
Question
2 marks
Q.4. What are the various methods used for speed control of DC motors?
Answer
- Armature voltage control: varying the DC voltage applied to the armature (via a controlled rectifier or chopper) while keeping field flux constant, providing speed control below base speed at constant torque capability.
- Field flux control: varying the field winding current (and hence flux) while keeping armature voltage constant, providing speed control above base speed at constant power capability, since reducing flux increases speed but reduces available torque.
- Armature resistance control: inserting external resistance in series with the armature circuit, a simple but inefficient method (large power dissipation in the resistor) mainly used in older, low-power DC drive applications.
- Combined (Ward-Leonard-style or modern power-electronic combined) control: using armature voltage control below base speed and field weakening above base speed together, providing the widest possible speed range while respecting the motor's rated torque and power limits.