Independent Electrical Contractors (IEC) Year 4 Practice Exam

Both AC and DC motor drives are used to control the speed of a motor. The drive adjusts the power supplied to the motor to reach and maintain a desired speed. For AC motors, this is done by changing the supply frequency and voltage through a variable-frequency drive. For DC motors, the drive varies the applied voltage (and current) to set the speed. While adjustments to acceleration, deceleration, and even direction can be achieved, the universal role of a motor drive in both types is to regulate speed.