What is the difference between an AC Drive and a Servo Drive?

• A. Servo Drives control speed as well as position and movements
• B. AC Drives control motor speed
• C. Servo Drives measure humidity
• D. AC Drives control motor speed. Servo Drives control speed as well as position and movements

Answer: (D)

The essential difference is in how they control the motor and what kind of feedback is used. An AC drive (variable-frequency drive) adjusts the speed of an AC motor by varying the supply frequency and voltage, providing good speed control but without requiring precise knowledge of the motor’s position. A servo drive uses closed-loop control with a position or motion feedback device (like an encoder or resolver). That feedback lets the drive know the exact position and adjust continuously to reach and hold a commanded position or follow a precise motion path, not just run at a set speed.

So, the correct view is that AC drives control motor speed, while servo drives control speed and position/motion through feedback. This distinction explains why servo systems are used for precise positioning and coordinated movements, whereas AC drives are common for general speed control of motors.