Speed measurement using rotary encoders for high performance AC drives

Most high performance speed control methods for electrical motors, such as AC vector control, use rotary encoders. Accuracy in obtaining the rotor speed from encoder signals is an essential requirement to achieve good dynamic response, but usually implies a delay in the speed control loop, which can cause stability problems. In this paper, the authors present alternatives for obtaining rotor speed from an encoder, highlighting their advantages and disadvantages, and ratifying them by means of simulation. They also show some experimental results obtained with an induction motor, controlled in field coordinates, using the proposed methods