Chapter 9 - Speed estimation and sensorless control of alternating current motors

Abstract

This chapter introduces position sensors required for the position/speed control in the motor drive systems and examines the speed estimation method from the position sensor signal. For the vector control of alternating current (AC) motors, the information on the rotor position is also necessary. A resolver used to obtain the information on the absolute rotor position required for the vector control of permanent magnet synchronous motors is introduced. A rotary encoder, which is the most widely used digital position sensor in the motor drive systems, used to obtain the rotor speed required for the vector control of induction motors is introduced. In addition, the speed estimation methods using the output signal of the rotary encoder are examined. Finally, the sensorless control methods of AC motors, which do not use these position sensors, are explored. For these sensorless methods, techniques based on back-electromotive force and techniques based on the characteristics of a motor itself are included.