Speed Estimation in Induction Motors Using Additional Windings

Induction motors are widely used in industrial and consumer applications by virtue of their ruggedness, reliability and low cost. Motion control methods of electrical motors such as vector control techniques require accurate position and speed signals fed to the controller. The conventional use of mechanical sensors for speed estimation in motor control makes it expensive and space consuming in applications that have limitations of space. Therefore, speed-sensorless methods for motor control have relevant scope in the industry. In this paper, a method for speed estimation of an induction motor using a few additional sensing windings within the stator is proposed. Rotor position information can be extracted from externally injected signals and from the induced voltages in these additional windings at different speeds and standstill. Tests have been conducted on an induction motor with the sensing windings wound on the stator. The signals measured from these windings are found to have effects from the rotation of the rotor due to slot harmonics. Results from finite element analysis and from the test bench measurements are discussed. The speed estimation is compared with the actual speed and the results show that this method promises efficient speed estimation in induction motors.