Sensorless Control of Induction Motor Drives Using Additional Windings on the Stator

Induction motors excel other types of electrical motors in various applications with their advantages such as low cost, ruggedness, etc. The vector control method which is widely preferred for induction motor control requires speed and position measurement fed back from the motor. Speed sensors called encoders which are conventionally employed for this measurement are costly and space consuming. A method of speed and position estimation using a few additional sensing windings on the stator of the induction motor is discussed in this paper. The effects of rotor slot harmonics and back-EMF are exploited in this method. Speed and position information can be extracted from externally injected signals and from the induced voltages in the additional windings at different speeds and standstill. The speed and position estimation algorithms are discussed. Simulations are carried out and measurements on a real motor are performed. It is shown that the current and voltage signals in the additional windings contain speed and position information that could be extracted and fed to the controller.