Sensorless speed control in induction motor drives

This paper describes a method of sensorless speed estimation that is low cost and easy to implement. It uses two different algorithms, and so compensates for the weaknesses of the individual algorithms producing a robust low cost application. A method is investigated that uses the rotor slot harmonics to estimate the speed of the motor above 300 rpm. At lower speeds the rotor slot harmonic method becomes unreliable, due to the difficulty in detecting the harmonics at lower speeds. A slip detection method, using an empirical formula is to be used during the speed "blind spot", providing speed estimation and so increasing the dynamic range of the system as a whole.