An improved method to measure speed in induction motors, based on induced irregularities

This work presents a method of speed estimation for induction motors, based on the introduction of dynamic irregularities in the rotor. The method allows an increase of the amplitude of the speed signals more than ten times with respect to normal eccentricities, without affecting the normal operation of the machine. With this method, and using only one eccentricity per pole, it has been shown that it is possible to measure speeds as low as 11 rpm. Adding more than one eccentricity per pole, it is possible to measure even lower speeds. Simulations and experimental results permit comparison of this new method with methods which use only normal eccentricities