The use of the modified Prony´s method for rotor speed estimation in squirrel cage induction motors

It is well known that rotor speed estimation assumes a paramount importance for the correct diagnosis of bearings, air-gap eccentricities or rotor bar defects. In this paper, a new technique for rotor speed estimation using a modified Prony´s method is proposed. The algorithm developed for this purpose, is based on tracking the frequencies of the rotor slot harmonics (RSH) which exist in stator currents of most squirrel cage induction motors. High order RSH are used in order to avoid possible effect of harmonics stemming from other sources. The proposed modified Prony´s method shows a great ability for tracking RSH frequencies and then the rotation speed. In addition, this technique can deal with non stationary signals and it requires only few data samples which reduce considerably the computational time and data storage requirements. Consequently, the proposed algorithm is suitable for online implementation. The method´s efficiency is verified by simulation and experimental tests.