Non-invasive slip measurement of induction motors

The paper deals with the accurate slip measurement of induction motors. The proposed procedure uses a non-invasive slip measurement scheme based on digital filtering and dynamic parameter estimation. The slip measurement is carried out without a speed sensor and is deduced utilizing the magnetic field in proximity of the induction motor. First the waveform of the induced e.m.f., taken from a search coil, is filtered using algorithms based on the discrete Fourier transform. Then the stator frequency and rotor frequency are obtained by comparing the filtered voltage with a mathematical model using an optimization procedure. The model´s parameters are varied until an adequate match is obtained with the filtered voltage. Experimental results are presented to validate this method