Sensorless speed measurement of induction motor using Hilbert transform and interpolated fast Fourier transform

A new scheme based on the Hilbert transform and the interpolated fast Fourier transform (IFFT) is proposed to improve the estimation accuracy of induction motor speed from motor current signals. The phase and amplitude fluctuation associated with the eccentricity harmonics is first demodulated by the Hilbert transform. IFFT is then performed to estimate the speed of induction motors running under constant speed and transient conditions. Simulations have shown considerable improvement in estimation accuracy using IFFT as compared to the FFT technique. An experimental study has further confirmed good agreement between the estimated motor speed using the proposed scheme and the measured speed using an encoder.