An FFT-based novel approach to noninvasive speed measurement in induction motor drives

A novel sensorless speed detection method based on the fast Fourier transform (FFT) spectral analysis is described. The main concern is the extraction of the speed information contained in the rotor slot-ripple harmonics created in the airgap of the induction motor using digital signal-processing techniques. A nonintrusive all-digital speed detector suitable for steady-state operation has been designed around an Intel/80386-based microcomputer equipped with a 80387 coprocessor. The detector performance with and without load over a wide range of speeds is described.<
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