A comparison of spectrum estimation techniques for sensorless speed detection in induction machines

This paper compares digital spectrum estimation techniques which can be used to extract speed information from rotor slot and eccentricity harmonics contained in the stator current. In previous work, the speed-related current harmonics have been shown to improve the performance of existing back EMF-based sensorless schemes, since they are parameter-independent and exist at virtually any nonzero speed. Digital filtering, however, requires a minimum data sampling time in order to achieve the desired resolution. The contribution of this paper is to determine the optimal method for accurately extracting the speed-related harmonics in the least amount of time. Several digital signal processing algorithms are investigated, including the fast Fourier transform and other traditional methods, as well as parametric techniques such as linear predictions. Each approach is evaluated on the criteria of accuracy, robustness and computation time given a short data record