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Rotor speed estimation in electrical drives via digital second order sliding differentiator

The rotor speed estimation problem in electrical drives, based on shaft encoder measurements, has been dealt with by means of a digital approximate differentiator. The proposed differentiator is based on a digital VSC which is able to perform real 2-sliding modes, so that the observer discontinuous control is confined to the second total derivative of the available encoder signal estimate, and its first derivative is then continuous. Simulation and experimental results, conducted on a field oriented induction motor drive, show the good behaviour of the proposed approximate differentiator, which has been compared with the Matlab-Simulink differentiator algorithm by using a DSP-based system.