A simple speed computation method for DFIM without measurements on rotor side

Abstract

A unique rotor speed computation method for a Doubly-Fed Wound Rotor Induction Machine (DFIM) without the need for any measurements on the rotor side including the rotor position, is proposed in this paper. The scheme is effective even under unbalanced supply conditions. The rotor speed is computed using easily measurable stator voltages and currents. The rotor currents are computed analytically using the measured stator voltages and currents, and computed position of the stator voltage vector from a stator side (PLL), avoiding intermediate transformations. Further, starting on the fly, improved immunity to machine parameter variation, accurate computation through the synchronous speed are the other advantages. Further, there is no need for integration of voltage or flux or heuristic mathematical calculations. The efficacy of the proposed method is validated viz. simulations using PSCAD/EMTDC and experimentations.