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This paper proposes a simple yet versatile rotor position computation algorithm (RPCA) for the rotor position and speed of a doubly fed induction machine. The rotor position is computed in a straightforward manner obviating the need for estimation. The resolved components of stator flux vector are computed using measurable stator and rotor quantities. Although it is an open-loop technique, it does not involve integration, recursive techniques, recomputations or programmable low-pass filters, etc. Starting on the fly, accurate computation near and through the synchronous speed, immunity against fluctuations in the grid voltage, and frequency are the other advantages of the algorithm. Reduced complexity and the computational burden facilitate the easy implementation of the algorithm on a low-cost fixed-point processor. Furthermore, unlike most techniques reported so far, there is no need to assume a constant stator flux since the algorithm is versatile to allow for variations in the grid or stator flux. For the purpose of verification, the proposed RPCA, employed in decoupled power control, is implemented for the laboratory test bench with a 3-hp doubly fed induction generator (grid-connected) system and a TMS320LF2407A DSP controller. The efficacy of the algorithm is demonstrated through the extensive experimental results. Overall, the very encouraging results endorse the proposed algorithm.
Date of Publication: Sept. 2012