Decoupled Power Control of Doubly-Fed Induction Generator Based on an Implicit Position and Speed Estimation Algorithm without the Flux Computation

Abstract

Owing to the increased attention on the need for deployment of renewable energy sources such as the wind energy, there is a growing interest in Doubly Fed Induction Generators (DFIG) which are suitable for variable speed constant frequency generation. Accurate information of the rotor position with respect to the stator is central to the effective decoupled control of real and reactive power in the DFIG. Typically sensorless estimation of the rotor position involves complex signal processing. This paper presents the implementation of a simple and implicit sensorless algorithm for estimating the rotor position and speed for decoupled control of the doubly-fed induction generator. The proposed algorithm does not involve the computation of stator magnetic flux directly or indirectly using the voltage integration, recursive techniques, re-computations or programmable low pass filters etc. Instead, it employs simple analytical equivalents for the resolved components of the stator flux which are derived from the basic equations governing the machine operation. Since the flux terms are replaced with other equivalent terms, the estimation process is devoid of computing any flux terms and requires only the measured stator voltage and the currents in stator and rotor windings apart from the machine parameters. Starting on the fly, accurate estimation near synchronous speed, immunity against variation in stator and rotor resistances or in the magnetizing inductance are the principal advantages of the algorithm. Reduced complexity and the computational burden facilitate the easy implementation of the algorithm on a low cost fixed point processor. Excellent agreement between the simulation and test results on a laboratory doubly-fed induction machine validates the proposed estimation algorithm. Further MATLAB/Simulink based simulation results are presented to validate the efficacy of the position estimation algorithm based vector control of a doubly-fed induction generator.