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In this paper, an improved speed sensorless control method including the maximum power point tracking (MPPT) algorithm for grid-connected squirrel-cage induction generator (SCIG) wind turbine systems using modified reduced-order generalized integrator (ROGI)–frequency-locked loop (FLL) with the DC offset compensation capability is proposed. The rotor flux linkages are estimated by the modified ROGI-FLL-based observer, of which the inputs are d-q axis rotor EMFs, and hence the position of rotor flux linkage can be obtained directly based on these estimated flux linkages using the arc tangent function. The DC offset in the estimated rotor flux linkages, which can cause oscillations in estimated rotor speed, leading to oscillations in SCIG stator active power due to power signal feedback (PSF)-MPPT algorithm, can be significantly reduced using the DC offset compensators included in modified ROGI-FLL structure. Moreover, the negative effects of high-frequency components on the performance of the rotor flux linkage estimation can be remarkably mitigated owing to the excellent high-frequency component rejection capability of ROGI. The dynamic response analysis of the modified ROGI-FLL with DC offset compensators is provided as well. The feasibility of the proposed method has been demonstrated in comparison with dual SOGI-FLL with DC offset compensator-based existing method. [ABSTRACT FROM AUTHOR]

In this article, an improved grid synchronization method for three-phase grid-feeding converters using a dual enhanced second-order generalized integrator (eSOGI) frequency-locked loop (FLL) is proposed. The eSOGI, of which gains can be adjusted based on the positive-sequence component of the grid voltage, is designed to estimate the grid voltage accurately. Moreover, to improve the grid frequency estimation under grid voltage sags, frequency rate limits is suggested in the FLL structure. The selection of the eSOGI-FLL parameters is described as well. After the estimated grid voltages are obtained using the dual eSOGI-FLL, they are used to synthesize the references in the dual-current controllers for positive- and negative-sequence components. Through the simulation and experimental results under grid voltage sags and distorted grid conditions, the improved power control performance of the proposed method has been demonstrated in comparison with those of the existing methods. [ABSTRACT FROM AUTHOR]

In this article, a novel sensorless control scheme for doubly fed induction generator (DFIG) wind turbine systems based on the second-order generalized integrator (SOGI) and rotor position correction (RPC) is proposed. The rotor speed can be estimated from the SOGI structure with the inputs of the measured rotor currents and the grid frequency. Since the SOGI has the characteristic of the adaptive filter, the accurate estimation of rotor speed can be achieved despite the harmonics in the measured quantities. The RPC uses the SOGI outputs and the rotor currents, which are found based on the measured stator currents and voltages, to eliminate the estimated rotor position error. The effects of parameter variation on the estimation are investigated as well. The simulation and experimental results have verified the validity of the proposed method under the wind speed fluctuations and adverse grid conditions. [ABSTRACT FROM AUTHOR]