Torque Of Doubly-fed Induction Generator Research Articles

Islanding Operation and Seamless Resynchronization in DFIG–SPV System Equipped With Functional Enhancements Through ATLLAD Control Framework

Doubly-fed induction generator (DFIG) and solar photovoltaic (SPV) array equipped hybrid wind-solar generation system is increasingly acknowledged as a viable techno-economic solution for remote-area electrification. Despite the progress made in this frontier, two major hurdles still persist. The first hurdle relates to the power inadequacy for local loads and the mode transitional features in DFIG-SPV system, during grid outages, which are rather frequent in remote-areas. Another issue in DFIG-SPV system at remote-areas is its functional vulnerability at the irregular grid conditions like unbalance and distorted voltages. Taking these aspects into consideration, this paper implements a new arc-tangent least logarithmic absolute difference (ATLLAD) based control framework for DFIG-SPV system. The operational scheme ensures disruption-free load power at islanding scenarios, while, the control strategy enables seamless transitions without inducing overcurrents or voltage spikes during mode switching. To deal with DFIG-side functional vulnerability at irregular grid conditions, ATLLAD-based control uses an innovative approach to impart an additional degree of freedom for the simultaneous suppression of DFIG torque oscillations and reduction in DFIG stator current disturbances. Meanwhile, the enhancement at the grid-side involves injection of improved quality grid currents despite the irregularities in the grid voltages and the load currents. Test results from an experimental-rig of the DFIG-SPV system illustrate satisfactory performance of ATLLAD control approach.

Normalized Maximum Correntropy Criterion Based Ripple Mitigation Strategy for Wind–Solar Hybrid Generation System Under Nonideal Grid Conditions

A doubly-fed induction generator (DFIG) integrated to a solar photovoltaic array for wind-solar hybrid power generation, exhibits large multiple-order ripples in DFIG torque as well as active and reactive grid powers, when subjected to a nonideal grid voltage scenario. In this context, this article aims to develop a ripple mitigation strategy based on a novel application of the normalized maximum correntropy criterion (NMCC). The NMCC-based strategy puts forth a comprehensive solution toward mitigating all the ripples emanating either due to voltage unbalance in the grid, or due to grid voltage distortions with both positive and negative sequences of any possible harmonic order. Additionally, the power ripples originating from unbalanced and nonlinear loads interfaced locally to the wind-solar hybrid system are also compensated. The strategy is devised to be parametrically robust and does not necessitate individual harmonics separation in either fluxes, voltages, or currents. Besides, need for inner loop PI, PR, or other complex regulators is also eliminated. Moreover, the control scheme is formulated as a modular structure to ensure distortion-less DFIG rotor currents and balanced-sinusoidal grid currents at nonideal voltages, even as the ripple mitigation loops are disabled. Experimental results from a laboratory test bench verify the effective operation of the NMCC-based control strategy.

Multi-Objective Control Strategy for Power Quality Improvement in Wind-Solar Distributed Generation System Under Harmonically Distorted Grid

Grid-interactive wind-solar distributed generation system (DGS) experiences substantial power quality (PQ) challenges pertaining to incessant voltage distortions in the utility grid and nonlinear loads at the point of common intersection. Such system non-idealities cause distortions in grid currents and infuse ripples in grid active and reactive powers. The effect of harmonically distorted voltages on DGS is further intensified in case of wind generation by means of a doubly-fed induction generator (DFIG), as its stator is directly coupled to the grid. Significant performance degradation with regard to distortions in DFIG currents, and ripples in stator power as well as DFIG torque, are observed. In this context, a control strategy, based on multiresonant higher order generalized integrator for harmonic estimation (MRHGI-HE) and a ϵ-normalized sign regressor least mean fourth (ϵ-NSRLMF) algorithm, for DGS employing solar photovoltaic array and DFIG-based wind generator, is presented in this article. Based on selected objective, the control approach puts-forth a feasible solution for alleviating the aforementioned PQ challenges. The MRHGI-HE provides improved harmonics estimation and superior disturbance rejection, than its conventional counterpart. Besides, ϵ-NSRLMF algorithm exhibits enhanced system dynamics, as compared with least mean fourth algorithm. The multiobjective control strategy is corroborated through extensive simulation and experimental studies, and results demonstrate the PQ improvements in the DGS.

Adaptive Fuzzy Control Scheme for Variable-Speed Wind Turbines Based on a Doubly-Fed Induction Generator

The purpose of this paper is to present a new adaptive fuzzy control scheme for grid-connected variable-speed wind turbines (WT) based on a doubly-fed induction generator (DFIG). The proposed controller simultaneously guarantees two independent control objectives: (1) DFIG torque control allowing the extraction of maximum available power from the wind, and (2) control of the stator reactive power to maintain a desirable power factor according to the grid requirements. Unlike many existing control designs developed for DFIG-based WT, the design of the proposed controller is based on nonlinear coupled models of WT, without attempting approximate linearization. To improve performance in operating conditions, the model uncertainties and the nonlinear functions appearing in the tracking errors dynamics are reasonably approximated by adaptive fuzzy systems. It is mathematically proven that the proposed adaptive fuzzy control scheme can guarantee that all signals of the closed-loop system are uniformly ultimately bounded. Simulation results show that the proposed control scheme has strong robustness against the system parameter variations and unstructured uncertainties.

Enhancement of demagnetization control for low-voltage ride-through capability in DFIG-based wind farm

Low voltage ride through (LVRT) is one of the most popular methods to protect doubly fed induction generator (DFIG) against balanced and unbalanced voltage dips. In this study, a novel LVRT capability strategy is enhanced using forcing demagnetization controller (FDC) in DFIG-based wind farm. Moreover, not only stator circuit but also rotor circuit were developed by electromotor force (EMF) for LVRT in DFIG-based wind farm. The transient stability performances of the DFIG with and without the FDC and EMF were compared for three- and two-phase faults. In addition to variations such as 34.5 kV bus voltage and terminal voltage of DFIG, speed of DFIG, electrical torque of DFIG and d-q axis rotor-stator current variations of DFIG were also evaluated. It was seen that the system became stable within a short time using the FDC and EMF.

Second-Order Sliding Mode Control of a Doubly Fed Induction Generator Driven Wind Turbine

This paper deals with power extraction maximization of a doubly fed induction generator (DFIG)-based wind turbine. These variable speed systems have several advantages over the traditional wind turbine operating methods, such as the reduction of the mechanical stress and an increase in the energy capture. To fully exploit this latest advantage, many control schemes have been developed for maximum power point tracking (MPPT) control schemes. In this context, this paper proposes a second-order sliding mode to control the wind turbine DFIG according to references given by an MPPT. Traditionally, the desired DFIG torque is tracked using control currents. However, the estimations used to define current references drive some inaccuracies mainly leading to nonoptimal power extraction. Therefore, using robust control, such as the second-order sliding mode, will allow one to directly track the DFIG torque leading to maximum power extraction. Moreover, the proposed control strategy presents attractive features such as chattering-free behavior (no extra mechanical stress), finite reaching time, and robustness with respect to external disturbances (grid) and unmodeled dynamics (generator and turbine). Simulations using the wind turbine simulator FAST and experiments on a 7.5-kW real-time simulator are carried out for the validation of the proposed high-order sliding mode control approach.