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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. [ABSTRACT FROM AUTHOR]

As the wind energy is progressively pursued to supplement conventional power generation, the stochastic wind behavior considerably deteriorates power quality (PQ) and stability of the connected grid. This article is attributed to the comprehensive control design of the grid-integrated doubly fed induction generator (DFIG) wind energy system that aims to address encountered wind variability and PQ intricacies. Battery energy storage with bidirectional dc–dc converter control is assimilated at the dc-link of the DFIG that regulates the dc-link voltage to mitigate the wind power fluctuations in specified grid power modes. A higher order adaptive control for grid-interfaced converter accurately computes desired weights of various components to exercise accurate power balance and PQ control. Moreover, a novel Jaya particle swarm optimization algorithm is adopted for the optimal tuning of wind maximum power point tracking and the dc-link voltage PI controller parameters that significantly improves steady-state and dynamic responses of both the controllers. The rotor speed converges faster with precise reference tracking that leads to almost zero steady-state error using optimized PI controller gains. Along with the attenuated initial overshoot and fast settling time during sudden large step wind speed change, the dc-link voltage also characterizes superior response with optimal tuning during load unbalance and abnormal grid voltage conditions. The presented control strategy analyzes the capability of DFIG system under variable wind-speed changes, specified grid power modes, load changes, and other grid disturbances. The satisfactory system response is endorsed through experimental results conducted on a laboratory prototype. [ABSTRACT FROM AUTHOR]

This article focusses on power quality issues related with the operation of a wind energy conversion system employing a doubly fed induction generator (DFIG), integrated with a solar photovoltaic array, under unbalanced, and distorted grid conditions. The multiple-order DFIG electromagnetic torque ripples and grid active power ripples, resulting from the unbalanced and distorted grid, can be mitigated, however, at the cost of highly unbalanced and distorted currents. This article provides a possible solution towards a tradeoff by developing a flexible ripple minimization technique based on a cross-feedback extended second order generalized integrator for harmonics sequence separation (CextSOGI-HSS). The CextSOGI-HSS based current compensation enables a controlled minimization of ripple as per the customizable flexibility quotient. Furthermore, the current compensation technique employs an improved recursive least squares (IRLS) adaptive filtering algorithm for processing DFIG stator currents and local load currents. The IRLS algorithm improves grid currents harmonics spectra by filtering-out higher order harmonics from DFIG stator currents and nonlinear load currents, meanwhile, the effects of any load or stator currents unbalance on grid currents are also mitigated. Test results from a developed laboratory prototype confirm the efficacy of the presented flexible ripple minimization control technique. [ABSTRACT FROM AUTHOR]

This article presents a simplistic control approach and multimode operation of a wind-solar-based ac/dc microgrid. The islanded microgrid consists of a doubly-fed induction generator (DFIG) for wind energy conversion, and a solar photovoltaic array for solar energy conversion. In this configuration, the stator terminals of DFIG are connected at the point of common intersection (PCI) of ac loads via a stator-side solid-state transition switch (SSSTS). The developed control strategy is designed to seamlessly disconnect and reconnect the DFIG stator from the PCI based on the SSSTS operation, without interrupting power to ac and dc loads in the microgrid. The disconnection of stator terminals is required in the event of a prolonged period of no wind generation from the DFIG. The controller is synthesized to ensure no or low transient effect during the transition between the two operating modes, i.e., DFIG stator connected mode (SCM) and stator disconnected mode (SDM). Further, the power quality enhancement of stator voltages and currents amidst nonideal ac loads is ensured without need for computationally exhaustive approaches involving sequence decompositions, notch filters, resonant regulators, or load current sensors. Moreover, the power quality enhancement at the DFIG stator is achieved without injecting any undue harmonics in the DFIG rotor currents. The effectiveness of this islanded microgrid is verified through obtained results from a developed laboratory prototype. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Unbalanced grid voltages, appearing at stator terminals of a doubly fed induction generator based wind energy conversion system, deteriorate its performance by instigating unwanted oscillations and distortions in output grid power and rotor currents, respectively, as well as by introducing unbalanced currents in the stator and the grid. This article aims to address these challenges using a coordinated control strategy based on an improved reduced order generalized integrator (IROGI) for positive and negative sequence estimation (PNSE). The IROGI–PNSE further enhances the control performance by eliminating the effects of dc component or unbalance in sensed voltages, on the grid synchronization. The coordinated control strategy uses hysteresis scheme for current control. The hysteresis-based current control requires fewer rotational transformations, and eliminates the need for PI/PIR regulators and notch filters for inner current control loops. This renders the control, computationally efficient. Moreover, the presented system is equipped to exhibit wind power leveling functionality through a battery energy storage. An approach, employing the region-specific wind speed frequency distribution graph, is utilized to constitute the power leveling operation modes. The effectiveness of the control scheme is demonstrated through test results on a prototype developed in the laboratory. [ABSTRACT FROM AUTHOR]