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In this paper, the active front-end (AFE) converter topology for the total harmonic distortion (THD) reduction in a wind energy system (WES) is used. A higher THD results in serious pulsations in the wind turbine (WT) output power and several power losses at the WES. The AFE converter topology improves the capability, efficiency, and reliability in the energy conversion devices; by modifying a conventional back-to-back converter, from using a single voltage source converter (VSC) to use pVSC connected in parallel, the AFE converter is generated. The THD reduction is achieved by applying a different phase shift angle at the carrier of digital sinusoidal pulse width modulation (DSPWM) switching signals of each VSC. To verify the functionality of the proposed methodology, the WES simulation in Matlab-Simulink® (Matlab r2015b, Mathworks, Natick, MA, USA) is analyzed, and the experimental laboratory tests using the concept of rapid control prototyping (RCP) and the real-time simulator Opal-RT Technologies® (Montreal, QC, Canada) is achieved. The obtained results show a type-4 WT with a total output power of 6 MVA, generating a THD reduction up to 5.5 times of the total WES current output by Fourier series expansion.

In this paper, an adaptive sliding mode speed control algorithm with an integral-operation sliding surface is proposed for a variable speed wind energy experimental system. In the control design, an estimator is designed to compensate for the uncertainties and the unknown turbine torque. In addition, the bound of the sliding mode is investigated to deal with uncertainties. The stability of the system can be guaranteed in the sense of the Lyapunov stability theorem. The laboratory size DC generator wind energy system is controlled using a buck-boost DC-DC converter interface. The control system is validated by experimentation and results demonstrate the achievement of favorable speed tracking performance and robustness against parametric variations and external disturbances.

Recent developments and trends in the electric power consumption indicate an increasing use of renewable energy. Renewable energy technologies offer the promise of clean, abundant energy gathered from self-renewing resources such as the sun, wind, earth and plants. Virtually all regions of the world have renewable resources of one type or another. By this point of view studies on renewable energies focuses more and more attention. The present paper intends to present different mathematical models related to different types of renewable energy sources such as: solar energy and wind energy. It is also presented the validation and adaptation of such models to hybrid systems working in geographical and meteorological conditions specific to central part of Transylvania region. The conclusions based on validation of such models are also shown.

Urban built environments have grown dramatically worldwide in the past few decades due to rapid economic and population growths. The potential utilization of renewable resources is highly desirable for a healthy urban environment. Hence, urban wind energy exploration has captured increasing attention from urban planners, architects, engineers, and researchers for the sustainable growth of urban environments and the well-being of urban dwellers. Advances in technologies in the design and installation of wind energy systems in buildings are paving the way to enhance wind energy generation in urban environments. This article presents a perspective of wind energy exploration based on building and urban aerodynamics. In particular, this article presents a review of current developments of wind energy systems in the built environments, factors affecting urban wind flow and resulting consequences, examples of recent designs of urban/building-based wind energy systems, including building integrated vertical axis wind turbine, power window, wind-induced vibration-based wind energy harvesters, double skin and other innovative building façade systems, and wind source exploration. The potential application of Artificial Intelligence (AI) and Machine Learning (ML) in the context of wind engineering and wind energy system is also presented. • This paper presents comprehensive review on wind energy system in urban environment. • It reviews current developments of wind energy systems in urban environment. • It summarizes factors affecting performance of wind energy system. • It provides outlook of future development of urban wind energy system. [ABSTRACT FROM AUTHOR]

Power management in a grid-integrated power system consisting of distributed renewable energy sources is necessitated by ever-increasing energy consumption, the high cost of production, the limited resource of fossil fuel, and the worsening global environment. Wind and solar power generation are two of the most promising renewable power generation technologies. The growth of wind and photovoltaic (PV) power generation systems has exceeded the most optimistic levels of expectations. Fuel cells (FCs) also have great potential to be green power sources of the future because of the many merits they have, such as high efficiency and zero or low emission of pollutant gases. In this paper the modeling, control, and analysis of grid-connected PV power, a proton exchange membrane fuel cell (PEMFC), and a wind energy system (WES) connected through a common DC bus linked to an AC grid is discussed. In coordination with the PEMFC, the hybrid system's output power becomes controllable so that full utilization of PV and wind power takes place based on its availability, and the DC bus voltage is maintained constant even at varying load conditions for the desired power sharing between the distributed generation (DG) sources, load, and the AC grid. The hybrid system is controlled through a combination of two proposed control modes, namely the DG control mode and grid control mode. The coordination of the power controller, voltage source converter controller, and load controller is such that the transition between the two control modes is done as smoothly as possible. Thus, the total DG power will be a combination of PV power, WES power, and power produced by the PEMFC. Any additional power if required up to the maximum loading will be supplied by grid. If the load exceeds its maximum value, then the load controller will carry out load shedding. The composite system is available for safe operation in on-grid as well as off-grid mode satisfying voltage and power balance constraints. Different modes of operation have been demonstrated to verify and validate the desired power management among the DG sources, load, and the grid. MATLAB/Simulink software was used for simulating the composite model. [ABSTRACT FROM AUTHOR]

This paper presents a robust controller for a variable speed wind turbine with a squirrel cage induction generator (SCIG). For variable speed wind energy conversion system, the maximum power point tracking (MPPT) is a very important requirement in order to maximize the efficiency. The system is nonlinear with parametric uncertainty and subject to large disturbances. A Takagi-Sugeno (TS) fuzzy logic is used to model the system dynamics. Based on the TS fuzzy model, a controller is developed for MPPT in the presence of disturbances and parametric uncertainties. The proposed technique ensures that the maximum power point (MPP) is determined, the generator speed is controlled and the closed loop system is stable. Robustness of the controller is tested via the variation of model's parameters. Simulation studies clearly indicate the robustness and efficiency of the proposed control scheme compared to other techniques. [ABSTRACT FROM AUTHOR]

Hydrogen can be stored, transported and used in a large number of applications in which fossil fuels are currently used. From a sustainable point of view, the synergy existing between hydrogen and renewable energy sources shows great potential. In this respect, hydrogen can be produced from water electrolysis using the electricity generated by renewable systems. This paper studies the integration of a 1 Nm 3 h −1 alkaline water electrolyser with photovoltaic solar energy (PVE) and wind energy (WE) in a stand-alone system. In particular, a one year energy balance of the conventional integration of the electrolyser with PVE and WE is carried out. To do so, actual weather data are used for irradiance, ambient temperature and wind speed, in addition to the technical specifications and characteristics of a 6.8 kWp PV generator and a 6 kW wind turbine. This energy evaluation reveals the main limitations of commercial electrolysers, such as the lower operating limit and the number of stops permitted by manufacturers. Two strategies are therefore proposed to improve the integration of conventional electrolysers, namely to allow the electrolyser to operate for a period of 10 min under the lower operating limit and to integrate a battery bank. Both strategies achieve successful results, with a reduction in the number of stops by up to 62.1% for the PVE integration and 63.1% for the WE, which should increase the electrolyser service life, and an increase in energy efficiency by up to 6.3% for the PVE integration and 7.6% for the WE. [ABSTRACT FROM AUTHOR]

In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min − 1 is studied. Specifically, a fault tolerant control (FTC) scheme is proposed to keep the turbine in operation in the presence of up to four simultaneous generator faults. The proposed controller structure consists of two layers: The upper layer is the baseline controller, which is separated into a partial load region with the generator torque as an actuating signal and the full-load operation region with the collective pitch angle as the other actuating signal. In addition, the lower layer is responsible for the fault diagnosis and FTC characteristics of the distributed generator drive train. The fault reconstruction and fault tolerant control strategy are tested in simulations with several actuator faults of different types.

• A new data-driven model for the wind power probabilistic prediction at any resolution in a horizon is developed. • An attention-assisted ordinary differential equation network based modeling method is proposed. • A new two-stage training process is introduced for the proposed data-driven modeling process. • Developed model predicts quantiles of the future wind power with addressing quantile-crossing issues. To improve the practicality, data-driven techniques of predicting the wind power generation and its uncertainty still need to address three technical challenges, uplifting the prediction accuracy via inventing an emerging data analytics mechanism, flexibly scaling up the prediction resolution from the data sampling resolution, and preventing invalid probabilistic prediction results. This study is thus motivated to investigate an advanced prediction method enabling highly accurate and valid probabilistic wind power predictions as well as the capability of a resolution scale-up. The long short term memory (LSTM) network combined with an attention-assisted ordinary differential equation network (AODEN), LSTM-AODEN, is developed for the first time in the literature to produce a novel deep network architecture for probabilistic wind power predictions via leveraging advantages of deep learning and ordinary differential equations. In the LSTM-AODEN, a two-stage training scheme, which sequentially develops one median prediction model and one multi-interval length prediction model, is proposed to fully eliminate quantile crossings and guarantee the validity of prediction results. Six evaluation metrics in computational experiments verify that the proposed LSTM-AODEN method leads to overall highly accurate and fully valid results of the point prediction, interval prediction, and quantile prediction compared to several classes of state-of-the-art probabilistic prediction methods. Meanwhile, the proposed method is proved to offer a unique capability of generating higher-resolution probabilistic wind power prediction results, which is gained from the AODEN, indicated by the lowest prediction errors. [ABSTRACT FROM AUTHOR]

A sliding mode voltage control strategy is proposed in this paper to capture the maximum electrical energy from wind. This control strategy mainly includes a fuzzy logic controller and a sliding mode voltage controller. The fuzzy logic controller is designed to derive the optimum DC-side voltage, while the sliding mode voltage controller is employed to track the derived optimum voltage with minimum steady-state error and hence to capture the maximum wind energy. This paper illustrates how major issues in the design and implementation of the two controllers can be handled effectively. Comparative experimental results demonstrate that significant performance improvements in maximum wind energy capture can be achieved by using the proposed control strategy. [ABSTRACT FROM AUTHOR]

With the rapid growth of the wind energy systems in the past years and their interconnection with the existing power system networks, it has become very significant to analyse and enhance the transient stability of the wind energy conversion systems connected to the grid. This study investigates the transient stability enhancement of a grid‐connected wind farm using doubly‐fed induction machine‐based flywheel energy storage system. A cascaded adaptive neuro‐fuzzy controller (ANFC) is introduced to control the insulated gate bipolar transistor switches‐based frequency converter to enhance the transient stability of the grid‐connected wind farm. The performance of the proposed control strategy is analysed under a severe symmetrical fault condition on both a single‐machine infinite bus model and the IEEE‐39 bus New England test system. The transient performance of the system is investigated by comparing the results of the system using the proposed ANFCs with that of the black‐box optimisation technique‐based proportional–integral controllers. The validity of the system is verified by the simulation results which are carried out using PSCAD/EMTDC environment. [ABSTRACT FROM AUTHOR]

A novel fuzzy integral sliding mode current control strategy is proposed to extract the maximum wind power and eliminate the high-order voltage harmonics at the generator side for a direct-driven wind energy system. In this control strategy, a fuzzy logic generator is employed to derive the peak power points based on the variations of measured DC-side voltage and current. An integral sliding mode current controller is then designed in this control strategy to track the peak power points. A harmonic compensator is also built inside the fuzzy logic generator for minimizing the voltage harmonics. Major issues in the design and implementation of the control strategy such as detailed design procedure and stability condition have been presented. Comparative experimental results have demonstrated the achievable significant improvements on the maximum power extraction and harmonic elimination by using the proposed control strategy as compared with a conventional control method. [ABSTRACT FROM AUTHOR]

—In this article, a novel control strategy is proposed to exploit the full capability, in terms of active filtering, of a wind energy conversion system based on a doubly fed induction generator. To achieve control of the wind energy conversion system, the rotor of the doubly fed induction generator is connected to the grid through a back-to-back pulse-width modulation converter. The proposed algorithm is applied to the rotor-side converter to ensure simultaneous active power production and power quality improvement. Depending on the nominal rotor-side converter power, the control strategy manages the wind energy conversion system function priorities between active power production, reactive power compensation, and current active–selective filtering without any system overrating. This study's main goal is to exploit the full capability of the rotor-side converter in terms of active and selective filtering. In fact, it is proposed to eliminate the whole harmonic currents if possible, or to compensate the fifth and the seventh predominant components and a part of the rest of the harmonic currents. Otherwise, one may filter a part of these two predominant harmonics in such a way that the rotor-side converter operates at its full capacitance. Simulation results demonstrate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper introduces an accurate procedure to choose the best site from many sites and suitable wind turbines for these sites depending on the minimum price of kWh generated. In this paper, a new proposed computer program has been introduced to perform all the optimization required to determine the size of the wind energy system for pairing between sites and wind turbines. Cost calculation method of energy has been introduced to determine the price of kWh generated from wind energy system. The data for five sites in Saudi Arabia and hundred wind turbines have been used as input data for the proposed computer program. These sites are Yanbo, Dhahran, Dhulom, Riyadh, and Qaisumah. This program is built in a generic form which allows it to be used with unlimited number of sites and wind turbines in all over the world. The salient results from this study are: Dhahran is the best site and the suitable wind turbine for this site is KMW-ERNO with 5.85 Cents/kWh, and the worst site to install wind energy system is Riyadh with minimum price of 12.81 Cents/kWh in case of using GE Energy 2 wind turbine. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to present an approach on optimizing the design of the omni-direction-guide-vane (ODGV) in order to maximise the performance of the vertical axis wind turbine (VAWT). An analytical model had been developed based on the continuity equation for assessing the impact of each design parameter of the ODGV to the VAWT performance. A 2-level full factorial design was further utilized for the verification of analytical findings with the aid of computational fluids dynamics (CFD) simulation. Three parameters, i.e. two guide vanes angles (θ and β) and ratio of VAWT diameter to distance between two guide vanes (b) were selected for the initial design of experiment (DOE) screening process. A total of 9 cases which include one centre point per block had been setup in CFD simulation. The DOE results suggested that the optimum point exists at the corner point (not at center point). Meanwhile, it was also pointed that strong interaction effect can be seen in θ with β, θ with b and β with b. It is worth to highlight that the analytical model overestimates the performance at larger θ since only one dimension steady flow is assumed. [Copyright &y& Elsevier]

The extraction of wind energy has been essential to fulfill the load demand which is not supplied by conventional sources at the end of 2012. In India, total capacity of wind power is very high, approximately 102,788 MW, in comparison to installed capacity. This paper reviews different permanent magnet synchronous generator (PMSG) operated in wind energy systems. A complete survey has been made towards the new contributions for harmonic compensation and new efficient topologies in the last five years to improve the efficiency, reliability and cost of the wind energy system. Different power electronic converters, which are connected between generator and the load/ grid, have been investigated on based on harmonic compensation, efficient working, and high power rating conversion. The wind generation system is still a challenge to extract smooth power from wind. To improve the power quality of the system such as islanding problem and power variation, different renewable storage systems are discussed and compared. Finally, discussion about the different controller is presented to fulfill the load or grid requirement. [ABSTRACT FROM AUTHOR]

The operation of wind‐driven single inverter‐battery‐assisted slip‐ring induction generator (SRIG) for stand‐alone power supplies has been proposed. For effective utilisation of wind energy, the proposed system will function as doubly fed induction generator (DFIG) or shorted stator induction generator (SSIG) depending upon the ac load requirement and available wind power, operating in four different modes. A method has been developed for the performance predetermination of such system. A supervisory control algorithm has been devised and implemented using TMS320LF2407A real time digital signal processor for the closed‐loop control of the proposed system. In this control algorithm, reliable and unambiguous feedback signals such as stator voltage, stator current and user command are used for decision making and for closed‐loop operation. The entire closed‐loop system with supervisory control algorithm has been tested in the laboratory with a 3.7 kW SRIG. The successful working of the proposed system with smooth changeover between the operating modes has been demonstrated with extensive experimental and simulation results. The advantage of the proposed wind energy system has also been brought out in comparison with classical back to back converter DFIG system for stand‐alone power supplies. [ABSTRACT FROM AUTHOR]

Abstract: The doubly fed induction generators (DFIGs) are preferred over other variable speed generators because of their advantages in terms of economy and control. One of the problems associated with high wind power penetration DFIG systems, however, is the inability of their converters to work properly under extreme low voltage conditions. This article presents a decoupled P–Q control strategy of a supercapacitor energy storage system, interfaced through a STATCOM, for low voltage ride through as well as damping enhancement of the DFIG system. The STATCOM meets the reactive power need under the depressed voltage condition, while the supercapacitor caters to the real power unbalance. An extensive dynamic model of the DFIG system including a supercapacitor DC–DC buck–boost converter and the STATCOM circuit has been developed. The fault ride-thorough capability of the generator has been investigated for a severe symmetrical three-phase to ground fault on the grid bus. Simulation results suggest that the proposed decoupled control of the supercapacitor STATCOM control strategy can help the DFIG ride through extreme low voltage conditions for significant duration. The proposed control strategy also damps the electromechanical transients, and thus quickly restores normal operation of the converters. [Copyright &y& Elsevier]

Abstract: Utilization of renewable energy resources appears to be one of the most efficient and effective ways in achieving sustainable development, that is now widely seen as important to worldwide public opinion. Among renewable energy sources, wind energy, which is a free, clean, and renewable source of energy, which will never run out, plays a big role. In this context, a number of studies on the efficient utilization of wind energy resources have been conducted by various investigators to attain sustainable development. Most of them have included their energetic aspects, while the number of studies conducted on their exergetic and exergoeconomic directions is relatively very low. In recent years, exergy, which is a means to sustainable development, has become a very effective tool in evaluating system effectiveness and in designing the system to maximize energy savings. Exergoeconomic analysis, which is a combination of exergy and economics, is also nowadays considered a powerful tool to study and optimize various types of energy-related systems. The present study comprehensively reviews the studies conducted on exergetic and exergoeconomic analysis and assessment of wind energy systems and suggests possible future works to be performed for the first time to the best of the authors’ knowledge. In this regard, an introductory information is given first. Next, wind energy systems exergetically and exergoeconomically analyzed and evaluated are presented and shortly described. The previously conducted studies on these systems are then reviewed and classified in the tabulated forms. Finally, the conclusions drawn are presented. It is expected that this comprehensive contribution will be very beneficial to everyone involved or interested in the energetic, exergetic and exergoeconomic design, analysis and performance evaluation of wind energy systems. [Copyright &y& Elsevier]

Abstract: A dynamic model of a variable speed stand alone wind generation system is developed. The transient performance of the system under variable wind gust and other disturbance conditions has been studied. It has been observed that a stand alone generator is very vulnerable to transient disturbances in the system. A variable susceptance excitation control system, installed at the generator terminal, has been shown to improve the dynamic performance of the system following transient disturbances. Additional pole-placement based PI and PID controllers in the excitation control circuit are shown to control the violently oscillating and even growing transients very effectively. The robustness of the proposed controller has been tested for various disturbances and also for a range of operation. [Copyright &y& Elsevier]

This paper gives an overview of the potential on multi-criteria assessment of hydrogen systems. With respective selection of the criteria comprising performance, environment, market and social indicators the assessment procedure is adapted for the assessment of the selected options of the hydrogen energy systems and their comparison with new and renewable energy systems.The single parameter assessment for each indicator is demonstrated as the traditional approach in the evaluation of the option under consideration which reflects a biased result depending on the selected indicator. In order to apply the multi-criteria approach to the hydrogen systems, it was necessary to use the multi-criteria procedure based on the sustainability index rating composed of linear aggregative functions of all indicators with respective weighting function.The example under consideration are hydrogen fuel cell systems with three options including natural gas turbine, photovoltaic and wind energy systems representing different renewable power plant option. These options are evaluated with the multi-criteria method comprising the following indicators: performance indicator, market indicator, environment indicator and social indicator. The indicators are composed of a number of sub-indicators agglomerated in respective indicators. The evaluation of options under consideration was performed under constraint expressing non-numeric relation among the indicators. The group comprises cases when priority is given to a single indicator and other indicators have the same value. [Copyright &y& Elsevier]

Increasing power demands require multiple generating units interconnected with each other to maintain the power balance of the system. This results in a highly dense power system consisting of multiple generating units which coordinate with each other to maintain the balanced performance of the system. Among different energy sources, the thermal source, the hydro energy source, the photovoltaic system, and the wind energy source are the most popular ones. Researchers have developed several optimization problems in the literature known as dispatch problems to model the system consisting of these different types of energy sources. The constraints for each system depend upon the generation type and the nature of the objective functions involved. This paper provides a state-of-the-art review of different dispatch problems and the nature of the objective functions involved in them and highlights the major constraints associated with each optimization function. [ABSTRACT FROM AUTHOR]

Wind energy is an abundant renewable energy resource that has been extensively used worldwide in recent years. The present work proposes a new Multi-Objective Optimization (MOO) based genetic algorithm (GA) model for a wind energy system. The proposed algorithm consists of non-dominated sorting which focuses to maximize the power extraction of the wind turbine, minimize the cost of generating energy, and the lifetime of the battery. Additionally, the performance characteristics of the wind turbine and battery energy storage system (BESS) are analyzed specifically torque, current, voltage, state of charge (SOC), and internal resistance. The complete analysis is carried out in the MATLAB/Simulink platform. The simulated results are compared with existing optimization techniques such as single-objective, multi-objective, and non-dominating sorting GA II (Genetic Algorithm-II). From the observed results, the non-dominated sorting genetic algorithm (NSGA III) optimization algorithm offers superior performance notably higher turbine power output with higher torque rate, lower speed variation, reduced energy cost, and lesser degradation rate of the battery. This result attested to the fact that the proposed optimization tool can extract a higher rate of power from a self-excited induction generator (SEIG) when compared with a conventional optimization tool. [ABSTRACT FROM AUTHOR]

The insulated gate bipolar transistor (IGBT) is a crucial component of power converters (PCVs) and is commonly used in several PCVs topologies. On the other hand, the investigation and the study of the IGBT component show several changes within its behavior and lifetime, while this component is highly influenced by the operating conditions. Indeed, the monitoring of this component is necessary to minimize unexpected downtime of the wind energy system (WES). However, an accurate prediction of IGBTs remaining useful life (RUL) is the key enabler for life-time-optimized operation. Consequently, this work proposes a new prognostic approach for online IGBTs monitoring that adopts the time-domain analysis to extract useful information that is used as an input in the generation of the health indicator. Moreover, this approach is based on combining both of principal component analysis (PCA) technique and the feedforward neural network (FFNN) technique. PCA is used to reduce features extracted from IGBTs and the FFNN is implemented to achieve online regression of the trend parameter obtained from the PCA technique. To investigate and evaluate the performance of our idea we used the NASA Ames Laboratory Prognostics Center of Excellence IGBTs accelerated aging database. Finally, the achieved results clearly show the strength of the new trend parameter for IGBTs RUL prediction. The most notable strong correlation within the proposed approach is in relation to accuracy value, with an acceptable average accuracy rate of 60.4%. [ABSTRACT FROM AUTHOR]

• A cost-effective SFCL-based low-voltage ride-through (LVRT) scheme is proposed for wind turbine. • Cooperative operation of SFCL device and modified converters controls is presented for improving SFCL performance. • Provide a cost-effective solution to eliminatiing impact of grid voltage magnitude on LVRT enhancement of resistive-SFCL device. • Superconducting tape usage and capital cost of SFCL can be visibly reduced. • Preferable comprehensive performance with wider adaptability and better cost-effectiveness than traditional control-based scheme and SFCL device-based scheme. Series single-resistor based scheme (SSRBS) can achieve a favorable low-voltage ride-through (LVRT) enhancement, also has the advantages of low costs and complexity. Its basic idea is to increase the terminal voltage of wind turbine generator (WTG) during grid faults by inserting a series single-resistor into the grid-side circuit. However, traditional SSRBSs cannot tackle different grid voltage sag events due to the constant resistance of the inserted resistor. Besides, as a device-based scheme, the SSRBSs have weak cost-effectiveness especially, utilizing the superconducting fault current limiter (SFCL). To solve these problems, this paper proposes a cost-effective LVRT scheme by cooperating a resistive-type SFCL and two modified controls. In the cooperative scheme, a surplus power dissipating mechanism based on SFCL is designed, which provides a novel way for SFCL to improve LVRT capability. Moreover, modified reactive power control for WTG is proposed to ensure that SFCL can dissipate constant surplus power irrespective of grid voltage magnitude and to provide reactive power support. Additionally, another modified WTG control is proposed for assisting with the SFCL to dissipate surplus power, which reduces the tape usage and energy-loss of SFCL, thus improving cost-effectiveness. Several cases demonstrate the feasibility and superiority of this scheme. [ABSTRACT FROM AUTHOR]

This paper discusses the integration of wind energy system in Derna, Libya to the main grid of General Electricity company of Libya (GECOL) through a back-to-back converter. The machine side converter is used to regulate the AC and DC voltages while the grid side converter is used to control the active and reactive power supplied by the wind energy system. To achieve a relatively simple and decoupled control, the controllers are implemented in the QD reference frame. The proposed system is simulated using MatLab/Simulink environment. The simulation results show the rapid response of the control system in following the commanded active and reactive power commands and the robustness of the proposed system to the changes in operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, a systematic synchronization procedure is proposed for a doubly fed induction generator (DFIG) during unbalanced grid voltage conditions. The initial induced voltage at the open stator terminal is required to synchronize with the grid voltage in magnitude, frequency and phase. An open stator negative sequence rotor current controller is implemented with the conventional DFIG vector controller, which allows the induced stator voltage to become as unbalanced as the grid voltage, hence enabling a smooth connection. A brief comparison is provided for practical issues such as controller structure variation between DFIG open stator and normal operating conditions, and initial encoder rotor angle measurement offset. The procedure is validated experimentally on a 2.2 kW laboratory-scaled DFIG test bench. [ABSTRACT FROM AUTHOR]