Research on Reactive Power Optimization of Offshore Wind Farms Based on Improved Particle Swarm Optimization

The lack of reactive power in offshore wind farms will affect the voltage stability and power transmission quality of wind farms.To improve the voltage stability and reactive power economy of wind farms,the improved particle swarmoptimization is used to optimize the reactive power planning in wind farms.First,the power flow of offshore wind farms is modeled,analyzed and calculated.To improve the global search ability and local optimization ability of particle swarm optimization,the improved particle swarm optimization adopts the adaptive inertia weight and asynchronous learning factor.Taking the minimum active power loss of the offshore wind farms as the objective function,the installation location of the reactive power compensation device is compared according to the node voltage amplitude and the actual engineering needs.Finally,a reactive power optimizationmodel based on Static Var Compensator is established inMATLAB to consider the optimal compensation capacity,network loss,convergence speed and voltage amplitude enhancement effect of SVC.Comparing the compensation methods in several different locations,the compensation scheme with the best reactive power optimization effect is determined.Meanwhile,the optimization results of the standard particle swarm optimization and the improved particle swarm optimization are compared to verify the superiority of the proposed improved algorithm.

Performance of the CMA-GD Model in Predicting Wind Speed at Wind Farms in Hubei, China

This study assesses the predictive capabilities of the CMA-GD model for wind speed prediction in two wind farms located in Hubei Province,China.The observed wind speeds at the height of 70m in wind turbines of two wind farms in Suizhou serve as the actual observation data for comparison and testing.At the same time,the wind speed predicted by the EC model is also included for comparative analysis.The results indicate that the CMA-GD model performs better than the EC model in Wind Farm A.The CMA-GD model exhibits a monthly average correlation coefficient of 0.56,root mean square error of 2.72 m s^(-1),and average absolute error of 2.11 m s^(-1).In contrast,the EC model shows a monthly average correlation coefficient of 0.51,root mean square error of 2.83 m s^(-1),and average absolute error of 2.21 m s^(-1).Conversely,in Wind Farm B,the EC model outperforms the CMA-GD model.The CMA-GD model achieves a monthly average correlation coefficient of 0.55,root mean square error of 2.61 m s^(-1),and average absolute error of 2.13 m s^(-1).By contrast,the EC model displays a monthly average correlation coefficient of 0.63,root mean square error of 2.04 m s^(-1),and average absolute error of 1.67 m s^(-1).

Two-stage ADMM-based distributed optimal reactive power control method for wind farms considering wake effects

Since the connection of small-scale wind farms to distribution networks,power grid voltage stability has been reduced with increasing wind penetration in recent years,owing to the variable reactive power consumption of wind generators.In this study,a two-stage reactive power optimization method based on the alternating direction method of multipliers(ADMM)algorithm is proposed for achieving optimal reactive power dispatch in wind farm-integrated distribution systems.Unlike existing optimal reactive power control methods,the proposed method enables distributed reactive power flow optimization with a two-stage optimization structure.Furthermore,under the partition concept,the consensus protocol is not needed to solve the optimization problems.In this method,the influence of the wake effect of each wind turbine is also considered in the control design.Simulation results for a mid-voltage distribution system based on MATLAB verified the effectiveness of the proposed method.

Grid Integration of Wind Generation Considering Remote Wind Farms:Hybrid Markovian and Interval Unit Commitment

Grid integration of wind power is essential to reduce fossil fuel usage but challenging in view of the intermittent nature of wind.Recently,we developed a hybrid Markovian and interval approach for the unit commitment and economic dispatch problem where power generation of conventional units is linked to local wind states to dampen the effects of wind uncertainties.Also,to reduce complexity,extreme and expected states are considered as interval modeling.Although this approach is effective,the fact that major wind farms are often located in remote locations and not accompanied by conventional units leads to conservative results.Furthermore,weights of extreme and expected states in the objective function are difficult to tune,resulting in significant differences between optimization and simulation costs.In this paper,each remote wind farm is paired with a conventional unit to dampen the effects of wind uncertainties without using expensive utility-scaled battery storage,and extra constraints are innovatively established to model pairing.Additionally,proper weights are derived through a novel quadratic fit of cost functions.The problem is solved by using a creative integration of our recent surrogate Lagrangian relaxation and branch-and-cut.Results demonstrate modeling accuracy,computational efficiency,and significant reduction of conservativeness of the previous approach.

Sub-synchronous frequency domain-equivalent modeling for wind farms based on rotor equivalent resistance characteristics

The equivalent simplification of large wind farms is essential for evaluating the safety of power systems.However,sub-synchronous oscillations can significantly affect the stability of power systems.Although detailed mathematical models of wind farms can help accurately analyze the oscillation mechanism,the solution process is complicated and may lead to problems such as the“dimensional disaster.”Therefore,this paper proposes a sub-synchronous frequency domain-equivalent modeling method for wind farms based on the nature of the equivalent resistance of the rotor,in order to analyze sub-synchronous oscillations accurately.To this end,Matlab/Simulink is used to simulate a detailed model,a single-unit model,and an equivalent model,considering a wind farm as an example.A simulation analysis is then performed under the sub-synchronous frequency to prove that the model is effective and that the wind farm equivalence model method is valid.

Characteristics of Lightning Damage to Coastal Wind Farms and Its Protective Measures

Firstly, characteristics of coastal wind farms were analyzed, and then lightning damage to coastal wind farms was discussed, finally main lightning protection measures were put forward from aspects of turbine blades, engine rooms and overvoltage protection. Besides conventional light- ning protection technology, local lightning protection, pre-discharge and lightning motoring and early warning techniques should be used to protect coastal wind farms against lightning.

Simulated Influence of Mountainous Wind Farms Operations on Local Climate

Renewable energy sources,especially wind power,were believed to be able to slow down global warming;however,evidence in recent years shows that wind farms may also induce climate change.With the rapid development of wind power industry,the number of wind farms installed in mountains has gradually increased.Therefore,it is necessary to study the impact of wind farms in mountainous areas on local climate.The Suizhou and Dawu wind farms in northern Hubei Province were chosen for the present study on the impact of wind farm operations on the local climate in mountainous areas.The mesoscale meteorological numerical model Weather Research and Forecasting Model(WRF)and the Fitch model,together with turbulence correction factor,were used to simulate wind farm operations and study their effects on local climate.The results showed the characteristics of wind speed attenuation in mountainous wind farms:the amplitude and range of wind speed attenuation were stronger in the nighttime than in the daytime,and stronger in summer than in winter.The surface temperature increased and became more significant in summer.However,a cooling variation was observed above the surface warming center.The height of this center was higher in the daytime than it was in the nighttime.The latent heat flux in the wind farms decreased at night,accompanied by an increase in sensible heat flux.However,these changes were not significant.Some differences were observed between the impact of wind farms on the climate in the plains and the mountains.Such differences are more likely to be related to complex terrain conditions,climate conditions,and the density of wind turbines.The present study may provide support for the development and construction of wind farms in mountainous areas.

Impact of the Objective Function on the Construction of Internal Grids of Wind Farms Using Genetic Algorithm

The macro complex of the construction industry is energy intensive. Solutions that enable the supply of this demand while meeting the principles of sustainability are needed. The construction of wind farms has been a strategy employed by many countries to produce clean energy. An increase in the construction of wind farms has also been witnessed in Brazil. This calls for different activities, such as the design and construction of infrastructure. This article focuses on the design of internal medium voltage distribution grids for wind farms. The purpose is to find a radial configuration that connects a set of wind generators to the substation, in an optimum way, minimizing operational and construction costs, reducing loss and therefore contributing to sustainability. In large farms, the project design consists of a large combinatorial optimization problem, given the large number of possible configurations to be deployed. Finding the best solution for the internal grid depends on the criterion adopted for the objectives pursued. This article analyzes the different criteria that can be adopted in the design of the wind farm’s internal grid using a methodology based on genetic algorithm (GA). Its aim is to identify their influence on the solution of the problem and help decision-making by finding the most adequate criterion for the objectives pursued. The results show that the design of the internal grid is sensitive to the criteria adopted for the objective function. In addition, the degree of sensitivity is analyzed, showing that, in some cases, the solutions are not economically attractive and do not contribute to the reduction of losses.

Ecological impacts of the expansion of offshore wind farms on trophic level species of marine food chain

The global demand for renewable energy has resulted in a rapid expansion of offshore wind farms(OWFs)and increased attention to the ecological impacts of OWFs on the marine ecosystem.Previous reviews mainly focused on the OWFs’impacts on individual species like birds,bats,or mammals.This review collected numerous field-measured data and simulated results to summarize the ecological impacts on phytoplankton,zooplankton,zoobenthos,fishes,and mammals from each trophic level and also analyze their interactions in the marine food chain.Phytoplankton and zooplankton are positively or adversely affected by the‘wave effect’,‘shading effect’,oxygen depletion and predation pressure,leading to a ±10% fluctuation of primary production.Although zoobenthos are threatened transiently by habitat destruction with a reduction of around 60% in biomass in the construction stage,their abundance exhibited an over 90% increase,dominated by sessile species,due to the‘reef effect’in the operation stage.Marine fishes and mammals are to endure the interferences of noise and electromagnetic,but they are also aggregated around OWFs by the‘reef effect’and‘reserve effect’.Furthermore,the complexity of marine ecosystem would increase with a promotion of the total system biomass by 40% through trophic cascade effects strengthen and resource partitioning alternation triggered by the proliferation of filter-feeders.The suitable site selection,long-term monitoring,and life-cycle-assessment of ecological impacts of OWFs that are lacking in current literature have been described in this review,as well as the carbon emission and deposition.

Detection of Nonlinear Behavior Induced by Hard Limiting in Voltage Source Converters in Wind Farms Based on Higher-order Spectral Analysis

In recent years, sub-synchronous oscillation accidents caused by wind power integration have received extensive attention. The recorded constant-amplitude waveforms can be induced by either linear or nonlinear oscillation mechanisms. Hence, the nonlinear behavior needs to be distinguished prior to choosing the analysis method. Since the 1960s, the higher-order statistics(HOS) theory has become a powerful tool for the detection of nonlinear behavior(DNB) in production quality control wherein it has mainly been applied to mechanical condition monitoring and fault diagnosis. This study focuses on the hard limiters of the voltage source converter(VSC) control systems in the wind farms and attempts to detect the nonlinear behavior caused by bi-or uni-lateral saturation hard limiting using the HOS analysis. First, the conventional describing function is extended to obtain the detailed frequency domain information on the bi-and uni-lateral saturation hard limiting. Furthermore, the bi-and tri-spectra are introduced as the HOS, which are extended into bi-and tri-coherence spectra to eliminate the effects of the linear parts on the harmonic characteristics of hard limiting in the VSC control system, respectively. The effectiveness of the HOS in the DNB and the classification of the hard-limiting types is proven, and its detailed derivation and estimation procedure is presented. Finally, the quadratic and cubic phase coupling in the signals is illustrated, and the performance of the proposed method is evaluated and discussed.

Dynamic Couplingand Cooperative Control for Multi-paralleled Doubly Fed Induction Generator Wind Farms during Symmetrical Low Voltage Ride-through in a Weak Grid

In multi-fed grid-connected systems,there are complex dynamic interactions between different pieces of equipment.Particularly in situations of weak-grid faults,the dynamic coupling between equipment becomes more pronounced.This may cause the system to experience small-signal instability during the fault steady-state.In this paper,multi-paralleled doubly fed induction generator(DFIG)-based wind farms(WFs)are taken as an example to study the dynamic coupling within a multi-fed system during fault steady-state of symmetrical low voltage ride-through(LVRT)in a weak grid.The analysis reveals that the dynamic coupling between WFs will introduce a damping shift to each WF.This inevitably affects the system’s dynamic stability and brings the risk of small-signal instability during fault steady-state in LVRT scenarios.Increasing the distance to fault location and fault severity will exacerbate the dynamic coupling between WFs.Because of the dynamic coupling,adjusting the control state of one WF will affect the stability of the remaining WFs in the system.Hence,a cooperative control strategy for multi-paralleled DFIG WFs is proposed to improve dynamic stability during LVRT.The analysis and the effectiveness of the proposed control strategy are verified by modal analysis and simu-lation.

Shared mooring systems for offshore floating wind farms: A review

Offshore wind energy,as a form of renewable power,has seen rapid development in recent years.While fixedbottom wind turbines are typically used in water depths less than 50 m,the utilization of floating offshore wind turbines(FOWTs)becomes essential for deeper waters.Secure and effective mooring systems play a crucial role in making FOWTs commercially viable.The concept of a shared mooring system offers an innovative solution for deploying floating wind farms in clusters or arrays,which can reduce overall construction costs for large-scale floating wind farms.It is imperative to optimize the shared mooring arrangement for maximum cost-effectiveness and wind farm stability.However,implementing a shared mooring system introduces complexity to the dynamics of FOWTs,requiring the development of advanced simulation tools to meet modelling requirements.Under the shared mooring arrangement,mooring lines and anchors face more significant challenges,such as chain-seabed interactions,soil cyclic weakening,and anchor out-of-plane loading,which underscore the need for innovative,reliable,and efficient shared anchor designs.This article offers an overview of the current research status on shared mooring systems for floating wind farms,which might serve as a valuable reference for the construction of large-scale floating wind farms worldwide.

Fast Protection for Collector Lines in Large-Scale Wind Farms Based on Random Matrix Theory

The impact of large-scale wind farms on power system stability should be carefully investigated,in which mal-functions usually exist in the collector line's relay protection.In order to solve this challenging problem,a novel time-domain protection scheme for collector lines,based on random matrix theory(RMT),is proposed in this paper.First,the collected currents are preprocessed to form time series data.Then,a real-time sliding time window is used to form a consecutive time series data matrix.Based on RMT,mean spectral radius(MSR)is used to analyze time series data characteristics after real-time calculations are performed.Case studies demonstrate that RMT is independent from fault locations and fault types.In particular,faulty and non-faulty collector lines can be accurately and efficiently identified compared with traditional protection schemes.

Resilient Power Systems Operation with Offshore Wind Farms and Cloud Data Centers

To enhance the resilience of power systems with offshore wind farms(OWFs),a proactive scheduling scheme is proposed to unlock the flexibility of cloud data centers(CDCs)responding to uncertain spatial and temporal impacts induced by hurricanes.The total life simulation(TLS)is adopted to project the local weather conditions at transmission lines and OWFs,before,during,and after the hurricane.The static power curve of wind turbines(WTs)is used to capture the output of OWFs,and the fragility analysis of transmission-line components is used to formulate the time-varying failure rates of transmission lines.A novel distributionally robust ambiguity set is constructed with a discrete support set,where the impacts of hurricanes are depicted by these supports.To minimize load sheddings and dropping workloads,the spatial and temporal demand response capabilities of CDCs according to task migration and delay tolerance are incorporated into resilient management.The flexibilities of CDC’s power consumption are integrated into a two-stage distributionally robust optimization problem with conditional value at risk(CVaR).Based on Lagrange duality,this problem is reformulated into its deterministic counterpart and solved by a novel decomposition method with hybrid cuts,admitting fewer iterations and a faster convergence rate.The effectiveness of the proposed resilient management strategy is verified through case studies conducted on the modified IEEERTS 24 system,which includes 4 data centers and 5 offshore wind farms.

Impact of Different AC Voltage Control Modes of Wind-farm-side MMC on Stability of MMC-HVDC with Offshore Wind Farms

Wind-farm-side modular multilevel converters(WFMMCs) used in modular multilevel converter based highvoltage direct current(MMC-HVDC) transmission systems must be able to control the AC grid voltage in offshore wind farms. Different AC voltage control strategies can significantly affect the dynamic characteristics of WFMMCs. However, existing studies have not provided a general methodology of controller parameter design, and few comparative studies have been conducted on control performance under varying operating conditions as well as the effects of different AC voltage control modes(AVCMs) on the stability of MMC-HVDCs with offshore wind farms. This paper provides a controller parameter design method for AVCMs, which is tested in various operating scenarios. Sequence impedance models of offshore wind farms and WFMMCs under different AVCMs are then developed. The effects of AVCMs on the small-signal stability of the interconnected system are then analyzed and compared using the impedance-based method. Finally, case studies are conducted on a practical MMC-HVDC system with offshore wind farms to verify the theoretical analysis.

Compact Real-time Simulator with Spatial-temporal Parallel Design for Large-scale Wind Farms

Real-time simulation of large-scale wind farms with detailed modeling can provide accurate insights into system transient behaviors,but entails challenges in computing resources.This paper develops a compact real-time simulator based on the field programmable gate array(FPGA)for large-scale wind farms,in which the spatial-temporal parallel design method is proposed to address the huge computation resource demand associated with detailed modeling.The wind farm is decoupled into several subsystems based on model consistency,and the electrical system and control system of each subsystem are solved in parallel.Both the module-level pipeline technique and superscalar pipeline technique are introduced to the wind farms’simulation to effectively improve the utilization of hardware resources.In case studies,real-time simulations of two modified wind farms are separately carried out on a single FPGA,including one with 13 permanent magnet synchronous generators under a time-step of 11µs,and the other with 30 squirrel-cage induction generators under a time-step of 8µs.Simulation tests,under different scenarios,are implemented to validate the numerical performance of the real-time simulator,and a comparison with the commercial tool PSCAD/EMTDC demonstrates the accuracy and effectiveness of the proposed design.

Stability Comparison Between Grid-forming and Grid-following Based Wind Farms Integrated MMC-HVDC

Grid-forming(GFM)control based high-voltage DC(HVDC)systems and renewable energy sources(RESs)provide support for enhancing the stability of power systems.However,the interaction and coordination of frequency support between the GFM-based modular multilevel converter based HVDC(MMC-HVDC)and grid-following(GFL)based RESs or GFM-based RESs have not been fully investigated,which are examined in this study.First,the detailed AC-and DC-side impedances of GFM-based MMC-HVDC are analyzed.The impedance characteristics of GFL-and GFM-based wind turbines are next analyzed.Then,the influences of GFL-and GFM-based wind farms(WFs)on the DC-and AC-side stabilities of WF-integrated MMC-HVDC systems are compared and evaluated.The results show that the GFM-based wind turbine performs better than the GFL-based wind turbine.Accordingly,to support a receiving-end AC system,the corresponding frequency supporting strategies are proposed based on the GFM control for WF-integrated MMC-HVDC systems.The GFM-based WF outperforms the GFL-based WF in terms of stability and response time.Simulations in PSCAD/EMTDC demonstrate the DC-and AC-side stability issues and seamless grid support from the RESs,i.e.,WFs,to the receiving-end AC system.

Model Predictive Control Based Coordinated Voltage Control for Offshore Radial DC-connected Wind Farms

In this study,a coordinated voltage control strategy based on model predictive control(MPC)is proposed for offshore radial DC-connected wind farms.Two control modes are designed in this strategy.In the economic operation mode,the wind farm controller generates optimal active power references as well as bus voltage references of medium-voltage collector for DC-connected wind turbine(DCWT)systems and high-voltage DC/DC converters,where the goal is to minimize power losses inside the wind farm and ensure that voltages are within a feasible range,all while tracking the power references.In the voltage control mode,the main control objective for the wind farm controller is to minimize voltage deviations from the rated voltage.With the MPC,the control objective and operation constraints can be explicitly represented in the optimization problem while considering the dynamic response of the DCWT system.In addition,a sensitivity coefficient calculation method for radial DC-connected wind farms is developed to improve computational efficiency.Finally,DC-connected wind farms with 20 wind turbines are used to demonstrate the performance of the proposed strategy.

A nonlinear wake model of a wind turbine considering the yaw wake steering

Duo to fluctuations in atmospheric turbulence and yaw control strategies,wind turbines are often in a yaw state.To predict the far wake velocity field of wind turbines quickly and accurately,a wake velocity model was derived based on the method of momentum conservation considering the wake steering of the wind turbine under yaw conditions.To consider the shear effect of the vertical incoming wind direction,a two-dimensional Gaussian distribution function was introduced to model the velocity loss at different axial positions in the far wake region based on the assumption of nonlinear wake expansion.This work also developed a“prediction-correction”method to solve the wake velocity field,and the accuracy of the model results was verified in wake experiments on the Garrad Hassan wind turbine.Moreover,a 33-kW two-blade horizontal axis wind turbine was simulated using this method,and the results were compared with the classical wake model under the same parameters and the computational fluid dynamics(CFD)simulation results.The results show that the nonlinear wake model well reflected the influence of incoming flow shear and yaw wake steering in the wake velocity field.Finally,computation of the wake flow for the Horns Rev offshore wind farm with 80 wind turbines showed an error within 8%compared to the experimental values.The established wake model is less computationally intensive than other methods,has a faster calculation speed,and can be used for engineering calculations of the wake velocity in the far wakefield of wind turbines.

Transient Stability Preventive Control of Wind Farm Connected Power System Considering the Uncertainty

To address uncertainty as well as transient stability constraints simultaneously in the preventive control of windfarm systems, a novel three-stage optimization strategy is established in this paper. In the first stage, the probabilisticmulti-objective particle swarm optimization based on the point estimate method is employed to cope with thestochastic factors. The transient security region of the system is accurately ensured by the interior point methodin the second stage. Finally, the verification of the final optimal objectives and satisfied constraints are enforcedin the last stage. Furthermore, the proposed strategy is a general framework that can combine other optimizationalgorithms. The proposed methodology is tested on the modified WSCC 9-bus system and the New England 39-bussystem. The results verify the feasibility of the method.