Power Fluctuation Of Wind Farm Research Articles

Turbulence coherence in wind farms: The role of turbines

Models for wind farm power fluctuations primarily focus on the impact of atmospheric turbulence. We employ large eddy simulations (LES) to demonstrate that dynamic changes in thrust (CT ) and power (CP ) coefficient affect the coherence of power fluctuations in turbine pairs. We consider various inflow wind speeds to examine the velocity and power coherence between consecutive turbine rows under three scenarios: (I) a fully developed region where all turbines operate below rated power, (II) the front row operates above rated power while the downstream row operates below rated power, and (III) both rows operate above rated power. In scenario I, the random sweeping hypothesis turbulence model by Tobin and Chamorro, JFM 855, 1116-1129 (2018) can effectively predict the coherence between the turbines. However, in scenarios II and III, the model fails to capture the simulation results. This discrepancy arises due to the operation of above-rated turbines, with dynamically varying CT and CP , which have a distinctly different effect on the flow than turbines operating with fixed CT and CP .

Reliability evaluation technique with the integration of wind power fluctuation through considering frequency regulation and failure restoration

The adequacy of power system can be elevated with the increasing grid-connected capacity of wind farm, and meanwhile, the power system reliability is also affected by the intermittent power fluctuation of wind farm. However, the traditional reliability evaluation technique cannot take the power fluctuation into account. Therefore, for considering the positive and negative influence of wind energy on the power system reliability, this paper proposes a reliability evaluation technique through considering static frequency regulation and failure restoration process. A failure restoration strategy which can be integrated into the reliability evaluation model is presented through designing system load curtailment, system frequency restoration, and system load restoration strategies. A series reliability calculating models which depended on the different failure restoration conditions are established. Case studies for different systems are investigated, and the results verify that the proposed method can consider both aspects of the positive and negative influence of wind farm on the power system reliability.

Analysis of power allocation strategies in the smoothing of wind farm power fluctuations considering lifetime extension of BESS units

The wind farm output power fluctuates because of the random intermittent speed of the wind. When the capacity of wind farms increases, the effect of wind power fluctuations on the power system stability becomes more considerable. Therefore, the fluctuations are mitigated by use of Battery Energy Storage System (BESS) units. The high cost of the BESS has always been one of the major challenges in the investment for the wind farms. Therefore, it is necessary to protect the lifetime of BESS units used in wind farms by using a proper power allocation for them. In this paper, a three-layer control method is proposed to reduce the required BESS in the wind farm, while satisfying the utility constraint and increasing the lifetime of the BESS units. Moreover, 9 power allocation strategies for charging/discharging process in the BESS units are investigated and the most appropriate strategy is introduced. The simulation results based on the output power data of a real 99 MW wind farm indicate that the proposed heuristic-based method is very successful in controlling the switching actions, because the maximum and the average achieved value of switching actions are equal to 2 and 1.14, respectively. In addition, the variance of the Number Of charging/discharging Cycles (NOC) of BESS units is 0.33 which reveals that the number of BESS units with switching actions higher than the average is very small. Moreover, the low average value of life-expended of all the BESS units represents the efficient performance of the proposed control method.

Performance Analysis and Optimization Research of Wind Power Forecasting System

The power fluctuation of wind farm will affect the operation of regional power grid, mainly due to the power fluctuation caused by voltage fluctuation. In order to submit information to power dispatching department as soon as possible, it is convenient for system dispatching. It is necessary to research and develop wind power forecasting technology, especially ultra-short term wind power forecasting technology. At present, the power forecasting system of the dispatching side and some wind farms in China has been widely used. However, the system has some shortcomings in stable operation. Combined with the actual production experience of the existing wind power prediction system, analyze the performance of the existing wind power prediction system, find out the problems that affect the smooth operation of the system, and refer to domestic and foreign data to provide targeted information for each problem. Finally, some constructive optimization Suggestions and a set of optimization scheme are given. In addition, according to the final proposed solution, this paper also developed an optimization model for wind power prediction system, and compared the changes in system performance before and after optimization to verify whether the optimization plan is correct.

Turbulence coherence and its impact on wind-farm power fluctuations

Using a physics-based approach, we infer the impact of the coherence of atmospheric turbulence on the power fluctuations of wind farms. Application of the random-sweeping hypothesis reveals correlations characterized by advection and turbulent diffusion of coherent motions. Those contribute to local peaks and troughs in the power spectrum of the combined units at frequencies corresponding to the advection time between turbines, which diminish in magnitude at high frequencies. Experimental inspection supports the results from the random-sweeping hypothesis in predicting spectral characteristics, although the magnitude of the coherence spectrum appears to be over-predicted. This deviation is attributed to the presence of turbine wakes, and appears to be a function of the turbulence approaching the first turbine in a pair.

Switched distributed load-side frequency control of power systems

This paper presents a frequency control scheme for transmission networks with multiple control areas using load-side controllers in cooperation with automatic generation control (AGC) to regulate the system frequency and the tie-line powers between control areas. In transmission networks, a switched consensus-based distributed controller is proposed for each load bus. Once the frequency violates a pre-defined threshold, load-side controllers will start to work in a frequency regulation mode (FRM) in which each controller communicates with neighboring controllers to discover the power imbalance of the corresponding control area. The control centre in each control area will send the tie-line power information to all the buses in the area, which together with the power imbalance of the area determines the control output of each load-side controller. After the frequency goes back to a satisfactory range, load-side controllers will switch to a load recovery mode (LRM) and shift their duties to the generators. Case studies involving a contingency of load increase and wind farm power fluctuation in the IEEE 118-bus multi-area system show that the performance of frequency and tie-line power regulation is improved significantly by the proposed control scheme compared with AGC and with minimized impacts on end-users.

Power Filtering Based Wind Farm Power Fluctuation Smoothing Control Strategy

The output active power of the wind-power generator fluctuates with the change of the wind speed, which affects the output power quality of the wind farm. In order to reduce output power fluctuation of wind farm, based on analyzing of Wind Power Fluctuation Spectrum, an active power smoothing control strategy had been proposed through the pitch angle control and speed control of the generator. The simulation results show that the proposed control strategy can effectively reduce the output active power fluctuations of wind farm.

Towards uncovering the structure of power fluctuations of wind farms.

The structure of the turbulence-driven power fluctuations in a wind farm is fundamentally described from basic concepts. A derived tuning-free model, supported with experiments, reveals the underlying spectral content of the power fluctuations of a wind farm. It contains two power-law trends and oscillations in the relatively low- and high-frequency ranges. The former is mostly due to the turbulent interaction between the flow and the turbine properties, whereas the latter is due to the advection between turbine pairs. The spectral wind-farm scale power fluctuations Φ_{P} exhibit a power-law decay proportional to f^{-5/3-2} in the region corresponding to the turbulence inertial subrange and at relatively large scales, Φ_{P}∼f^{-2}. Due to the advection and turbulent diffusion of large-scale structures, a spectral oscillation exists with the product of a sinusoidal behavior and an exponential decay in the frequency domain.

Wind farm power fluctuations and spatial sampling of turbulent boundary layers

The fluctuations in power output from wind farms display significantly reduced spectra compared to single wind turbines due to power smoothing and averaging. In order to better understand these spectral features and to relate them to properties of turbulent boundary layers, we perform a wind tunnel experiment in which we measure spatio-temporal characteristics of an experimental surrogate of the power output from a micro wind farm with 100 porous disk models. The experimental results show that the frequency spectrum of the total wind farm power follows a power law with a slope between $-5/3$ and $-2$, and up to lower frequencies than seen for any individual turbine model. In agreement with previous studies in the literature, peaks in the spectrum are observed at frequencies corresponding to the mean flow convection time between consecutive turbines. In the current work we interpret the sum of power extraction from an array of turbines as a discrete spatial filtering of a turbulent boundary layer and derive the associated transfer function. We apply it to an existing model for the wavenumber–frequency spectrum of turbulent boundary layers. This approach allows us to verify the individual roles of Doppler shift and broadening of frequencies on the resulting spatially sampled frequency spectrum. Comparison with the wind tunnel data confirms that the approach captures and explains the main features in the spectrum, indicating the crucial role of the interaction between the spatial sampling and the space–time correlations inherently present in the flow. The frequency spectrum of the aggregated power from a wind farm thus depends on both the spectrum of the incoming turbulence and its modulation by the spatial distribution of turbines in the boundary layer flow.

A significant reduction in the costs of battery energy storage systems by use of smart parking lots in the power fluctuation smoothing process of the wind farms

Wind farm power fluctuations resulted from the wind random nature bring a significant challenge to the wind turbine generators operating in the maximum power point tracking. Furthermore, the smoothing process of a large wind farm in which the Battery Energy Storage System (BESS) is used, needs a considerable initial investment cost. Utilizing Smart Parking Lots (SPLs) can be considered as an applicable solution. In this paper, assuming conventional parking lots in Tehran converted to an SPL set in a near future and thus establishing an enormous charging/discharging capacity, the smoothing process is performed on a 51 MW wind farm. For this purpose, a coordinated control system based on two control algorithms is proposed. The first proposed algorithm chooses eligible SPLs for charging/discharging activity before receiving a new sample of the wind farm output power. Afterwards, the second proposed algorithm determines qualified vehicles in selected SPLs. The main aim is to minimize the number of SPLs (vehicles) taking part in the process. According to the simulation results, the required BESS capacity in the power smoothing process of a typical wind farm decreases considerably when the proposed approach is applied. Thus, the investment cost of BESS is reduced significantly.

Cooperative Control of SFCL and SMES for Enhancing Fault Ride Through Capability and Smoothing Power Fluctuation of DFIG Wind Farm

This paper deals with a cooperative control of a resistive type superconducting fault current limiter (SFCL) and a superconducting magnetic energy storage (SMES) for enhancing fault ride through (FRT) capability and smoothing power fluctuation of the doubly fed induction generator (DFIG)-based wind farm. When the system faults occur, the SFCL is used to limit the fault current, alleviate the terminal voltage drop, and transient power fluctuation so that the DFIG can ride through the fault. Subsequently, the remaining power fluctuation is suppressed by the SMES. The resistive value of the SFCL as well as the superconducting coil inductance of the SMES are simultaneously optimized so that a sudden increase in the kinetic energy in the DFIG rotor during faults, an initial stored energy in the SMES coil, an energy loss of the SFCL, and an output power fluctuation of the DFIG are minimum. The superior control effect of the cooperative SFCL and SMES over the individual device is confirmed by simulation study.

Mitigation of windfarm power fluctuation by adaptive linear neuron‐based power tracking method with flexible learning rate

Most wind turbine generators installed in large windfarms are of variable speed types operating at the maximum power point tracking mode to generate the maximum amount of power. Owing to this fact and regarding the random nature of the windspeed, the output power of the windfarm fluctuates. Fluctuating power is a serious problem for high capacity power plants and should be smoothed. As an effective factor on the required battery energy storage system (BESS) capacity value, tracking is the most important part performed by a coordinated control system in the power smoothing process. An ADAptive LInear NEuron (ADALINE)-based power tracking method with a flexible learning rate is proposed in this study. Furthermore, a particle swarm optimisation-based calculation of the learning rate is presented for optimising the proposed tracking method which reduces the required BESS capacity and the investment cost. Moreover, a charging/discharging algorithm for the BESS units is proposed which decreases the number of required BESS units and increases their useful life by reducing the switching activity as well. To evaluate the performance of the proposed coordinated control approach, the real output data of a 99 MW windfarm are tested. The simulation results verify the effectiveness of the proposed approach.

Optimal Configuration Method of Hybrid Energy Storage System for Wind Farm

According to the demand of wind farm power fluctuations stabilize and the characteristics of hybrid energy storage system. Taking vanadium redox flow battery (VRB) and supercapacitor (SC) as research object, a hybrid energy storage system optimal configuration model is builted. Combined with expert systems and improved genetic algorithm proposed a hybrid energy storage system to optimize the allocation method. The method first established desire output curve of the wind farm based on grid energy saving efficiency and static voltage stability indicators, then introduce coordinate control strategy based on expert system to improved genetic algorithm to get the result of optimal configuration and verify the correctness of this model and method. Finally, analysis the performance of VRB and SC in a typical days wind farm output situation, verify the conclusions of experts coordinated control strategy can extend the vanadium battery life.

A Long-Term Frequency Dynamic Simulation Method of Power System with the Wind Farm Based on Quasi-Steady State Simulation

With the continuous improvement of wind power penetration, the impact of the random fluctuation characteristics of wind power on the frequency control of the power system is growing. Currently, researchers began to study the methods of wind farms participation in frequency control to reduce the frequency adjustment pressure of other power plants and increase the wind power penetration. However, the existing simulation software for the short and long term frequency control of the power system is not so good. So in order to analyze the impact of load fluctuations or wind farm power fluctuations on system frequency control, this paper propose a frequency fluctuation simulation method based on the quasi-steady-state method.

A Control Strategy for Smoothing Active Power Fluctuation of Wind Farm with Flywheel Energy Storage System Based on Improved Wind Power Prediction Algorithm

The fluctuation of active power output of wind farm has many negative impacts on large-scale wind power integration into power grid. In this paper, flywheel energy storage system (FESS) was connected to AC side of the doubly-fed induction generator (DFIG) wind farm to realize smooth control of wind power output. Based on improved wind power prediction algorithm and wind speed-power curve modeling, a new smooth control strategy with the FESS was proposed. The requirement of power system dispatch for wind power prediction and flywheel rotor speed limit were taken into consideration during the process. While smoothing the wind power fluctuation, FESS can track short-term planned output of wind farm. It was demonstrated by quantitative analysis of simulation results that the proposed control strategy can smooth the active power fluctuation of wind farm effectively and thereby improve power quality of the power grid.

Energy Storage Control Based on Wind Farm

With the increase in wind power generation and network capacity, Wind farm power fluctuations on the grid greatly. In order to improve the operational stability of wind farm grid, at its outlet to increase the energy storage system for the new environmentally friendly vanadium redox flow battery (VRB) to effectively regulate the grid power. According to the VRB equivalent mathematical model using a bidirectional DC/AC converter as VRB storage system power regulator, the corresponding charge discharge control and energy management strategy are designed , and grid-connected wind farm system with VRB energy storage unit are modeled and simulated. Simulation results show that the fluctuations in wind speed Circumstances, the VRB energy storage system can quickly and effectively smooth the fluctuations of the active power of the wind farm output, and can provide reactive support to the grid, effectively improve the operating performance of wind farm.

Operation Scheme for a Wind Farm to Mitigate Output Power Variation

Because of the nature of wind, the output power of wind turbines fluctuates according to wind speed variation. Therefore, many countries have set up wind-turbine interconnection standards usually named as Grid-Code to regulate the output power of wind farms to improve power system reliability and power quality. This paper proposes three operation modes of wind farms such as maximum power point tracking (MPPT) mode, single wind turbine control mode and wind farm control mode to control the output power of wind turbines as well as overall wind farms. This paper also proposes an operation scheme of wind farm to alleviate power fluctuation of wind farm by choosing the appropriate control mode and coordinating multiple wind turbines in consideration of grid conditions. The performance of the proposed scheme is verified via simulation studies in PSCAD/EMTDC with doubly-fed induction generator (DFIG) based wind turbine models.

Compensation for the Power Fluctuation of the Large Scale Wind Farm Using Hybrid Energy Storage Applications

This paper proposes an application of superconducting flywheel energy storages (SFESs) to compensate the power fluctuation of the large scale wind farm. Based on the global interest against global warming, the power capacity of the renewable generation, especially wind generation, has been increased steeply. However, since wind generations depend on the natural wind speed completely, the power output cannot be controlled. The power fluctuation caused by the non-controllable output characteristic may create voltage problem for local system and frequency problem for whole power system. To solve those problems, the hybrid application of the large-capacity battery energy storage system (BESS) and the high-speed superconducting flywheel energy storage system (SFES) are considered in Heangwon wind farm in Cheju Island in Korea. Through the case studies based on the site-measured output data, the optimal power and energy capacity of the BESSs and SFES are figured out.

Integration of an Energy Capacitor System With a Variable-Speed Wind Generator

This paper presents a system using an energy capacitor system (ECS) to smoothen the output power fluctuation of a variable-speed wind farm. The variable-speed wind turbine driving a permanent-magnet synchronous generator is considered to be connected to the ac network through a fully controlled frequency converter. The detailed modeling and control strategy of the frequency converter as well as variable-speed operation of a wind turbine generator system are demonstrated. Afterward, a suitable and economical topology of ECS composed of a current-controlled voltage-source inverter, dc-dc buck/boost converter, and an electric double layer capacitor (EDLC) bank is presented, including their control strategies. Exponential moving average is used to generate the real input power reference of ECS. Another novel feature of this paper is the incorporation of a fuzzy-logic-controlled reference signal adjuster in the control of the dc-dc buck/boost converter, in which the stored energy of the EDLC bank is utilized in an efficient way. Due to this controller, the energy storage capacity of the EDLC bank can be reduced in size, thus resulting in reduction of the overall cost of the ECS unit as well as decrease in irrepressible operations during high and low energy levels of the EDLC bank. Finally, extensive simulation results are presented that validate the effectiveness of the proposed system to smoothen the output power fluctuation of the variable-speed wind farm.