Wind Farm Integration Research Articles

Integration of wind and solar farms in a doubly fed induction generator using hybrid GA-ANN controllers

• An emulated wind turbine (WT) drive system is used. • The THD values for source current are 3.03% for PI and 1.93% for GA-ANN. • Landsman converter has proved to be more efficient. • The gain of 4 and an output voltage of 1200 v which is more when compared to Zeta and Flyback converters. Because of global warming concerns and the aim of decreasing nonrenewable energy sources, the direction of power production is being steered towards sustainable power sources rather than conventional ones. Hence, a n emulated wind turbine (WT) drive system is used in this study to assess the behavior of a grid-connected Doubly Fed Induction Generator (DFIG) based wind energy system. In order to ensure uniform and continuous power supply from renewable sources to the grid, a hybrid microgrid system has been created by taking into account a PV fed Landsman converter as part of the design. The control of wind generators is divided into two parts: rotor control and grid control. The grid side control is achieved via the use of a PI controller, and the rotor side control is achieved through the combination of the stator flux and the D -q reference frame. The suggested system manages actual and reactive power, as well as DC link voltages, in an efficient manner, and this has been shown at a variety of various speeds (sub and super synchronous). This paper presents a new Artificial Neural Network (ANN)-based tracking of the Maximum Power Point (MPP) for PV-fed Landsman converters that is based on the Genetic Algorithm (GA). The controlling mechanism is tested on an emulated wind turbine that is driven for concurrent control of the DC tie potential, active and reactive powers using MATLAB and an experimental bench configuration. By using this methodology, the THD values for source current utilizing the PI and GA-ANN based systems, are obtained as 3.03% and 1.93%, respectively. Also, the employment of Landsman converter has proved to be more efficient with the gain of 4 and an output voltage of 1200 V which is more when compared to Zeta and Flyback converters.

Assessment of the grid-related loss of offsite power to the nuclear power plants in the presence of wind farms

Grid stability affects the progression of loss of offsite power scenarios to the nuclear power plants, as the most dominant core-damage-inducing initiating event. The ever-increasing tendency toward integration of large-scale wind farms into the transmission systems drastically challenges their dynamic behavior.In this study, we proposed a dynamic-probabilistic framework to evaluate the effect of wind penetration scenarios on the frequency of occurrence of LOOP to the NPPs. We developed 30 initial grid states, including 3 wind penetration percentages, 5 operational loading levels, in both optimal and normal power flows.We estimated 150 GR-LOOP frequencies for 5 NPP locations upon 3Ph-Shc faults on the transmission lines. Extending from 1.3 × 10−7 to 9.6 × 10−5 (year)−1 for the safest to the riskiest situations, the mean GR-LOOP frequencies have been assessed as 1.74 × 10−5, 2.96 × 10−5, and 2.77 × 10−5 (year)−1, for grids with 0%, 10%, and, 20% penetration percentage of installed wind generation, respectively.Our results indicate the undeniable influence of variations in the operational loadings and the wind penetration percentage on the GR-LOOP frequency, in addition to the NPPs’ locations. Such intensification effect was more pronounced in instantaneous frequencies of unique states than in the averaged ones. Furthermore, we observed more outstanding growth in the corresponding values of optimal cases. Our findings suggested that the reliability of the offsite grid to the NPPs be considered as a decision-making criterion, in addition to the existing security and economic issues in the grids with wind penetration.

Economic Enhancement of Wind–Thermal–Hydro System Considering Imbalance Cost in Deregulated Power Market

Studying the property of the combination of renewable energy sources in the existing power systems is of great importance, and especially in the case of deregulated systems. The uncertainty of renewable sources is the largest barrier to integrating renewable-energy-producing units into the existing electrical infrastructure. Due to its uncertainty, integrating wind power into an existing power system requires extra consideration. In this work, the impacts of wind farm (WF) integration and a pumped hydroelectric storage system (PHES) on the electric losses, voltage profiles, generation costs, and system economy in a deregulated power market were studied. A comparative study was performed to determine the impact of wind farm integration on regulated and deregulated environments. Four locations in India were chosen at random for this work, and we used the real-time statistics for the actual wind speeds (AWSs) and forecasted wind speeds (FWSs) for each chosen location. To determine the system economy, surplus charge rates and deficit charge rates were developed to evaluate the imbalance cost resulting from the mismatch between the predicted and actual wind speeds. Considering the effect of the imbalance cost, the system profit/day varies by an average of 1.6% for the locations studied. Because of the reorganization of the power system, consumers constantly look for reliable and affordable power that is also efficient. As a result, the system security limit may be breached, or the system may run in a dangerous state. Lastly, in this paper, an economic risk analysis is presented with the help of heuristic algorithms (i.e., artificial bee colony algorithm (ABC) and moth–flame optimization algorithm (MFO)), along with sequential quadratic programming (SQP), and the way in which the PHES is used to compensate for the deviation in the WF integration in the real-time electricity market is also presented. The value at risk (VaR) and conditional value at risk (CVaR) were used as the economic risk analysis tools. According to the work, with the increase in the wind generation, the system risk improves. The results show that, as the wind generation increases by three times, there is an improvement in the risk coefficient values by 1%. A modified IEEE 14-bus test system was used for the validation of the entire work.

An active primary frequency regulation strategy for grid integrated wind farms based on model predictive control

The increasing penetration level of wind power can reduce the dependency on fossil fuels, but it is accompanied with challenges such as the jeopardized dynamic stability of the frequency of power grid. As an effective method to improve frequency dynamic stability, primary frequency regulation (PFR) is conventionally based on the feedback of measured frequency, by which means it is conducted through analyzing historical information. By taking the predictive information into account, this paper introduces an active PFR (APFR) strategy for grid integrated wind farms (WFs) to enhance control performance of PFR. According to small-signal models of power system integrated with WFs based on conventional PFR and APFR, the state-space predictive models are established to obtain the predictive states. Then, to take active measures to deal with the electrical load disturbance, the predicted frequency is optimized in a receding horizon period by adjusting the PFR power reference of WFs flexibly. Moreover, a finite terminal weighting matrix based Lyapunov​ function is presented to prove the asymptotic stability of the closed-loop model predictive control system. Finally, extensive case studies based on the standard test systems are performed to validate the effectiveness of the theoretical analysis and the superiority of APFR strategy.

Comparison of Impact on Turbine Shafts Torsional Behavior for Integration of Two Types of Wind Farm into a Series-Compensated Transmission System

Deep decarbonization is the goal of modern power systems, so it is inevitable that large-scale wind farms will be integrated into systems. This also gives rise to many problems, which have been studied in detail in the literature. However, these studies basically have two deficiencies. One is to assume that traditional generator units are fully loaded, and the other is not to compare the differences in the impact of different types of wind farm. This paper discusses these two points in detail. Taking a series-compensated transmission system as the research object, and assuming that the wind farm only replaces part of the power of the traditional generator unit in the transition period of energy conversion, the difference between the torsional vibration behaviors of the traditional unit caused by adopting different types of wind farm is discussed. The results of the study show that the impact of integration of the type 3 wind farm is dominated by the induction generator effect of doubly fed induction generator units. The penetration rate as low as 19% could cause instability. However, the paralleled metal-oxide varistor can effectively improve the stability. For the type 4 wind farm, the dominant factor turns out to be the de-rating operations of the steam turbine generator unit. The allowable penetration rate depends on the turbine damping. When the turbine damping is sufficient, the penetration rate can be as high as 87.5%. In conclusion, in order to integrate wind farms into a series compensated transmission system, one should not only focus on the compensation factor to avoid the sub-synchronous torsional vibrations, but also pay attention to the types of wind farm as well as the penetration rate. The findings can be used as the decision-making basis for the integration of wind farms during the energy transition period.

Improved Frequency Control Strategy for Offshore Wind Farm Integration via VSC-HVDC

Voltage source converter based high voltage DC system (VSC-HVDC) has become a very promising solution to integrate offshore wind farm. However, the equivalent inertia of the modern power system with large renewable energy integration becomes small, which will arouse some frequency stability problems. To tackle this problem, this paper proposes an improved frequency regulation strategy for VSC-HVDC integrated offshore wind farm. Firstly, in the frequency decrease stage, the rotor kinetic energy of wind turbines (WTs) is used to suppress the decrease of the frequency, and the control parameters are determined to make full use of the mechanical power and rotor kinetic energy of WTs, the frequency nadir is improved. Secondly, in the rotor speed recovery stage, the DC capacitors of VSC-HVDC are used to release power to compensate the deficiency value of wind farm output power and avoid the secondary frequency drop (SFD) problem. Lastly, the simulation is conducted in PSCAD/EMTDC to validate the effectiveness of the proposed coordinated frequency control strategy.

Deep Neural Network Configuration Sensitivity Analysis in Wind Power Forecasting

The trend toward increasing integration of wind farms into the power system is a challenge for transmission and distribution system operators and electricity market operators. The variability of electricity generation from wind farms increases the requirements for the flexibility needed for the reliable and stable operation of the power system. Operating a power system with a high share of renewables requires advanced generation and consumption forecasting methods to ensure the reliable and economical operation of the system. Installed wind power capacities require advanced techniques to monitor and control such data-rich power systems. The rapid development of advanced artificial neural networks and data processing capabilities offers numerous potential applications. The effectiveness of advanced deep recurrent neural networks with long-term memory is constantly being demonstrated for learning complex temporal sequence-to-sequence dependencies. This paper presents the application of deep learning methods to wind power production forecasting. The models are trained using historical wind farm generation measurements and NWP weather forecasts for the areas of Croatian wind farms. Furthermore, a comparison of the accuracy of the proposed models with currently used forecasting tools is presented.

Reactive Voltage Control Strategy for PMSG-Based Wind Farm Considering Reactive Power Adequacy and Terminal Voltage Balance

To improve the ability of the power system to accommodate high penetration wind power, wind turbines (WTs) need to realize the mode transformation from grid-following to grid-forming, thus actively participating in the voltage regulation of the power grid with a high proportion of wind power. In this work, a reactive voltage control strategy for wind farms considering reactive power adequacy and terminal voltage balance is proposed. Firstly, the expression of the maximum reactive power regulation capacity of WT, namely reactive power adequacy, is derived under the complete wind condition based on the mathematical model and operating characteristics of WT, to study the influence of wake effect on reactive power adequacy of a wind farm. Then, the point of common coupling (PCC) voltage and terminal voltage are expressed analytically based on the radiative topology equivalent model of a wind farm, to analyze the influence of electrical distance on active power loss of wind farm. Finally, the calculation method of the adaptive gain coefficient of WT is put forward, which comprehensively considers the input wind speed and the electrical distance, to regulate the PCC voltage and terminal voltage simultaneously. The comprehensive effectiveness of the proposed strategy is demonstrated on a permanent magnet synchronous generator (PMSG)-based wind farm integration simulation model. While supporting the PCC voltage, the proposed strategy maintains the balance of the terminal voltage in the wind farm, thereby improving the friendliness of wind power grid connection.

Evaluation of wind farm aggregation using probabilistic clustering algorithms for power system stability assessment

Wind farm integration in large-scale power systems for performing stability assessment requires significant modelling efforts and high computational time. In these cases, wind farm clustering is used to simplify the simulation efforts, but still, it requires a large number and composition of clusters to represent the abrupt change in wind speed and direction. A probabilistic clustering approach could be useful in such a case, which can identify the most probable cluster(s) in a wind regime within a timeframe, such as one year. This paper has presented a probabilistic clustering framework to represent the most recurring aggregated wind farm model throughout the whole year by implementing four clustering algorithms, namely (i) K-means, (ii) hierarchical, (c) fuzzy c-means, and (d) DBSCAN (density-based spatial clustering of applications with noise). The performance of the aggregated wind farm model has been compared with the detailed wind farm model in assessing the small-disturbance, frequency, and voltage stability of a power system. The simulation results show that the aggregated equivalent models (as identified by the probabilistic clustering approach) present the same level of accuracy while performing the simulation 10-times faster. This simulation efficiency could be very useful for performing dynamic studies for large-scale power systems.

Mitigation of background harmonic amplification caused by offshore wind farm long AC cable integration

The high voltage alternating current transmission with submarine cables is the common scheme to integrate offshore wind farms close to the land. Due to the capacitive effect of AC cables, the association of the long AC cables and the onshore grid can cause resonances, which may amplify grid background harmonics. This paper focuses on the mitigation of background harmonic amplification caused by offshore wind farm integration. First, the background harmonic amplification mechanism in the offshore wind farm integration system is analysed qualitatively, and the mitigation approaches are given in principle. Then, taking a practical project as a study case, the harmonic modelling methods of the offshore grid and the onshore grid are elaborated, including the harmonic models of wind turbines, transformers, cables, the high voltage and the extra-high voltage transmission grid, and the low voltage distribution network. According to the established harmonic models, the cause of background harmonic amplification is analysed. On this basis, two mitigation methods of installing the series blocking filter and the shunt filter are compared and the recommended mitigation scheme is proposed. Finally, the feasibility of the proposed scheme is verified by calculation results under different grid operating conditions.

Towards integrated wind farm control: Interfacing farm flow and power plant controls

AbstractConcepts for control of wind farms (WFs) can be clustered into two distinct concepts, namely, wind power plant control (WPPC) and wind farm flow control (WFFC). WPPC is concerned with the connection to the power system, compliance with grid codes, and provision of power system services. This comprises the traditional way of operating a WF without consideration of aerodynamic turbine interaction. However, flow phenomena like wake effects can have a large impact on the overall performance of the WF. WFFC considers such aerodynamic phenomena in the WF operation. It can be viewed as a new feature that shall be integrated with the existing control functions. The interaction of these different control concepts is discussed in this article, leading to an identification of the challenges whose solutions will contribute to a successful integration of electrical system and aerodynamic aspects of WF control.

Impact of Wind Farm Integration on LMP in Deregulated Energy Markets

The integration of renewable energy generation affects the operating characteristics of a power system, such as electric losses, voltage profile, generation cost, system stability, and reliability of the system. The installation of renewable energy generation units in non-optimal locations may increase system losses, costs, voltage fluctuations, etc. The main hurdle in integrating renewable energy generation units with an existing electrical grid is the uncertainty of renewable sources. This paper presents the impact of wind farm integration on the system economy in a wind-integrated deregulated power market. The importance of deregulation in terms of the system generation cost, bus voltage profile, and locational marginal pricing (LMP) are also studied in this work. LMP is the main parameter responsible for handling the system economy (i.e., profit of generating units and profit of customers). Considering the variable nature of wind flow, three different real-time wind speed datasets are used to validate this work. Bus sensitivity factor (BSF) is considered for equating the optimal position of the wind farm in the integrated system. Five different optimization techniques, i.e., sequential quadratic programming (SQP), artificial bee colony (ABC) algorithms, particle swarm optimization (PSO), ant colony optimization (ACO) algorithm, and slime mold algorithm (SMA), are introduced to solve the optimal power flow problem. The SMA and ACO are used for the first time in this type of economic assessment (i.e., impact valuation of LMP) in a deregulated power system, which is the novelty of this work. The entire work is performed in a modified IEEE 30 bus test system.

Open-circuit Fault Riding Through of Receiving AC Terminal in HVDC Transmission System for Offshore Wind Farms

Abstract Flexible high voltage direct current (HVDC) transmission system is indispensable for long-distance and high power transmission capacity in offshore wind farms. The AC open-circuit fault of the receiving terminal is quite severe, where the power transmission might be suddenly cut down to zero. As a result, a severe over-voltage will occur on the HVDC side and modular multilevel converter (MMC) submodule capacitor. In this paper, the over-voltage suppression mechanism is put forward to augment the AC open circuit fault at the sending and receiving terminal of the MMC-HVDC system. First, the formulation mechanism of DC over-voltage in the MMC-HVDC integrated wind farm is studied. Then, three different over-voltage suppression mechanisms, namely wind turbine pitch control, crowbar control, and submodule redundancy, are put forward to suppress the aforesaid over-voltage in the MMC-HVDC system. The simulations are carried out in PSCAD based on a test case, and the simulation results are used to confirm the efficiency of the proposed overvoltage suppression techniques.

Wind farm dynamic effect mitigation on power sharing and stability of MTDC grid through a supplementary controller

Effective and reliable integration of offshore wind farm to AC grid is easily achieved via multi-terminal HV direct current (MTDC) grid network. But the dynamics of wind power put stress on the converter terminals which may deteriorate its performance and life span. Therefore, a suitable control scheme is needed which minimizes the dynamic effect of wind farm power on the MTDC grid. This paper presents a supplementary linear quadratic regression (LQR) based control strategy to minimize the effect of wind farm power variability on dynamic power sharing capability of voltage source converter (VSC) terminals. The feedback gains with penalty weights of LQR control strategy optimizes the performance using linear matrix inequality (LMI) approach. The asymptotic convergence of LQR based controller is derived using the Lyapunov stability theorem. In addition to control design to achieve optimal power sharing in MTDC grid, an independent control is also applied on wind farm to exploit maximum power. This is achievable using sliding mode controller (SMC) on wind farm side. The active power sharing capability and DC voltage regulation with proposed control strategy follows smoothly with negligible oscillations against the dynamics of wind farm power variability and changes in converter terminal reference power. The proposed control approach remains effective to distribute the power flow among un-faulted converters against outage of converter terminals. This control strategy is able to share proportionate power according to converter rating, maintain minimum DC voltage deviation, even with time-varying power flow from the wind farm side. The performance of proposed control strategy is validated on five terminal MTDC system through MATLAB® simulations.

WAMS Based Real-Time Voltage Stability Monitoring for Various Load Models in the Presence of a DFIG Integrated Wind Farm

With rising global energy demand, transmission lines are operated at their limits, causing electrical grids to operate under extreme voltage instability conditions. To meet the increased load-demand and the forced tendency across the globe of tilting towards even more renewable generation, solar and wind farms are integrated with increased size and capacity. These uncontrolled natural power injection again may affect the system’s voltage stability. To avoid blackouts and to achieve the maximum voltage stability of power systems, operators need to do effective real-time grid monitoring and control at load terminals. Load models are important in the analysis of voltage stability, and accurate load models are useful in analysing the voltage stability conditions. Phasor-measurement-unit (PMU) based wide-area monitoring and smart-automation is an innovative technology for measuring load voltage magnitude, phase angle, and frequency variations in a DFIG integrated large wind power system. This research paper focuses on estimating the real-time voltage stability through the use of linear, nonlinear, and dynamic load models in presence of a DFIG based wind-farm in WSCC three-machine nine-bus power network using PMU data. This study is carried out using MATLAB-Simulink software.

Delay dependent wide area damping controller with actuator saturation and communication failure for wind integrated power system

Integration of wind farm with power system introduces nonlinearity and complexity of the power system, which deteriorates the performance of a wide area damping controller (WADC). A WADC is designed in this paper for wind energy conversion system (WECS) integrated power system taking the communication latency and communication failure of the wide area measurement system (WAMS) into consideration. Apart from communication delay and communication failure, the effect of saturation is also considered in this paper. A state feedback stabilizing controller is designed using linear matrix inequality (LMI) platform. The control signal chosen here is combination of local and global signal to ensure stability during communication failure. The inter-area oscillation is reduced by controlling the reactive power of the wind farm. The effectiveness of the controller developed is verified using a WECS integrated modified 11-bus test system and modified IEEE 39-bus test system. The simulation results show that the designed controller guarantees stability and also can eliminate inter-area oscillations effectively of a WECS integrated power system.

Coordinated control by ADRC strategy for a wind farm based on SCIG considering low voltage ride-through capability

Wind farms are integrated with the power grid system to provide active and reactive power. Because in a wind farm, wind turbines (WTs) are highly coupled to their operating conditions, a central wind farm supervisory unit must take into account these conditions when producing power control references for each WT. The aim of this paper is to manage and control the active and reactive power of wind farms based on squirrel cage induction generators and back-to-back converters. The proportional distribution algorithm is used for distributing wind farm power to individual WTs. In addition, we consider the development of a local power management and control units for WTs. This is in order to extract the maximum available power from the wind, and to provide the active and reactive power predetermined by the transmission system operator, or to satisfy the grid code requirements considering Low Voltage Ride-through capability. The power dispatch strategy is to be used on all WTs using the distribution algorithm while ensuring the control loops using the proposed Active Disturbance Rejection Control strategy. The results demonstrate that the proposed strategies are efficient and can guarantee the safe integration of wind farms into the grid while respecting grid code requirements and power system stability.

Offshore wind speed short-term forecasting based on a hybrid method: Swarm decomposition and meta-extreme learning machine

As the share of global offshore wind energy in the electricity generation portfolio is rapidly increasing, the grid integration of large-scale offshore wind farms is becoming of interest. Due to the intermittency of wind, the stability of power systems is challenging. Therefore, accurate and fast offshore short-term wind speed forecasting tools play important role in maintaining reliability and safe operation of the power system. This paper proposes a novel hybrid offshore wind forecasting model based on swarm decomposition (SWD) and meta-extreme learning machine (Meta-ELM). This approach combines the advantages of SWD which has proven efficiency for non-stationary signals, with Meta-ELM which provides faster calculation with a lower computational burden. In order to enhance accuracy and stability, the signal is decomposed by implementing a swarm-prey hunting algorithm in SWD. To validate the model, a comparison against four conventional and state-of-the-art hybrid models is performed. The implemented models are tested on two real wind datasets. The results demonstrate that the proposed model outperforms the counterparts for all performance metrics considered. The proposed hybrid approach can also improve the performance of the Meta-ELM model as a well-known and robust method.

Application of Joint Raw Moments-Based Probabilistic Power Flow Analysis for Hybrid AC/VSC-MTDC Power Systems

A joint raw moments-based analytical method (JRMAM) is first proposed herein to deal with probabilistic power flow (PPF) of hybrid AC/VSC-MTDC (Alternate Current/Voltage Source Control-Multiple Terminal Direct Current) power systems with integration of the offshore wind farms. JRMAM is able to overcome the challenges of some existing combined methods in estimating the high order moments of target outputs, and the dramatic time consumption of Monte Carlo simulation method (MCSM) in performing the PPF analysis particularly due to the complication of its deterministic power flow (DPF) model. The proposed JRMAM has a further superiority on efficiency, even compared to the joint cumulants-based analytical method (JCAM). As a preliminary step, discrete Fourier transformation matrix (DFTM) method is applied to calculate the joint raw moments of random inputs which are required by conducting JRMAM, and the probability density function (PDF) of outputs can be estimated by means of the Gram-Charlier expansions (GCE) based on the results obtained from JRMAM. Two modified IEEE test cases connected with DC subsystems through the VSC devices are adopted to verify the effectiveness and the scalability of JRMAM, where the result of MCSM is treated as a reference, and the properties of the hybrid AC/VSC-MTDC power system with these master-slave controlled VSCs are investigated for a further acceleration on PPF analysis.

Resilient DC Voltage Control for Islanded Wind Farms Integration Using Cascaded Hybrid HVDC System

To integrate large-scale islanded onshore wind power with different sizes, this paper proposes an integration system based on the cascaded hybrid HVDC transmission system, which consists of LCC and several MMCs in series connection at the DC side of the rectifier. A large-scale wind farm is connected with one LCC and one MMC while several small-scale wind farms are connected with MMCs directly. Owing to the hierarchical integration arrangement, the operating flexibility can be improved with reduced capacity and the number of step-up interfacing transformers. A resilient DC voltage control is proposed for the integration system to adaptively redistribute power among the converters during wind power fluctuations. Firstly, the topology and operating characteristics of the wind power integration system are introduced. Then, a resilient DC voltage control is proposed to ensure stable operation during wind power curtailments. Finally, a simulation model of the hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC to verify the effectiveness. The research results show that the system provides a new option for long-distance transmission of large-scale islanded wind power.