Connected Wind Farm Research Articles

Relative stability evaluation of HVDC-connected wind farms

The small-signal stability of high voltage direct current (HVDC)-connected wind farms (WFs) is a challenging issue in modern power systems. The relative stability, i.e., the stability margin, of such a typical multiple-input multiple-output (MIMO) system is quite difficult to be quantified. This paper evaluates the relative stability of HVDC-connected WFs using a new stability index based on the ν-gap metric. We first develop a MIMO model represented by a transfer function matrix of the HVDC-connected WFs. Then, a new stability index, i.e., the robust stability margin, based on the ν-gap metric is proposed to quantify the relative stability of such a MIMO system. Finally, we propose a method to compute the stable region of control parameters based on the corresponding stability criterion of ν-gap metric. Case studies are given to demonstrate the effectiveness of the proposed method.

Security constrained economic dispatch with VSC-HVDC connected wind farms

The rise in wind power in electrical networks creates complex challenges for transmission system operators (TSOs), particularly regarding real-time operation. TSOs rely on grid codes to enforce wind farm (WF) participation in primary frequency control (PFC), like conventional plants. This paper addresses this need by proposing a security constrained economic dispatch (SCED) model with VSC-HVDC connected WFs based on variable speed wind generators. A key differentiator from existing models is the explicit calculation of the spinning reserve and the droop parameter of the WFs. This method uses the deloading schemes related to blade pitch angle and mechanical rotor speed to ensure compliance with grid codes related to PFC. We show that the wind speed and these deloading schemes significantly impact the WF droop parameter. For efficient studies, linear shift factors are used to model the transmission grid and the VSC-HVDC connected WFs. The performance of the SCED model was assessed using two standard test systems that incorporate WFs connected by VSC-HVDC lines. Its effectiveness was confirmed by comparing it with the security constrained optimal power flow (SCOPF). The results showed agreement between both models, with differences less than 3 % and with the SCED saving about 70 % of the computing time.

Self-filtering based on the fault ride-through technique using a robust model predictive control for wind turbine rotor current

This paper studies the possibility of connecting Wind Farms (WF) to the electric grid with the use of finite space model predictive command (FS-MPC) to manage wind farms to improve the quality of the current output from the doubly-fed induction generator (DFIG) with considering fault ride-through technique. This proposed system can generate active power and enhance the power factor. Furthermore, the reduction of harmonics resulting from the connection of non-linear loads to the electrical grid is achieved through the self-active filtering mechanism in DFIGs-WF, facilitated by the now algorithm proposed. FS-MPC technique has the ability to improve system characteristics and greatly reduce active power ripples. Therefore, MATLAB software is used to implement and verify the safety, performance, and effectiveness of this designed technique compared to the conventional strategy. The results obtained demonstrated the effectiveness of the proposed algorithm in handling the four operational modes (Maximum power point tracking, Delta, Fault, and Filtering). Additionally, the suggested technique exhibited flexibility, robustness, high accuracy, and fast dynamic response when compared to conventional strategies and some recently published scientific works. On the other hand, the THD value of the current was significantly reduced, obtaining at one test time the values 56.87% and 0.32% before and after filtering, respectively 27.50% and 0.26% at another time of testing, resulting in an estimated THD reduction percentage of 99.43% and 99.05%, respectively. These high percentages prove that the quality of the stream is excellent after applying the proposed strategy.

Analysis and research on short-circuit current characteristics and grid access faults of wind farms with multi-type fans

As the grid-connected capacity of a large number of wind farms continues to increase, their short-circuit current will have a great impact on protection. Therefore, accurate short-circuit current calculation is beneficial for correct protection action evaluation. Considering the issues related to the diversity of wind turbine types in wind farms and the inability to accurately simulate the failure transient process in previous studies, this research focuses on investigating the impact of control strategies during faults on the transient process of wind turbines. In this paper, the single-machine equivalent model of doubly-fed induction generators (DFIG) and permanent magnet synchronous machine (PMSM) is established by considering the types of wind turbines, and the calculation method of short-circuit current of hybrid wind farms is further proposed by using the classification aggregation equivalent effect method. The accuracy of short-circuit current calculation proposed in this article was verified on RTDS, and a power grid fault analysis method suitable for wind farm connection was proposed based on the characteristics of equivalent circuits of DFIG and PMSM during fault steady-state.

Power-from-Shore Optioneering for Integration of Offshore Renewable Energy in Oil and Gas Production

Despite the widespread usage of high-voltage alternating current (HVAC) for the connection of offshore wind farms (OWF), its use to power-from-shore (PFS) offshore oil and gas (O&G) production sites is often not feasible. Its limitations for long-distance subsea transmission are usually found at 50–70 km from shore and might be even shorter when compared commercially to a direct-current (DC) alternative or conventional generation. Therefore, this research paper aims to address the standardization of offshore transmission with a particular focus on the high-voltage direct current (HVDC) alternative. While the distance is typically not a limiting factor when using DC, and the voltages used are rather standard, the concept of power envelopes can be quite useful in addressing the high variability of offshore site power requirements and setting a design baseline that would lead to improved lead time. In this article, a full back and front-end genetic optioneering model purposely built from the ground up in Python language is used to #1 define up to three DC power envelopes that would cater to most of the candidate’s requirements and #2 provide the lowest cost variance. The results will demonstrate that this can be achieved at a minor overall cost expense.

Dynamic stability reinforcement in remote wind farm connections: POD-SSSC coordination with fuzzy logic control using RTDS

Dynamic stability reinforcement in remote wind farm connections: POD-SSSC coordination with fuzzy logic control using RTDS

Hybrid Machine Learning-Based Intelligent Distance Protection and Control Schemes With Fault and Zonal Classification Capabilities for Grid- Connected Wind Farms

Hybrid Machine Learning-Based Intelligent Distance Protection and Control Schemes With Fault and Zonal Classification Capabilities for Grid- Connected Wind Farms

STATCOM APPLICATION TO INCREASE VOLTAGE STABILTY OF WIND FARMS

The integration ratio of wind farms to the grid is increased tremendously derived by the need for cleaner and renewable energy. However, the stability of the grid is a major concern due to large wind and other renewable resource-based power plants. Thus, wind turbine generators must adhere to the regulations of other conventional forms of generation. To boost stability, especially voltage-based, Flexible AC Transmission Systems such as Static Var Compensators (SVC) or Static Synchronous Compensator (STATCOM) are put in the vicinity of the wind farm's connection point to the grid. This study is intended to model and simulate dynamically a wind farm using the Doubly Fed Induction Generator (DFIG) turbine type and STATCOM under faulty conditions. The model is implemented inside the DigSILENT Power Factory simulation tool. The results show that STATCOM can improve the voltage stability of wind farms at the point of connection to the grid.

Optimization of wind power connection in power systems considering transmission switching technique and distribution factors

The optimal wind power generation connection in power systems is a growing field of study recently. Accordingly to the literature, the Optimal Transmission Switching technique and the Power Transfer Distribution Factors have been applied to the optimization problem of the capacity of wind power connection. This paper proposes a new methodology for maximization of wind power connection that integrates these two methods mentioned. The optimization process is based on the linearized power flow and chooses the best line for a firm wind farm connection from a list of possible candidates. The proposed algorithm is evaluated considering the 11-Bus tutorial system, the IEEE New England and IEEE-118 systems.

Assessment of Flicker Emission in a Grid Connected Wind Farms

Wind farms in Tamil Nadu's Coimbatore district have identified several issues, including flickering emissions, frequent generator tripping, and power evacuation issues caused by a weak grid. Taking into consideration the scarcity of research on flickering emissions, this work focuses on the causes of short-term flicker severity (Pst) in wind farms that export generated power to industrial loads. To identify the scenarios that cause flickering, simulation models of fixed speed wind farm and variable speed wind farm with controllers were developed using DIgSILENT power factory software. The flicker emissions were measured at the wind farm substations using Fluke and Dranetz PX5.8 power quality analyzers in accordance with the IEC 61400-21 standard. To validate the simulation model, the results from the flickermeter during the simulation and the field measurements were compared. According to the results of this research, both fixed and variable speeds produce flicker emissions that exceed the IEC standard limit, that causes the power electronics-based industrial drives to fail to operate. The controllers were developed to improve the performance of wind farms that will benefit the current and future wind energy-efficient conversion systems.

The Impact of Integration of the VSC-HVDC Connected Offshore Wind Farm on Torsional Vibrations of Steam Turbine Generators

For remote offshore wind farms, transmitting power to the main onshore grid via a Voltage Source Converter High Voltage Direct Current (VSC-HVDC) system is the mainstream of power transmission. It is not only cost-effective in long-distance transmission, but also can fully meet the grid side requirements such as black start, voltage support, fault ride through and frequency support. However, it still has some problems, such as the possible impact on the power grid needing to be paid attention to. In this paper, its impact on the torsional responses of turbine generator units neighboring to the onshore side of AC bus is studied by using the DIgSILENT PowerFactory software. It is found that the effects of the Sub-Synchronous Torsional Interaction (SSTI) with onshore controls and the generator de-rating operations can significantly affect the damping ratio of turbine torsional modes, whereas the effects of the machine configurations and the amount of wind farm power integrated can affect the electrical torque disturbance. The most noteworthy is that their effects can be superimposed on each other if these factors act simultaneously, which would lead to increased vibrations and reduce the turbine shaft’ s life. The findings will be helpful for avoiding accidents caused by torsional vibrations when it is going to integrate a VSC-HVDC connected wind farm into a power grid.

Analysis of grid-connected operation characteristics and limit access capacity of offshore wind farms

Wind power is a relatively ripe renewable energy power generation technology, which has the superiority of large-scale development and utilization. Large-scale deep-sea wind farms are a significant direction for wind power development. With the continuous growth of the capacity of a single offshore wind farm, it is necessary to study the impact of grid connection of large-capacity offshore wind farms on the normal operation of the power grid, which can guarantee the safety and stability of the power grid. Based on the smooth working of the power system, it is meaningful to determining the limit access capacity of offshore wind farms for guiding offshore wind power planning. In this paper, an evaluation index system for the operation characteristics of offshore wind farms integrated into regional power grids is constructed, and based on that, the influence of offshore wind farms on the safety, stability, economy and power quality of regional power system operation is studied, and the grid-connected power limit of offshore wind farms is further calculated.

Application of Association Rule Mining in offshore HVAC transmission topology optimization

This work develops a hybrid optimization method for determining optimal radial transmission topologies for the connection of offshore wind farms combining Association Rule Mining (ARM) and a greedy algorithm. The method is capable of optimally placing offshore substations and accounts for Capital Expenditures (CAPEX), Corrective Maintenance (CM), losses and Expected Energy Not Transmitted (EENT). The stochastic nature of wind is also considered. First, an inequality based apriori algorithm is applied to a randomly generated population of Offshore Wind Power Plant (OWPP) pairs within a specified search domain. This way, a set of simple constraints is obtained reducing the effective combinatorial search space. A verified optimal greedy algorithm is then applied to efficiently search the reduced search space for the lowest cost radial topology to connect offshore wind. The hybrid approach is shown to introduce minimal error given a sufficient sample population while greatly extending the feasible problem size of the greedy search algorithm.

Measurement and simulation of power quality issues in grid connected wind farms

Wind energy sources are crucial if they are to be effectively exploited in the grid network. But, the grid connection brings the problems of power evacuation, power quality issues and unwanted tripping of generators. The paper presents the issues in the power quality of a variable speed wind farm synchronous generator located at Tamilnadu (India). According to IEC 61,400–21, the power quality events such as voltage fluctuation, harmonics and flicker are measured by power quality analysers connected at the selected locations in the wind farm. A wind turbine model and its control strategy are developed using the DIgSILENT simulation software. The control schemes for the generator side and the grid side converters are implemented to assure the power quality problems. With the simulation model, various circumstances and their effect on the performance of the wind farm are analysed. The results of the simulation are related to the recorded waveform to validate the model of the wind farm. This study will be useful for the turbine operators and manufacturers to assess the causes and severity of power quality issues well in advance to implement the necessary remedial measures.

Research on the Probabilistic Load Flow Method of Power System Considering Wind Power Integration

Abstract Due to the uncertainty of renewable energy and load, probabilistic power flow as an effective method to analyse the probabilistic properties of power systems. In this paper, a linearized ac probabilistic power flow model is established, and Monte Carlo simulation method is used to analyze the probabilistic power flow of the power grid containing wind farms. By connecting wind farm to node 13 of IEEE14-bus system, the voltage accumulative distribution curves of node 4, node 5 and node 13 are obtained. The results show that the random output of wind farm increases the fluctuation of node voltage, and the fluctuation phenomenon of node voltage becomes serious as the distance of the access point of the wind farm approaches. By connecting wind farms at node 4 and node 14, the voltage accumulative distribution curves of access nodes were obtained. Through comparison, it is concluded that the access of wind farm has a small effect on the voltage of PQ nodes close to PV nodes, but has great influence on the voltage of PQ nodes away from PV nodes. By adding wind farms at node 13, the active power cumulative distribution curves of branch 2-5, branch 3-4, branch 5-6 and branch 6-13 were obtained. By comparison, the active power flow of different branches of the system is affected differently after access to the wind farm. The fluctuation of the active power flow of the branch becomes serious with the shortening of the distance from the access point of the wind farm. The simulation analysis can provide more comprehensive and useful information for the planning and operation personnel of power system including wind farm.

Adaptive Parameter Estimation for Static Var Generators Based on Wind Speed Fluctuation of Wind Farms

The emergence of flexible AC transmission technology provides a new technical means for ensuring the reliable grid connection and stable operation of wind farms. Among them, the static reactive power generator has a fast response speed, which can accurately compensate for the reactive power of the wind farm and improve the power factor; this is widely used in wind farms. To obtain accurate static var generator (SVG) parameters to meet the reliability requirements of a power system, we propose an adaptive estimation method that considers the wind speed fluctuation of wind farms. First, analyzing the dynamic SVG characteristics allowed us to establish a mathematical model. Then, the corresponding relationship between the sensitivity values of the parameters to be identified and the fluctuating wind speed was established, and low and high wind speed models were constructed. Finally, for accurate estimation considering wind speed fluctuation, the parameter initial values are obtained by combining the low wind speed and high wind speed model identification parameters, and we introduce the multimode hybrid estimation of the SVG parameters, providing a new method for accurately identifying the SVG model parameters. The simulation results of the parameter estimation demonstrate the accuracy and stability of the proposed method.

Measurement and Simulation of Power Quality Issues in Grid Connected Wind Farms

Measurement and Simulation of Power Quality Issues in Grid Connected Wind Farms

Security-Constrained Unit Commitment for Hybrid VSC-MTDC/AC Power Systems With High Penetration of Wind Generation

This paper presents the solution to the security-constrained unit commitment (SCUC) problem for hybrid voltage source converter (VSC) based multi-terminal DC/AC (VSC-MTDC/AC) power systems with high penetration of wind generation. The formulated SCUC model presents a detailed representation of the VSCs with two different VSC control strategies considered, constant DC voltage control (master-slave control) and DC voltage droop control. In addition, Grid Code for wind farm connection is considered. Benders decomposition is used to solve the formulated SCUC problem by decomposing it into a master problem for solving unit commitment (UC) and hourly transmission security check subproblems. The final SCUC solution provides an economic and secure operation and control strategy for the meshed MTDC/AC system. Numerical tests illustrated the efficiency of the proposed SCUC model.

Research on Fault Ride Through Control Strategy of Wind Farm via MMC-HVDC Networking System

Large-scale long-distance grid connection of wind farms has problems such as high line losses and small transmission capacity. The use of modular multilevel flexible direct current transmission (MMC-HVDC) for power transmission is an effective solution. And the recovery of system safety and stability under fault conditions is a hot spot for research. For the problem of DC bus voltage rise caused by symmetrical faults on the grid side, the AC voltage step-down method of the wind farm side converter station (WFMMC) is used for coordinated control with the self-regulating energy-consuming circuit. The capacity required for the self-regulating dissipation resistor is reduced while ensuring that the wind farm networked MMC-HVDC system can traverse the fault stably and smoothly; And the controller for suppressing negative sequence current is designed to effectively mitigate the three-phase current imbalance caused by asymmetric faults occurring on the grid side. The active power is transferred to the grid side while protecting the switching devices from damage. Finally, the correctness and effectiveness of the proposed scheme are verified in the PSCAD/EMTDC simulation software.

Optimal Allocation Algorithm of Grid Side Energy Storage Capacity under Large Scale Wind Farm Connection

For grid energy storage capacity configuration is not reasonable, problems such as instability in crossing the river power fluctuations, are proposed based on a large scale wind power grid side under the condition of energy storage capacity of the optimal allocation algorithm, through the use of large-scale wind farm access method to achieve the optimal design of power grid model, so as to quickly solve the micro grid energy storage capacity planning cost and energy consumption data, according to the results. The operation parameters, energy loss and other numerical values of the model in the power grid are controlled, and according to the calculation results. Finally, the experiment proves that the optimization configuration algorithm of the power grid side energy storage capacity under the large-scale wind farm access has higher practicability and accuracy in the practical application process, and fully meets the research requirements.