Wind Farm System Research Articles

Assessing the Impact of DFIG Synthetic Inertia Provision on Power System Small-Signal Stability

Synthetic inertia provision through the control of doubly-fed induction generator (DFIG) wind turbines is an effective means of providing frequency support to the wider electrical network. There are numerous control topologies to achieve this, many of which work by making modifications to the DFIG power controller and introducing additional loops to relate active power to electrical frequency. How these many controller designs compare to one-another in terms of their contribution to frequency response is a much studied topic, but perhaps less studied is their effect on the small-signal stability of the system. The concept of small-signal stability in the context of a power system is the ability to maintain synchronism when subjected to small disturbances, such as those associated with a change in load or a loss of generation. Amendments made to the control system of a large-scale wind farm will inevitably have an effect on the system as a whole, and by making a DFIG wind turbine behave more like a synchronous generator, which synthetic inertia provision does, may incur consequences relating to electromechanical oscillations between generating units. This work compares the implications of two prominent synthetic inertia controllers of varying complexity and their effect on small-signal stability. Eigenvalue analysis is conducted to highlight the key information relating to electromechanical modes between generators for the two control strategies, with a focus on how these affect the damping ratios. It is shown that as the synthetic inertia controller becomes both more complex and more effective, the damping ratio of the electromechanical modes is reduced, signifying a decreased system stability.

Comparative Studies on the Impedance Models of VSC-Based Renewable Generators for SSI Stability Analysis

Recently, emerging oscillation issues have been caused by subsynchronous interaction (SSI) between voltage source converters (VSCs) based renewable generators and ac/dc grids. To investigate the dynamics of SSI, several impedance models (IMs) of VSC have been developed in previous studies. They are established in different reference frames and consider the entire or just parts of the control systems. However, it is still an unanswered question whether or not the existing IMs are suitable for SSI analysis and to what extent the IMs with different modeling details affect subsynchronous dynamics. To fill in this gap, this paper, first, reviews the existing IMs of VSC and clarifies their relationship. Then, their frequency characteristics are examined so as to select the proper models for the studies of sub-/supersynchronous and high-frequency dynamics. Next, both zero-pole and IM-based SSI analyses are carried out on a simplified system and a real-world wind-farm system that suffered actual SSI incidents. The results indicate that the outer-loop control has a significant impact on the subsynchronous dynamics, and only those IMs taking full-scale controls and frequency-coupling effects into account can reflect SSI accurately. Finally, both modal analysis and electromagnetic transient simulations have been conducted to verify the theoretical results.

Evaluating the Environmental Impacts and Energy Performance of a Wind Farm System Utilizing the Life-Cycle Assessment Method: A Practical Case Study

The ever-increasing popularity of finding alternative forms of renewable energy has seen an increased interest and utilization of wind energy. The objective of this research therefore, is to evaluate the environmental impacts and energy performance of wind farms. This study was operationalized in Jordan using a life-cycle assessment (LCA) method. The environmental impact is evaluated through lifecycle emissions that include all emissions during various phases of the project. The energy performance is illustrated by the energy indicators. The latter is the energy payback ratio (EPR) and the energy payback time (EPT). This study was conducted on a 38 Vestas V112 3-MW wind turbine located in the southern region of Tafilah in Jordan that is host to the country’s first wind farm. SimaPro 7.1 software was used as the modeling platform. Data for this study were collated from various sources, including, manufacturers, the wind turbine farm, and local subcontractors. A software database was used for the modeling process, and the data obtained modeled in accordance with ISO 14040 standards. The findings of this study indicate that the impacts of the transportation and installation phases were moderate, with the largest negative environmental impact deriving from the manufacturing phase. To remedy some of the negative impacts in these phases, green cement was used for the turbine foundation to limit the environmental impacts to be had during the installation phase, while the transportation phase saw the utilization of locally-manufactured turbines. Furthermore, an evaluation of the study’s results revealed that the energy payback period of the wind farm is approximately 0.69 year (8 months), while the payback ratio is 29, and the annual CO2 saving estimated to be at 2.23 × 108 kg, 3.02 × 108 kg, 3.10 × 108 kg for an annual generated power of 371, 501, and 515 GWh/year.

Online Tracking of Reactive Power Reserve For Wind Farms

Effective monitoring of VAR capability and reactive power reserve (RPR) of wind farms is an essential approach to assess stability performance of power systems with high wind penetration. However, such information is essentially difficult to obtain because it is not only impacted by many factors like wind conditions and external power grid approximation, but also subject to internal operation constraints of wind farms. An optimal sensitivity based online tracking scheme and its algorithm is proposed in this paper to obtain accurate RPR of wind farms and adapt to impacting factors and internal constraints aforementioned. The simulation results based on an actual wind farm system in China further confirm the effectiveness of the proposed approach.

Accurate aggregated modelling of wind farm systems in modified sequence domain for stability analysis

With the wind power penetration rate continuously rising, a suitable wind farm model considering both accuracy and simplicity is required for power system stability analysis. To accomplish this goal, an accurate aggregated modified sequence impedance model of the wind farm is established in this paper. The modified sequence impedance model of wind turbine generator is established, which considers the coupling between the positive- and negative-sequence impedances. The modified sequence impedances of the ac collection system, transformers, and ac grid are also derived. In this way, the impedance network of the entire wind farm system can be formed and simplified to acquire the accurate aggregated modified sequence impedance. Furthermore, the proposed model is compared with the traditional single-machine aggregated model which shows the necessity of establishing the accurate aggregated model. It is worth noting that the differences among each wind turbine generator’s operation points can be included in the proposed model. Compared with the results of impedance measurements of a target wind farm, the accuracy of the proposed aggregated sequence impedance model of the wind farm is verified in frequency domain. The application of the proposed model in the stability analysis of a grid-connected wind farm is also presented with consideration of the ac grid strength. What is more, the effect of the inertial controller on the wind farm system stability is also analyzed to make the impact of this study much more appealing and up to date.

Summary of Technical Specifications for Offshore Wind Farm Facilities

[Introduction] This paper aims to promote the establishment of a complete technical standards system for offshore wind farms. [Method] The problems existing in the construction of offshore wind farms in China were pointed out, the standards for offshore wind farm facilities at home and abroad were summarized, and the exploration and effectiveness of the technical specifications for offshore wind power facilities by China Classification Society(CCS) were introduced. [Result] Despite the rapid development of offshore wind power in China, the supporting technical specifications for offshore wind power facilities have not been followed up in time, and the whole life cycle technical specifications system, including design, construction, installation, operation and maintenance and abandonment, has not been established. Although Europe has a mature specifications system for offshore wind power facilities, it cannot be completely copied and used, such as the LRFD method of structural design which is related to the environmental conditions and reliability index of the sea area, and the partial factor applicable to the European sea area is not applicable to the Chinese sea area. [Conclusion] Therefore, the technical specification system for the domestic offshore wind power facilities requires the joint efforts and cooperation of the industry, traditional ocean engineering specialty should play a greater role in this field, and the research achievements by CCS in this field can provide some reference values for the establishment of the technical specification system.

A Trajectory Piecewise-Linear Approach to Nonlinear Model Order Reduction of Wind Farms

This paper presents a method to develop computationally efficient dynamic model of a wind farm suitable for large disturbance simulation. The method based on a trajectory piecewise linear approximation uses single and multiple training trajectory to develop a nonlinear reduced order model. Simulation results using a small demonstration wind farm system and a large practical wind farm system are discussed to demonstrate the effectiveness of the model in capturing dynamic behavior of wind farm following large disturbances.

Effects of environmental and turbine parameters on energy gains from wind farm system: Artificial neural network simulations

Artificial neural network modelling has been employed to investigate the effects of various environmental and machine factors on the energy gain from wind farm systems. Numerical comparison of artificial neural network and nonlinear regression from XLSTAT showed that ANN possessed better numerical accuracy in predicting multivariate data. Several artificial neural network models are developed and tested with several structures to obtain the best prediction performance in energy gain from different wind farms in Jordan. The best performing artificial neural network model was used to predict the energy gain from wind farm based on changes in annual wind speed, turbine rotor diameter and turbine power. As a result of 20% increase in turbine power, 14.4%–31% energy gains were recorded across different wind farms. The proposed artificial neural network model was also a good predictor for energy cost resulting from specific wind farm design.

Optimal active power control based on MPC for DFIG-based wind farm equipped with distributed energy storage systems

An optimal active power control scheme based on model predictive control (MPC) is proposed for a doubly-fed induction generator (DFIG)-based wind farm equipped with distributed energy storage systems (ESSs). A two-stage optimal control scheme is proposed. In the first stage, the power reference of each WT and the total power command of ESSs are generated, aiming to reduce the fatigue load of WTs by minimizing variations of thrust force and shaft torque. In the second stage, the charge/discharge power of ESSs are optimized to achieve the fair power sharing and maximize the capacity margin. An MPC based optimization problem is formulated for the constrained multiple input and multiple output (MIMO) wind farm system. The dynamics of converters and WTs are taken into account by the MPC. With the proposed control scheme, the active power references are optimized between WTs and ESSs according to their local wind conditions. Fatigue loads of WTs are reduced efficiently by coordinating the DFIG-based WTs and distributed ESSs. A wind farm with 10 DFIG-based WTs was used to validate the control performance of the proposed optimal active power control scheme.

GenCo's mid‐term optimal operation analysis: interaction of wind farm, gas turbine, and energy storage systems in electricity and natural gas markets

In this study, optimised and coordinated operation planning of a generation company's (GenCo's) generation portfolio consisting of a wind farm, a gas turbine, and energy storage systems [battery and natural gas (NG) energy storage systems] is modelled. In this model, all the electrical energy (EE) and NG trades are performed through long-term contracts and spot markets in a deregulated environment. It is assumed that EE is traded through day-ahead market and bilateral contracts while NG is traded via a daily spot market in conjunction with baseline and intra-day mid-term contracts. The proposed framework enables the GenCo to maximise its profit in operation planning horizon by coordinating different types of contracts and energy arbitrage. The operation planning model is presented as a mixed-integer linear programming problem. Five case studies are implemented in GAMS software to evaluate the effectiveness of the proposed model and analyse different factors affecting benefits of the GenCo.

Harmonic resonance overvoltage due to main transformer energization in large wind farms, Zafarana, Egypt

Abstract When a large power transformer is energized, a high magnitude inrush current may result in harmonic resonance overvoltage (HRO), if the system has resonance phenomenon. Such overvoltages may cause large stresses on the system. This paper investigates the energization of two winding 220/22 kV main power transformer in a weak system of a grid-connected wind farm. To achieve this aim, the produced HRO during the energization of the main power transformers and the affecting factors are investigated. In addition, the effect of the sympathetic inrush phenomena is studied. Finally, the sequential energization of the three-phase transformer and the pre-insertion resistor method are discussed as mitigation methods. The investigated scenarios and results will contribute in developing the power system restoration procedures for existent wind farm, its extension, and future-planned wind farms.

Design and energy analyses of alternative methanol production processes driven by hybrid renewable power at the offshore Thebaud platform

In the present study, novel processes for the offshore production of methanol via alternative routes than reforming of synthesis gas are investigated. Two process schemes are defined differing in the carbon source in input, i.e. the catalytic hydrogenation of carbon dioxide and the direct oxidation of methane via radical gas reaction. Both the schemes are considered to be installed at the main facility of the Canadian Sable Offshore Project in the Atlantic Ocean, the gas production Thebaud platform. Both offshore wind farm and solar parabolic trough systems are integrated to supply electricity and heat power to each process. The Aspen HYSYS is used to simulate the chemical processes, while Homer Pro and System Advisor Model are adopted for the design of feasible renewable energy plants. A thermodynamic modelling through energy analysis is conducted to evaluate and compare the energy efficiencies of sub-systems and overall schemes. Moreover, a preliminary design analysis is performed to estimate the footprint required for the components of the two schemes located on the offshore facility. The present results reveal that the methane-to-methanol process makes more efficient use of the integrated renewable sources but requires relatively higher space at the installation than the other scheme.

Simulation and experiment of a turbine access system with three-axial active motion compensation

This study aims to investigate a new turbine access system (TAS) for offshore wind farms in Taiwan Strait sea conditions having a wave period of 7.5 s and a significant wave height of 1.5 m, including the novel system integration of mechanism design, hydraulic driving system, and control system. The dynamic co-simulation of TAS is achieved firstly for confirming the system design and parameters. After that, a full-scale test rig is set up for experimental verification. The vertical height, the roll angle and the vertical acceleration of the TAS end effector can be reduced effectively through the active motion compensation control for improving the access safety of the offshore wind turbine.In simulation, the dynamic modelling of mechanism is implemented by software ADAMS. The hydraulic driving system and the control system are derived mathematically in this study and implemented via MATLAB/SIMULINK. Then, the dynamic simulation of TAS is achieved through the co-simulation of ADAMS and MATLAB/SIMULINK for verifying the active compensation control performance of TAS. In addition, fuzzy sliding mode control is used to develop the roll and pitch controllers for improving the compensation performance.In the experiment, a full-scale test rig of TAS is set up for verifying the effect of active compensation control system experimentally. Through the active compensation control experiment in the full-scale test rig, the vertical height, the rolling angle and the vertical acceleration of the TAS end effector can be reduced and validated by practical experiments.

Optimal Operation of Wind Farm for Reducing Power Deviation Considering Grid-Code Constraints and Events

In wind farm (WF) systems, the set-points of wind turbine generators (WTGs) is determined by the wind farm operator. A change in the value of set-point in two consecutive intervals leads to power fluctuations in the WF system, i.e. power deviation. A large amount of power deviation may adversely affect the operation of the WF system. Therefore, this paper proposes a strategy for operation of a WF system to minimize the power deviation of WTGs during operation time. By using the proposed strategy, the change in set-points of WTGs is minimized and the output power of WTGs is therefore smoother and avoids unnecessary fluctuations. Several grid-code constraints are also considered for operation of the WF system. This ensures the WF system to operate in compliance with the requirements from transmission system operator. Besides, an additional strategy is also proposed to monitor all events in the WF system. Whenever an event occurs in the system, the set-points of WTGs are rescheduled considering the event. Therefore, the proposed operation strategy is also capable of handling events in the WF system. Finally, the simulation results with and without the proposed method are compared to show the effectiveness of the proposed method.

Improved Blocking Scheme for CPL Current Protection in Wind Farms Using the Amplitude Ratio and Phase Difference

Large-scale wind generators connected to a power system turn the collector system into a multi-power wind farm network. With increasing fault current supplied by wind generators, the collector power line (CPL) current protection may lose selectivity. Directional elements are widely used to block the CPL current protection. However, wind generators are different from synchronous generators. The reliability and adaptability of traditional directional elements used in wind farms have not been well researched. For this reason, the fault current characteristics of doubly fed induction generators (DFIGs) are first analyzed in different low voltage ride-through (LVRT) strategies. It is concluded that the traditional directional elements may be insufficiently sensitive or malfunctioning to block the CPL current protection in wind farms. Hence, constructing the amplitude ratio and phase difference-based directional blocking scheme is proposed in view of the DFIG weak-feed. The proposed scheme, based on the system side and CPL current, is easy to implement and suitable for the application. Finally, the simulation of a DFIG-based wind farm system with the four CPLs is carried out with MATLAB/Simulink. The simulation results show good preference, strong adaptability, and high reliability for the proposed method, and the validity is demonstrated.

Frequency regulation participation of offshore wind farm integrated by diode‐rectifer HVDC system

Large-scale wind farms integrated with multi-terminal direct current (MTDC) system decouples the frequency between the wind farms and the receiving end, resulting in weakened frequency regulation ability of the onshore AC grid. Recently a new topology is proposed, called diode rectifier based HVDC, which recouples the wind farm and onshore AC system due to its characteristics, where offshore AC voltage changes with the DC voltage of HVDC system. A coordinated power control strategy for frequency regulation participation is proposed in this paper for offshore wind farms connected with diode-rectifier based high voltage direct current (HVDC) system. Considering the primary frequency and inertia response control, variable power supplementary control is implemented in wind turbines, and a telecommunication-less method of frequency event detection via detection of offshore AC voltage is proposed, avoiding communication delay and communication failure. Simulations using EMTDC/PSCAD show that frequency dip can be accurately detected by the AC voltage of offshore wind farm, and wind farm can quickly compensate active power.

Parameters tuning of doubly fed induction generator systems with static synchronous compensator based on Chaos orthogonal particle swarm optimization

For Double-Fed Induction Generator (DFIG) wind farm systems with Static Synchronous Compensator (STATCOM), by optimizing multiple proportional integral (PI) controllers parameters of DFIG and STATCOM, the performance of the wind power system is significantly improved and the voltage of point of common coupling (PCC) is quickly restored when a low voltage due to a grid fault. Chaos orthogonal particle swarm optimization is proposed to make the integral time absolute error (ITAE) of active power of DFIG, DC-link voltage of converter of DFIG and voltage of PCC minimum. The orthogonal method is used to get the range of parameters and identify the weight relations between different indicators. And then the chaos algorithm is used to initialize the algorithm. Finally, the particle swarm optimization (PSO) can effectively improve the efficiency of the optimization. Based on MATLAB/Simulink, the simulations of wind farm containing STATCOM incorporated into the infinite system under different conditions both show that the application optimized PI controllers have good dynamic performance, which validates the effectiveness of the optimization algorithm.

Design of robust model predictive controllers for frequency and voltage loops of interconnected power systems including wind farm and energy storage system

The controllers are used to reduce fluctuations in frequency deviations and tie-line power flow exchange of an interconnected power system due to load and voltage disturbances. This study proposes a control strategy based on model predictive control (MPC) procedures with various design schemes for an unequal two-area interconnected power system. The study model comprises voltage excitation and frequency loops with necessary interactions between them. Flywheel as an energy storage system along with wind energy are engaged in the model under study. The tuning parameters of MPC-based controllers are obtained by quadratic problem solver. The validity of the proposed MPC-based controllers is extensively confirmed using the simulation results under different disturbance conditions such as different loadings and voltage changes. The effectiveness of the MPC based on controllers is compared to classical controllers and recent controllers based on optimisation techniques such as genetic algorithm. In addition, the quality specifications of the dynamic responses of the anticipated MPC-based controllers are reported to signify their values. The quality indices along with comparative performance point out the good performance of the demonstrated MPC-based controllers for various estimated novel scenarios.

Optimization and control of offshore wind systems with energy storage

Wind energy is widely exploited as a promising renewable energy source worldwide. In this article, an optimization method for the control and operation of the offshore wind farm as an integrated system considering its operational, economic and environmental impacts is proposed. The state of the offshore wind farm development, and the challenges faced by the offshore wind farms, including the challenges of economic costs, operational reliability, and environmental impacts are reviewed and summarized. A systematic methodology is proposed to optimize the costs of an offshore wind farm system based on a framework that extends from the supervisory level dispatch strategies to individual pitch control for load reduction and fatigue mitigation. This holistic approach is able to improve the efficiency and economic performance of a wind farm through overall system optimization, while explicitly operating each wind turbine using a formally designed control framework leading to an extension of their service lifespan. This work provides thorough introduction and innovative solutions for many economic and environmental issues in offshore wind farm development and has strong application potential.

Research on Integrated Monitoring System of Offshore Wind Farm

Due to the wide distribution of offshore wind farms and the harsh climate of the sea, the operation of wind farms is very difficult. It is unrealistic to manage offshore wind farms according to the operation and management mode of land based wind farms. In order to ensure the safety, stability and economic operation of the offshore wind farm, the intelligent operation of the offshore wind farm is realized. A complete offshore operation monitoring technology scheme is proposed in this paper. Recently, operators can conduct centralized monitoring of wind farms on land onshore centralized control center, and offshore booster stations can be operated on an “unattended” mode. The long term wind farm runs on the way of “no man on duty and few people are on duty”. Meanwhile, it supports operation managers to realize remote centralized monitoring of wind farms in remote centers.