Stability Of Wind Farm Research Articles

Adaptive third order terminal sliding mode power control of DFIG based wind farm for power system stabilisation

A Doubly Fed Induction Generator (DFIG) based wind farm (DFIGWF) has been proposed in this paper for improving the stability of wind farm with multi machine power system by implementing of an adaptive third order terminal sliding mode power controller for rotor side converter. In comparison to the conventional one our proposed strategy significantly improves the active power output by DFIGWF at after fault state. Subsequently electrical power output is amended by generators, and this improves the stability of system. The overall improvement in the relative oscillations of the generators present in different areas of a standard IEEE 6 machine 30 bus power system is analyzed by comparing the critical clearing time of the proposed control strategies with conventional one.

A Method of Reduced-Order Modal Computation for Planning Grid Connection of a Large-Scale Wind Farm

For planning the grid connection of a wind farm, small-signal stability needs to be examined to ensure the stability of wind farm as a standalone system. However, for a large-scale wind farm with m wind turbine generators (WTGs), the dimension of state matrix is nm if on average the order of dynamic models of the WTGs is n. Thus, when the number of the WTGs in the wind farm is over several hundred or more, high-dimensional numerical difficulty of modal computation may occur. Therefore, in this paper, we propose a method of reduced-order modal computation for the application in planning the grid connection of the large-scale wind farm. Dimensions of matrices involved in the reduced-order modal computation are m and n such that the numerical difficulty of modal computation is effectively avoided. In the paper, the effectiveness of proposed method of reduced-order modal computation is demonstrated and evaluated by an illustrative simple example wind farm and an example large-scale wind farm with 200 WTGs.

A Method of Boosting Transient Stability of Wind Farm Connected Power System Using S Magnetic Energy Storage Unit

A Method of Boosting Transient Stability of Wind Farm Connected Power System Using S Magnetic Energy Storage Unit

H∞ Current Controller of WRIM Based Flywheel Storage System under Unbalanced Stator Voltage

Flywheel storage systems (FSSs) are commonly associated with wind farms to support them to provide services to the grid such as power smoothing, frequency control, and voltage control. Although FSSs are not concerned by the grid code requirements, their stability and availability under unbalanced stator voltages are very important to ensure both wind farm stability and supply quality. In this context, this paper proposes a robust H ∞ controller for wound rotor induction machine (WRIM) driven FSS under stator voltage unbalance. The controller purpose is to suppress rotor current oscillations resulting from the negative sequence as well as to guarantee the system robustness in the presence of parameter uncertainties. The robust controller design based on mixed-sensitivity H ∞ control that guarantees the robust stability (RS) and robust performance (RP) is presented in detail. The performance of the H ∞ controller has been evaluated with simulations in MATLAB/Simulink using simpower systems for both unbalanced stator voltage and parameter uncertainties.

Transient Stability Enhancement of DFIG based Offshore Wind Farm Connected to a Power System Network using STATCOM

This paper presents the transient stability enhance of DFIG-based offshore wind farm connected power system network using STATCOM. The studied system is simulated in MATLAB/Simulink platform for study the effect of transient disturbances like, three phases to ground fault, sudden load change, voltage sag & swell. A fully aggregate model of wind DFIG is used for simulation study of system. The DFIG based wind generator, more sensitive to the grid faults than other wind generators. During transient disturbances DFIG terminal voltage reduced below the critical value and hence DFIG trips. The external reactive power support is required for stabilization of wind farm during the transient disturbances. In studied system STATCOM is used to fulfil the reactive power requirement to stabilize the wind farm. In presence of STATCOM, DFIG does not trip during transient disturbances of power system and all bus voltages & DFIG terminal voltage are also improved.

Analysis of Influencing Factors on Transient Voltage Stability of a Grid-connected DFIG-based Wind Farm

A simulation model of WSCC three-machine nine-node system integrated with a wind farm based on double fed induction generator (DFIG) was established using the power system analysis toolbox PSAT, and the outlet bus of DFIG was set as PV node. Some influencing factors on the transient voltage stability of grid-connected wind farm were analyzed, when short circuit fault occurs in the power grid side. The results show that fault clearing time, capacity of wind farm, location of short circuit fault, and reactive power compensation have all influences on the transient voltage stability of the wind farm. According to different locations of short circuit in the power grid, the grid-connected wind farm has different minimum capacity which can guarantee the transient voltage stability. The static var compensator (SVC) installed in the wind farm can improve the transient voltage stability only for the short circuit point which is far from the grid entry point of wind farm in electrical distance.

Stabilization of Wind Farm by Using PMSG Based Wind Generator Taking Grid Codes into Consideration

This paper presents a new operational strategy for a large-scale wind farm (WF) which is composed of both fixed speed wind turbines with squirrel cage induction generators (FSWT-SCIGs) and variable speed wind turbines with permanent magnet synchronous generators (VSWT-PMSGs). FSWT-SCIGs suffer greatly from meeting the requirements of fault ride through (FRT), because they are largely dependent on reactive power. Integration of flexible ac transmission system (FACTS) devices is a solution to overcome that problem, though it definitely increases the overall cost. Therefore, in this paper, a new method is proposed to stabilize FSWT-SCIGs by using VSWT-PMSGs in a WF. This is achieved by injecting the reactive power to the grid during fault condition by controlling the grid side converter (GSC) of PMSG. The conventional proportional-integral (PI)-based cascaded controller is usually used for GSC which can inject small amount of reactive power during fault period. Thus, it cannot stabilize larger rating of SCIG. In this paper, a suitable fuzzy logic controller (FLC) is proposed in the cascaded controller of GSC of PMSG in order to increase reactive power injection and thus improve the FRT capability of WF during voltage dip situation due to severe network fault. To evaluate the proposed controller performance, simulation analyses are performed on a modified IEEE nine-bus system. Simulation results clearly show that the proposed method can be a cost-effective solution which can effectively stabilize the larger rating of SCIG compared to conventional PI based control strategy.

Modeling and Stability Analysis of DC-Link Voltage Control in Multi-VSCs With Integrated to Weak Grid

This paper contributes to giving physical insights into stability of DC-link voltage control in multi-wind turbines integrated to weak grid. Wind farm stability operation will suffer from integrating to weak AC grid, due to strong coupling between the wind turbines control and grid dynamics. Multi-VSCs model is presented for DC-link voltage control stability analysis with effect of coupling among VSCs and grid strength. Based on the model, self-impact components and interaction-impact components are presented to study interactions among VSCs. Impacts of VSCs interactions on stability of DC-link voltage control are studied by investigating self-impact and interaction-impact components variations with considering grid strength, operating point and control loop bandwidth. It is found that interactions between VSC1 and VSC2 become more serious with decline of grid strength, decaying stability of VSCs. Theoretical analysis is verified with simulation of two parallel wind turbines connected to weak grid.

A comprehensive comparison of STATCOM versus SVC-based fuzzy controller for stability improvement of wind farm connected to multi-machine power system

Stabilization of wind farm (WF) is considered one of the major serious issues for developing power systems based on renewable energy sources. A comparison of dynamic performances for FACTS devices like STATCOM and SVC is presented in this paper. Such devices are employed to stabilize WF integrated with multi-machine power system (WFMPS). Fuzzy logic controller (FLC) has been employed for controlling FACTS devices to enhance WFMPS performance under different abnormal conditions. Three-phase to ground short circuit fault has been taken into consideration in different locations of system. MATLAB/Simulink is used to perform the modeling and simulation of WFMPS. The obtained results demonstrate the effect of both SVC- and STATCOM-based FLC on damping the system oscillations and improving the system dynamic performance in the post-fault duration. The comparison confirms superior dynamic performance and fast fault recovery of STATCOM-based FLC through different fault conditions compared with SVC-based FLC.

风电场无功电压模糊多目标决策方法

针对风电场并网运行难以有效兼顾稳定性与经济性的问题，提出了风电场运行经济性和稳定性目标，其中经济性目标考虑风电场有功损耗指标，稳定性目标考虑风电场无功源无功裕度和风电场电压偏差两个指标。在此基础上，建立了风电场无功电压多目标优化控制模型。该模型以SVC与双馈风电机组的无功功率为控制对象，运用模糊多目标决策方法将风电场无功电压优化转换为一个多目标、多约束的非线性规划问题，并采用粒子群算法进行求解。仿真算例结果表明，所提出的优化决策方法能够实现风电场运行经济性和稳定性的双重目标，在提高风电场电压稳定性的同时，合理降低了风电场损耗。 To solve stability and economy coordinated problem caused by wind farm integration, the targets of stability and economy are put forward, in which economy target considers active power loss, and stability target includes reactive power reserve capacity and voltage deviation of wind farm. Based on this, an optimization control model of reactive power and voltage fuzzy multi-objective decision making method of wind farm is established, in which the reactive power of SVC and DFIG are taken as control objectives, and the fuzzy multi-objective decision making method is used to convert the optimization of reactive power and voltage into a multi-objective and multi-constrained nonlinear programming problem. The particle swarm algorithm (PSO) is adopted to solve the built model. The simulation example results show that the proposed method can achieve the dual targets of economy and stability of wind farms, and can improve the voltage stability of wind farms, and reasonably re-duce the power loss of wind farms.

Comparison between FSIG and DFIG wind turbines for wind farm stabilization

Comparison between FSIG and DFIG wind turbines for wind farm stabilization

A Combined Approach of Using an SDBR and a STATCOM to Enhance the Stability of a Wind Farm

This paper presents a method to enhance the stability of a grid-connected wind farm composed of a fixed-speed wind turbine generator system (WTGS) using a combination of a small series dynamic braking resistor (SDBR) and static synchronous compensator (STATCOM). The SDBR and STATCOM have active and reactive power control abilities, respectively, and a combination of these units paves the way to stabilize well the fixed-speed wind farm. In this paper, a centralized control scheme of using an SDBR and a STATCOM together is focused, which can be easily integrated with a wind farm. Different types of symmetrical and unsymmetrical faults are considered to evaluate the transient performance of the proposed control scheme, applicable to a grid-connected wind farm. The effect of a multimass drive train of a fixed-speed WTGS in fault analysis, along with its importance in determining the size of the SDBR to augment the transient stability of a wind farm, is investigated. Extensive simulation analyses are performed to determine the approximate sizes of both SDBR and STATCOM units. Dynamic analysis is performed using real wind speed data. A salient feature of this work is that the effectiveness of the proposed system to minimize the blade-shaft torsional oscillation of a fixed-speed WTGS is also analyzed. Simulation results show that a combination of a small SDBR and STATCOM is an effective means to stabilize the wind farm composed of a fixed-speed WTGS.

Design and Simulation of a New Sliding Mode Controller for STATCOM Based Wind Farm

Sliding mode controller (SMC) is a highly significant nonlinear controller under condition of certain and partly uncertain dynamic parameters of system. This paper focused on design and implementation of a sliding mode controller for STATCOM. Intend for its application to wind farm connection to the grid. The proposed inverse system sliding mode controller based on nonlinear feedback linearization technology for system decoupling, which enhance the transient stability of wind farms and stabilizes the grid voltage about the given operating point when the fault occurs closer to the wind farms. The simulation results have shown the improved performance of the proposed controller has better control effectiveness and efficiency compared with the conventional controller of inverse system , the proposed controller on wind power system and which assist in improving capability of the wind farms to ride through disturbances, dynamic power flow control of the transmission lines, enhancing power oscillation damping under a sudden fault. Moreover, the proposed control scheme is very simple and easy to implement.

Comparative Study of the Behavior of a Wind Farm Integrating Three Different FACTS Devices

Improving grid connection of wind farms is a relevant issue to be addressed, especially for fixed-speed wind turbines. Certain elements, such as FACTS (Flexible AC Transmission Systems), are able to perform voltage and reactive power regulation in order to support voltage stability of wind farms, and compensate reactive power consumption from the grid. Several devices are grouped under the name of FACTS, which embrace different technologies and operating principles. Here, three of them are evaluated and compared, namely STATCOM (Static Synchronous Compensator), SVC (Static Var Compensator) and SSSC (Static Synchronous Series Compensator). They have been modeled in MATLAB / Simulink, and simulated under various scenarios, regarding both normal operation and grid fault conditions. Their response is studied together with the case when no FACTS are implemented. Results show that SSSC improves the voltage stability of the wind farm, whereas STATCOM and SVC provide additional reactive power.

Simulation of the Affected Wind Power Transient Stability by Means of SVC and STATCOM

In the paper the models of IG and DFIG have been analyzed, and then the two reactive power compensations SVC and STATCOM have been introduced. Finally, use the simulation software of power system PSCAD to simulate the process of wind power integrating into grid. In the simulation results, it’s obvious that the DFIG has better transient stability than IG; install SVC or STATCOM can improve transient stability of wind farm, but SVC is apt to cause harmonic pollution, and STATCOM can improve transient stability to both kinds of generators.

Wind Speed Prediction Based on Improved Grey Neural Network Model

Wind speed forecasting is an effective method to improve power stability of wind farm. Grey system theory have certain advantages in the study of poor information and uncertainty problems, it is suitable for the system with limited computing power and data storage capacity, such as wind turbine control system. In order to further improve the prediction accuracy of grey model, we combined GM (1, 1) model and BP neural network prediction model in this paper, and improved the combined model by background value optimizing and introducing genetic algorithm. Through analyzing the simulation results and comparing the forecasting results with the actual wind speed, it is clear that the improved combined prediction model is superior to pure grey forecasting model and it meets the needs of the wind power control.

Active power variation in wind farms by varying the number of wind turbine units

Aggregated representation of wind turbine units in the wind farm has been normally adopted for modelling and analysis of dynamic performance, with power variation obtained by change of wind speed in the literature. This paper presents a different scenario of power variation of wind farms by the addition and removal of turbines in wind farms and its implication in modelling and stability of wind farms. The steady-state and dynamic stability with the aggregated model of the wind farm has been analysed with variation in the number of turbine units and has been corroborated with time domain simulation in DIgSILENT Power Factory software. It has been concluded that the variation in the number of wind turbines generators connected to the same transmission line has a minimal impact on the stability in nonseries-compensated line; however, significant impact on the stability has been observed in series-compensated system.

Wind turbine converter control interaction with complex wind farm systems

This study presents wind turbine converter stability analysis of wind farms in frequency domain. The interaction between the wind turbine control system and the wind farm structure in wind farms is deeply investigated. Two wind farms (i.e. Horns Rev II and Karnice) are taken into consideration in this study. It is shown that wind farm components, such as long high-voltage alternating current cables and park transformers, can introduce significant low-frequency series resonances seen from the wind turbine terminals that can affect wind turbine control system operation and overall wind farm stability. The same wind turbine converter control strategy is evaluated in two different wind farms. It is emphasised that the grid-side converter controller should be characterised by sufficient harmonic/noise rejection and adjusted depending on wind farms to which it is connected. Various stability indices such as gain margin, vector gain margin and phase margin are used in order to emphasise the differences between the two wind farms.

Fault Ride through Capability Improvement of Wind Turbine Based DFIG Considering an Optimized Crowbar Along with STATCOM under Grid Fault Condition

Grid disturbances, especially grid faults, have very unfavorable effect on the performance of wind turbine based Doubly Fed Induction Generator (DFIG). In this study active and reactive powers control of DFIG with STATCOM has been carried out to improve Fault Ride Through (FRT) capability of a wind turbine. In order to excel improvement of the DFIG behavior under grid fault disturbances, an optimized crowbar protection method is also considered together with STATCOM. The optimized protection crowbar resistance is achieved through Analytical Hierarchy Process (AHP) algorithm. Simulations results illustrate that an optimized crowbar protection method along with STATCOM has improved the stability of wind farm and provide grid code requirement compared with that of methods without using the optimized crowbar resistance.

Method for Enhancement of Power Quality at Point of Common Coupling of Wind Energy System

In this paper a compensation strategy based on a particular Custom Power System (CUPS) device, the Unified Power Quality Compensator (UPQC) has been proposed. A customized internal control scheme of the UPQC device was developed to regulate the voltage in the WF terminals, and to mitigate voltage fluctuations at grid side. The voltage regulation at WF terminal is conducted using the UPQC series converter, by voltage injection “in phase” with point of common coupling (PCC) voltage. On the other hand, the shunt converter is used to filter the WF generated power to prevent voltage fluctuations, requiring active and reactive power handling capability. The sharing of active power between converters is managed through the common DC link. Therefore the internal control strategy is based on the management of active and reactive power in the series and shunt converters of the UPQC, and the exchange of power between converters through UPQC DC–Link. This approach increases the compensation capability of the UPQC with respect to other custom strategies that use reactive power only. The proposed compensation scheme enhances the system power quality, exploiting fully DC–bus energy storage and active power sharing between UPQC converters, features not present in DVR and D–STATCOM compensators. Simulations results show the effectiveness of the proposed compensation strategy for the enhancement of Power Quality and Wind Farm stability.