Power Control Of Wind Farm Research Articles

Lifetime extension of waked wind farms using active power control

This paper studies a new active power control (APC) of waked wind farms in order to extend the lifetime of highly loaded wind turbines. We demonstrate that the structural fatigue loading of a single turbine can be significantly alleviated, while the wind farm power production follows a power reference signal. Then, an optimization problem, subjected to a data-driven fatigue load model, is formulated to balance the lifetime fatigue loading of the wind turbines operating within a waked wind farm. A Game-Theoretic (GT) approach is employed to find a lifetime fraction, wherein a wind turbine should actively reject its own dynamic loadings due to turbulence. A large-eddy simulation model is employed for resolving the turbulent flow, the wake structures and its interaction with the atmospheric boundary layer. The applicability and key features of the controller are discussed with a wind farm example consisting of 2×2 turbines. The overall increase of wind farm lifetime is evaluated using the damage equivalent load (DEL) of the tower base fore-aft bending moment of the individual wind turbines.

Active Power Control of Wind Farm Equipped DFIG Wind Turbines with Energy Storage System

Active Power Control of Wind Farm Equipped DFIG Wind Turbines with Energy Storage System

Energy storage of DFIG based wind farm using D-STATCOM

<p>To accommodate the regularity of wind energy; a storage device is required for the wind turbine. This paper proposesa constant power control for wind farm based Doubly Fed Induction Generator, the suggested storage device is supercapacitor which is connected to every wind turbine of the wind farm, it provides output power stability and compensates the deviations between the available wind energy input and the desired active power output. A Distribution – Static Synchronous Compensator (D-STATCOM) is connected at the point of connection of the wind farm, it controls the active and reactive power according to the demand from orpower generation to the electrical grid. The coordinated approach between the supercapacitors and the D-STATCOM mitigates the voltage magnitude fluctuations of the wind farm and provides support to the active power. Simulation studies are carried out inMATLAB/Simulink.

Closed-loop active power control of wind farm based on frequency domain analysis

To further improve the wind power quality and stability, it is necessary to break the existing open-loop wind farm scheduling method and bring new strategies in both wind farm and wind turbine active power control. In this paper, a closed-loop active power control method is proposed based on the active power tracking dynamic characteristics of wind turbines, where the power fluctuations caused by the modeling errors and wind turbulence are isolated and suppressed by a proportional-integral (PI) controller. The PI controller parameters are obtained through the frequency domain analysis with bode diagrams. Then a frequency-domain aggregation and approximation method is proposed to establish the wind farm active power tracking model, and the wind farm-level controller is obtained similarly with the unit-level one but with an event-driven integral structure. Simulation results show the significant improvement and good robustness of the proposed controller.

A constrained wind farm controller providing secondary frequency regulation: An LES study

Active power control for wind farms is needed to provide ancillary services. One of these services is to track a power reference signal with a wind farm by dynamically de- and uprating the turbines. In this paper we present a closed-loop wind farm controller that evaluates 1) thrust coefficients on a seconds-scale that provide power tracking and minimize dynamical loading on a farm level and 2) yaw settings on a minutes-scale that maximize the possible power that can be harvested by the farm. The controller is evaluated in a high-fidelity wind farm model. A six-turbine simulation case study is used to demonstrate the time-efficient controller for different controller settings. The results indicate that, with a power reference signal below the maximal possible power that can be harvested by the farm with non-yawed turbines, both tracking and reduction in dynamical loading can be ensured. In a second case study we illustrate that, when a wind farm power reference signal exceeds the maximal possible power that can be harvested with non-yawed turbines for a time period, it can not be tracked sufficiently. However, when solving for and applying optimized yaw settings, tracking can be ensured for the complete simulation horizon.

Distributed coordinated active and reactive power control of wind farms based on model predictive control

This paper proposes a distributed coordinated active and reactive power control scheme for wind farms based on the model predictive control (MPC) along with the consensus-based distributed information synchronization and estimation, which can optimally dispatch the active power of wind turbines (WTs) and regulate the voltages within the wind farm. For the active power control, the pitch angle and generator torque of WTs are optimally controlled to alleviate fatigue loads of WTs while tracking the power reference of the wind farm required by system operators. For the reactive power/voltage control, the reactive power outputs of WTs are controlled to mitigate the voltage deviations and simultaneously optimize reactive power sharing. Considering the high R/X ratio of the wind farm collector systems, the impact of active power variations on voltages is taken into account to improve the voltage regulation. The proposed scheme is center-free and only requires a sparse communication network. Each WT only exchanges information with its immediate neighbors and the local optimal control problems are solved in parallel, implying good scalability and flexibility for large-scale wind farms. The predictive model of a WT is derived and then the MPC problem is formulated. A wind farm with ten WTs was used to verify the proposed control scheme.

Wind tunnel validation of a closed loop active power control for wind farms

As the wind energy penetration increases, it is becoming more important for wind farms to contribute to frequency regulation, i.e. active power control on the power grid. However, before such controllers can be widely used in industry, they need to be thoroughly validated. This paper contributes to this task by presenting an experimental setup suitable for validation of wind farm control algorithms in wind tunnel experiments. A model free closed loop active power control is implemented on model wind turbines, and tested in a wind tunnel at University of Oldenburg under different operating conditions. Obtained results show that the proposed controller is sufficient for following power references, which is in accordance to numerical studies available in the literature. It is also verified that the controller can react to different disturbances, including variations in the wind farm power reference, and shut-downs of certain turbines in the wind farm. Furthermore, the possibility of coupling the proposed controller with control algorithms for reduction or fairer distribution of structural toads in the wind farm is also demonstrated.

A constrained model predictive wind farm controller providing active power control: an LES study

The objective of active power control in wind farms is to provide ancillary grid services. Improving this is vital for a smooth wind energy penetration in the energy market. One of these services is to track a power reference signal with a wind farm by dynamically de- and uprating the turbines. In this paper we present a computationally efficient model predictive controller (MPC) for computing optimal control signals for each time step. It is applied in the PArallelized Large-eddy simulation Model (PALM), which is considered as the real wind farm in this paper. By taking measurements from the PALM, we show that the closed-loop controller can provide power reference tracking while minimizing variations in the axial forces by solving a constrained optimization problem at each time step. A six turbine simulation case study is presented in which the controller operates with optimised turbine yaw settings. We show that with these optimized yaw settings, it is possible to track a power signal that temporarily exceeds the power harvested when operating under averaged greedy control turbine settings. Additionally, variations in the turbine’s force signals are studied under different controller settings.

Constant power control of variable speed wind farm for primary frequency control support

The increasing penetration level of wind energy conversion systems (WECSs) into power systems imposes new requirements on the contribution of WECSs in the frequency control system. These requirements can be fulfilled by modifying the conventional control system of WECS. However, special attention should be paid to the frequency response of WECS, which should be high enough to contribute to frequency control, but should not lead to instability of WECS. Since a wind farm contains many turbines, determining the optimal response is very difficult. In this paper, by coordinating the WECSs of a variable speed wind farm, a pre-scheduled power can be tracked. Therefore, the fluctuation of the output power is mitigated; an optimal frequency response is achieved and the stability of WECSs is guaranteed. Simulation results show the capability of the proposed scheme to enable the wind farm tracks a pre-scheduled power and improves frequency control.

Active and reactive power control of wind farm for enhancement transient stability of multi‐machine power system using UIPC

This study discusses the connection of wind farms (WFs) to power system through unified inter-phase power controller (UIPC) for enhanced transient stability of the power system. The power circuit of the UIPC is based on the conventional inter-phase power controller (IPC), which its phase-shifting transforms are substituted by two series converters and one shunt converter. During fault condition, the WF connected through UIPC acts as STATCOM with capability of the active and reactive power control at UIPC connecting point. Based on the UIPC model and low-voltage ride-through requirements of the new grid codes, a control system for active and reactive powers control is proposed for enhancement transient stability of power system. The proposed approach is validated in a four-machine two-area test system. Power systems computer aided design (PSCAD)/EMTDC simulation results demonstrate that the UIPC provides an effective solution for enhancement of transient stability of power system including WFs.

Reactive Power Control of DFIG-Based Wind Farm for Participation in Voltage Control

The voltage control is one of the main parameters of the security of the electrical grid which allows to guarantee the overall operation of the system and to reduce the losses in the grid. The objective of this article is to develop a control strategy that allows the network operator to involve a wind farm based on DFIG in primary voltage control. A control algorithm based on the regulation of reactive power of a wind farm is proposed. This algorithm allows distributing the setpoints of the reactive power in a proportional manner on all the turbines so as to better exploit the reactive capacity of the various elements of the wind farm while respecting the limits of voltage and current generators. The paper analyses in Matlab-Simulink environment the dynamic behavior of the wind farm to the primary voltage for medium wind speed and for different turbines operating situations and it studies the implemented control strategies and the performance of the algorithm used for the distribution of the active and reactive power references.

A Robust Two-Level Coordinated Static Voltage Security Region for Centrally Integrated Wind Farms

Integration of centralized wind farms may induce cascading tripping incidents, which brings about critical challenges to secure operation of power grid. One of the major risks is the lack of coordinated voltage/reactive power control for multiple wind farms. Therefore, a robust master-slave two-level coordinated static voltage security region (VSR) is proposed in this paper, along with detailed modeling of the network topology and wind farms to achieve coordination among wind farms. The slave VSR on the wind-farm-side is designed to guarantee the operation of each wind unit within a secure range in order to protect wind units from serious over-voltage and low-voltage problems, whereas the master system-wide VSR aims to coordinate centralized wind farms to ensure security both under normal operating conditions and $\boldsymbol {N - 1}$ contingency conditions. Furthermore, a hierarchically iterative coordination method is introduced to compute the voltage security range of each wind farm through the iteration process. A modified six-bus system with two wind farms, a real system from Northern China, and a large system with 972 wind units are studied, and results verify the effectiveness of the proposed two-level VSR and the hierarchically iterative coordination method.

Active Power Control of DFIG-Based Wind Farm for Improvement of Transient Stability of Power Systems

This paper proposes a method to control the output power of a wind farm with the aim of improving the transient stability of a multi-machine power system. Doubly fed induction generators (DFIG) are considered for the variable speed wind farms. The variation of the frequency of the DFIG terminal bus is used to modulate the torque reference and thus the output power of the DFIG in the post-disturbance condition. This in turn modifies the electrical power of the nearby alternators and causes improvement of stability. The proposed control technique is validated in WSCC 3-machine 9-bus system and IEEE 16-machine 68-bus system. The study is carried out in PSCAD/EMTDC as well as in MATLAB platforms.

Approximate dynamic programming based supplementary reactive power control for DFIG wind farm to enhance power system stability

Reactive power control of doubly fed induction generators (DFIGs) has been a heated topic in transient stability control of power systems in recent years. By using a new online supplementary learning control (OSLC) approach based on the theory of approximate dynamic programming (ADP), this paper develops an optimal and adaptive design method for the supplementary reactive power control of DFIGs to improve transient stability of power systems. To augment the reactive power command of the rotor-side converter (RSC), a supplementary controller is designed to reduce voltage sag at the common coupling point during a fault, and to mitigate active power oscillation of the wind farm after a fault. As a result, the transient stability of both DFIGs and the power system is enhanced. For the supplementary controller design, an action dependent cost function is introduced to make the OSLC model-free and completely data-driven. Furthermore, a least-squares based policy iteration algorithm is employed to train the supplementary controller with convergence and stability guarantee. By using such techniques, the supplementary reactive power controller can be trained directly from data measurements, and therefore, can adapt to system or external changes without an explicit offline system identification process. Simulations carried out in Power System Computer Aided Design/ Electro Magnetic Transient in DC System (PSCAD/EMTDC) show that the OSLC based supplementary reactive power controller can significantly improve the transient performance of the wind farm and enhance the transient stability of the power system after sever faults.

Reactive power and voltage control in grid-connected wind farms: an online optimization based fast model predictive control approach

This paper presents the application of an online optimization based fast model predictive control scheme to grid-connected wind farms for reactive power and voltage control. A linear prediction model of the network was used to predict the behavior of the system for a certain prediction horizon, while a modified quadratic programming problem was used for the optimization process. The proposed controller was tested in a 5-bus test system hosting three sub-wind farms of total 36 MW active power production capacity connected in series to the external network. The controller performed its control action by changing the reactive power output of the sub-wind farms and voltage set-points of an online load tap changer transformer to respect the safety limit imposed on the bus voltages and desired reactive power exchange.

Optymalne sterowanie grupy farm wiatrowych w oparciu o system WindEx

The aim of this paper is to present achievements obtained in implementing the framework project N R01 0021 06 in the Power System Department of Lublin University of Technology. The result of the work was “A system of optimal wind farm power control in the conditions of limited transmission capabilities of power networks”, which one of two main modules is a state estimator. The featured wind farm control system was integrated with a SCADA dispatcher system WindEx using the WebSVC service.

An Optimal Reactive Power Control Strategy for a DFIG-Based Wind Farm to Damp the Sub-Synchronous Oscillation of a Power System

This study presents the auxiliary damping control with the reactive power loop on the rotor-side converter of doubly-fed induction generator (DFIG)-based wind farms to depress the sub-synchronous resonance oscillations in nearby turbogenerators. These generators are connected to a series capacitive compensation transmission system. First, the damping effect of the reactive power control of the DFIG-based wind farms was theoretically analyzed, and a transfer function between turbogenerator speed and the output reactive power of the wind farms was introduced to derive the analytical expression of the damping coefficient. The phase range to obtain positive damping was determined. Second, the PID phase compensation parameters of the auxiliary damping controller were optimized by a genetic algorithm to obtain the optimum damping in the entire subsynchronous frequency band. Finally, the validity and effectiveness of the proposed auxiliary damping control were demonstrated on a modified version of the IEEE first benchmark model by time domain simulation analysis with the use of DigSILENT/PowerFactory. Theoretical analysis and simulation results show that this derived damping factor expression and the condition of the positive damping can effectively analyze their impact on the system sub-synchronous oscillations, the proposed wind farms reactive power additional damping control strategy can provide the optimal damping effect over the whole sub-synchronous frequency band, and the control effect is better than the active power additional damping control strategy based on the power system stabilizator.

Damping control strategies of inter-area low-frequency oscillation for DFIG-based wind farms integrated into a power system

This study investigates the inter-area low-frequency damping control strategies of a doubly fed induction generator (DFIG)-based wind farm through oscillation transient energy function (OTEF) analysis. Based on the OTEF descent expressions, the feasibility of damping the inter-area low-frequency oscillation is theoretically analyzed through the active/reactive power control of grid-connected wind farms. Additional damping control strategies with the active/reactive power loop of the DFIG-based wind farm are presented using the feedback signal of the transmission line active power flow based on the power system stabilizer (PSS) control method. Transient simulation on different damping gain coefficients are conducted for justification. Following the OTEF mechanism analysis, an additional fuzzy damping control strategy with the active/reactive power loop is proposed by identifying the oscillation phase and the severity to prevent different damping gain coefficients from affecting the presented PSS damping control method. Transient and dynamic simulation results and comparisons showed that both additional control strategies with the active and reactive power loops of the DFIG-based wind farm can damp the inter-area low-frequency oscillation of the integrated power system. The additional damping control strategy with the reactive power loop can damp the transmission line active power oscillation better than that with the active power loop as well as prevent an increase in the torsional oscillation of the wind turbine shaft. The proposed additional fuzzy control strategy with the active/reactive power loop has better damping performance than the presented PSS control, especially for damping the inter-area low-frequency oscillation.

A Multi-Objective Optimization Approach to Active Power Control of Wind Farm

With more and more wind farms integrated into the power grid, the stability and security of the grid can be significantly affected by the wind-farm-generated power, due to the intermittent and volatile nature of the wind-farm-generated power. Therefore, control of the wind-farm power to meet the stability and quality requirements becomes important. Active control of wind-farm power, however, is challenging because the wind-farm output power can only be reliably predicted for a short period of time (i.e., ultrashort term power prediction), and large variations exist in the wind-turbine output power. In this paper, an optimal active power control scheme is proposed to maximize the running time of each wind turbine, and minimize the on-and/or-off switching of wind turbines, resulting in substantial reduction of wind-turbine wear and thereby, maintenance cost, and extension of wind-turbine lifetime, all together, a significant saving of operation cost of the whole wind farm. The proposed approach is illustrated by implementing it to the active power allocation of a wind-farm model in simulation.

Study on Automatic Active Power Control System of Wind Farms

Based on a "wind power remote monitoring system" project, this paper focus on the modeling and simulation of the wind power variant pitch control system, and also the wind generator active power control OPC CLIENT interface programming. Using the VC++ language and MFC, OPC CLIENT interface was designed for the start-stop control of fan and the active power control of wind farms, which enables the wind farm to accurate and rapid response of the wind power grid load instruction of automatic generation control (AGC). Further, based on the MATLAB/SIMULINK platform, we analyzed the variable pitch control system of the variable pitch wind turbine by modeling and simulation with the Denmark's VESTAS V80-2000 (2MV).