Grid-connected Wind Farm Research Articles

Voltage stability analysis of grid-connected wind farms with FACTS: Static and dynamic analysis

ABSTRACTRecently, analysis of some major blackouts and failures of power system shows that voltage instability problem has been one of the main reasons of these disturbances and network collapses. In this article, a systematic approach to voltage stability analysis using various techniques for the IEEE 14-bus case study is presented. Static analysis is used to analyze the voltage stability of the system under study, while the dynamic analysis is used to evaluate the performance of compensators. The static techniques used are power flow, V–P curve analysis, and Q–V modal analysis. In this study, Flexible Alternating Current Transmission system (FACTS) devices—namely, static synchronous compensators (STATCOMs) and static var compensators (SVCs)—are used as reactive power compensators, taking into account maintaining the violated voltage magnitudes of the weak buses within the acceptable limits defined in ANSI C84.1. Simulation results validate that both the STATCOMs and the SVCs can be effectively used to e...

A Fuzzy Clustering Algorithm-Based Dynamic Equivalent Modeling Method for Wind Farm With DFIG

With the increasing capacity of grid connected wind farms, the influence of wind power to stable operation of an electric power system is becoming more and more important. In order to analyze the active power output characteristics of wind farm, a multimachine representation dynamic equivalent method based on the fuzzy clustering algorithm is proposed. First, indicators which can characterize the active power output performance of a doubly fed induction wind generator (DFIG) are researched. Second, a fuzzy C-means (FCM) clustering algorithm is first applied to the modeling of wind farm. DFIGs are divided into groups by analyzing the indicator data with FCM. Finally, DFIGs of the same group are equivalent as one DFIG to realize the dynamic equivalent modeling of wind farm with DFIG. Simulation results demonstrated that the established dynamic equivalent model can reflect the active power dynamic response characteristics of wind farm with DFIG effectively; meanwhile, the model of wind farm is simplified and computation complexity is reduced.

Flexible transmission expansion planning associated with large‐scale wind farms integration considering demand response

With increasing large-scale wind farms being integrated into the power grids, transmission expansion planning (TEP) increasingly requires more flexibility to account for the intermittency as well as other uncertainty factors involved in the process. In this study, a probabilistic TEP model is proposed for planners to tackle the variability and uncertainty factors associated with grid connected wind farms. Both load forecast and wind power output uncertainties are considered in the proposed model. Other factors considered in the model include the forced outage rates of transmission lines and generators, and the wind speed correlation between wind farms. Moreover, the incentive-based demand response (IBDR) program is introduced as a non-network solution instead of the conventional network expansion approaches. The utilities will pay IBDR providers for their contributions to peak demand reduction. The proposed TEP model can find the optimal trade-off between transmission investment and demand response expenses. The hierarchical Bender's decomposition algorithm integrated with Monte Carlo simulation is employed to solve the proposed model. Case studies are given using the Garver's six-bus system and the IEEE-reliability test system to show the effectiveness of the method.

Scenario-based stochastic optimal operation of wind, photovoltaic, pump-storage hybrid system in frequency- based pricing

This paper proposes the operating strategy of a micro grid connected wind farm, photovoltaic and pump-storage hybrid system. The strategy consists of two stages. In the first stage, the optimal hourly contractual agreement is determined. The second stage corresponds to maximizing its profit by adapting energy management strategy of wind and photovoltaic in coordination with optimum operating schedule of storage device under frequency based pricing for a day ahead electricity market. The pump-storage hydro plant is utilized to minimize unscheduled interchange flow and maximize the system benefit by participating in frequency control based on energy price. Because of uncertainties in power generation of renewable sources and market prices, generation scheduling is modeled by a stochastic optimization problem. Uncertainties of parameters are modeled by scenario generation and scenario reduction method. A powerful optimization algorithm is proposed using by General Algebraic Modeling System (GAMS)/CPLEX. In order to verify the efficiency of the method, the algorithm is applied to various scenarios with different wind and photovoltaic power productions in a day ahead electricity market. The numerical results demonstrate the effectiveness of the proposed approach.

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.

Investigation on Probabilistic Small-Signal Stability of Power Systems as Affected by Offshore Wind Generation

This paper investigates the impact of the complementarity, connection technology and network control strategy of offshore wind generation on the probabilistic small-signal stability of power systems. The cumulant-based theory is firstly applied to assess the variances of both the complementarity of combined wind power and the probabilistic small-signal stability of power systems. These variances are later employed as two indices to explain how the different complementarity levels, connection topologies and DC network control schemes of offshore wind generation affects the probabilistic distribution of critical eigenvalue and thus the probabilistic small-signal stability. In the paper, an example of 16-machine 5-area power system with three grid-connected offshore wind farms is presented. The index of probabilistic small-signal stability is computed and then compared under two complementarity conditions, two typical HVDC transmission systems through which the offshore wind farms are connected, and two DC grid control schemes, respectively. It is demonstrated that complementarity can effectively enhance probabilistic stability and multi-terminal HVDC may have either beneficial or detrimental impact on small-signal stability depending on the control pattern and setting when compared with point-to-point topology.

Transient stability enhancement of a grid‐connected wind farm using an adaptive neuro‐fuzzy controlled‐flywheel energy storage system

With the rapid growth of the wind energy systems in the past years and their interconnection with the existing power system networks, it has become very significant to analyse and enhance the transient stability of the wind energy conversion systems connected to the grid. This study investigates the transient stability enhancement of a grid-connected wind farm using doubly-fed induction machine-based flywheel energy storage system. A cascaded adaptive neuro-fuzzy controller (ANFC) is introduced to control the insulated gate bipolar transistor switches-based frequency converter to enhance the transient stability of the grid-connected wind farm. The performance of the proposed control strategy is analysed under a severe symmetrical fault condition on both a single-machine infinite bus model and the IEEE-39 bus New England test system. The transient performance of the system is investigated by comparing the results of the system using the proposed ANFCs with that of the black-box optimisation technique-based proportional–integral controllers. The validity of the system is verified by the simulation results which are carried out using PSCAD/EMTDC environment.

Erratum: Transient stability enhancement of a gridconnected wind farm using an adaptive neurofuzzy controlled‐flywheel energy storage system

Erratum: Transient stability enhancement of a gridconnected wind farm using an adaptive neurofuzzy controlled‐flywheel energy storage system

Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through

The Voltage Source Converter-HVDC (VSC-HVDC) system applied to wind power generation can solve large scale wind farm grid-connection and long distance transmission problems. However, the low voltage ride through (LVRT) of the VSC-HVDC connected wind farm is a key technology issue that must be solved, and it is currently lacking an economic and effective solution. In this paper, a LVRT coordinated control strategy is proposed for the VSC-HVDC-based wind power system. In this strategy, the operation and control of VSC-HVDC and wind farm during the grid fault period is improved. The VSC-HVDC system not only provides reactive power support to the grid, but also effectively maintains the power balance and DC voltage stability by reducing wind-farm power output, without increasing the equipment investment. Correspondingly, to eliminate the influence on permanent magnet synchronous generator (PMSG)-based wind turbine (WT) systems, a hierarchical control strategy is designed. The speed and validity of the proposed LVRT coordinated control strategy and hierarchical control strategy were verified by MATLAB/Simulink simulations.

Particle Swarm Optimization-based Superconducting Magnetic Energy Storage for Low-voltage Ride-through Capability Enhancement in Wind Energy Conversion System

— This article presents a novel application of the particle swarm optimization technique to optimally design all the proportional–integral controllers required to control both the real and reactive powers of the superconducting magnetic energy storage unit for enhancing the low-voltage ride-through capability of a grid-connected wind farm. The control strategy of the superconducting magnetic energy storage system is based on a sinusoidal pulse-width modulation voltage source converter and proportional–integral-controlled DC-DC converter. Control of the voltage source converter depends on the cascaded proportional–integral control scheme. All proportional–integral controllers in the superconducting magnetic energy storage system are optimally designed by the particle swarm optimization technique. The statistical response surface methodology is used to build the mathematical model of the voltage responses at the point of common coupling in terms of the proportional–integral controller parameters. The effectiveness of the proportional–integral-controlled superconducting magnetic energy storage optimized by the proposed particle swarm optimization technique is then compared to that optimized by a genetic algorithm technique, taking into consideration symmetrical and unsymmetrical fault conditions. A two-mass drive train model is used for the wind turbine generator system because of its large influence on the fault analyses. The systemic design approach is demonstrated in determining the controller parameters of the superconducting magnetic energy storage unit, and its effectiveness is validated in augmenting the low-voltage ride-through of a grid-connected wind farm.

Impact of grid connection of large-scale wind farms on power system small-signal angular stability

The grid connection of a large-scale wind farm could change the load flow/configuration of a power system and introduce dynamic interactions with the synchronous generators (SGs), thus affecting system small-signal angular stability. This paper proposes an approach for the separate examination of the impact of those affecting factors, i.e., the change of load flow/configuration and dynamic interactions brought about by the grid connection of the wind farm, on power system small-signal angular stability. Both cases of grid connection of the wind farm, either displacing synchronous generators or being directly added into the power system, are considered. By using the proposed approach, how much the effect of the change of load flow/configuration brought about by the wind farm can be examined, while the degree of impact of the dynamic interaction of the wind farm with the SGs can be investigated separately. Thus, a clearer picture and better understanding of the power system small-signal angular stability as affected by grid connection of the large-scale wind farm can be achieved. An example of the power system with grid connection of a wind farm is presented to demonstrate the proposed approach.

Asymmetrical Fault Ride Through as Ancillary Service by Constant Power Loads in Grid-Connected Wind Farm

The introduction of distributed generation (DG) into low voltage (LV) systems demands that the generation system remain grid connected during voltage sags to ensure the operational stability. The DG consisting of fixed speed squirrel cage induction generator (SCIG)-based wind turbines is unable to provide reactive power control and needs a dedicated compensating device. Under asymmetrical grid faults the negative sequence flux circulation in the airgap introduces the torque oscillations that lead to the reduction of lifetime of the generation system. This paper proposes the use of distributed constant power loads (CPLs) for asymmetrical fault ride through (FRT) instead of using a centralized STATCOM. It has also been observed that the compensation of negative sequence voltage improves the performance of SCIG by eliminating the torque ripples. The compensation of positive sequence voltage avoids a possible voltage collapse at the LV distribution level and improves the reliability and stability of the wind farm. Centralized compensation of the asymmetrical grid fault by a STATCOM is compared with the distributed compensation by CPLs. The results suggest that each individual CPL injects lower current for maximum FRT enhancement compared to a dedicated STATCOM.

Operation and Protection of Grid Connected Wind Farm

Operation and Protection of Grid Connected Wind Farm

A Study on the Application of DC HTS cable systems to enhance power transfer limits of a grid-connected offshore wind farm

This paper introduces two on-going projects for DC high temperature superconducting (HTS) cable systems in South Korea. This study proposes the application of DC HTS cable systems to enhance power transfer limits of a grid-connected offshore wind farm. In order to develop the superconducting DC transmission system model based on HTS power cables, the maximum transfer limits from offshore wind farm are estimated and the system marginal price (SMP) calculated through a Two-Step Power Transfer (TSPT) model based on PV analysis and DC-optimal power flow. The proposed TSPT model will be applied to 2022 KEPCO systems with offshore wind farms.

A novel control method for a VSC-HVDC system in a grid-connected wind farm

The voltage source converter-high voltage direct current (VSC-HVDC) transmission is the ideal integration technology for grid-connected wind farms. A passivity-based control (PBC) method for VSC-HVDC when the wind farm voltage is unbalanced is proposed in this paper. The mathematical model of a VSC with unbalanced voltage is established. The PBC theory including dissipation inequality and system strict passivity is introduced, and then the stability of PBC is proven in light of the Lyapunov stability theory. According to PBC theory, a Euler--Lagrange mathematical model of a VSC is constructed. After that, the strict passivity of the VSC is proven. On the premise of the power factor being 1, the PBC controller for the VSC-HVDC system is designed under d-q coordination. The control law is deduced in detail. In order to accelerate the convergence speed, dampers are added to the PBC controller. The decoupled control of the active power and the reactive power is achieved by this method. The dynamic and steady performances of the VSC-HVDC system in a grid-connected wind farm when the wind farm voltage is unbalanced are significantly improved. Furthermore, the robustness of the system is enhanced. The simulation results verify the feasibility and correctness of the method.

Doubly Fed of Induction Generators Wind Turbine Frequency Control Based on Power Curve of Inertia Control and Pitch Angle Control

With many grid-connected wind farms of Doubly-fed Induction Generator (DFIG) type taking the palce of conventional synchronous generators, the frequency control ability of the system will decrease. But the existing control strategy based on maximum wind power tracking of DFIG can not response to the deviation of the system frequency. This paper proposes a new hybrid frequency control strategy based on the research of the frequency response to the doubly fed induction wind turbine curves switching inertia control loop and the ability for the pitch angle control participating in the system primary frequency modulation. The strategy reduces the initial rate of change and the steady state error of system frequency with the combined action of the curves switching inertial control and pitch frequency control. Finally, the simulation results of the two areas with four generators validate the effectiveness of the strategy.

A Set-Membership Affine Projection Algorithm-Based Adaptive-Controlled SMES Units for Wind Farms Output Power Smoothing

This paper presents a novel adaptive control scheme of the superconducting magnetic energy storage (SMES) units with the purpose of smoothing the wind farms' output power. The adaptive control scheme is based on the set-membership affine projection algorithm (SMAPA), which provides a faster convergence and less computational complexity than the normalized least-mean-square algorithm. In this study, two grid-connected fixed-speed wind farms are considered. The control strategy of the SMES units is based on a pulse width modulation (PWM) voltage source converter (VSC) and a dc-dc converter. The VSC and dc-dc converter is used to control the reactive and active power exchange with the power system, respectively. The SMAPA-based adaptive proportional-integral (PI) controllers are utilized to control both converters. For realistic responses, real wind speed data extracted from Hokkaido Island, Japan, and two-mass drive train model of the wind turbine generator system are used in the analyses. Also, a real 10 MVA SMES unit that was installed at a power plant in Kameyama, Japan, is connected to the point of common coupling of the wind farms. The validity of the proposed control scheme is verified by the simulation results, which are performed using PSCAD/EMTDC environment. With the SMAPA-based adaptive-controlled SMES units, the wind farms' output power can be smoothed easily avoiding huge effort for fine tuning the controllers' parameters.

Technical and Economic Analysis on Grid-Connected Wind Farm Based on Hybrid Energy Storage System for Active Distribution Network

Active distribution network with energy storage system is an important outlet for a mass of distributed renewable energy connected to the grid. In this context, a hybrid energy storage system is proposed based on NaS battery and lithium ion battery, that the former is the main large scale energy storage technology world-widely used and developed and the latter is a flexible way to have both power and energy capacities. The hybrid energy storage system, which takes advantage of the two complementary technologies to provide large power and energy capacities, is chosen to do an evaluation of economical-environmental based on critical excess electricity production (CEEP), CO2 emission, annual total costs calculated on the specific given condition using Energy PLAN software. The result shows that hybrid storage system has strengths in environmental benefits and also can absorb more discarded wind power than single storage system and is a potential way to push forward the application of wind power and even other types of renewable energy resources.

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.

Analytical Study on the Effect of Coordinated Application of Distributed Grid Connection and SVG on Wind Farms to Increase Power Quality in Fuxin Rural Power Grid

power quality problems such as high line loss, low voltage exist commonly in rural power grid of China due to few supply points, long power transmission and distribution line. Huge fund is required to increase the quantity of supply points in rural power grid; installation of var compensators on line nodes could not solve power quality problems on the whole line. At the same time, as distributed power supply, wind power is also restricted by peak regulation, insufficient line output capacity and other factors in large scale centralized grid-connected output, wind curtailment often occurs. In order to solve the above-mentioned two problems simultaneously, electric power of wind farm may be output via nearby rural power grid line, thus not only utilization rate of wind power is increased, but also power quality of rural power grid is improved.This paper takes an example of a district in Fuxin City, summarizes power quality change data of relevant rural power grid before and after the distributed grid connection of wind farm is made, the analysis shows that distributed grid connection of wind power could improve load flow distribution of the power system, reduce system transmission loss in this district obviously, increase economical efficiency of the system operation effectively. At the same time, effectiveness of static var generator in substation to overcome the impact of such grid connection mode on power grid is verified.