Power System Including Wind Farms Research Articles

Analyzing the Effect of Lightning Channel Impedance on the Lightning Overvoltages in Wind Turbines

Lightning is a natural phenomenon that can cause serious damage to power systems including wind farms. Wind Turbines (WTs) are tall structures and are often installed in areas with high lightning activity levels which makes them exposed to direct strikes. One of the parameters affecting the performance of the lightning protection system is the impedance of the lightning channel. In this paper, the effects of this impedance on the lightning overvoltages in wind turbines, and the energy absorbed by Surge Arresters (SAs), as the main lightning protection device, are investigated. The case study is carried out on a WT with 2 MVA of rated power where a direct lightning strike with a maximum current magnitude of 50 kA is struck to one of the WT's blades. Accurate models, designed for transient studies, are used for modeling different parts of the WT. The results of different scenarios are compared, and it is shown that as the value of lightning channel impedance gets higher, the overvoltage caused by the corresponding lightning strike, with the same current magnitude, increases too. In addition, it is shown that the higher the lightning channel impedance, the higher the absorbed energy by the arrester. This shows the importance of the lightning channel impedance's effect on high-voltage studies of WTs, as it can help in selecting proper lightning protection devices.

Pharmacophore-Modeling-Based Optimal Placement and Sizing of Large-Scale Energy Storage Stations in a Power System including Wind Farms

The world is targeting fully sustainable electricity by 2050. Energy storage systems have the biggest role to play in the 100% renewable energy scenario. This paper presents an optimal method for energy storage sizing and allocation in a power system including a share of wind farms. The power system, which is used as a test system, is a modified version of the IEEE 39 bus system. The optimization is applied using novel pharmacophore modeling (PM), which is compared to state-of-the-art techniques. The objective of the optimization is to minimize the costs of power losses, peak demand and voltage deviation. The PM optimization is applied using two methods, namely, weighting factor and normalization. The optimization and simulation are applied in the DIgSILENT power factory software application. The results show that normalization of PM optimization drives the power system to less cost in terms of total power losses by up to 29% and voltage deviation by up to 4% and better covers peak demand than state-of-the-art optimization techniques.

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

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

Design of adaptive wide-area damping controller based on delay scheduling for improving small-signal oscillations

The main aim of this paper is to compensate the delays resulted from communication links transmitting wide-area measurement signals in a new large-scale power system. The proposed controller is based on adaptive delay compensation which is able to handle the uncertainty arising from the phase delay by means of scheduling the delay’s value. In this design, further to compensation of WAMS’s delays, the delay due to internal structure of closed-loop system is also modeled, and by using synthesis H∞/H2 technique, its robustness has been evaluated by defining an objective function. Then, by means of small-signal stability analysis, a wide-area damping controller has been employed for coordination of FACTS devices including STATCOM and HVDC with the controller of rotor-side-convertor (RSC) in DFIG. The simulations have been implemented on 8-area power system including wind farms and FACTS devices through different scenarios.

Designing of wide-area damping controller for stability improvement in a large-scale power system in presence of wind farms and SMES compensator

The main aim of this paper is the stability improvement of a large-scale power system including wind farms and SMES (Superconducting Magnetic Energy Storage) compensator. For this purpose, at first, the mathematical model of the whole system is extracted in order to accurately investigate the role of wind farms and SMES in the stability studies. The stability analysis is based on the design of damping controllers which is provided through the global signals dependent on the time delay and local signals without the time delay. In modeling of the time delay, damping factor of inter-area oscillation mode is used to obtain larger delay margin, and then, the Lyapunov-Krasovskii function and inequality integral are employed to evaluate the stability condition related to the time delay. The controllability/observability index is used to choose the best candidate signals in the input of WADC (Wide-Area Damping Controller) in order to enhance the residual value of the weakest critical mode identified by modal analysis. The simulation results are investigated through different scenarios of wind turbine and power system in non-linear time domain as well as frequency domain using eigenvalues analysis. The results verify the effectiveness of the proposed controller under various time delays.

Generation and transmission expansion planning with high penetration of wind farms considering spatial distribution of wind speed

This paper represents the effect of wind speed’s spatial distribution on the simultaneous generation and transmission expansion planning of power systems including wind farms. To this end, wind farm’s capacity factor is used as a practical parameter to model its output power. It is shown that ignoring wind speed’s spatial distribution affects the expected exploitable wind power. In other words, the utilizable wind power of a wind farm in a power system would be overestimated if the spatial distribution of the wind speed is not considered and the wind farm’s owner expects more utilizable wind power than what happens in the real world.The objective function of the proposed mixed integer linear programming (MILP) model is to minimize total cost which includes three main parts: 1. The total investment cost of thermal generation units, transmission lines, and wind farms, 2. Expected operation cost of thermal generators, which is related to fuel consumption and penalty of the CO2 emission, and 3. Expected loss cost of transmission lines. Furthermore, it is investigated that how different values of operation cost, as well as CO2 emission tax, affect the proposed expansion planning model. Two test systems, namely IEEE 24-bus RTS and IEEE 118-bus test systems, are employed to evaluate the effectiveness of the proposed method. The results show that ignoring wind speed’s spatial distribution not only changes the optimal plan but also makes the planner expect a further reduction in the value of objective function. This outcome is particularly true for high values of operation cost and emission taxes of greenhouse gases as well as high wind power penetration levels.

A Novel Design of Decentralized LFC to Enhance Frequency Stability of Egypt Power System Including Wind Farms

This paper presents a real hybrid power system in Egypt, which includes both conventional generation units and Renewable Energy Sources (RESs) for studying the Load Frequency Control (LFC) problem. The conventional generation system in the Egyptian Power System (EPS) is decomposed into three dynamic subsystems; non-reheat, reheat and hydro power plants. Moreover, real wind speed data extracted from Zafarana location in Egypt is used for achieving a realistic wind power study. Each subsystem of the EPS has its own characteristics compared to the others. Moreover, the physical constraints of the governors and turbines such as Generation Rate Constraints (GRCs) of power plants and speed governor dead band (i.e., backlash) are taken into consideration. Therefore, this paper proposes a decentralized controller for each subsystem independently, to guarantee the stability of the overall closed-loop system. Hence, an optimal PID controller-based Particle Swarm Optimization (PSO) algorithm is proposed for every subsystem separately to regulate the frequency and track the load demands of the EPS. The performance of the proposed decentralized controller of each subsystem is compared to the centralized one under different operational scenarios. The EPS is tested using the nonlinear simulation by Matlab/SIMULINK. The obtained results reveal the superior robustness of the proposed decentralized controller against different load disturbance patterns, real wind power fluctuations and EPS uncertainties.

Security and Stability Analysis of Wind Farms Integration into Distribution Network

With the increasing share of the wind power in the power system, wind power fluctuations will cause obvious negative impacts on weak local grid. This paper firstly establish electromechanical transient simulation model for doubly fed induction wind turbine, then use Matlab/Simulink to achieve power flow calculation and transient simulation of power system including wind farms, the local synchronous generator, load, etc, finally analyze wind power on the impact of the local power grid under typical circumstances. The actual calculated results indicate that wind mutation causes little effect on the power grid, but when the three-phase short circuit fault happens, active power of wind power decreases sharply and the voltage of location of wind power into the grid also drop sharply, finally wind farm split from power system. This situation is not conducive to security and stability of the local power grid. It is necessary to develop security and stability measures in the future.

Symbiotic organisms search algorithm for automatic generation control of interconnected power systems including wind farms

Automatic generation control (AGC) plays an important role in power systems, where it maintains the system frequency and tie-line power flow at their desired values. This study presents a novel symbiotic organisms search (SOS) algorithm in order to optimally design the proportional–integral–derivative (PID) controllers in the AGC of interconnected multiple-area power systems including wind farms uncertainty and system non-linearity. The PID controllers’ parameters define the design variables of the optimisation problem. The SOS algorithm is applied to different objective functions such as integral square error and integral absolute of error. The efficacy of the proposed controller is compared with other competing evolutionary algorithms-based proportional–integral or PID controller. The system performance is evaluated under different operating conditions such as different loading, variation of system parameters, and an addition of wind energy uncertainty. For obtaining realistic responses, real wind speed data that extracted from Zafarana location in Egypt is used in this study. The validity of the proposed controller is extensively confirmed using the simulation results. With the SOS-based PID controllers, the dynamic responses for the AGC of interconnected power systems, including wind farms uncertainty can be further enhanced.

Reliability Assessment of Wind Power System Considering Multi-Objective Models

The integration of wind farms has a significant impact on the power system reliability. An appropriate model used to assess wind power system reliability is needed. Establishing multi-objective models (wind speed model, wind turbine generator output model and wind farm equivalent model) and based on the non-sequential Monte Carlo simulation method to calculate risk indicators is a viable method for quantitatively assessing the reliability of power system including wind farms. The IEEE-RTS 79 test system and a 300MW wind farm are taken as example.The calculation resluts show that using the multi-objective models can improve accuracy and reduce error; the higher average wind speed obtains the better system reliabitity accordingly.

Hierarchical Wide-Area Control of Power Systems Including Wind Farms and FACTS for Short-Term Frequency Regulation

In this work a hierarchical scheme is proposed for the coordinated control of conventional synchronous generators, wind farm converters and flexible ac transmission systems. It comprises two levels, namely a fully decentralized set of controllers associated with the involved devices and a centralized coordinating controller based on synchronized wide-area signals provided by phasor measurement units. The proposed hierarchy of controllers is mainly focused on two objectives: transient frequency support and inter-area oscillations damping. Several works have recently proved that the fast-acting power converters of variable-speed generators can greatly improve the short-term frequency regulation capability in scenarios with a large penetration of wind energy. A case study is included showing that the dynamic performance and stability of power systems can indeed be enhanced when windmill converters are properly coordinated via a wide-area centralized controller.

Stabilization of Power System Including Wind Farm by PWM Voltage Source Converter and Chopper Controlled SMES

This paper presents a dynamic model of Superconducting Magnetic Energy Storage (SMES) device developed, which can significantly decrease the voltage and power fluctuations of grid connected fixed speed wind generators. The SMES system with a voltage–source IGBT converter and two–quadrant DC–DC chopper is analyzed as a controllable energy source. The objective of the proposed SMES control strategy is to smooth the wind farm output by absorbing or providing real power. Moreover, its reactive power output can also be controlled to keep the wind farm terminal voltage constant. The control methodology of SMES system is suitable for the two objectives stated above. The performance of the proposed system is evaluated by dynamic simulations using a test power system. Real wind speed data is used in the simulation analyses, which validates the effectiveness of the proposed control strategy. Simulation results clearly show that the proposed control strategy can smooth well the wind generator output power and also maintain the terminal voltage at rated level. Key words: Minimization of fluctuations; superconducting magnetic energy storage (SMES); wind generator stabilization; voltage source converter (VSC); DC–DC chopper

The Study of Wind Farm’s Equivalence Method and Verification

When the scale of wind farm is increased quickly, if not considering the impedance of the collection system within wind farm, the bigger error in power flow calculation may be caused. In this paper a simple equivalence method calculating the collector system equivalence impedance by using the equivalence power loss is proposed and wind farm’s equivalence output power model considering wake effect and wind speed is established. The models are applied in power flow calculation of the natural wind farm connected to Urumqi grid, Xinjiang. The results compared with original system power flow show that this method has lower error. By using the losses in the collector system, the method of computing the equivalence impedance is verified in this paper. The equivalence impedance of collector system is calculated from total active power loss and total reactive power loss and current flow of the collector system. The error analysis showed that the equivalence impedance of collector system has lower error. The test results show that the proposed equivalence method is effective and logical and has a certain practicality. The reference is given for farther studying safety and stability operation of electric power system including wind farm.

Research on Environmental Economic Dispatch of Power System Including Wind Farm

In power market environment with energy conservation and emission reduction, clean energy power has an increasingly important position because of its low cost and environmental pollution. This paper researches on power system dynamic economy dispatch including wind system. The model of environment economic dispatch including wind power is established with the lowest generating cost of total power system as the objective function. The various constraint conditions are considered with conventional thermal power units and wind power. According to actual load data in a certain area, simulation test is completed using particle swarm optimization algorithm which has advantage of strength searching capability and fast optimizing. Simulation results show that the mathematical model is correct and the optimization algorithm is effective. Meanwhile, the application of the relative entropy balance theory is on evaluation and selection to the decision results.

A unified approach for the solution of power flows in electric power systems including wind farms

This paper proposes a solution approach of the power flow problem to assess the steady-state condition of power systems with wind farms in a single frame of reference, in which the state variables of the wind generators are combined with the nodal voltage magnitudes and angles of the entire network for a unified iterative solution through the Newton–Raphson method. Different wind energy conversion systems (WECS) are mathematically derived from the steady-state representation of the induction generator. Suitable strategies for initializing the state variables of the wind generators are also proposed in this paper. Lastly, three numerical examples are presented to numerically illustrate the applicability of the proposed approach.

Development of linear models of static var compensators and design of controllers suitable for enhancing dynamic/transient performance of power systems including wind farms

In this work the design of controllers with fixed-gain PID and multiple-stage lead-lag compensators is investigated for improving further the dynamic impact of static var compensators (SVCs). The analysis is based on the linearization of the power system under study and the proper shift of critical eigenvalues, associated with the SVC and electric network, to desired locations. In order to linearize the SVC an established 4th order model is used and the development of a more complex model is attempted. Finally, a 16th order linear model is developed for the SVC by implementing system identification methods, and this model is used along with the 4th order model to design two different controllers with fixed-gain PID and a multiple-stage lead-lag compensator. The suitability and effectiveness of the resulted controllers are tested by performing digital simulations of a Greek power system which includes a wind farm.

Transient Stability Augmentation of Power System Including Wind Farms by Using ECS

This paper presents a new method to enhance the transient stability of multimachine power system including wind farms, when a severe network disturbance occurs in the power system. For this purpose, the energy capacitor system (ECS) composed of power electronic devices and electric double layer capacitor (EDLC) is proposed. The control scheme of ECS is based on a sinusoidal PWM voltage source converter (VSC) and fuzzy logic controlled dc-dc buck/boost converter using insulated gate bipolar transistors (IGBT). Two wind farms are considered to be connected to the power system. Two-mass drive train model of wind turbine generator system (WTGS) is used in the analyses as the drive train modeling has great influence on the dynamic characteristics of WTGS. Real wind speed data are used in the analyses to obtain realistic responses. Different types of symmetrical and unsymmetrical faults are considered as the network disturbance. Simulation results clearly show that the proposed ECS can enhance the transient stability of wind generators in multimachine power system as well as their low voltage ride through (LVRT) capability.

Development of linear models of Static Var Compensators suitable for enhancing performance of power systems including wind farms

In this work, the design of fixed-gain Proportional?Integral?Derivative (PID) controllers with multiple stage lead-lag compensators are investigated for improving further the dynamic impact of Static Var Compensators (SVCs). The analysis is based on the linearisation of the power system under study and the proper shift of critical eigenvalues, associated with the SVC and electric network, to the desired locations. In order to linearise the SVC an established fourth order model is used and the development of more complex models is attempted. This study deals with the development procedure of two different high order models for the SVC. Finally, one of them is adopted along with the fourth order model in order to design two different fixed-gain PID controllers with the multiple stage lead-lag compensator. The suitability and effectiveness of the resulted fixed-gain PID controllers is tested by performing digital simulations of a Greek power system including a wind farm under investigation.