Reduced-order model of Type-C wind turbine generators

This paper presents a wind turbine generator (WTG) reduced-order model for time domain simulations. Selective modal analysis is used to reduce the model order by focusing on the most relevant modes and variables. In most cases, a single relevant mode is found; thus, a first-order model that captures the relevant mode is derived. Depending on the WTG dynamics, in some cases, reduced-order models of higher order are required. The proposed model is applied to both 4-bus and 39-bus test systems. The results show that the proposed reduced-order model closely resembles the impact of WTGs in a power system, even when large perturbations occur. Line and synchronous generator (SG) outages are taken into account. The proposed model reduces the simulation time and the power system model complexity.     

Towards reactive power dispatch within a wind farm using hybrid PSO

With the increasing penetration of wind power generation, the stringent grid codes are imposed by the system operators insisting the wind turbines to behave similar to that of synchronous generators. As a part of fulfilling the grid code in terms of steady state reactive power injection at point of common coupling, in this research work, the problem of optimal reactive power dispatch within a wind farm is formulated and a hybrid particle swarm optimization algorithm is proposed to get the optimal solution. The effectiveness of the proposed method is tested by simulations of the power collection grid of practical off-shore wind farm. The test results are compared with interior-point method based non-linear constrained optimization tool, fmincon, in Matlab. The analysis is carried out considering with and without wake effects on the wind farm at various grid bus voltage conditions. The test results demonstrate the effectiveness of the proposed method in achieving optimal solution for various operating conditions.     

Analysis of voltage stability uncertainty using stochastic response surface method related to wind farm correlation

Wind speed follows the Weibull probability distribution and wind power can have a significant influence on power system voltage stability. In order to research the influence of wind plant correlation on power system voltage stability, in this paper, the stochastic response surface method (SRSM) is applied to voltage stability analysis to establish the polynomial relationship between the random input and the output response. The Kendall rank correlation coefficient is selected to measure the correlation between wind farms, and the joint probability distribution of wind farms is calculated by Copula function. A dynamic system that includes system node voltages is established. The composite matrix spectral radius of the dynamic system is used as the output of the SRSM, whereas the wind speed is used as the input based on wind farm correlation. The proposed method is compared with the traditional Monte Carlo (MC) method, and the effectiveness and accuracy of the proposed approach is verified using the IEEE 24-bus system and the EPRI 36-bus system. The simulation results also indicate that the consideration of wind farm correlation can more accurately reflect the system stability.     

Static VAR compensation of a fixed speed stall control wind turbine during start-up

An installed 900 kW fixed speed stall controlled soft-started wind turbine connected to a weak distribution grid was modeled under start-up conditions. Generator and soft-start control and design parameters were not available, so a modeling process independent of this information was developed. Field measured transients were closely reproduced in simulation using a full-order generator model with generic parameters and a thyristor-based graduated interconnection to the grid. A Static VAR Compensator model was then added to the wind turbine model to explore a method of reducing start-up transients. It was found that for the specific transients modeled, a 300 kVAR SVC supplied sufficient reactive power to limit line voltage variations to within 3% of steady state values. Model details and simulation output are presented in this paper.     

Mathematical modelling of a wind power system with an integrated active filter

A novel technical solution of the power quality and electromagnetic compatibility (EMC) problems has been proposed through computer-aided design of a wind power system. In the considered wind power system, an AC power source generates the power, which is comparable to the consumed power. Consumer equipment is represented by a switch-mode power supply. Instead of the standard solution for the power quality and EMC problems, where a harmonic filter is placed between the load side and the wind-driven power generator, an active power filter has been integrated into the AC/DC/AC converter of the wind power system. A mathematical model of the AC/DC/AC converter built upon the multi-phase bridge-element concept has been introduced. A computer program for analysis of electromagnetic processes in a wind power system has been developed. A practical example of a wind power system has been analysed where the system frequency response is calculated using the developed mathematical model.     

Hybrid wind power balance control strategy using thermal power,hydro power and flow batteries

The increased number of renewable power plants pose threat to power system balance. Their intermittent nature makes it very difficult to predict power output, thus either additional reserve power plants or new storage and control technologies are required. Traditional spinning reserve cannot fully compensate sudden changes in renewable energy power generation. Using new storage technologies such as flow batteries, it is feasible to balance the variations in power and voltage within very short period of time. This paper summarises the controlled use of hybrid flow battery, thermal and hydro power plant system, to support wind power plants to reach near perfect balance, i.e. make the total power output as close as possible to the predicted value. It also investigates the possibility of such technology to take part in the balance of the Lithuanian power system. A dynamic model of flow battery is demonstrated where it evaluates the main parameters such as power, energy, reaction time and efficiency. The required battery size is tested based on range of thermal and hydro power plant reaction times. This work suggests that power and energy of a reasonable size flow battery is sufficient to correct the load and wind power imbalance.     

Digital control and integration of a 192 MW wind farm with doubly fed induction generator into the Brazilian power system

This paper reports on design of digital control for wind turbines and its relation to the quality of power fed into the Brazilian grid on connecting to it a 192 MW wind farm equipped with doubly fed induction generators. PWM converters are deployed as vector controlled regulated current voltage sources for their rotors, for independent control of both active and reactive power of those generators. Both speed control and active power control strategies are analyzed, in the search for maximum efficiency of conversion of wind kinetic energy into electric power and enhanced quality of delivered power.     

Simulations of wind power integration with complementary power system planning tools

This paper describes a procedure for simulations of wind power integration in a deregulated power system with two complementary planning tools. The first planning tool is a joint market model (JMM) taking into account the day-ahead market and the regulating power market using 1 h average time steps. The second tool is the stepwise power flow (SPF) model simulating the frequency deviations and power balancing within the hour, e.g. based on 5 min average time steps. Input data is shared by the two tools, and the simulation results from JMM are used in the SPF simulations to ensure consistent results. JMM simulations are performed using two different scenarios for the development in the Nordic power system. The first scenario is the most likely development for 2010, and the second is a high-wind scenario assuming 10% of the electricity consumption in the Nordic countries supplied by wind power. Subsequently, a worst case 1 h period is selected from the JMM simulations, converted to the more detailed grid representation in SPF, and finally simulated and analysed with SPF.     

基于实测数据的风电场风速-功率模型的研究

建立准确的风电场模型是风电接入系统相关研究的基础。首先通过对某双馈风电机组的标准功率特性曲线和实测风速-功率散点图进行对比,针对它们之间的差异问题,建立基于实测运行数据的风电机组风速-功率模型。其次,针对地形复杂、机组排列不规则的大型风电场风速差异性问题,利用K-means聚类算法对风电场内所有风电机组按实测风速数据进行聚类划分,建立了整个风电场的等效风速模型,进而给出了基于实测运行数据的风电场风速-功率模型。然后,以某实际风电场为例,对该风电场内的风电机组按风速进行K-means聚类划分,结果显示该划分结果与简单按地理位置的机群划分结果有明显差异。最后,对传统的风速-功率模型和所提出的风速-功率模型输出结果进行比较,结果证明所提出的模型相对于传统模型而言,准确性有了较大的提高。     

基于全景精细化模型的风电场能量管理系统研制及应用

为了提高风电场能量管理和运行控制水平,基于风电场分布式能量管理系统(EMS) 的体系结构,研发了基于全景精细化模型的风电场EMS。首先,阐述了风电场在能量管理层面面临的主要技术挑战及EMS功能层次划分,然后分别从公用数据平台、精细化建模、实时态势感知、评估预警、优化调度、有功/无功协调控制等多个层面介绍各关键模块的信息流和主要功能。所研发的智能化风电场能量管理系统已经在多家风电场投入应用。     

Line overload alleviation through corrective control in presence of wind energy

With the growth of wind energy for power generation, several transmission system operators (TSOs) have increasing difficulties to forecast congestions due to the unpredictable nature of the energy source. This paper proposes to enhance congestion management using a real time supervisor. This supervisor performs automatic and dynamic re-dispatchings using both variable speed wind generators and conventional generators. In order to minimize production constraints, the real time congestion management system is based on an indicator of the efficiency of a re-dispatching on the power flowing in an overloaded line. This approach leads to reduced re-dispatching costs and increased network reliability. The simulation of the IEEE 14-bus test power system enhanced by the supervision system is done using the software “EUROSTAG”. Grid integration of renewable generation is therefore increased through renewable production maximization while ensuring network security.     

Fixed-order controller for reduced-order model for damping of power oscillation in wide area network

The interconnected power systems are complex and stabilizing control design still remains challenging task. The use of wide area monitoring system (WAMS) offers an integrated measurement-based and model-based control, which suits to the operation of large electric power system (EPS), along with online analysis. This paper presents a study on fixed-order controller design for equivalent network of coherent generator in order to stabilize inter-area electromechanical oscillations in the system. Firstly, the coherent generators in each area of large EPS are determined by mutual information theory, which represents the dynamic equivalence. Then network of each area with input–output variables of the selected generator that participates dominantly is reduced to lower size by square-root variant of balanced truncation algorithm. The dynamics and important oscillation modes are verified in equivalent representation of each area. Finally a local controller (decentralized) in each coherent area and a centralized controller between two coherent areas for selected generator are designed by reducing the H^∞ norm of its closed loop transfer function as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned PSS. The decentralized controller for selected generator is fed by local bus power or generator’s speed signal. On other hand, the centralized controller uses difference of power flow/speed of generators as input signal to dampen the oscillations between equivalent networks of two areas. The simulation results reveal effective damping of power/speed oscillations achieved by designed controller with respect to conventional PSS implemented. The robustness of controller is verified for heavy and light load operating conditions.     

Renewable energy credit driven wind power growth for system reliability

Environmental concerns over electric power generation from conventional sources has led to widespread public support for renewable energy sources. Governments throughout the world have responded by providing various forms of financial incentives to promote power generation from renewable energy sources. The rapid growth of wind power since the last decade has primarily been driven by governmental subsidies. Long-term growth of wind power should, however, be driven by sustainable market mechanisms. A potential solution is to recognize monetary values to the environmental benefits from renewable energy sources, and to specify targets for their growth. The environmental benefits from wind sources can be leveraged to allow market competition of these sources with the less costly conventional generating sources. A probabilistic method to evaluate the impact of renewable energy credit and wind penetration level on the cost and adequacy of power generating systems is presented in this paper. The technique incorporates reliability and economic analyses and is applied to a published test system to illustrate the results and their influence on key system variables. The paper provides useful information to system planners and policy makers on wind energy application in electric power systems.     

国外风力发电导则及动态模型简介

分析了美国、丹麦、德国、苏格兰以及爱尔兰等欧美国家输电网运行公司针对风力发电制定的电网导则及其对风力发电动态仿真提出的要求,讨论了四种典型风力发电机组的动态建模,并给出了恒速感应式风力发电机组和变速双馈风力发电机组的仿真实例.仿真结果表明风力发电机组具有很多不同于同步电机或马达类负荷的特性,应认真研究其对电力系统规划和运行的影响.电网导则的更新以及风机的动态建模是目前电力系统面临的重要课题.     

Evolution of primary frequency control requirements in Great Britain with increasing wind generation

With the increase of renewable generating capacity following the ambitious targets set by many governments for the next decades, there will be major changes in power generation and challenges for balancing transmission grids. In particular, primary frequency control requirements will be increased following a potential reduction of system inertia.An assessment of the frequency response reserve needed is made through use of a simple model of the Great Britain transmission grid for different loads and wind power penetration. This model analyses the effect of changing the system inertia and the effectiveness of standard frequency response as well as dynamic frequency control support.It is observed that an increased wind power generation requires substantial additional reserves for primary frequency control if the wind turbines do not contribute to the overall system inertia. However, it is also shown that these reserves can be dramatically reduced if the system is provided with fast acting response by dynamic frequency control support.     

考虑弃风的DFIG风电场动态等值模型

我国弃风现象严重,在此大环境下,为了得到更为准确的风电场模型,提出了一种考虑弃风的双馈感应异步发电机(DFIG)风电场的建模方法。该方法考虑了由于尾流效应导致风电场内各台风力机输入风速不同,兼顾调度部门向风电场下达的弃风指令,提出了以风能利用率Cp为分群指标,建立了DFIG风电场的多机等效动态模型,大幅度提高了仿真速度。该方法更贴近风电场实际运行情况,分群指标易于得到。通过PSCAD算例仿真及结果对比,表明该风电场等值模型的输出在稳态和故障情况下都能更好地拟合详细模型。     

Soft methodology selection of wind turbine parameters to large affect wind energy conversion

In recent years the use of renewable energy including wind energy has risen dramatically. Because of the increasing development of wind power production, improvement of the control of wind turbines using classical or intelligent methods is necessary. To optimize the power produced in a wind turbine, it is important to determine and analyze the most influential factors on the produced energy. To build a wind turbine model with the best features, it is desirable to select and analyze factors that are the most influential to the converted wind energy. This process includes several ways to discover a subset of the total set of recorded parameters, showing good predictive capability. The method of ANFIS (adaptive neuro fuzzy inference system) was applied to the data resulting from this investigation. The ANFIS process for variable selection was implemented in order to detect the predominant variables affecting the converted wind energy. Then, it was used to determine how four parameters, blade pitch angle, rotor speed, wind speed and rotor radius, affect the wind turbine power coefficient. The results indicated that of all the parameters examined, blade pitch angle is the most influential to wind turbine power coefficient prediction, and the best predictor of accuracy.     

Steady-state assessments of PMSGs in wind generating units

The number of fully-rated converter wind turbine generators equipped with a Permanent Magnet Synchronous Generator (PMSG) has sensibly increased in the late years. The optimal utilization and controllability of a PMSG is achieved using a Pulse Width Modulation – Voltage Source Converter (PWM-VSC) that allows interfacing the electric machine with the distribution network by means of a DC link. The generator/Machine-Side Converter (MSC) controls the operation of the PMSG. This paper proposes a methodology to assess the feasibility of the steady-state working points of PMSG based wind turbines without running a set of time-consuming time-domain simulations. Three control objectives for MSC are usually considered: stator voltage control, unitary power factor control and torque control. The aim of the present paper is that of providing an analytical methodology to check the feasibility of the steady-state working points dictated by different control strategies of the MSC starting from the specific operational constraints provided by the wind power plants characteristics. The effectiveness of the proposed methodology is demonstrated comparing numerical results of a MATLAB® implementation against dedicated time-domain simulations. Simulations results demonstrated the appropriate performance of the proposed methodology characterized by the almost negligible computational time required.     

Stochastic optimal power flow incorporating offshore wind farm and electric vehicles

In this paper, an optimal power flow model of a power system, which includes an offshore wind farm and plug-in electric vehicles (PEVs) connected to grid, is presented. The stochastic nature of wind power and the uncertainties in the EV owner’s behavior are suitably modelled by statistical models available in recent literatures. The offshore wind farms are assumed to be composed of doubly fed induction generators (DFIGs) having reactive power control capability and are connected to offshore grid by HVDC link. In order to obtain the optimal active power schedules of different energy sources, an optimization problem is solved by applying recently introduced Gbest guided artificial bee colony algorithm (GABC). The accuracy of proposed approach has been tested by implementing AC–DC optimal power flow on modified IEEE 5-bus, IEEE 9-bus, and IEEE 39-bus systems. The results obtained by GABC algorithm are compared with the results available in literatures. This paper also includes AC–DC optimal power flow model, implemented on modified IEEE-30 bus test system by including wind farm power and V2G source. It has been shown that the uncertainty associated with availability of power from wind farm and PEVs affects the overall cost of operation of system.     

Offshore wind farm with a series multiterminal CSI HVDC

This paper presents an integrated design of an offshore wind farm and an interconnection circuit based on a series multiterminal HVDC link with current source inverters (CSI). The transmission converters are used to achieve variable speed operation for a group of generators, and this enables use of very simple generators. The series converter connection eliminates offshore transformers. The paper discusses the control systems for both, generator side and grid side converters. A 200 MW wind farm is simulated on PSCAD/EMTDC platform and the responses confirm satisfactory operation for a range of wind speed changes. It is shown that each generator group can operate with a different and optimal frequency and that wind variations on individual units cannot jeopardize system stability. The main challenges for the proposed topology are system insulation and management of transmission line losses, and the paper studies some possible solutions.