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.     

Probabilistic evaluation of reserve requirements of generating systems with renewable power sources: The Portuguese and Spanish cases

This paper presents an application of probabilistic methodologies to evaluate the reserve requirements of generating systems with a large penetration of renewable energy sources. The idea is to investigate the behavior of reliability indices, including those from the well-being analysis, when the major portion of the renewable sources comes from wind power and other intermittent sources. A new simulation process to address operating reserve adequacy is introduced, and the correspondent reliability indices are observed. Case studies on the Portuguese and Spanish generating systems are presented and discussed.     

Security-constrained power generation scheduling with thermal generating units,variable energy resources,and electric vehicle storage for V2G deployment

This paper investigates the role of integration of distributed storage with high penetration of variable renewable sources in power systems. The paper analyzes the impact of such integrations on the security, emission reduction, and the economic operation of electric power systems. The paper also identifies strategies for a larger penetration of variable generation resources without compromising the power system security. Mixed integer linear programing (MILP) is applied for the optimization of the day-ahead hourly security-constrained unit commitment. The assimilation of EVs (both as a provider and a utilizer of energy), renewable energy sources, and smart grid is regarded as a novel, low-cost, and low-emission solution to the existing challenges of electric power systems including the means of storing large quantities of energy considering variable renewable energy sources and large carbon footprints of conventional thermal units. Numerical studies are conducted in this paper to showcase the potential impacts of EV fleets as battery storage for peak load shaving, minimizing power grid operation costs and hourly wind curtailments, and optimizing the environmental impacts based on hourly commitment and dispatch of thermal generating units.     

Reduction of power fluctuation by distributed generation in micro grid

Renewable forms of energy such as wind power or photovoltaic energy are environmentally focused, but the fluctuation of the output power of such renewable forms of energy may cause excessive variation of the voltage or frequency of the grid. Increasing the amount of renewable energy would degrade the quality of the grid. Micro grids, in which dispersed power sources compensate variations in the generation of renewable energy, can expand the limits of installation of renewable forms of energy by maintaining the quality of the interconnected grid. This paper discusses the use of gas turbines to absorb power variations from wind generation and the loads. In order to control the output power, gas turbines must run under partial load, which results in lower efficiency. An evaluation of the micro grids is made with consideration of their efficiency, the installed capacity of wind power generation systems, and frequency stability for islanded operation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 22–29, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20462     

Power quality evaluation in smart grids considering modern distortion in electric power systems

High power quality level is required in smart grids especially for non-stationary situations due to increased use of nonlinear loads and PQ disturbances such as dips, swells, transients and interruptions. Many power quality indices (PQIs) are available. In this paper a new fuzzy-wavelet packet transform-based power quality Index (FWPTPQI) is developed to amalgamate existing power quality indices as the output of a fuzzy based module based on fuzzy inference systems, knowledge base and existing PQI as input. Fuzzy systems allow handling the uncertainties associated with the electric power quality evaluation. The proposed approach has been applied to two case studies; stationary balanced and non-stationary unbalanced three-phase systems. The results are compatible with prevalent situations. The new index gives significant sense of the quality of transmitted electrical power. A comparative study of using different wavelet basis functions is considered and results indicate that Daubechies 10 and Daubechies 15 could be considered as the overall best wavelet basis functions. Since the new index represents an amalgamation of the PQ indices with less number of wavelet coefficients, it helps reduce the size of data processed which is required in smart grid applications.     

新能源电力系统概率预测理论与方法及其应用

高比例新能源已成为中国电力系统发展的突出特征,间歇性新能源发电的不确定性给电力系统安全与经济运行带来极大挑战.准确可靠的供需预测是新能源电力系统分析与运行控制的基础,传统确定性预测难以消除预测误差,概率预测可实现对预测不确定性的有效量化,为电力系统分析与运行控制提供关键信息支撑.文中对新能源电力系统概率预测理论与方法及...     

Design and evaluation of PV-wind hybrid system with hydroelectric pumped storage on the National Power System of Egypt

National and international policies encourage increased penetration of solar and wind energy into electrical networks in order to reduce greenhouse gas emission. Solar radiation and wind speed variations complicate the integration of wind and solar generation into power systems and delay the transition of these sources from centralized to distributed energy sources. The increased penetration of nontraditional energy sources into the electric grid stimulates the demand for large capacities in the field of energy storage. A mathematical model, which describes the operation of a proposed hybrid system, including solar PV, wind energy, and a pumped storage hydroelectric power plant is developed in this paper. This hydropower plant utilizes seawater as a lower reservoir, and only a tank has to be built in order to reduce the installation cost of the storing system. The pumped storage power plant used for compensation of the variation of the output energy from the PV and wind power plants by discharging water from the upper reservoir, which is previously pumped in the case of surplus energy from PV and wind turbine power plants. The impact of the proposed system on the grid utility is investigated in accordance with the values of energy exchange(deficits and surpluses of energy) between the considered hybrid system and the grid. The optimum design is determined by the pump and turbine capacities, upper reservoir volume, and the volume of water left in the tank for emergencies. Different scenarios of the optimum operations are presented for analysis. The results obtained from the examined scenarios indicate the ability of such a hybrid energy system to reduce the exchange of energy with the grid. This paper indicates the technical feasibility of seawater pumpedstorage hydropower plant for increasing the Egyptian national grid's ability to accept high integration of renewable energy sources.     

直流电网核心装备及关键技术展望

直流电网技术是解决区域内高比例可再生能源并网和消纳问题的有效技术手段,但构建直流电网将面临技术、装备和标准等方面的诸多挑战。基于直流电网的技术特点,分析了高比例可再生能源并网、远海风电并网、直流配电网等3种典型应用场景,详细阐述了直流电网关键技术和核心设备的最新研究进展,研究提出了直流电网技术的发展方向,分析了未来直流电网发展需要研究的关键技术,指出未来随着直流电网基础理论体系的完善,以及关键技术、核心设备的突破,直流电网技术将在全球广泛互联的能源网络中发挥更大的作用。     

Impact of hybrid wind and hydroelectric power generation on the operational performance of isolated power systems

In recent years, electric power systems are adopting new technologies in their structure in order to achieve better performance and efficiency in the electricity production, transmission and distribution. This fact together with additional financial incentives being developed in many countries have increased considerably the number of power generating units using renewable energy sources. However, a major drawback of these units is their dependency on unexpected weather conditions such as the wind speed and the rainfalls in the respective hydrologic areas. The purpose of this paper is to investigate the impact of wind parks and hydroelectric power plants on the reliability and operational performance of isolated power systems. A probabilistic methodology has been developed for simulating more efficiently and realistically the reliability and operational performance of these power systems. This is an effective computational methodology that is based on the Monte-Carlo sequential simulation approach and it evaluates the reliability and operational indices of the conventional thermal and hydroelectric power plants, the wind parks and the overall indices of the system. An appropriate model based on the power system of a Greek island is used and the obtained results are presented for a number of case studies representing various planning and operating schemes in order to deduce the optimal one.     

A Determination Method for the Optimal Operation of Controllable Generators in Micro Grids That Copes with Unstable Outputs of Renewable Energy Generation

Micro grids are expected to be one of the most realistic energy systems for efficient use of renewable energy sources with few adverse effects on the main electric power grids. However, it is difficult to maintain the supply‐and‐demand balance because distributed renewable energy generation units (DREGs), such as photovoltaic generation systems and wind turbine generation systems, generate a significant portion of electrical energy in the micro grids. Therefore, an operation planning method is needed considering the uncertainty in weather prediction in order to ensure stable micro grid operations. This paper presents an optimization method for operation plans of controllable generators in micro grids that copes with the uncertainty of DREG outputs. In the proposed method, the optimal operation plans are determined by, depending on the problem conditions, either an enumeration method or Tabu Search with preprocessing. Numerical simulations were carried out for a micro grid model in order to verify the usefulness of the proposed method. In the simulations, the daily operation plan and the modified half‐hourly one were determined by the proposed method. As a result, we could obtain the optimal plans which had enough reserve margins for coping with the fluctuations caused by DREGs and demand.     

考虑自组织临界条件的区域电网风电极限渗透功率评估方法

随着电力系统中风电装机容量的不断增长,如何评估已有区域电网的最大风电极限渗透功率成为了一个重要问题。通过分析复杂电力系统的自组织临界性,提出了基于区间最优潮流的连锁故障模型来评估系统风电极限接入容量的新方法。该方法将风电出力的波动性建模为区间数,通过区间连锁故障模型模拟在风电比例不断增长情况下的电网连锁故障概率与连锁故障规模的规律,获得电网出现自组织临界特性时的风电渗透平均功率,并以此作为电网的最大风电渗透容量。通过在IEEE30节点系统和IEEE118节点系统上的仿真实验,验证了该方法可合理地测量电力系统的极限风电接入容量。     

Balancing risk and cost in fuzzy economic dispatch including wind power penetration based on particle swarm optimization

Utilization of renewable energy resources such as wind energy for electric power generation has assumed great significance in recent years. Wind power is a source of clean energy and is able to spur the reductions of both consumption of depleting fuel reserves and emissions of pollutants. However, since the availability of wind power is highly dependent on the weather conditions, the penetration of wind power into traditional utility grids may incur certain security implications. Therefore, in economic power dispatch including wind power penetration, a reasonable tradeoff between system risk and operational cost is desired. In this paper, a bi-objective economic dispatch problem considering wind penetration is formulated, which treats operational costs and security impacts as conflicting objectives. Different fuzzy membership functions are used to reflect the dispatcher’s attitude toward the wind power penetration. A modified multi-objective particle swarm optimization (MOPSO) algorithm is adopted to develop a power dispatch scheme which is able to achieve compromise between economic and security requirements. Numerical simulations including sensitivity analysis are reported based on a typical IEEE test power system to show the validity and applicability of the proposed approach.     

Comparative evaluation of two models of UPQC for suitable interface to enhance power quality

Majority of the dispersed generations from renewable energy sources are connected to the grid through power electronic interface, which introduce additional harmonics in the distribution systems. Research is being carried out to integrate active filtering with specific interface such that a common power quality (PQ) platform could be achieved. For generalized solution, a unified power quality conditioner (UPQC) could be the most comprehensive PQ protecting device for sensitive non-linear loads, which require quality input supply. Also, load current harmonic isolation needs to be ensured for maintaining the quality of the supply current.     

考虑新能源随机波动和T接线的城市电网连锁故障风险评估

新能源的大量接入给城市电网的安全运行和重要用户可靠供电带来很大挑战,其功率的随机波动易引发电网出现连锁故障风险。提出了一种考虑新能源出力随机波动和城市电网110 kV网架T接线开关投切的连锁故障风险评估方法。该方法在连锁故障发生概率和后果严重度的计算中都计及了系统状态的概率分布特性的影响,并采用基于半不变量法的概率潮流计算反映系统状态与新能源功率二者的概率分布特性之间的关系。另外,建立包含110 kV网架T接线开关投切的最小切负荷的混合整数非线性规划模型,并以最小切负荷量来表征系统在连锁故障的严重度。此优化模型通过决策故障下的各组T接线开关的投切状态,减少连锁故障下的切负荷量,进而有效降低连锁故障的风险。同时,通过机会约束描述重要用户负荷节点电压的安全运行范围,以确保重要用户负荷不停电的概率满足给定的置信水平,从而保证重要用户的安全可靠供电。最后,通过某个实际城市片区电网算例验证了所提出的连锁故障风险评估方法的正确有效性。     

A comprehensive review on the grid integration of doubly fed induction generator

As a result of the growing demand for electricity and environmental constraints, the generation of electrical energy from renewable sources of energy has increased recently. The renewable energy sources, especially wind power plants are integrated to power networks all around the world. The rising share of wind turbine energy, in the existing power system, has created new opportunities and challenges. For wind turbine energy generation doubly fed induction generators are most suitable due to their various advantages over fixed speed wind turbine systems. These generators have ability to improve stability and power quality of the existing power systems. Therefore more attention has been paid by many researchers recently to address various challenges of grid connection of DFIG. A comprehensive survey, of different issues associated with integration of DFIG based system into the grid is presented in this paper.     

Battery energy storage technology for power systems—An overview

The penetration of renewable sources (particularly wind power) in to the power system network has been increasing in the recent years. As a result of this, there have been serious concerns over reliable and satisfactory operation of the power systems. One of the solutions being proposed to improve the reliability and performance of these systems is to integrate energy storage devices into the power system network. Further, in the present deregulated markets these storage devices could also be used to increase the profit margins of wind farm owners and even provide arbitrage. This paper discusses the present status of battery energy storage technology and methods of assessing their economic viability and impact on power system operation. Further, a discussion on the role of battery storage systems of electric hybrid vehicles in power system storage technologies had been made. Finally, the paper suggests a likely future outlook for the battery technologies and the electric hybrid vehicles in the context of power system applications.     

Analysis of renewable energy integration into the transmission network

The increasing use of renewable energy contributes to climate change mitigation. However, a massive penetration of these latter systems into the power grid creates technical challenges due to the intermittent nature of these resources. A methodology to identify and overcome these challenges is presented in this work. A detailed network analysis is performed to simulate the impact of renewable sources on the grid and accordingly suggest mitigation methods. Different case studies were carried out on the Moroccan grid taking into consideration the country actual installed and planned renewable farms including concentrated solar power (CSP), photovoltaics (PV), and wind plants with doubly-fed induction generators (DFIG). A PSS®E software simulation tool is used in this work to conduct power flow analysis on the network’s lines, bus bars, and transformers. It is also used to investigate the voltage profile and stability of the electric grid. In addition, an N-1 contingency analysis is done to identify their impact on the reliability and security of supply. Finally, this paper presents solutions to reinforce the transmission grid.     

兼顾技术性和经济性的储能辅助调峰组合方案优化

高比例可再生能源发电并网给电力系统调峰带来了较大压力,应用储能辅助调峰是解决系统调峰问题的有效途径,但现阶段储能的高成本限制了其规模化应用。为充分发挥有限储能的调峰作用,降低储能调峰的容量需求,文中提出一种储能与正常调峰、深度调峰、投油调峰和启停调峰等常规手段优化组合调峰的实用方法。分别建立基于年调峰不足概率的技术性指标和基于年调峰费用的经济性指标的计算模型,构建组合调峰方案的技术性指标曲面和经济性指标曲面,将两个曲面交线处的组合调峰方案作为不同可再生能源渗透水平下电力系统的组合调峰优化方案。最后,以含风电、光伏发电的区域型系统和规划的全国系统为例,制定和分析了不同可再生能源渗透率下系统的组合调峰优化方案。     

采用变速恒频机组的风电场并网问题研究综述

随着风电技术以及电力电子技术的不断进步,越来越多采用变速恒频机组的风电场被接入电网.变速恒频机组相对于传统的恒速恒频机组,在电机结构和控制机理上更为先进,能够实现更为灵活的电网接入.虽然变速恒频机组在一定程度上增强了电力系统的稳定性,但一些新问题也随之而来,例如先进的控制器显著增加了系统的复杂性、风机的功率变换器发出谐波电流降低了系统的电能质量等.此外,如何通过给变速恒频机组增加附加控制器,实现其与传输系统及储能系统的协调控制,以改善系统性能,也是当今学术界的一个重要课题.文中对上述这些采用变速恒频机组的风电场并网问题的最新研究成果进行了综述.     

Energy storage system-based power control for grid-connected wind power farm

Wind power is characterized as intermittent with stochastic fluctuations, which can result in deviation of grid frequency and voltage when the wind power ratio is high enough. These effects have a definite impact on stability and power quality of grid operation. This paper proposes an energy storage system (ESS) based power control for a grid-connected wind power system to improve power quality and stability of the power system. Vanadium redox flow battery (VRB), as an environmentally-friendly battery provided with many advantages, is employed in the ESS. A dynamic mathematical model of VRB is built by using an equivalent circuit, and its charging and discharging characteristics are analyzed. The VRB’s stable voltage is available in a wide range (around 20–80% state of charge), which is suitable for utilization of a single-stage AC/DC converter in the VRB-based ESS. With a proposed energy storage control method, VRB-based ESS is added at the exit of the grid-connected wind farm to filter fluctuations of wind power, which ensures that smooth power will be injected into the grid and which improves power quality of the power system. Simulations and experiments are carried out to verify the proposed power control method for these grid-connected wind power systems. The grid-connected wind farm with VRB-based ESS, wind speed (characterized as gust and stochastic wind), and wind turbines are modeled in simulations. Simulation results show that the grid-injected active power from the wind farm is effectively smoothed, and reactive power support can be provided for the grid by the designed VRB-based ESS. Experimental verification is achieved with a low power bench, where a RT-LAB real-time simulation platform and a direct torque controlled induction motor simulate a real wind turbine and a wind speed model is built in the RT-LAB real-time simulation platform. The experimental results verify the proposed scheme through demonstrating a stable and smooth power flow injected into the grid though the wind power fluctuated.