Reliability evaluation of generating systems containing wind power and energy storage

Global environmental concerns associated with conventional energy generation have led to the rapid growth of wind energy in power systems. Many jurisdictions around the world have set high wind penetration targets in their energy generation mix. Wind speed is variable in nature, and power output from a wind farm is not readily controllable. High wind penetration can lead to high-risk levels in power system reliability and stability. In order to maintain the system stability, wind energy dispatch is usually restricted and energy storage is considered to smooth out the fluctuations and improve supply continuity. The benefits from using energy storage are highly dependent on the operating strategies associated with wind and storage in the power system. A simulation technique that can consider wind farm and energy storage operating strategies is presented. Different operating strategies are compared and the resulting benefits are evaluated. The system impacts of energy storage capacity and operating constraints, wind energy dispatch restrictions, wind penetration level and wind farm location on the reliability benefits from energy storage are illustrated.     

Generating capacity adequacy evaluation of small stand-alone power systems containing solar energy

This paper presents a time sequential simulation method for generating capacity adequacy evaluation of small stand-alone power systems containing solar energy (PSCSE) operating in parallel with battery storage. The reliability performance of such a system is quite different from one containing only conventional generation. This is due to the chronological random nature of the solar radiation level and the dependencies associated with the power output of every photovoltaic (PV) generating unit at the site location. The adequacy of a PSCSE depends on various factors such as the solar radiation level, the battery size and charging (discharging) capability, the failure/repair characteristics of the diesel generator (DG) and the PV unit, the system load profile and peak load and the solar energy penetration level in the system etc. The methodologies, results and discussions presented in this paper should provide valuable information to utilities involved in planning and operating stand-alone systems utilizing both conventional and solar energy.     

Combined design and load shifting for distributed energy system

Renewable distributed energy generation (DEG) system plays an important role in future power developments and is one of the options to reduce energy consumption. It is envisaged that energy efficiency of DEG systems can be improved via load shifting (LS). This study proposed a heuristic-based numerical approach to perform LS analysis on renewable stand-alone DEG systems. The technique is an extension from a method known as the Electric System Cascade Analysis (ESCA). The new technique, which focuses on efficient electricity utilisation is able to determine the optimal: (i) load profiles, (ii) capacity of power generator, (iii) capacity and power of energy storage (ES) and (iv) charging/discharging schedule of ES. The stage-wise technique allows user to compare and determine the optimal design in a flexible way while having a better understanding of the selection of options. The application of ESCA-LS on a case study revealed that after incorporation of direct LS (load manipulation) in addition to LS by ES (supply manipulation), the power generators and ES capacity can be further reduced. While reduction of 3.1 % for solar-PV installation area and 3.9 % for biomass power generator is recorded, ES power-related capacity and energy-related capacity managed a higher reduction of up to 19.0 and 13.2 % for the main case study     

Flow shop scheduling with grid-integrated onsite wind power using stochastic MILP

Over the last decade, manufacturing companies have identified renewable energy as a promising means to cope with time-varying energy prices and to reduce energy-related greenhouse gas emissions. As a result of this development, global installed capacity of wind power has expanded significantly. To make efficient use of onsite wind power generation facilities in manufacturing, production scheduling tools need to consider the uncertainty attached to wind power generation along with changes in the energy procurement cost and in the products’ environmental footprints. To this end, we propose a solution procedure that first generates a large number of wind power scenarios that characterise the variability in wind power over time. Subsequently, a two-stage stochastic optimisation procedure computes a production schedule and energy supply decisions for a flow shop system. In the first stage, a bi-objective mixed integer linear programme simultaneously minimises the total weighted flow time and the expected energy cost, based on the generated wind power scenarios. In the second stage, energy supply decisions are adjusted based on real-time wind power data. A numerical example is used to illustrate the ability of the developed decision support tool to handle the uncertainty attached to wind power generation and its effectiveness in realising energy-related objectives in manufacturing.     

Space-time wind speed forecasting for improved power system dispatch

To support large-scale integration of wind power into electric energy systems, state-of-the-art wind speed forecasting methods should be able to provide accurate and adequate information to enable efficient, reliable, and cost-effective scheduling of wind power. Here, we incorporate space-time wind forecasts into electric power system scheduling. First, we propose a modified regime-switching, space-time wind speed forecasting model that allows the forecast regimes to vary with the dominant wind direction and with the seasons, hence avoiding a subjective choice of regimes. Then, results from the wind forecasts are incorporated into a power system economic dispatch model, the cost of which is used as a loss measure of the quality of the forecast models. This, in turn, leads to cost-effective scheduling of system-wide wind generation. Potential economic benefits arise from the system-wide generation of cost savings and from the ancillary service cost savings. We illustrate the economic benefits using a test system in the northwest region of the United States. Compared with persistence and autoregressive models, our model suggests that cost savings from integration of wind power could be on the scale of tens of millions of dollars annually in regions with high wind penetration, such as Texas and the Pacific northwest.     

基于介电弹性体的振荡水柱波浪能发电模拟分析

振荡水柱式(OWC)波浪能采集装置结构简单、成本低;介电弹性体作为发电机可以收集人体能、海洋能、风能等,能量密度高、耐冲击、环境适应性强,利用OWC驱动介电弹性体形变发电应用前景好。在FLUENT中建立二维数值水槽OWC模型分析气室内波高和压强的变化规律;在Abaqus有限元分析系统中将波浪进入气室的模拟压强施加到介电弹性体薄膜模型产生形变,采用Simulink计算介电弹性体发电量。结果表明:介电弹性体发电量随着薄膜面积、气室压强增加而增大;随着薄膜厚度、预拉伸强度增大而减小,并且这两者对发电量影响较大。     

泛在电力物联网实施策略研究

建设泛在电力物联网是实现能源转型目标的必要手段。从电力系统发展历程和面临的问题出发,论述了泛在电力物联网的意义,提出了实施策略和可能遇到的问题。为实现能源转型,风电光电等可再生能源装机容量不断增加。这些能源的随机性给电力系统的功率平衡造成巨大压力,有时不得不弃掉一部分风电光电。为了维持电力系统的稳定运行、提高风电光电的利用率,必须对可控负荷和分散式发电进行控制。因此,需要用互联网连接可控负荷和分散式发电,形成泛在电力物联网。常规发电厂、大型风电场、光电站等已经和电力系统连接了,调度可以直接控制。因此,泛在电力物联网主要任务是连接负荷和分散式发电,尤其是可控负荷。电动汽车是可控负荷中最容易实现可控的,其次是热水器、电热锅炉和空调等。利用泛在电力物联网,协同控制风电光电、可控负荷、分散式发电等,可以提高风电光电利用率,实现能源转型目标。     

弃风条件下考虑机群电价差异的风电场控制策略

基于风电存在弃风限电以及不同电价的情况,提出一种最大化风电场收益的控制策略。在风电场自动发电控制系统和不同机群能量管理系统之间搭建一套协调控制系统。该协调控制系统基于不同机群的上网电价,考虑机群最大发电能力,将发电指标合理分配给不同机群,在保证机组运行可靠、安全的前提下让电价高的机组优先发电,让电价低的机组满足最小运行负荷,从而实现收益最大化。通过计算不同机群的理论功率,最终得出实际提升的收益。     

Performance aspects of mains connected small-scale wind turbines

Small-scale wind turbines are seen as potentially playing an important part in the future UK electricity generation mix. As such it is important that the necessary turbine and generator systems are well matched in order to maximise power output and energy capture. A turbulent wind model is described that is suitable for use with small-scale wind turbines. The model is used along with models of the turbine, generator and power conversion system to study potential problems that can exist with incorrect turbine design. The wind model is verified by comparison with measured data while the generator and power converter model are verified by laboratory test. A small 2.5 kW, `H' bladed vertical axis wind turbine is then studied to examine the effect that different blade sections may have in turbulent winds. A symmetrical blade section is seen to cause potential stall problems while these are avoided by the use of a cambered blade section     

Wind-driven stand-alone DFIG with battery and pumped hydro storage system

A wind-driven doubly fed induction generator (DFIG) along with the battery and pumped hydro storage plant (PHSP) has been devised for supplying isolated loads. PHSP-based storage system is economical and viable for the MW level wind-turbine system. The proposed scheme employs a squirrel-cage induction machine (SCIM) coupled with reversible pump turbine for PHSP. The battery storage is also included in this system to cope up with the intermittent nature of wind and fast-changing load. A simple control strategy has been implemented for maintaining the set values of voltage magnitude and frequency at the stator terminals of DFIG, which serve as a virtual grid for connecting ac loads and SCIM. Based on the availability of power in the wind, PHSP and battery, various operating modes of the proposed system have been clearly identified for supplying the isolated loads. These operating modes are clearly demonstrated through the analysis developed for this purpose and validated through experimental results. The salient features of the proposed system over the existing stand-alone wind-driven generators are (i) structural simplicity, i.e., employing only one power electronic converter, (ii) wide speed operation of wind-driven DFIG, (iii) reduced battery capacity, (iv) high energy storage using PHSP and (v) availability of continuous power to the isolated loads.     

Optimizing Decision-Making of A Smart Prosumer Microgrid Using Simulation

Distributed renewable energy sources offer significant alternatives for Qatar and the Arab Gulf region’s future fuel supply and demand. Microgrids are essential for providing dependable power in difficult-to-reach areas while incorporating significant amounts of renewable energy sources. In energy-efficient data centers, distributed generation can be used to meet the facility’s overall power needs. This study primarily focuses on the best energy management practices for a smart microgrid in Qatar while taking demand-side load management into account. This article looked into a university microgrid in Qatar that primarily aimed to get all of its energy from the grid. While diesel generators are categorized as a dispatchable distributed generation with energy storage added to handle solar radiation from the sun and high grid power operating costs in the suggested scenario, wind turbines and solar Photovoltaic (PV) are classified as non-dispatchable distributed generators. The resulting linear math issues are assessed and displayed in MATLAB optimization software using a mixed-integer linear programming (MILP) strategy. According to the simulation results, the suggested energy management strategy reduced the university microgrid’s grid power costs by 38.8%, making it an affordable solution which is somehow greater than the prior case scenario’s 23% savings. The installed solar system capacity’s effects on the economy, society, and finances were also assessed, and it became clear that the best option for the smart microgrid was determined that would be 325 kW of solar PV, 25 kW of wind turbine, and 600 kW of diesel generators, respectively. Given the current situation, university administrators are urged to participate in distributed generators and adopt cutting-edge designs for energy storage technologies due to the significant environmental and financial benefits.     

Reliability/cost implications of utilizing photovoltaics in small isolated power systems

The rapid growth of renewable energy applications in electric power systems dictates a need to develop comprehensive techniques that can be used to evaluate the economics involved and the reliability of power supply that can be achieved from the utilization of these energy sources. Photovoltaic (PV) arrays have the potential to significantly reduce operating costs in remote small systems which are generally supplied using costly diesel fuel. This paper presents a simulation method that provides objective indicators to help system planners decide on appropriate installation sites, selection of PV arrays or diesel units in capacity expansion and optimum PV penetration levels when utilizing PV energy in small isolated systems.     

Determination methodology for optimising the energy storage size for power system

A methodology for determining the optimal size of energy storage system (ESS) integrated with thermal power system is presented in this study. The optimal size is characterised by the rated stored energy and the maximum power rating of installed ESS for which the power system can achieve maximum revenue. Therefore the ESS cost formulation is conducted by analysing economic cost benefit measures considering life cycle of ESS. Since unit commitment (UC) scheduling is an important and integral part of power system cost optimisation, this study considers the operating schedule of thermal units (TU) while resolving ESS schedule. This proposed method uses tabu search (TS)-based evolutionary technique for solving this optimisation problem. TS is included in this algorithm to avoid re-evaluation of already evaluated ESS size which is powered by max priority heap and hash table data structure. The weekly schedule period is considered instead of daily to achieve more precise results. The proposed method is applied in two different power systems to determine the appropriate size of to be installed ESS. Experimental results reported that establishing the proposed method is an effective one to compute the optimal size of ESS for different sized power systems.     

Modelling distributed generations in three-phase distribution load flow

The mathematical models of distributed generations (DGs) are integrated into three-phase distribution load flow program to analyse and simulate the penetrations of DGs for distribution systems. DGs can utilise the traditional energy sources such as oil and coal or renewable energy sources such as wind, solar and fuel cell and use rotating generators or converters to transfer energy to power grids. According to the characteristics of output power, DGs can be specified as constant power factor model, constant voltage model or variable reactive power model in the load flow analysis. These three models are all derived and integrated into the proposed load flow method. Test results demonstrate the validity and capability of the proposed method.     

储能在电网中的应用价值及其商业模式

随着风电、光伏渗透率逐渐增大,其并网给电网稳定运行带来了诸多挑战。储能技术可以有效平抑新能源功率波动,增强新能源发电可控性,提高新能源的并网接入能力,因此在电网中配置储能的相关研究与技术受到越来越多的关注。以储能系统接入电网的功能为切入点,针对储能系统在调频、调峰、备用容量和延缓输配电扩容升级等4种场景中的应用价值进行研究和归纳,讨论了储能相关商业模式的发展前景和未来待研究的关键科学问题。     

Novel maximum-power-extraction algorithm for PMSG wind generation system

The paper focuses on the development of a novel maximum-power-extraction algorithm (MPEA) including a maximum-power error-driven (MPED) mechanism and a maximum-power differential-speed (MPDS) control, for a wind generation system with a permanent-magnet synchronous generator (PMSG). In the proposed MPEA scheme, the MPED mechanism, operating like a traditional hill-climbing method, drives the output power gradually increasing to its maximum value by regulating the direction of current command according to the power variation trend. The MPDS control produces an additional step of current command based on the instantaneous difference of generator speeds, so that it can prevent the wind turbine from stalling at the suddenly dropping wind speed and achieve the object of maximum power extraction instantly as a stiff wind flowing through the wind turbine. In addition, the output is connected to a utility grid for providing energy flexibility via a unipolar full-bridge inverter controlled by a digital signal processor. The grid-connected experimentations of the proposed MPEA scheme, without any mechanical sensors for a wind-power emulation system via a PMSG driven by an induction motor, are given to examine its feasibility in practical applications     

风光储联合发电运行技术研究

随着能源需求的日益增长和新能源的快速发展,利用风能、太阳能的发电技术已经逐步成熟,且在电网中的渗透率也在不断提高。为弥补风能、太阳能发电所带来的功率不稳定、电能质量低等问题,有必要对风能、太阳能、储能联合发电进行深入研究。文中依据简单平抑方法、考虑一定约束的平抑方法、考虑功率预测与人工智能的平抑方法对储能的平抑控制策略进行了归纳总结。在储能平抑风光波动的研究中滤波算法是最为常见的方法,加入一定的约束会使平抑效果更佳,储能平抑配合精准的预测使整个系统更加平滑。多储能技术混合可以发挥各储能技术优越性。加入储能装置的风光储互补系统可以有效降低原风光互补系统对电网的不利影响。可以在更高程度上平滑风光发电系统的输出特性,增加电网对可再生能源的吸收接纳程度,取得良好的经济和社会效益。     

燃料电池分布式供能技术发展现状与展望

燃料电池作为一种清洁高效的发电方式,兼具效率高、排放低、安全无噪音等优点,是分布式供能领域的一项重要技术。燃料电池既可以利用传统煤炭、天然气,也可以融合可再生能源实现削峰填谷。在传统煤电领域,散煤的利用是环境污染的重要来源,通过直接碳燃料电池技术,有望解决散煤利用效率低下、污染严重的问题。联合天然气管网,基于燃料电池的微型热电联供系统可实现能源的梯级利用,相比传统的热电分供模式可大大提高能源利用效率。同时,电解池作为燃料电池的逆过程,可将可再生能源富余电力转化为化学能进行储存,实现"三弃"电力的有效转化,在可再生能源的分布式供应系统中具有广阔的发展前景。     

风电并网价值分析

风电的接入因能替代常规机组发电而具有正向价值,同时也因会改变系统中不同类型机组的运行方式而带来负向价值。为衡量风电并网价值,建立了含风电机组日前优化调度模型,模型中考虑了不同机组的特性及负荷与风电的随机性和误差,从风电渗透率、负荷与风电预测误差和负荷与风电相关性3方面分析了它们对风电价值的影响。结果表明：风电并网容量较小时,风电具备减小系统运行成本的价值;风电并网容量较大时,机组启停费用增加,致使风电不具备并网的价值。     

Probabilistic technique for sizing FACTS devices for steady-state voltage profile enhancement

A novel and simple stochastic-based approach to determine the optimal sizing of multiple flexible AC transmission systems (FACTS) devices in a power system for steady-state voltage profile enhancement is presented. In this context, investigations have been conducted on a published test system taking into consideration the uncertainty of the system load and generator scheduling. Two FACTS schemes are considered, namely a thyristor controlled series capacitor (TCSC) and two static synchronous compensators (STATCOMs) and a unified power flow controller (UPFC) and a STATCOM. The TCSC and UPFC are employed in the system to adjust the natural power sharing of two different parallel transmission lines and therefore enable the maximum transmission capacity to be utilised. Risk indices to estimate the likelihood that the voltage magnitude at a certain bus falls below a desired value is also presented.