Why microgrids are becoming an important part of the energy infrastructure

The term “microgrid” is somewhat non-specific and always changing. This is not necessarily a bad thing. In one form or another, microgrids have been in the energy service toolbox for 30 years. However, with the evolution of software systems, cost reductions in energy technology, and increasing customer drive for sustainability, reliability, resilience, and cost predictability, microgrids have become more capable today and have experienced a surge in deployment. Make no mistake, the growth is customer driven. So, what does the future hold for microgrids? If customers continue to seek cost predictability, sustainability, and reliability/resilience in their energy services, then long-term growth in the microgrid industry should be obvious, even in the face of resistance from utilities and policymakers. Where will microgrids be in 2035? 2050? Will utilities embrace microgrids? Will policymakers become facilitators of microgrids? Will municipalities and rural cooperatives use microgrids to hedge costs and improve sustainability and resilience for their citizens/members? This article will discuss the trends and drivers stemming from the early days of microgrids that still exist today which likely lead to an institutionalization and growth of microgrids in the future.     

Missing discourse on microgrids – The importance of transmission and distribution infrastructure

The current discourse on microgrids is mostly limited to enhancing resiliency and misses the importance of existing transmission and distribution (T&D) infrastructure. Using a conceptual framework and ten microgrid case studies, we illustrate that T&D infrastructure affects the anticipated benefits of microgrids. Currently microgrids are often constructed in lieu of T&D improvements. In the long run, microgrids can work with existing T&D infrastructure to improve the reliability, efficiency and environmental sustainability of the electrical grid.     

基于电气关联强度的虚拟微电网划分方法

随着智能电网与能源互联网研究的兴起,分布式可再生能源和储能设备的不断接入,配电网的智能化发展已成为一种必然趋势。而大量现存的传统配电网如何适应自由、对等、灵活的目标,成为迫切需要解决的问题。文中提出基于电网的电气关联强度将传统配电网划分成若干具有强内部聚合特性的虚拟微电网,并提出了基于扩展信息、物理、社会经济(CPS)的虚拟微电网实施框架,以及边界划分、资源优化部署、协同能量管理的三阶段研究问题。针对第一个研究问题,通过定义电气关联强度,对复杂网络中经典的Newman快速分区算法进行改造,实现对虚拟微电网边界的自动优化。通过仿真算例验证了该方法的合理性和效率。     

Blockchain for decentralized transactive energy management system in networked microgrids

The proliferation of distributed energy resources is reshaping the landscape of power distribution systems, including a network of autonomous microgrids. Networked microgrids transact energy for managing the efficiency, reliability, resilience, security, and sustainability of electric power services. This article offers a vision and analyzes a scheme developed for networked microgrids that utilizes blockchain technologies to optimize the financial and physical operations of power distribution systems. Blockchain provides a powerful and trustworthy path for launching distributed data storage and management, the article explores the possibility of customizing blockchain technologies to meet socioeconomic requirements of transactive energy management at the power distribution level. Then, a set of interoperable blockchains embedded with self-enforcing smart contracts is proposed to manage energy and financial flows among transacting microgrids in a credible manner. The article presents additional smart contract measures for securing optimal energy transactions between networked microgrids and the local distribution grid. It is concluded that blockchain technologies embedded in transactive energy will play a significant role in the evolution of traditional power distribution systems to active distribution networks.     

Multi-actor perspective,socio-technical barriers,and microgrid development in China

The microgrid is a new concept in China and may potentially play an important role in enhancing the resilience and sustainability of electricity generation and distribution. However, the development of microgrids faces many challenges. This study examines the barriers to microgrid development using a case study of a pilot zone in Qingdao. Drawing on the theories of multi-level perspective and multi-actor perspective, we presented new empirical evidence on how the pilot microgrid projects were rendered difficult by the resistance from the existing industrial regime and the challenging economic and socio-political environments. The monopoly of state-owned grid operators in electricity transmission and distribution is difficult to break at a local level. The findings deepen our understanding of the challenges encountered by innovators in China’s microgrid development and hold implications for policymakers in making more targeted policy mixes to support energy transition activities.     

基于电动汽车的极端场景多微电网韧性提升策略研究

极端场景下微电网与主网断开形成多个孤岛时,微电网内重要负荷的持续可靠供电面临极大挑战。微电网群内的电动汽车储能参与负荷支撑是提高系统韧性的有效技术手段。针对微电网孤岛供电问题,提出了一种基于电动汽车储能的多微电网两阶段韧性提升策略。首先,建立正常运行时多微电网能量管理模型,通过协调系统内各类发电资源进行能量互济,实现运行成本最小化。然后,针对台风极端事件引起的孤岛微电网持续可靠供电问题,通过多微电网各类发电资源和电动汽车储能进行能量互济,构建了多微电网两阶段韧性提升模型,最大限度地减少切负荷量,使系统运行成本最优。最后,采用Shapley值对涌现收益进行合理分配,并通过与传统多微电网能量管理方法进行对比,验证了所提韧性提升策略的有效性。     

Colorado clean energy policy landscape: A case study

For decades, countries, states, and municipalities have established energy policies to address local air pollution and global climate change goals. The thousands of policies and measures enacted globally take various forms but are aimed at different sectors of the economy. These policies are the result of a complicated process of analysis, budgeting, management, and politics. Still, greenhouse gas emissions have continued to rise globally. Good models remain rare that bridge the gap between high level aspirations and implementation. The U.S. state of Colorado offers an example over the last two years for bridging the aspiration and implementation gap. This paper provides an overview of the recent legislative sessions, and how the policies enacted support the Colorado Climate Change Roadmap.     

Pathways to eliminate carbon emissions via renewable energy investments at higher education institutions

Higher education institutions are among the many public and private sector entities that have committed to long-term sustainability goals in response to the threat of climate change. A key challenge for these institutions is establishing a commitment to make targeted investments in renewable energy technologies in support of emissions reduction goals. Such strategies require a vision to simultaneously coordinate strategic investments in renewable energy technologies with tactical operational decisions to achieve the desired benefits. In this paper, we formulate and solve a least-cost renewable energy capacity investment planning model to determine pathways to achieve emissions reduction strategies. Specifically, we apply our model to Rutgers University to evaluate its target of 100 % carbon neutrality. Using these insights, we share recommendations on how these strategies can be executed. This research serves as a springboard for administrators to assess and deploy their emissions reduction strategies, while ensuring system and financial constraints are satisfied.     

基于能源与信息技术的海岛微电网应用实践

近年来,随着岛屿开发成为热点,海岛微电网建设中存在的诸多问题日益凸显。首先介绍了已有微电网分类及存在的问题,其次分析了能源与信息技术的发展现状和关键技术,最后以并网型和离网型两类海岛为例,阐述连云港地区基于先进能源与信息技术的海岛微电网建设应用实践,为岛屿能源互联网构建提供示范参考。     

Hybrid fuel cells technologies for electrical microgrids

Hybrid systems are characterized by containing two or more electrical generation technologies, in order to optimize the global efficiency of the processes involved. These systems can present different operating modes. Besides, they take into account aspects that not only concern the electrical and thermal efficiencies, but also the reduction of pollutant emissions. There is a wide range of possible configurations to form hybrid systems, including hydrogen, renewable energies, gas cycles, vapour cycles or both. Nowadays, these technologies are mainly used for energy production in electrical microgrids. Some examples of these technologies are: hybridization processes of fuel cells with wind turbines and photovoltaic plants, cogeneration and trigeneration processes that can be configured with fuel cell technologies, etc. This paper reviews and analyses the main characteristics of electrical microgrids and the systems based on fuel cells for polygeneration and hybridization processes.     

Measuring persistence of energy savings after COVID-19

Publicly funded energy efficiency projects require measurement to inform climate and energy policy, craft program budgets, and determine the cost-benefit ratios of different projects. One of the key inputs into cost-benefit analyses is the concept of an effective useful life, or EUL. This value, typically measured in years, lets programs and policy makers estimate how many years the energy savings will last. For most programs, this measurement is done based on manufacturing assumptions, i.e. the laboratory determined that an LED lightbulb would last for 10,000 h, or 15 years. New programs, using a methodology known as “advanced measurement and verification (AM&V)” measure the EUL using a survival analysis of the savings. We ask the question, “At what point will this project be savings less than 50% of what it saved on day 1.” We measure the energy consumption of a facility at the meter level to determine how much energy is being used compared to when the measure was installed. COVID-19 has thrown a wrench in the ability to compare energy use across years. Not only is there a disruption from COVID-19 directly, but entire industries have fundamentally changed the way that they operate their buildings and run their businesses. We are able to extract out the impacts of COVID for many of our building’s models, but not all. Using methods derived from independent, third-party evaluators, we have developed a new way to measure the ongoing persistence of energy savings using self-report data from participants at the project level, rather than at the savings level. Doing this will allow us to compare the data from pre-COVID with the new world full of post-COVID data, and to assess the true impacts of COVID on the energy efficiency industry’s most basic cost-effectiveness assumptions.     

考虑热泵负荷和分布式光伏的配微网协调调度

随着农村清洁供热改造以及城镇分布式光伏建设的不断推进,配电网中出现了大量农村微电网。分布式光伏的强随机性和波动性给电网的运行调控带来了诸多挑战,电网面临剧烈的潮流波动和严重的电压越限等问题。首先,构建了计及热泵、光伏和储能的配微网分解协调模型,其中热泵用等效状态空间模型描述;然后,提出一种配微网有功无功协调优化方法,并采用改进的Benders分解算法进行求解;最后,在D141-M4算例系统上进行了算例测试。测试结果表明,所提方法可以在保证用户舒适度的前提下,有效降低电网峰值负荷,并提升电压安全水平。     

Priority-based Energy Management Technique for Integration of Solar PV,Battery, and Fuel Cell Systems in an Autonomous DC Microgrid

Recent times have witnessed a significant positive trend in adoption of renewable energy sources and DC-based loads, which questions the efficiency and reliability of existing structure of electrical power system. DC microgrids are identified as potential solutions for addressing India's and other developing nations' rural electrification. This paper presents an energy management technique for isolated DC microgrids for academic readers, as well as provides an introduction to not-familiarized readers for understanding the common design challenges for implementing off-grid power systems. The principle of the proposed technique is based on law of energy conservation defined by the energy balance equation and is implemented by synthesizing the instantaneous current reference and hysteresis control with source priority, which was validated by rigors simulation studies in Matlab/Simulink. Furthermore, in order to demonstrate the modularity and scalability of the algorithm, it was tested on a prototype hardware test setup at the Solar Energy Research Centre, VIT University.     

Optimal Control of Active Power of Two Micro-grids Interconnected with Two AC Tie-Lines

Active power balance and frequency control are important tasks in the daily management of a power system. With the integration of several microgrids in the modern power system, the balancing of sources of energy has become a major concern for electrical power engineers and researchers worldwide. New power systems require more flexibility in optimization and control design to ensure their ability to maintain the balance between generation and load of the system. The present paper discusses an optimal control design for minimization of the power flow in tie-lines and frequency deviations in the microgrid, which will lead to power balance between the generation and load demand of the system. The system being studied consists of two microgrids, each made up of a wind farm, conventional power system (large hydro or thermal plant), photovoltaic system, battery energy storage system and the system load. Optimal control theory is applied to control the power flow between two microgrids. The Matlab environment is used for simulations.     

多微电网互联系统的储能容量配置

随着微电网的发展,微电网之间互联的研究逐渐兴起。为了满足多微电网系统的电能质量和运行稳定性等要求,储能系统发挥着重要作用。同时,为了实现微电网互联运行的经济性最优,需要对多微电网的储能系统进行协调容量配置。建立了层级式微电网互联模型,以传输功率损耗最低作为互联微电网之间以及微电网与大电网之间的功率交换原则,基于多微电网互联系统功率交换和分时售/购电价,建立以多微电网系统经济性最优为目标的目标函数,采用改进的粒子群算法对该模型进行优化求解,最终获得储能系统的容量配置参数。实验结果表明,在满足系统稳定性的前提下,文中提出储能系统容量配置方法使得多微电网系统的经济性更优。     

多微电网互联系统能量管理方法研究

随着微电网技术的快速发展,一定区域范围内的多个微电网能够互联互供满足区域供电需求,催生了多微电网系统的发展。多微电网系统是微电网的延伸和深化,对多微电网系统进行合理有效的管理成为解决微电网规模化运行的关键问题。多微电网存在着较多的分布式电源,风、光出力的不确定性也将影响到多微电网的运行。建立了多时间尺度能量管理,基于预测数据确定日前计划,在此之上,实时调度中对可再生能源最恶劣的运行条件进行优化。引入了考虑风、光不确定性的微电网能量管理系统鲁棒优化模型。通过列约束生成算法(CCG)对双层鲁棒优化问题进行求解。通过算例仿真,验证了所提微电网互联系统能量管理方法的有效性。     

基于机会约束规划的综合能源微网群协调运行策略研究

随着我国分布式能源系统的迅速发展,在用能侧出现大量的综合能源微网,而相邻综合能源微网以微网群的形式协同运行将是综合能源微网今后发展的重要趋势。基于此,提出了一种适用于综合能源微网群的协调运行方法。该方法旨在协调分属不同利益主体的综合能源微网,在共享有限信息和彼此独立决策的条件下,寻求微网群系统的最优运行方案。考虑到综合微网群系统中通常含有较多可再生能源,为了提高运行方案应对可再生能源出力不确定性的鲁棒性,采用机会约束规划方法,以有效抑制不确定性的影响。最后,通过对含电力-天然气的微网群系统算例进行分析,结果表明,与传统集中方法相比,所提方法能较好提升系统的经济性和安全性,实现二种特性的权衡。     

一种交直流混合微网能量路由器及其运行模态分析

为更好协调和控制交直流混合微网间能量传输,提出一种交直流混合微网能量路由器。建立所提出能量路由器数学模型,分析该能量路由器不同工作模态时级联整流级相量关系,并推导各混合运行模态限制性条件。针对该交直流混合微网能量路由器,提出相应控制策略,可实现H桥级联整流电路各级独立在AC-DC、DC-DC、DC-AC运行模式间无缝切换以达到交直流混合微网间能量的统一协调与管理。同时,减少了各微网间电力电子变换器的使用,提高各交直流微网间能量传输效率。仿真与实验结果验证了该交直流混合微网能量路由器电路拓扑的实用性及各运行模态时控制策略的正确性与有效性。     

大扰动时交流微电网的运行与控制研究综述

交流微电网是促进新能源消纳、缓解能源危机与环境问题的有效手段.分布式微源是微电网的重要组成部分,一般通过电力电子接口逆变器并入电网.因而,微电网的运行特性受微源接口逆变器控制主导,呈现惯性小、过流能力弱、非线性强、抗干扰能力差等特征.这些特征导致微电网在大扰动时易发生逆变器烧毁甚至不可逆失稳等问题,严重影响微电网安全稳定运行.针对大扰动时交流微电网的运行与控制问题,首先分别从微电网电流特性与稳定运行特性2个角度进行总结.然后,梳理了微电网典型限流控制策略以及稳定性提升控制策略的研究现状,包括其主要适用场景及优缺点.最后,从多物理场耦合、多时间尺度交互、系统稳定判据、信息物理安全等方面探讨了微电网安全可靠运行所面临的主要挑战,并展望了微电网智能化、高可靠供电的发展前景.     

A hybrid method for simultaneous optimization of DG capacity and operational strategy in microgrids utilizing renewable energy resources

Recently, microgrids have attracted considerable attention as a high-quality and reliable source of electricity. In this work energy management in microgrids is addressed in light of economic and environmental restrictions through (a) development of an operational strategy for energy management in microgrids and (b) determination of type and capacity of distributed generation (DG) sources as well as the capacity of storage devices (SD) based on optimization. Net Present Value (NPV) is used as an economic indicator for justification of investment in microgrids. The proposed NPV-based objective function accounts for the expenses including the initial investment costs, operational strategy costs, purchase of electricity from the utility, maintenance and operational costs, as well as revenues including those associated with reduction in non-delivered energy, the credit for reduction in levels of environmental pollution, and sales of electricity back to the utility. The optimal solution maximizing the objective function is obtained using a hybrid optimization method which combines the quadratic programming (QP) and the particle swarm optimization (PSO) algorithms to determine the optimum capacity of the sources as well as the appropriate operational strategy for the microgrid. Application of the proposed method under different operational scenarios serves to demonstrate the efficiency of the proposed scheme.