Valuation of distributed energy resources in active distribution networks

In concert with the transformation of conventional passive power distribution system, distributed energy resources (DERs) have progressively become participants in the provision of electricity services in active distribution networks (ADNs). In this paper, we propose a systematic valuation process to quantify the value of DERs in the ADN context. The paper first provides comprehensive insights into the impacts of DERs on ADN and the society as a whole. Given the technological, locational, and temporal diversity of DERs, a two-part scheme is developed to value and compensate DER portfolios proposed by customers and independent third parties. In particular, DERs are valued for their benefits and costs in both short and long terms. An integrated resource planning model is formulated to quantify the value of a given DER portfolio to be installed, where bi-level optimization techniques are applied to coordinate decisions on ADN planning and operations. In order to determine the short-term operation benefits of the DER portfolio on a continuous basis, a retail market operation model is developed based on peer-to-peer energy transactions among prosumers, when the impacts of DERs on ADN operations are monetized by distribution locational marginal prices. It is finally concluded in the paper that the proposed valuation scheme will not only contribute to the proactive investment of DERs in ADN but also help enhance the role of DERs in offering affordable, reliable, resilient and sustainable electricity services to customers.     

One metric to rule them all: A common metric to comprehensively value all distributed energy resources

Traditional energy and demand savings metrics for distributed energy resources (DER) do not accurately describe the value of DERs to meet future energy needs, minimize grid investments, maintain reliability, and reduce greenhouse gasses. This problem is exacerbated in an increasingly renewable grid in which DER impact varies significantly with time and location. Moreover, different DERs are also valued using disparate metrics; this fragmented DER valuation and procurement creates process and economic inefficiencies. A new path forward is the Total System Benefits metric (TSB); the TSB aggregates all electric system benefits, and relevant environmental externalities that accrue to DERs. The TSB is the only metric that comprehensively values DER’s to meet future electric system needs and environmental policy goals. This common metric will enable electricity planners, regulators, utilities, and implementers to best deploy and track DER to meet electric grid and environmental policy needs. This paper explains why the TSB is the right metric to value all DER, data requirements to develop the TSB, how to express DER in terms of the TSB, and lessons learned so far from California's implementation of the TSB.     

Risk Assessment at the Edge: Applying NERC CIP to Aggregated Grid-Edge Resources

Distributed energy resources (DERs) promise to deliver benefits for both utilities and consumers by dynamically interoperating utility systems with customer-owned grid-edge technologies. These small energy-consuming devices are increasingly being aggregated for participation in grid markets, planning and operations. A cyber attack penetrating the control system of aggregated DERs could negatively impact the operation of the grid. In the worst case, the power grid could be severely damaged and physical safety compromised.In this paper we analyze cybersecurity risks associated with the aggregation of DERs and develop an approach to mitigating that risk. The approaches to both cyber risk analysis and mitigation were developed during a recent research project that serves as an example of how the approaches could be applied. However, both the risk analysis and mitigation are applicable to the broader domain of all DERs. An important conclusion is that the successful cyber compromise of aggregated DERs could have a significant impact on the bulk power system. This is the case even if each individual DER falls below the threshold of compliance with bulk-grid cybersecurity standards.For this reason, we specifically investigate how National Electricity Reliability Corporation’s Critical Infrastructure Protection requirements could flow down to interactions between DER aggregators and the DERs themselves in order to protect the grid from these bulk-scale cyber attack impacts.     

智能配电网建设中的继电保护问题 讲座二 配电网故障分析计算问题及其发展

传统短路电流的计算方法已难以适应分布式电源接入后配电网短路电流的计算。介绍了配电网短路电流的近似计算公式。分析配电网故障时分布式电源(DER)短路电流输出的特点,给出了用于短路电流输出计算的DER等效电路。指出传统短路故障计算机算法用于配电网存在的问题,介绍了一种高效率的基于端口补偿原理的配电网短路故障计算方法。利用模变换法推导出小电流接地故障暂态分析等效电路,更正了目前普遍使用的等效电路的错误。     

一种分布式电源并网监控通信适应性评价方法

分布式电源(DER)与配电网之间以及DER之间的通信不畅,会导致DER并网后对电网的电能质量、继电保护、孤岛问题产生不利影响,进一步影响整个电网的经济性和安全性。文中综合考虑技术性、经济性、适应性、扩展性和对DER的支撑性,设计了一种DER并网监控的解决方案,并提出了含DER的配电网通信方式适应性评价指标体系。根据DER并网监控通信需求,提出一种模糊一致的层次分析评价方法,并选择多种通信方式进行适应性评价。该评价方法结合了主客观需求,为含DER并网的配电网通信平台建设提供了可行性依据。     

含分布式能源直流配电网的优化调度

直流配电网对促进分布式可再生能源消纳、解决传统交流配电网发展瓶颈等方面具有巨大优势。基于直流配电网现有讨论和研究,针对含多种分布式能源（distributed energy resource,DER）的直流配电网,讨论其组网方式与系统结构,重点研究适用于接有多种分布式能源的直流配电网的优化调度方法,设计各并网单元运行策略及直流配电网多时段优化调度策略,并建立了综合考虑运行成本、环境效益以及系统损耗的多目标优化调度模型。通过算例的计算和分析,表明所提优化调度方法在促进接入多种分布式能源后直流配电网的优化运行以及接入分布式能源前后配电网优化目标的改善方面具有良好作用,验证了该方法的有效性。     

规模化分布式能源参与大电网安全稳定控制的机制初探

碳达峰、碳中和目标驱动能源结构转型,规模化分布式能源(DER)并网将成为一个突出问题.为保障大电网安全稳定运行、支撑可再生能源可持续消纳,探索DER参与大电网安全稳定控制的形式,提出基于虚拟电厂(VPP)的交互机制.首先,分析双碳目标下电力系统的衍变过程,剖析其安全稳定运行所面临的挑战.其次,阐述VPP的定义、组成结构和功能特征,揭示其整合海量异构型DER以与大电网友好交互的内涵.然后,构建基于多代理技术的VPP分层调控架构,提出其内部运行及参与大电网安全稳定控制的机制.最后指出,VPP是新型电力系统消纳高比例可再生能源的新型技术形态,该领域有若干技术问题需要重点关注.     

含分布式能源的配电网实时最优潮流分布式算法

提出一种含分布式能源的配电网实时最优潮流分布式算法。首先,该算法在获取电压状态量的实时数据后,利用原问题的二阶泰勒展开对状态量进行一次修正,并将修正结果用于控制量的计算和分布式能源的功率控制,给出了该方法在连续执行后的可行性分析。然后,利用海森阵的稀疏特性,提出了海森阵元素的分解、并行计算方法和修正方程的分布式高斯消去法,从而实现算法的分布式求解。最后,通过算例分析验证了所提算法的可行性和有效性。     

孤岛状态下含分布式电源的配电系统可靠性分析

分析了孤岛状态下含分布式电源的配电系统可靠性。针对配电网孤岛运行的特点,提出了可靠性分析的复合随机性负荷模型,提出了既能反映系统充裕度又体现动态特性的可靠性计算方法和衡量指标。计算结果表明,所提的模型、计算方法和衡量指标能充分反映分布式电源在不同程度上提高配电系统的可靠性,为系统的规划设计提供了重要参考。     

Controlling the renewable microgrid using semidefinite programming technique

Given the significant concerns regarding carbon emissions from fossil fuels, global warming and energy crisis, renewable distributed energy resources (DERs) are going to be integrated in smart grids, which will make the energy supply more reliable and decrease the costs and transmission losses. Unfortunately, one of the key technical challenges in power system planning, control and operation with DERs is the voltage regulation at the distribution level. This problem stimulates the deployment of smart sensors and actuators in smart grids so that the voltage can be stabilized. The observation from the microgrid incorporating DERs is transmitted to the control center via wireless communication systems. In other words, the proposed communication infrastructure provides an opportunity to address the voltage regulation challenge by offering the two-way communication links for microgrid state information collection, estimation and stabilization. Based on the communication infrastructure, we propose a least square based Kalman filter algorithm for state estimation and an optimal feedback control framework for stabilizing the microgrid states. Specifically, we propose to optimize the performance index by using semidefinite programming techniques in the context of smart grid applications. At the end, the efficacy of the developed approaches is demonstrated using a microgrid incorporating multiple DERs.     

电力市场环境下虚拟电厂两阶段能量经济优化调度

随着分布式可再生能源在电网中的渗透率不断增加,虚拟电厂作为一种高效管理分布式可再生能源的技术已经引起国内外学者的广泛关注。提出一种非管制电力市场环境下的虚拟电厂两阶段能量经济优化调度方法,该方法将虚拟电厂的调度分为日前和日内2个阶段。在日前阶段,基于预测信息制定次日的最优调度计划并与日前电力市场签订协议;在日内阶段,以日前计划为参考,采用模型预测控制策略调整日内的运行计划,以消除由于预测误差导致的净负荷波动,同时尽可能减少来自日内平衡市场的罚款,降低总体运行成本。所提出的模型均使用商业求解器Gurobi进行求解。仿真数值结果表明：所提出的算法通过日前计划和日内调控的手段提高了可再生能源设备的利用率,具备一定的经济性和实用性,为虚拟电厂的经济调度提供了新的思路和途径。     

电力市场环境下虚拟电厂两阶段能量经济优化调度

随着分布式可再生能源在电网中的渗透率不断增加,虚拟电厂作为一种高效管理分布式可再生能源的技术已经引起国内外学者的广泛关注。提出一种非管制电力市场环境下的虚拟电厂两阶段能量经济优化调度方法,该方法将虚拟电厂的调度分为日前和日内2个阶段。在日前阶段,基于预测信息制定次日的最优调度计划并与日前电力市场签订协议;在日内阶段,以日前计划为参考,采用模型预测控制策略调整日内的运行计划,以消除由于预测误差导致的净负荷波动,同时尽可能减少来自日内平衡市场的罚款,降低总体运行成本。所提出的模型均使用商业求解器Gurobi进行求解。仿真数值结果表明：所提出的算法通过日前计划和日内调控的手段提高了可再生能源设备的利用率,具备一定的经济性和实用性,为虚拟电厂的经济调度提供了新的思路和途径。     

A review of decentralized and distributed control approaches for islanded microgrids: Novel designs,current trends,and emerging challenges

Distributed energy resources (DER) on the demand side have been fast growing, which could boost energy resilience by uninterruptedly supplying the commercial and residential sectors in the form of islanded microgrids when the utility electricity grid is out of service. Nevertheless, simply applying the centralized hierarchical control strategies, traditionally used for utility electricity grids, onto the islanded microgrids would encounter several critical issues. For instance, the control goals in secondary and tertiary control could be activated tardily, the single-point fault could cause critical system failure, and the properties of dynamic plug and play would be hard to achieve. To this end, decentralized and distributed control approaches have been explored to cope with the issues. Specifically, compared to the centralized hierarchical control, decentralized and distributed control strategies can (i) respond to disturbances more promptly, enhancing the performance of islanded microgrids with limited resources; (ii) guarantee system stability especially when a fault occurs and certain DERs are disconnected from the network; and (iii) facilitate deeper penetration of DERs in the microgrid, owning to the low computational complexity and sparse communication network. In this article, the common approaches for decentralized and distributed control are reviewed, and the current design trends and critical technical challenges are discussed to offer a comprehensive understanding of decentralized and distributed controlled microgrids.     

Peer-to-peer (P2P) electricity trading in distribution systems of the future

Recent years distribution systems have been witnessed a rapid interconnection of distributed energy resources (DER), solar energy generation and electric vehicles (EV) in particular. To this end, residential and commercial electricity customers equipped with DERs are transforming their roles from pure electricity consumers to prosumers that can switch between electricity consumers and producers. Indeed, if properly managed, DERs of prosumers could bring significant benefits to distribution system operations. Peer-to-peer (P2P) electricity trading in distribution systems has been recently explored, in order to properly manage existing prosumers and to continually promote a deeper penetration of prosumers. This article discusses two types of P2P mechanisms, namely auction-based and bilateral contract-based P2P electricity trading mechanisms, and analyze their effectiveness in properly managing electricity trading among prosumers in distribution systems of the future.     

基于均衡理论的虚拟电厂市场参与模式及方法

随着化石能源的枯竭与其对环境的污染，分布式发电这种经济、环保、灵活的新型发电方式逐渐得到广泛的应用。但分布式电源大量并入电网将带来电能质量问题，影响电网安全稳定运行。虚拟电厂的出现有效解决了这些问题，它通过对分布式电源进行协调优化，减小了分布式电源并网对电网产生的冲击，提高了电网运行稳定性。然而目前虚拟电厂与主网之间的协调研究仍有待深入，因此提出了虚拟电厂与主网之间交互迭代的市场均衡方法，对虚拟电厂的出力与主网的电价迭代求解从而实现收敛。首先，对虚拟电厂的定义与内部主体进行分析，进而将虚拟电厂与主网之间的协调优化表述为两个层次之间的市场均衡问题，提出虚拟电厂与主网交互的双层模型，分别构建以自身成本最小化为目标，计及分布式能源运行约束与电网安全约束的虚拟电厂与主网数学模型，并采用迭代算法对模型进行求解。算例分析表明提出的市场均衡方法在考虑虚拟电厂对主网影响的同时能够有效降低虚拟电厂与主网协调的复杂程度，同时减小运行总成本，提升经济效益。     

From microgrids to aggregators of distributed energy resources. The microgrid controller and distributed energy management systems

Microgrids are a collection of distributed energy resources (DER) within a specific boundary, with a control system for their management and operations at the point of interconnection with the distribution utility. As microgrid concepts evolve, they are being applied to aggregations of DER outside boundaries with appropriate controls for operation with transmission and distribution utilities and participation in markets. This article marks this evolution and points towards the common functionalities of microgrid controllers and distributed energy management systems for integration of DER into transmission and distribution operations and markets.     

采用基于市场控制的微网分布式能量优化方法

为了控制微网内各类分布式能源的协调运行,同时适应能源互联网的核心理念,提出了采用基于市场控制的微网分布式能量优化方法。首先,从理论上论证了该方法与集中式能量优化方法的等价性,并建立了分布式能量优化的通用流程。然后,基于启发式规则,系统地提出了分布式电源、可平移负荷、储能、联络线等资源的投标策略。最后,通过仿真计算,验证了该方法在削峰填谷、经济性以及提高可再生能源消纳率等方面的效果。所提出的方法利用各分布式能源的分布式决策代替传统的集中式优化,能够更好地保护用户隐私,并能够适应各种类型的分布式能源以标准化方式接入不同规模微网的要求。     

A three-phase community microgrid comprised of single-phase energy resources with an uneven scattering amongst phases

This paper considers a three-phase, low voltage community network with both grid-connected and autonomous modes of operation, which is composed of a group of residential houses and some single-phase, converter-interfaced distributed energy resources (DER) with equal and arbitrarily scattering of the DERs among the phases. The vigorous operation of such a microgrid system is examined with the proposed management techniques. In such a network, it is highly probable for one phase to have a high generation capacity while the other phases experience a higher demand; a technically challenging problem for a network operating in autonomous mode. In this paper, it is proposed for the single-phase DERs of such a system to operate under a droop-based voltage control technique while an appropriate technique is proposed to facilitate the transmission of the excess power from one phase to other phases. The proposals are validated by extensive digital simulations in PSCAD/EMTDC for several scenarios to demonstrate the feasibility of operating such a system and the efficacy of the proposed techniques.     

Distributed Control Strategy of Microgrid Based on the Concept of Cyber Physical System

For distributed energy resources (DERs) in islanded microgrid (MG), to improve the control effect on the output voltages and frequency from droop control, a novel distributed control strategy is proposed in this article based on the concept of cyber physical system (CPS). The novel control structure is consisted by the cyber and the physical layers. In the cyber layer: firstly, the communication structures of overall microgrid and single DER are constructed; then, based on the communication structures, the influence of time-delay (delay) and packet loss (loss) on consensus control is analyzed in this article; And then, an event-triggered mechanism combined with adapt virtual leader-following consensus control (AVLFCC) and predictive compensation is proposed in this layer. It is used to solve the problem of time-varying delay and loss rate in the process of consensus control. In the physical layer: firstly, the droop control is used as the primary control on the output voltages and frequency of DERs; then, a novel secondary control method is proposed by using the event-triggered mechanism. And finally, the simulation results confirm the effectiveness of the novel distributed control strategy under communication problems (delay and loss) and during plug-and-play operation.     

Optimal Aggregation Approach for Virtual Power Plant Considering Network Reconfiguration

As an aggregator of distributed energy resources (DERs) such as distributed generator, energy storage, and load, the virtual power plant (VPP) enables these small DERs participating in system operation. One of the critical issues is how to aggregate DERs to form VPPs appropriately. To improve the controllability and reduce the operation cost of VPP, the complementary DERs with close electrical distances should be aggregated in the same VPP. In this paper, it is formulated as an optimal network partition model for minimizing the voltage deviation inside VPPs and the fluctuation of injection power at the point of common coupling (PCC). A new convex formulation of network reconfiguration strategy is incorporated in this approach which can guarantee the components of the same VPP connected and further improve the performance of VPPs. The proposed approach is cast as an instance of mixed-integer linear programming (MILP) and can be effectively solved. Moreover, a scenario reduction method is developed to reduce the computation burden based on the k-shape algorithm. Numerical tests on the 13-bus and 70-bus distribution networks justify the effectiveness of the proposed approach.