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.     

Energy requirement for distributed energy resources with battery energy storage for voltage support in three-phase distribution lines

Integration of distributed energy resources (DER) into distribution systems is a new concept for improving system capacity and stability, feeder voltage, and supply quality and reliability. This paper has addressed voltage support in distribution systems by energy injection from a battery storage distributed energy system. An operation strategy for an inverter interface battery energy storage DER has been developed for maximum improvement in feeder voltage with minimum energy injection from the DER. A control strategy has been proposed for inverter based battery storage DER to regulate network voltage effectively, through operating the DER to generate real (P) and reactive (Q) power with Q priority. The implementation of the inverter interface DER with battery energy storage will save fuel cost of DER but be of much higher capital cost than using a rotary generator. The proposed technique has been evaluated by simulation on a three-phase distribution system with time varying loads. Test results indicate that DER operating with Q priority offers the best solution for maximum voltage improvement. The results also confirm that DER injecting P and Q at the ratio of maximum voltage sensitivity of line presents better solution for power loss reduction than the solution offered by the DER operating with Q priority.     

Controlling and optimizing resilient distributed energy resources and microgrids with a demand-side operation platform

Moving to true grid resiliency requires multiple distributed energy resources, but these DERs must be properly controlled for each installation’s needs. This article answers these DER and microgrid resiliency questions and suggests some best practices for optimal financial and operational control in our New Energy Landscape.     

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.     

Analysis and visualization method for understanding the voltage effect of distributed energy resources on the electric power system

While adding distributed energy resources (DER) to a distribution circuit will affect numerous aspects of operation, bus voltage is a critical aspect that must be maintained within acceptable limits. It is therefore critical to: (1) quantify how DER installation will affect the voltage, (2) visualize the voltage change, and (3) predict the voltage change of the alternatives within the DER operational space. These three goals are achieved through the development of a simple voltage change potential (VCP) visualization method that can be determined using the basic characteristics of an inverter-based DER installation. The VCP results compare favorably with equivalent complete non-linear Matlab/Simulink™ models of DER implementation in distribution circuits at a fraction of the computational time. Calculation of VCP also enables a new control method that uses circuit information and simple equations to provide situation-dependent and optimal voltage regulation.     

Adaptive coordinated feeder flow control in distribution system with the support of distributed energy resources

This paper aims to minimize the feeder power flow deviation from scheduled value by balancing generation and load demand within the distribution system under various local disturbances. The available distributed energy resources (DER) can be properly utilized to control the feeder flow which gains significant advantages (i) to support load frequency control (LFC) problem at transmission level (ii) reduces unscheduled interchange in feeder which is priced higher (iii) increased reliability of the grid. The deviation in feeder flow is reduced by properly coordinating the power output from DER such as fuel cell, battery storage system and responsive loads (demand response) through an adaptive fuzzy controller with optimally tuned gains using particle swarm optimization. The level of participation from each DER units are decided using fuzzy inference system based on the availability of resources and level of disturbance. The photovoltaic array and wind turbine are also considered in the system and always operated at the maximum power point. The proposed method is examined on IEEE 37 bus system implemented in the MATLAB based Power Analysis Toolbox (PAT) for performing time-domain dynamic analysis. It is shown that the proposed adaptive controller exhibits better performance for various disturbance conditions.     

Retail pricing responses to the challenge of distributed energy resources

The recent growth in distributed energy resources has raised issues of how to ensure that utilities recover allowed fixed costs for customer and distribution system services. This paper presents the issues related to DER in the context of both traditional cost-of-service and rate design methods, and economically efficient retail pricing. The objective is to clarify certain misconceptions and recommend retail pricing solutions.     

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.     

Integration of distributed energy resources into low voltage grid: A market-based multiperiod optimization model

This paper develops a multiperiod optimization model for an interconnected micro grid with hierarchical control that participates in wholesale energy market to maximize its benefit (i.e. revenues-costs). In addition to the operational constraints of distributed energy resources (DER) including both inter-temporal and non-inter-temporal types, the adequacy and steady-state security constraints of micro grid and its power losses are incorporated in the optimization model. In the presented model, DER are integrated into low voltage grid considering both technical and economical aspects. This integration as a micro grid can participate in wholesale energy market as an entity with dual role including producer and consumer based on the direction of exchanged power. The developed model is evaluated by testing on a micro grid considering different cases and the results are analyzed.     

基于分层储能的主动配电网需求响应控制策略研究及实现

开展需求响应(Demand Response, DR)和提高分布式发电(Distributed Generation, DG)渗透率可以有效地缓解输电和发电建设要求。传统配电网的无法适应DER高渗透率接入,基于价格和激励的需求响应在现有的政策和市场环境下推广应用驱动力不够。为了解决上述问题,将配电网储能系统进行分层分级,通过层级分权和责任授权发挥储能系统的主动性,不同层级的储能通过自主协调进行需求响应。该方法可提高分布式电源的渗透率,延缓配电网升级改造提升资产利用率,满足区域配电网稳定运行、电能质量、供电可靠性等,促进储能在电力系统中的应用。基于该研究成果研制的主动配电网需求侧管理系统已应用于国家能源应用技术研究及工程示范项目,实践验证了策略的有效性和实用性。     

Distributed intelligence: A critical piece of the microgrid puzzle

Electric utilities are adding distributed computing capabilities across distribution systems at an accelerated rate. In fact, IDC predicts that the industrial IoT market – which includes utility applications – will exceed $745 billion in 2019, with $61 billion of that serving the utilities sector. Utility IoT applications involve an array of sensors from the substation down to customer premises that provide data and automated controls. As microgrids draw more interest to promote grid stability and DER integration, intelligent sensor networks – and the analytics they support – will become an increasingly important management tool. This article explores some ways sensor data, analytics and distributed computing can and are supporting new distributed energy resource strategies and initiatives.     

Multi-agent system for energy resource scheduling of integrated microgrids in a distributed system

This paper proposes a multi-agent system for energy resource scheduling of an islanded power system with distributed resources, which consists of integrated microgrids and lumped loads. Distributed intelligent multi-agent technology is applied to make the power system more reliable, efficient and capable of exploiting and integrating alternative sources of energy. The algorithm behind the proposed energy resource scheduling has three stages. The first stage is to schedule each microgrid individually to satisfy its internal demand. The next stage involves finding the best possible bids for exporting power to the network and compete in a whole sale energy market. The final stage is to reschedule each microgrid individually to satisfy the total demand, which is the addition of internal demand and the demand from the results of the whole sale energy market simulation. The simulation results of a power system with distributed resources comprising three microgrids and five lumped loads show that the proposed multi-agent system allows efficient management of micro-sources with minimum operational cost. The case studies demonstrate that the system is successfully monitored, controlled and operated by means of the developed multi-agent system.     

基于目标级联分析法的分布式主体可交易能源模型

可交易能源是一种价格引导交易和优化运行的机制,兼顾经济交易与系统优化运行,属于学科融合范畴的新概念.在分布式能源稳步增长和分布式发电市场化的背景下,面向分布式主体的可交易能源机制极具研究前景.为此,设计具体的可交易能源架构,实现分布式主体物理元素建模.随后,用目标级联分析法(ATC)理论实现经济交易与系统优化运行的结合,为ATC理论在系统优化运行中提供经济学视角.最后,通过算例分析验证了所提模型能够降低与电网的能量互动的同时兼顾主体运营收益,且能够提供多元的交易策略以及交易方式,形成多种利益分配结果.     

A dynamic model for distributed energy resource expansion planning considering multi-resource support schemes

In this paper, a system dynamics based model is developed to investigate the impacts of multi-resource regulatory policies on distributed energy resource (DER) expansion planning. DERs usually include a variety of renewable and fossil based generation technologies such as wind and gas engine resources, combined heat and power (CHP), demand response (DR) and energy storage. The intermittent nature and uncertainty in power generation of some of these resources and other uncertainties that exist in the market environment would cause investors to encounter risk in their investment decisions. Implementation of any supporting policy affects any investor’s behavior and investment level of other investors. Regulators should properly identify long-term impacts of their support policies in the energy resource expansion in order to choose a proper support scheme. These support schemes should ensure the long-term market stability. It is important for a DER investor to properly identify his/her long-term investment behavior to select an appropriate strategy. In this paper, the system dynamics method is used to investigate these issues. The impacts of various multi-resource regulatory policies on market dynamics are modeled and compared with the single-resource support schemes ones. In this study, support schemes are considered for supporting DR, wind resources, CHPs and photovoltaic resources.     

Transmission pricing of distributed multilateral energy transactions to ensure system security and guide economic dispatch

In this paper, the authors provide a simulations-based demonstration of a hybrid electricity market that combines the distributed competitive advantages of decentralized markets with the system security guarantees of centralized markets. In this market, the transmission service provider (TSP) guides an electricity market toward the optimal power flow (OPF) solution, even when maximizing its own revenue. End users negotiate with each other to determine an energy price and then submit separate bids for transmission to the TSP. The TSP returns with prices for transmission, allowing end users to respond. In simulations, this hybrid-decentralized market approaches the near-optimal results of fully coordinated and constrained markets. Additionally, this market exhibits properties that remove incentives for the TSP to withhold capacity. This hybrid market leads a market toward the optimum while allowing the TSP and the end users to act out of self-interest.     

基于分布式可再生能源发电的能源互联网系统

以分布式可再生能源发电为基础,构建可以实现实时、高速、双向的电力数据读取和可再生能源接入的能源互联网系统.能源互联网系统由智能能量管理系统、分布式可再生能源、储能装置、变流装置和智能终端等组成.智能能量管理系统提供了一个可视化的操作平台,除了可以实现常规的能量管理,还可以实现可再生能源的"即插即用",并根据系统需要,自主实现孤岛运行和并网之间的切换;储能装置在改善电能质量、提高系统稳定性、电源备用和提高经济效益方面具有重大的作用,是能源互联网系统不可缺少的组成部分;电力电子变压器的应用使可再生能源发电达到电网接入要求.最后确定了控制策略、电力电子变流技术和储能技术3个能源互联网的未来主要研究方向.     

An economic evaluation for an autonomous independent network of distributed energy resources

This paper proposes a method for the economic evaluation of an autonomous independent network of distributed energy resources. There are existing proposals for such networks; the system that we are proposing and analyzing in this study is called Microgrid. Microgrid is a new framework of power delivery system that is formed by small, modular generation systems connected to each other to create a small autonomous grid. This paper estimates the total costs to consumers in a Microgrid with optimized operation of distributed generators and energy storage systems. This estimation includes not only installation and operation costs but also the additional expenses to construct the Microgrid itself. In addition, power interruption costs are also taken into account to consider the reliability enhancement created by the Microgrid. The paper attempts to determine whether or not it is economical for consumers to form this kind of autonomous independent network.     

MAS-based solution to energy management strategy of distributed generation system

This paper focuses on the energy management issue of a Distributed Generation System (DGS) for ensuring energy supply with high security. Firstly, considering that the DGS is composed of many types of Distributed Energy Resources (DERs) and a group of loads, a Multi-Agents System (MAS) based two hierarchical decentralized coordinated control scheme is constructed to deal with the complex energy management problem of the DGS, and JADE platform is applied to implement the MAS based energy management strategies. Then, the mode switching behaviors of each DER or load unit are described based on Petri Net (PN) models. And a Voltage Security Assessment (VSA) L-index is constructed. According to the L-index, four different operating modes of the DGS are determined and the coordinated control commands in the upper level agent are drafted. Based on PN models, according to the coordinated control commands, the switching control strategies are designed in the lower level respective unit agent to ensure secure energy supply against variable operating conditions. Moreover, the decentralized continuous controller in the lower level unit agent is also presented to dynamically regulate the output performance. Finally, the validity of proposed control scheme is demonstrated by means of simulation results.     

Economic framework for compensating distributed energy resources: Theory and practice

We offer an economic framework for analyzing the compensation that DERs should receive for energy exported to the grid. This economic framework requires that the prices paid to DER owners be based upon the forward-looking, economic costs that their utility avoids when it buys the energy from the customer. We explain why this results in efficient ‘build or buy’ and ‘purchase and install’ decisions of the utility and DER customer, respectively.     

A protection scheme for microgrid with multiple distributed generations using superimposed reactive energy

With the growing integration of distributed generation, distribution networks have evolved toward the concept of microgrids. Microgrids can be operated in either the grid-connected mode to achieve peak shaving and power loss reduction or the islanded mode to increase the reliability and continuity of supply. These two modes of operation cause a challenge in microgrid protection, because the magnitude of fault current decreases significantly during the transition of a microgrid from the grid-connected mode to the islanded mode. This paper proposes a protection scheme for the microgrid based on superimposed reactive energy. The proposed scheme uses the Hilbert transform to calculate the superimposed reactive energy (SRE). The sequence components of superimposed current are adopted to detect fault incidents in the microgrid. The faulty phase and section are recognised by using the directional characteristics of SRE along with a threshold value. Moreover, a relay structure, which enables the proposed protection scheme, is designed. The significant feature of the proposed protection scheme is that it has the ability to protect the looped and radial microgrids against solid and high-impedance faults. To verify the efficacy of the proposed approach, extensive simulations have been carried out using the MATLAB/SIMULINK software package. The results show that the proposed scheme successfully identifies and isolates various types of fault in a microgrid and performs well with different fault resistances and fault locations.