Smart Microgrids: Overview and Outlook

The idea of changing our energy system from a hierarchical design into a set of nearly independent microgrids becomes feasible with the availability of small renewable energy generators. The smart microgrid concept comes with several challenges in research and engineering targeting load balancing, pricing, consumer integration and home automation. In this paper we first provide an overview on these challenges and present approaches that target the problems identified. While there exist promising algorithms for the particular field, we see a missing integration which specifically targets smart microgrids. Therefore, we propose an architecture that integrates the presented approaches and defines interfaces between the identified components such as generators, storage, smart and \dq{dumb} devices.Comment: presented at the GI Informatik 2012, Braunschweig Germany, Smart Grid Worksho

Intelligent Microgrids

Center for Electromechanic

Various approaches for power balancing in grid-connected and islanded microgrids

One of the promising solutions to reduce power imbalance, an undesired impact of intermittent renewable energy sources, is to supply the loads by means of local distributed energy resources in the form of a microgrid. Microgrids offer several benefits such as reduction of line losses, increased system reliability, and maximum utilisation of local energy resources. A microgrid, during its islanded operation, is more susceptible to the frequency and voltage fluctuation caused by a sudden dispatch either from the generation or load. Therefore, additional control is required to manage either the output power from the generation side or the demand from the end-user side. Thus, appropriate and efficient control and monitoring systems need to be installed. However, the cost of such a system will reduce the rate of investment return on microgrid projects. This research has focused on developing various techniques to maintain the voltage and frequency within acceptable limits in microgrids, taking into account various influencing factors. This study proposes an additional active power management technique through the use of inverters, that can maintain the microgrid’s frequency when the generated power in the microgrid is much higher than its demand. Also, to facilitate the microgrid’s transition from grid-connected to islanded mode, the inverters can be controlled with a soft starting ramp. Moreover, a control function employing a droop control method is proposed in order to reduce the output power of the renewable sources when the microgrid frequency is much higher than the nominal frequency. On the other hand, when the demand is higher than the generated power, managing the demand under a demand response program is proposed as a means of maintaining the microgrid stability. This is an inexpensive solution which will not reduce the rate of investment return on the microgrid project. However, this requires the installation of appropriate enabling technologies at the utility and end-user sides. Moreover, the participation from demand response participants is influenced by the profit earned from engaging in the program. Therefore, in this research, the technical and economic benefits of demand response deployment are analysed in detail. The execution of the demand response program through load-shifting, reducing the appliances’ consumed power, and load-shedding causes customer discomfort. To minimise this discomfort, in this thesis, suitable strategies are suggested for various groups of loads. Furthermore, each load profile contains information on its capacity, flexibility, and operating time. The proposed approach ensures that the loads with a larger capacity and flexibility are the most preferred ones to be controlled during demand response events so that customer discomfort and the number of affected loads can be minimised. Also, this study examines the load’s economic value, power losses, emission factor, and cost of energy production to maximise the microgrid operator’s profit as a result of deploying the demand response program. Meanwhile, to encourage end-users’ engagement in demand response programs, the microgrid operator should offer incentives to the customer as compensation for any incurred costs and discomfort felt. The given incentives should be such that both the microgrid operator and the end-user gain the maximum profit. Therefore, this study proposes an approach for calculating the level of incentives that should be given to the participants by comparing the differences between ongoing revenue and the cost of energy with and without demand response

Functional Analysis of the Microgrid Concept Applied to Case Studies of the Sundom Smart Grid

The operation of microgrids is a complex task because it involves several stakeholders and controlling a large number of different active and intelligent resources or devices. Management functions, such as frequency control or islanding, are defined in the microgrid concept, but depending on the application, some functions may not be needed. In order to analyze the required functions for network operation and visualize the interactions between the actors operating a particular microgrid, a comprehensive use case analysis is needed. This paper presents the use case modelling method applied for microgrid management from an abstract or concept level to a more practical level. By utilizing case studies, the potential entities can be detected where the development or improvement of practical solutions is necessary. The use case analysis has been conducted from top-down until test use cases by real-time simulation models. Test use cases are applied to a real distribution network model, Sundom Smart Grid, with measurement data and newly developed controllers.. The functional analysis provides valuable results when studying several microgrid functions operating in parallel and affecting each other. For example, as shown in this paper, ancillary services provided by an active customer may mean that both the active power and reactive power from customer premises are controlled at the same time by different stakeholders.© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Evolution of microgrids with converter-interfaced generations: Challenges and opportunities

© 2019 Elsevier Ltd Although microgrids facilitate the increased penetration of distributed generations (DGs) and improve the security of power supplies, they have some issues that need to be better understood and addressed before realising the full potential of microgrids. This paper presents a comprehensive list of challenges and opportunities supported by a literature review on the evolution of converter-based microgrids. The discussion in this paper presented with a view to establishing microgrids as distinct from the existing distribution systems. This is accomplished by, firstly, describing the challenges and benefits of using DG units in a distribution network and then those of microgrid ones. Also, the definitions, classifications and characteristics of microgrids are summarised to provide a sound basis for novice researchers to undertake ongoing research on microgrids

A review of microgrid development in the United States – A decade of progress on policies, demonstrations, controls, and software tools

Microgrids have become increasingly popular in the United States. Supported by favorable federal and local policies, microgrid projects can provide greater energy stability and resilience within a project site or community. This paper reviews major federal, state, and utility-level policies driving microgrid development in the United States. Representative U.S. demonstration projects are selected and their technical characteristics and non-technical features are introduced. The paper discusses trends in the technology development of microgrid systems as well as microgrid control methods and interactions within the electricity market. Software tools for microgrid design, planning, and performance analysis are illustrated with each tool's core capability. Finally, the paper summarizes the successes and lessons learned during the recent expansion of the U.S. microgrid industry that may serve as a reference for other countries developing their own microgrid industries

EcoBlock: Grid Impacts, Scaling, and Resilience

Widespread deployment of EcoBlocks has the potential to transform today's electricity system into one that is more resilient, flexible, efficient and sustainable. In this vision, the system will consist of self- su cient, renewable-powered, block-scale entities that can deliberately adjust their net power exchange and can optimize performance, maintain stability, support each other, or disconnect entirely from the grid as needed. This report is intended as an independent analysis of the potential relationships, both constructive and adverse, between EcoBlocks and the grid

Online Cooperative Feedback Control of Residential Community Microgrids with 100% Renewable Energy

The emerging of renewable distributed energy resources (DER) in the residential community opens the door to forming a residential community microgrid for enhancing energy resiliency when the main grid is out of service. However, traditional microgrid controls via the hierarchical feedforward tertiary, secondary, and primary control framework may not be effective for such residential community microgrids, because of high volatility, low inertia, and insufficiency of DERs along with limited supporting facilities. This paper discusses an online feedback scheme, which cooperates the three control layers in real time to ensure operational stability of the microgrid. Besides, to economically dispatch scarce DERs in the tertial feedback control, this paper deduces an increment cost model of battery storage assets based on their degradation costs and depth of discharges. The model is of low computational complexity, thus can be naturally embedded in the proposed online cooperative feedback control scheme to calculate marginal price in real-time. Small-signal analysis and Simulink simulation are conducted to illustrate stability of the proposed online cooperative feedback control scheme, and its economic advantages over the traditional feedforward control scheme