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

Estudio sobre conexión en paralelo de generadores utilizando relés de sincronización

When performing the synchronization of generators with the purpose to enter parallel to a SEP is necessary to know the basic electrical parameters intervening in this process to facilitate the implementation of these maneuvers, besides knowing the best choices that have to make this process it done efficiently and safely. Currently exist electronic equipment that perform synchronization automatically of generators, this is the case of relays synchronization and protection that allow synchronization and in some cases protect the generator of electrical failure. Selected four relays existing in the Ecuadorian market and analyze its features and benefits when synchronizing generators.Cuando realizamos la sincronización de generadores con la finalidad que ingresen en paralelo a un SEP, es necesario conocer los parámetros eléctricos fundamentales que intervienen en este proceso, lo que facilitara la implementación de este tipo de maniobras, además de conocer las mejores alternativas que tenemos para realizar este proceso, para que se realice de una manera eficiente y segura. En la actualidad existen equipos electrónicos que realizan la sincronización de generadores de forma automática, este es el caso de los relés de sincronización y protección que permiten realizar la sincronización y en algunos casos proteger de fallas eléctricas al generador. Seleccionamos cuatro relés de sincronización existentes en el mercado ecuatoriano y analizamos sus características y beneficios al momento de realizar la sincronización de generadores

Reliable and Robust Cyber-Physical Systems for Real-Time Control of Electric Grids

Real-time control of electric grids is a novel approach to handling the increasing penetration of distributed and volatile energy generation brought about by renewables. Such control occurs in cyber-physical systems (CPSs), in which software agents maintain safe and optimal grid operation by exchanging messages over a communication network. We focus on CPSs with a centralized controller that receives measurements from the various resources in the grid, performs real-time computations, and issues setpoints. Long-term deployment of such CPSs makes them susceptible to software agent faults, such as crashes and delays of controllers and unresponsiveness of resources, and to communication network faults, such as packet losses, delays, and reordering. CPS controllers must provide correct control in the presence of external non-idealities, i.e., be robust, and in the presence of controller faults, i.e., be reliable. In this thesis, we design, test, and deploy solutions that achieve these goals for real-time CPSs. We begin by abstracting a CPS for electric grids into four layers: the control layer, the network layer, the sensing and actuation layer, and the physical layer. Then, we provide a model for the components in each layer, and for the interactions among them. This enables us to formally define the properties required for reliable and robust CPSs. We propose two mechanisms, Robuster and intentionality clocks, for making a single controller robust to unresponsive resources and non-ideal network conditions. These mechanisms enable the controller to compute and issue setpoints even when some measurements are missing, rather than to have to wait for measurements from all resources. We show that our proposed mechanisms guarantee grid safety and outperform state-of-the-art alternatives. Then, we propose Axo: a framework for crash- and delay-fault tolerance via active replication of the controller. Axo ensures that faults in the controller replicas are masked from the resources, and it provides a mechanism for detecting and recovering faulty replicas. We prove the reliable validity and availability guarantees of Axo and derive the bounds on its detection and recovery time. We showcase the benefits of Axo via a stability analysis of an inverted pendulum system. Solutions based on active replication must guarantee that the replicas issue consistent setpoints. Traditional consensus-based schemes for achieving this are not suitable for real-time CPSs, as they incur high latency and low availability. We propose Quarts, an agreement mechanism that guarantees consistency and a low bounded latency- overhead. We show, via extensive simulations, that Quarts provides an availability at least an order of magnitude higher than state-of-the-art solutions. In order to test the effect of our proposed solutions on electric grids, we developed T-RECS, a virtual commissioning tool for software-based control of electric grids. T-RECS enables us to test the proper functioning of the software agents both in ideal and faulty conditions. This provides insight into the effect of faults on the grid and helps us to evaluate the impact of our reliability solutions. We show how our proposed solutions fit together, and that they can be used to design a reliable and robust CPS for real-time control of electric grids. To this end, we study a CPS with COMMELEC, a real-time control framework for electric grids via explicit power setpoints. We analyze the reliability issues..

Performance evaluation of information and communications technology infrastructure for smart distribution network applications

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.Current electrical networks require secure, scalable and cost-effective Information and Communications Technology (ICT) solutions to facilitate the novel functionalities required by Smart Grids. Countries around the globe are investigating alternative energy sources to mitigate the current energy crisis and environmental issues experienced by many countries due to global warming, rapid growth of population, inefficient energy management, dwindling fossil fuel resources, etc. Therefore, alternative or renewable energy sources, such as wind, solar, hydro, combined heat and power, etc., are required to mitigate such a crisis and such sources will also need to be integrated in to the power grid in a distributed manner. Such distributed energy sources are mainly connected to the distribution networks and introduce huge challenges to the distribution network operator (DNO). Many of these challenges cannot be dealt with effectively using existing network operation mechanisms therefore the research and development of novel ICT solutions to support smart distribution network operation is required. This research investigated suitable ICT solutions to enable the Smart Grid to tackle these challenges and proposes ICT infrastructure models that can be used for simulation studies in order to investigate cost-effective, scalable and secure solutions for the DNOs. Initially, a Quality of Service (QoS) monitoring test-bed was proposed to evaluate the performance of bandwidth intensive applications, such as smart meter data transmission. Simulation studies for different communication technologies, cellular and Power Line Communication (PLC), were also carried out and the simulation models were verified using experimental test results. Finally, the modelling and analysis of smart metering infrastructure was carried out using simulation and extensive studies were performed to evaluate the data transmission rate performance for different configurations of smart meters and concentrators

Substation automation systems and IEC 61850: interoperability testing

Dissertação de mest., Engenharia Electrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011The Substation Automation System (SAS) is the backbone of the Energy Power System (EPS) and IEC 61850 is becoming its single most important standard. This is a world wide accepted standard that is being adopted by the industry in order to provide for all current and future needs. This standard defines not only the communication protocols but also its own Substation Configuration Language (SCL) and even best practices for related engineering processes. In order to keep up with the current fast technological developments the substation data model is separated from the communication protocols allowing both to be changed without affecting each other. Also defined in the standard is an extensive conformance testing procedure in order to guarantee that different vendors interpret and implement the standard correctly. The substation and its SAS must undergo thourough testing procedures specificaly in the Factory Acceptance Test (FAT) and Site Acceptance Test (SAT). The conformance tests insures that the SAS devices, the Intelligent Electronic Devices (IEDs), conform to the same standard but on its own does not guarantee its interoperability. An automated testing tool capable of, quickly and easily, testing the SAS functions (IEDs interoperability) provides significant savings in both time and money to the testing process. This work aim is to develop such a tool, capable of interoperability testing. In order to achieve such big accomplishment this initial work focus on only two of the most used functions of the SAS: switching and interlocking. A simulation model, built on top of OMNeT++, for both the IEDs and the substation was developed. In this work an initial stage prototype with an IED simulation model capable of communicating with real devices will be developed. In a later stage, postponed for future work, the substation simulation model will be extended in order to include real-time interaction with external devices that emulate the substation switchgear

On reliability and performance analyses of IEC 61850 for digital SAS

fi=vertaisarvioitu|en=peerReviewed

Real-time modeling and simulation of distribution feeder and distributed resources

Includes bibliographical references.2015 Fall.The analysis of the electrical system dates back to the days when analog network analyzers were used. With the advent of digital computers, many programs were written for power-flow and short circuit analysis for the improvement of the electrical system. Real-time computer simulations can answer many what-if scenarios in the existing or the proposed power system. In this thesis, the standard IEEE 13-Node distribution feeder is developed and validated on a real-time platform OPAL-RT™. The concept and the challenges of the real-time simulation are studied and addressed. Distributed energy resources include some of the commonly used distributed generation and storage devices like diesel engine, solar photovoltaic array, and battery storage system are modeled and simulated on a real-time platform. A microgrid encompasses a portion of an electric power distribution which is located downstream of the distribution substation. Normally, the microgrid operates in paralleled mode with the grid; however, scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. The microgrid can operate in grid connected and islanded mode, both the operating modes are studied in the last chapter. Towards the end, a simple microgrid controller modeled and simulated on the real-time platform is developed for energy management and protection for the microgrid

Mikroverkkojen ja hajautettujen energiaratkaisujen suojaus IEC 61850 -standardiin perustuen

Microgrids are a potential part of the future smart distribution grid with capability of island operation, envisioned to support the goals of increased use of renewable and distributed energy resources, active consumer participation and improved quality of electricity supply in the future power systems. This thesis examines the implementation of protection systems for microgrids and distributed energy resources using the IEC 61850 standard series. IEC 61850 is one of the core smart grid standards originally developed for substation automation, but extended in its usage to many areas including distributed energy resources. The main objectives of this thesis are analysing the implementation of microgrid protection, usage of IEC 61850 in distribution applications, and applicability of Multipower test environment of VTT Technical Research Centre of Finland in researching these subjects. A literature review of microgrid protection issues and proposed protection schemes as well as an overview of the IEC 61850 standard series and its extensions are presented. An adaptive protection scheme is implemented in an example microgrid configuration of the Multipower environment using IEC 61850, and its correct operation verified during islanding and in the case of a communication network failure. Finally, recommendations are given on the future development and research topics of the Multipower environment, including integration of different distributed energy resource units from other VTT research areas such as fuel cells and electrical vehicles to the system, studying the usage of different networks for communication inside the environment and testing of harmonization between IEC 61850 and other smart grid standards

Detection and Mitigation of Cyber Attacks on Time Synchronization Protocols for the Smart Grid

The current electric grid is considered as one of the greatest engineering achievements of the twentieth century. It has been successful in delivering power to consumers for decades. Nevertheless, the electric grid has recently experienced several blackouts that raised several concerns related to its availability and reliability. The aspiration to provide reliable and efficient energy, and contribute to environment protection through the increasing utilization of renewable energies are driving the need to deploy the grid of the future, the smart grid. It is expected that this grid will be self-healing from power disturbance events, operating resiliently against physical and cyber attack, operating efficiently, and enabling new products and services. All these call for a grid with more Information and Communication Technologies (ICT). As such, power grids are increasingly absorbing ICT technologies to provide efficient, secure and reliable two-way communication to better manage, operate, maintain and control electric grid components. On the other hand, the successful deployment of the smart grid is predicated on the ability to secure its operations. Such a requirement is of paramount importance especially in the presence of recent cyber security incidents. Furthermore, those incidents are subject to an augment with the increasing integration of ICT technologies and the vulnerabilities they introduce to the grid. The exploitation of these vulnerabilities might lead to attacks that can, for instance, mask the system observability and initiate cascading failures resulting in undesirable and severe consequences. In this thesis, we explore the security aspects of a key enabling technology in the smart grid, accurate time synchronization. Time synchronization is an immense requirement across the domains of the grid, from generation to transmission, distribution, and consumer premises. We focus on the substation, a basic block of the smart grid system, along with its recommended time synchronization mechanism - the Precision Time Protocol (PTP) - in order to address threats associated with PTP, and propose practical and efficient detection, prevention, mitigation techniques and methodologies that will harden and enhance the security and usability of PTP in a substation. In this respect, we start this thesis with a security assessment of PTP that identifies PTP security concerns, and then address those concerns in the subsequent chapters. We tackle the following main threats associated with PTP: 1) PTP vulnerability to fake timestamp injection through a compromised component 2) PTP vulnerability to the delay attack and 3) The lack of a mechanism that secures the PTP network. Next, and as a direct consequence of the importance of time synchronization in the smart grid, we consider the wide area system to demonstrate the vulnerability of relative data alignment in Phasor Data Concentrators to time synchronization attacks. These problems will be extensively studied throughout this thesis, followed by discussions that highlight open research directions worth further investigations