Self-organizing Coordination of Multi-Agent Microgrid Networks

abstract: This work introduces self-organizing techniques to reduce the complexity and burden of coordinating distributed energy resources (DERs) and microgrids that are rapidly increasing in scale globally. Technical and financial evaluations completed for power customers and for utilities identify how disruptions are occurring in conventional energy business models. Analyses completed for Chicago, Seattle, and Phoenix demonstrate site-specific and generalizable findings. Results indicate that net metering had a significant effect on the optimal amount of solar photovoltaics (PV) for households to install and how utilities could recover lost revenue through increasing energy rates or monthly fees. System-wide ramp rate requirements also increased as solar PV penetration increased. These issues are resolved using a generalizable, scalable transactive energy framework for microgrids to enable coordination and automation of DERs and microgrids to ensure cost effective use of energy for all stakeholders. This technique is demonstrated on a 3-node and 9-node network of microgrid nodes with various amounts of load, solar, and storage. Results found that enabling trading could achieve cost savings for all individual nodes and for the network up to 5.4%. Trading behaviors are expressed using an exponential valuation curve that quantifies the reputation of trading partners using historical interactions between nodes for compatibility, familiarity, and acceptance of trades. The same 9-node network configuration is used with varying levels of connectivity, resulting in up to 71% cost savings for individual nodes and up to 13% cost savings for the network as a whole. The effect of a trading fee is also explored to understand how electricity utilities may gain revenue from electricity traded directly between customers. If a utility imposed a trading fee to recoup lost revenue then trading is financially infeasible for agents, but could be feasible if only trying to recoup cost of distribution charges. These scientific findings conclude with a brief discussion of physical deployment opportunities.Dissertation/ThesisDoctoral Dissertation Systems Engineering 201

Sistema de gestión de energía descentralizado basado en multiagentes para operación de múltiples microrredes

Microgrids have experienced a significant development in recent years because they represent a technical alternative to respond to contingencies in electrical distribution networks and increase the level of distributed generation, among other benefits. The objective of this study is to design an architecture based on multi-agent systems that can be used to manage the operating mode of a distributed microgrid system in an islanded environment. In such architecture, the correct connection of the common bus that links all the microgrids with the multi-agent system is maintained, and overloads and deep discharges in the batteries are avoided. The methodology implemented here is empirical-analytical. The simulation is based on a review of the state of the art that was conducted to find a strategy that can coordinate a composite microgrid system where the microgrids are connected to the same distribution system operating in islanded mode. The system was simulated using OpenDSS-G and Python. The results obtained suggest that a decentralized energy management system based on the theory of multi-agent systems can have important benefits; for example, the autonomous nature of microgrids for power generation in non-interconnected areas. Finally, multi-agent theory can be employed to create more reliable distributed generation systems (due to their autonomous decision-making capacity), meet the electrical demands of neighboring microgrids, and jointly prevent overcharges and deep discharges in batteries.En años recientes, las microrredes han logrado un considerable desarrollo debido a que representan una alternativa técnica para responder a contingencias en la red de distribución, como también a incrementar el nivel de generación distribuida, entre otros beneficios. Por tal motivo, el presente artículo presenta un modelo de gestión energética basado en sistemas multiagentes para microrredes que operan en modo isla. El objetivo de esta investigación es el diseño de un sistema multiagente que permita gestionar el funcionamiento de un conjunto de microrredes distribuidas en un entorno aislado, además de mantener la correcta conexión con el bus común que une todas las microrredes, el sistema multiagente debe evitar sobrecargas y descargas profundas en las baterías. La metodología implementada es de tipo empírico analítica, la simulación comienza con una revisión del estado del arte, en búsqueda de una estrategia que permita coordinar un sistema de microrredes compuesto, donde estas están conectadas al mismo sistema de distribución operando en modo isla. La simulación del sistema se realizó mediante OpenDSS-G y Python. Los resultados obtenidos sugieren que un sistema de gestión de energía descentralizado, basado en la teoría de sistemas de agentes múltiples, puede tener importantes beneficios como, por ejemplo, el carácter autónomo de las microrredes para la generación de energía en zonas no interconectadas. Finalmente, con la teoría de multiagente se pueden crear sistemas de generación distribuida más confiables debido a su capacidad autónoma de toma de decisiones, para cubrir demandas eléctricas desde microrredes vecinas y conjuntamente prevenir sobrecargas y profundas descargas en las baterías

Inter-Microgrid Operation: Power Sharing, Frequency Restoration, Seamless Reconnection and Stability Analysis

Electrification in the rural areas sometimes become very challenging due to area accessibility and economic concern. Standalone Microgrids (MGs) play a very crucial role in these kinds of a rural area where a large power grid is not available. The intermittent nature of distributed energy sources and the load uncertainties can create a power mismatch and can lead to frequency and voltage drop in rural isolated community MG. In order to avoid this, various intelligent load shedding techniques, installation of micro storage systems and coupling of neighbouring MGs can be adopted. Among these, the coupling of neighbouring MGs is the most feasible in the rural area where large grid power is not available. The interconnection of neighbouring MGs has raised concerns about the safety of operation, protection of critical infrastructure, the efficiency of power-sharing and most importantly, stable mode of operation. Many advanced control techniques have been proposed to enhance the load sharing and stability of the microgrid. Droop control is the most commonly used control technique for parallel operation of converters in order to share the load among the MGs. But most of them are in the presence of large grid power, where system voltage and frequency are controlled by the stiff grid. In a rural area, where grid power is not available, the frequency and voltage control become a fundamental issue to be addressed. Moreover, for accurate load sharing a high value of droop gain should be chosen as the R/X ratio of the rural network is very high, which makes the system unstable. Therefore, the choice of droop gains is often a trade-off between power-sharing and stability. In the context, the main focus of this PhD thesis is the fundamental investigations into control techniques of inverter-based standalone neighbouring microgrids for available power sharing. It aims to develop new and improved control techniques to enhance performance and power-sharing reliability of remote standalone Microgrids. In this thesis, a power management-based droop control is proposed for accurate power sharing according to the power availability in a particular MG. Inverters can have different power setpoints during the grid-connected mode, but in the standalone mode, they all need their power setpoints to be adjusted according to their power ratings. On the basis of this, a power management-based droop control strategy is developed to achieve the power-sharing among the neighbouring microgrids. The proposed method helps the MG inverters to share the power according to its ratings and availability, which does not restrict the inverters for equal power-sharing. The paralleled inverters in coupled MGs need to work in both interconnected mode and standalone mode and should be able to transfer between modes seamlessly. An enhanced droop control is proposed to maintain the frequency and voltage of the MGs to their nominal value, which also helps the neighbouring MGs for seamless (de)coupling. This thesis also presents a mathematical model of the interconnected neighbouring microgrid for stability and robustness analysis. Finally, a laboratory prototype model of two MGs is developed to test the effectiveness of the proposed control strategies

Communication Based Control for DC Microgrids

Centralized communication-based control is one of the main methods that can be implemented to achieve autonomous advanced energy management capabilities in DC microgrids. However, its major limitation is the fact that communication bandwidth and computation resources are limited in practical applications. This can be often improved by avoiding redundant communications and complex computations. In this paper, an autonomous communication-based hybrid state/event driven control scheme is proposed. This control scheme is hierarchical and heuristic, such that on the primary control level, it encompasses state-driven local controllers, and on the secondary control level, an event-driven MG centralized controller (MGCC) is used. This heuristic hybrid control system aims at reducing the communication load and complexity, processor computations, and consequently system cost while maintaining reliable autonomous operation during all possible scenarios. A mathematical model for the proposed control scheme using Finite State Machines (FSM) has been developed and used to cover all the possible modes/sub-modes of operation, and assure seamless transitions among them during various events. Results of some case studies involving severe operational scenarios were presented and discussed. Results verify the validity and effectiveness of the proposed communication-based control scheme

A Hybrid State/Event Driven Communication-based Control for DC Microgrids

The U.S. electric power industry is undergoing unprecedented changes triggered by the growing electricity demand, and the national efforts to reduce greenhouse gas emissions. Moreover, there is a call for increased power grid resiliency, survivability and self-healing capabilities. As a result of these challenges, the smart grid concept emerged. One of the main pillars of the smart grid is microgrids. In this thesis, the technical merits of clustering multiple microgrids during blackouts on the overall stability and supply availability have been investigated. We propose to use the existing underground distribution grid infrastructure, if applicable, during blackouts to form microgrid clusters. The required control hierarchy to manage microgrid clusters, and communicate with the Distribution Network Operator (DNO) has been discussed. A case study based on IEEE standard distribution feeders, and two microgrid models, has been presented. Results show that clustering microgrids help improve their performance and that the microgrid total rotating mass inertia has a direct impact on the overall stability of a microgrid cluster. The design and control of individual microgrids have been given genuine attention in this thesis since they represent the main resiliency building block in the proposed clustering approach. Therefore, a considerable portion of this thesis is dedicated to present studies and results of designing, simulating, building and testing a direct current (DC) microgrid. The impact of various operational scenarios on DC microgrid performance has been thoroughly discussed. Specifically, this thesis presents the design and implementation of the City College of New York (CCNY) DC microgrid laboratory testbed. The experimental results verify the applicability and flexibility of the developed microgrid testbed. An autonomous communication-based centralized control for DC microgrids has been developed and implemented. The proposed controller enables a smooth transition between various operating modes. Finite state machine (FSM) has been used to mathematically describe the various operating modes (states), and the events that may lead to mode changes (transitions). Therefore, the developed centralized controller aims at optimizing the performance of MG during all possible operational scenarios, while maintaining its reliability and stability. Results of selected drastic cases have been presented, which verified the validity and applicability of the proposed controller. Since the proposed microgrid controller is communication-based, this thesis investigates the effect of wireless communication technologies latency on the performance of DC microgrids during islanding. Mathematical models have been developed to describe the microgrid behavior during communication latency. Results verify the accuracy of the developed models and show that the impact may be severe depending on the design, and the operational conditions of the microgrid just before the latency occurs. We propose to use the existing underground distribution grid infrastructure, if applicable, during blackouts to form microgrid clusters. The required control hierarchy to manage microgrid clusters, and communicate with the Distribution Network Operator (DNO) has been discussed. A case study based on IEEE standard distribution feeders, and two microgrid models, has been presented. Results show that clustering microgrids help improve their performance and that the microgrid total rotating mass inertia has a direct impact on the overall stability of a microgrid cluster. The design and control of individual microgrids have been given genuine attention in this thesis since they represent the main resiliency building block in the proposed clustering approach. Therefore, a considerable portion of this thesis is dedicated to present studies and results of designing, simulating, building and testing a direct current (DC) microgrid. The impact of various operational scenarios on DC microgrid performance has been thoroughly discussed. Specifically, this thesis presents the design and implementation of the City College of New York (CCNY) DC microgrid laboratory testbed. The experimental results verify the applicability and flexibility of the developed microgrid testbed. An autonomous communication-based centralized control for DC microgrids has been developed and implemented. The proposed controller enables a smooth transition between various operating modes. Finite state machine (FSM) has been used to mathematically describe the various operating modes (states), and the events that may lead to mode changes (transitions). Therefore, the developed centralized controller aims at optimizing the performance of MG during all possible operational scenarios, while maintaining its reliability and stability. Results of selected drastic cases have been presented, which verified the validity and applicability of the proposed controller. Since the proposed microgrid controller is communication-based, this thesis investigates the effect of wireless communication technologies latency on the performance of DC microgrids during islanding. Mathematical models have been developed to describe the microgrid behavior during communication latency. Results verify the accuracy of the developed models and show that the impact may be severe depending on the design, and the operational conditions of the microgrid just before the latency occurs

Coupling Neighboring Microgrids for Overload Management Based on Dynamic Multicriteria Decision-Making

A microgrid (MG) is expected to supply its local loads independently; however, due to intermittency of wind and solar-based energy resources as well as the load uncertainty, it is probable that the MG experiences power deficiency (overloading). This problem can be mitigated by coupling the overloaded MG to another neighboring MG that has surplus power. Considering a distribution network composed of several islanded MGs, defining the suitable MGs (alternative) to be coupled with the overloaded MG is a challenge. An MG overload management technique is developed in this paper, which first identifies the overloaded MG(s) and then selects the most suitable alternative. The alternative selection is based on different criteria, such as available surplus power, reliability, supply security, power loss, electricity cost, and CO2 emissions in the alternative MGs. Moreover, the frequency and voltage deviation in the system of coupled MGs are considered in the selection. A dynamic multicriteria decision-making algorithm is developed for this purpose. To contemplate the uncertainties in the considered distribution network, a cloud theory-based probabilistic analysis is deployed as the research framework and the performance of the developed technique is evaluated in MATLAB

ICT-Enabled Control and Energy Management of Community Microgrids for Resilient Smart Grid Operation

Our research has focused on developing novel controllers and algorithms to enhance the resilience of the power grid and increase its readiness level against major disturbances. The U.S. power grid currently encounters two main challenges: (1) the massive and extended blackouts caused by natural disasters, such as hurricane Sandy. These blackouts have raised a national call to explore innovative approaches for enhanced grid resiliency. Scrutinizing how previous blackouts initiated and propagated throughout the power grid, the major reasons are lack of situational awareness, lack of real-time monitoring and control, underdeveloped controllers at both the transmission and distribution levels, and lack of preparation for major emergencies; and (2) the projected high penetration of renewable energy resources (RES) into the electric grid, which is mainly driven by federal and state regulatory actions to reduce GHG emissions from new and existing power plants, and to encourage Non Wire Solutions (NWS). RESs are intermittent by nature imposing a challenge to forecast load and maintain generation/demand balance. The conceived vision of the smart grid is a cyber-physical system that amalgamates high processing power and increased dependence on communication networks to enable real-time monitoring and control. This will allow for, among other objectives, the realization of increased resilience and self-healing capabilities. This vision entails a hierarchical control architecture in which a myriad of microgrids, each locally controlled at the prosumer level, coordinates within the distribution level with their correspondent distribution system operator (i.e. area controllers). The various area controllers are managed by a Wide Area Monitoring, Protection and Control operator. The smart grid has been devised to address the grid main challenges; however, some technical barriers are yet to be overcome. These barriers include the need to develop new control techniques and algorithms that enable flexible transitions between operational modes of a single controller, and effective coordination between hierarchical control layers. In addition, there is a need to understand the reliability impacts of increased dependence on communication networks. In an attempt to tackle the aforementioned barriers, in my work, novel controllers to manage the prosumer and distribution networks were developed and analyzed. Specifically, the following has been accomplished at the prosumer level, we: 1) designed and implemented a DC MG testbed with minimal off-the-shelf components to enable testing new control techniques with significant flexibility and reconfiguration capability; 2) developed a communication-based hybrid state/event driven control scheme that aims at reducing the communication load and complexity, processor computations, and consequently system cost while maintaining resilient autonomous operation during all possible scenarios including major emergencies; and 3) analyzed the effect of communication latency on the performance of centralized ICT-based DC microgrids, and developed mathematical models to describe the behavior of microgrids during latency. In addition, we proposed a practical solution to mitigate severe impacts of latency. At the distribution level, we: 1) developed a model for an IEEE distribution test network with multiple MGs integrated[AM1] [PL2] ; 2) developed a control scheme to manage community MGs to mitigate RES intermittency and enhance the grid resiliency, deferring the need for infrastructure upgrade; and 3) investigated the optimal placement and operation of community MGs in distribution networks using complex network analysis, to increase distribution networks resilience. At the transmission level (T.L), New York State T.L was modeled. A case study was conducted on Long Island City to study the impact of high penetration of renewable energy resources on the grid resilience in the transmission level. These research accomplishments should pave the way and help facilitate a smooth transition towards the future smart grid.