Multi-agent system based active distribution networks

This thesis gives a particular vision of the future power delivery system with its main requirements. An investigation of suitable concepts and technologies which creates a road map forward the smart grid has been carried out. They should meet the requirements on sustainability, efficiency, flexibility and intelligence. The so called Active Distribution Network (ADN) is introduced as an important element of the future power delivery system. With an open architecture, the ADN is designed to integrate various types of networks, i.e., MicroGrid or Autonomous Network, and different forms of operation, i.e., islanding or interconnection. By enabling an additional local control layer, these so called cells are able to reconfigure, manage local faults, support voltage regulation, or manage power flow. Furthermore, the Multi-Agent System (MAS) concept is regarded as a potential technology to cope with the anticipated challenges of future grid operation. Analysis of benefits and challenges of implementing MAS shows that it is a suitable technology for a complex and highly dynamic operation and open architecture as the ADN. By taking advantages of the MAS technology, the AND is expected to fully enable distributed monitoring and control functions. This MAS-based ADN focuses mainly on control strategies and communication topologies for the distribution systems. The transition to the proposed concept does not require an intensive physical change to the existing infrastructure. The main point is that inside the MAS-based ADN, loads and generators interact with each other and the outside world. This infrastructure can be built up of several cells (local areas) that are able to operate autonomously by an additional agent-based control layer. The ADN adapts a MAS hierarchical control structure in which each agent handles three functional layers of management, coordination, and execution. In the operational structure, the ADN addresses two main function parts: Distributed State Estimation (DSE) to analyze the network topology, compute the state estimation, and detect bad data; and Local Control Scheduling (LCS) to establish the control set points for voltage coordination and power flow management. Under the distributed context of the controls, an appropriate method for DSE is proposed. The method takes advantage of the MAS technology to compute iteratively the local state variables through neighbor data measurements. Although using the classical Weighted Least Square (WLS) as a core, the proposed algorithm based on an agent environment distributes drastically computation burden to subtasks of state estimation with only two interactive buses and an interconnection line in between. The accuracy and complexity of the proposed estimation are investigated through both off-line and on-line simulations. Distributed and parallel working of processors improves significantly the computation time. This estimation is also suitable for a meshed configuration of the ADN, which includes more than one interconnection between each pair of the cells. Depending on the availability of a communication infrastructure, it is able to work locally inside the cells or globally for the whole ADN. As a part of the LCS, the voltage control function is investigated in both steady-state and dynamic environments. The autonomous voltage control within each network area (cell) can be deployed by a combination of active and reactive power support of distributed generation (DG). The coordinated voltage control defines the optimal tap setting of the on-load tap changer (OLTC) while comparing amounts of control actions in each area. Based on the sensitivity factors, these negotiations are thoroughly supported in the distributed environment of the MAS platform. To verify the proposed method, both steady-state and dynamic simulations are developed. Simulation results show that the proposed function helps to integrate more DG while mitigating voltage violation effectively. The optimal solution can be reached within a small number of calculation iterations. It opens a possibility to apply the proposed method as an on-line application. Furthermore, a distributed approach for the power flow management function is developed. By converting the power network to a represented graph, the optimal power flow is understood as the well-known minimum cost flow problem. Two fundamental solutions for the minimum cost flow, i.e., the Successive Shortest Path (SSP) algorithm and the Cost-Scaling Push-Relabel (CS-PR) algorithm, are introduced. The SSP algorithm is augmenting the power flow along the shortest path until reaching the capacity of at least one edge. After updating the flow, it finds another shortest path and augments the flow again. The CS-PR algorithm approaches the problem in a different way which is scaling cost and pushing as much flow as possible at each active node. Simulations of both meshed and radial test networks are developed to compare their performances in various network conditions. Simulation results show that the two methods can allow both generation and power flow controller devices to operate optimally. In the radial test network, the CS-PR needs less computation effort represented by a number of exchanged messages among the MAS platform than the SSP. Their performances in the meshed network are, however, almost the same. Last but not least, this novel concept of MAS-based AND is verified under a laboratory environment. The lab set-up separates some local network areas by using a three-inverter system. The MAS platform is created on different computers and is able to retrieve data from and to hardware components, i.e., the three-inverter system. In this set-up, a configuration of the power router is established in a combination of the three-inverter system with the MAS platform. Three control functions of the inverters, AC voltage control, DC bus voltage control, and PQ control, are developed in a Simulink diagram. By assigning suitable operation modes for the inverters, the set-up successfully experiments on synchronizing and disconnecting a cell to the rest of the grid. In the MAS platform, an obvious power routing strategy is executed to optimally manage power flow in the lab set-up. The results show that the proposed concept of the ADN with the power router interface works well and can be used to manage electrical networks with distributed generation and controllable loads, leading to active networks

Modeling the controlled delivery power grid

Competitive energy markets, stricter regulation, and the integration of distributed renewable energy sources are forcing companies to reengineer energy production and distribution. The Controlled Delivery Power Grid is proposed as a novel approach to transport energy from generators to consumers. In this approach, energy distribution is performed in an asynchronous and distributed fashion. Much like the Internet, energy is delivered as addressable packets, which allow a controlled delivery of energy. As a proof-of-concept of the controllable delivery grid, two experimental test beds, one with integrated energy storage and another with no energy storage, were designed and built to evaluate the efficiency of a power distribution and scheduling scheme. Both test beds use a request-grant protocol where energy is supplied in discrete quantities. The performance of the system is measured in terms of the ability to satisfy requests from consumers. The results show high satisfaction ratios for distribution capacities that are smaller than the maximum demand. The distribution of energy is modelled with graph theory and as an Integer Linear Programming problem to minimize transmission losses and determine routes for energy flows in a network with distributed sources and consumers. The obtained results are compared with a heuristic approach based on the Dijkstra\u27s shortest path algorithm, which is proposed as a feasible approach to routing the transmission of packetized energy

Smart grid

Tese de mestrado integrado em Engenharia da Energia e do Ambiente, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2016The SG concept arises from the fact that there is an increase in global energy consumption. One of the factors delaying an energetic paradigm change worldwide is the electric grids. Even though there is no specific definition for the SG concept there are several characteristics that describe it. Those features represent several advantages relating to reliability and efficiency. The most important one is the two way flow of energy and information between utilities and consumers. The infrastructures in standard grids and the SG can classified the same way but the second one has several components contributing for monitoring and management improvement. The SG’s management system allows peak reduction, using several techniques underlining many advantages like controlling costs and emissions. Furthermore, it presents a new concept called demand response that allows consumers to play an important role in the electric systems. This factor brings benefits for utilities, consumers and the whole grid but it increases problems in security and that is why the SG relies in a good protection system. There are many schemes and components to create it. The MG can be considered has an electric grid in small scale which can connect to the whole grid. To implement a MG it is necessary economic and technical studies. For that, software like HOMER can be used. However, the economic study can be complex because there are factors that are difficult to evaluate beyond energy selling. On top of that, there are legislation and incentive programs that should be considered. Two case studies prove that MG can be profitable. In the first study, recurring to HOMER, and a scenario with energy selling only, it was obtained a 106% reduction on production cost and 32% in emissions. The installer would have an $8 000 000 profit in the MG’s lifetime. In the second case, it was considered economic services related to peak load reduction, reliability, emission reduction and power quality. The DNO had a profit of$41,386, the MG owner had $29,319 profit and the consumers had a$196,125 profit. We can conclude that the MG with SG concepts can be profitable in many cases

Smart grid architecture for rural distribution networks: application to a Spanish pilot network

This paper presents a novel architecture for rural distribution grids. This architecture is designed to modernize traditional rural networks into new Smart Grid ones. The architecture tackles innovation actions on both the power plane and the management plane of the system. In the power plane, the architecture focuses on exploiting the synergies between telecommunications and innovative technologies based on power electronics managing low scale electrical storage. In the management plane, a decentralized management system is proposed based on the addition of two new agents assisting the typical Supervisory Control And Data Acquisition (SCADA) system of distribution system operators. Altogether, the proposed architecture enables operators to use more effectively—in an automated and decentralized way—weak rural distribution systems, increasing the capability to integrate new distributed energy resources. This architecture is being implemented in a real Pilot Network located in Spain, in the frame of the European Smart Rural Grid project. The paper also includes a study case showing one of the potentialities of one of the principal technologies developed in the project and underpinning the realization of the new architecture: the so-called Intelligent Distribution Power Router.Postprint (published version

Convertidores de potencia para microrredes y sistemas de generación distribuidos

This paper presents an overview and critical discussion about the utilization of power converters in several microgrid configurations that incorporate non-conventional renewable energy sources and energy storage. The methodology is developed over 69 works published in this research topic. The papers are selected from databases in electrical engineering, e.g., IEEExplore, ScienceDirect, Springer, MDPI, etc. Then, the papers are classified depending on its focus, i.e., power converters in microgrids or power converters in distribution systems. At least, three classifications are proposed and one of them is made over more than 40 papers about power converters used in microgrids and electric distribution systems. Given the wide variety of microgrids and their configurations, the selection of appropriate power converters for every scenario is not trivial; therefore, this work also classifies the converters in their most common application, their advantages and disadvantages, and also point out the study domain, i.e., simulation or physical implementation. One of the main conclusions made from the overview is a gap identified in the study of direct current/ direct current microgrids despite being the simplest configuration among the three analyzed configurations. This is because hybrid and alternate current microgrids are more widely used since they allow taking advantage of the infrastructure of the current electrical systems.Este artículo presenta una visión general y una discusión crítica sobre la utilización de convertidores de potencia en varias configuraciones de microrredes que incorporan fuentes de energía renovable no convencionales y almacenamiento de energía. La metodología se desarrolla sobre 69 trabajos publicados en este tema de investigación. Los documentos se seleccionan de bases de datos en ingeniería eléctrica, p. ej. IEEExplore, ScienceDirect, Springer, MDPI, etc. Luego, los artículos se clasifican según su enfoque, es decir, convertidores de potencia en microrredes o convertidores de potencia en sistemas de distribución. Se proponen al menos tres clasificaciones y una de ellas se realiza sobre más de 40 artículos sobre convertidores de potencia utilizados en microrredes y sistemas de distribución eléctrica. Dada la gran variedad de microrredes y sus configuraciones, la selección de convertidores de potencia apropiados para cada escenario no es trivial; por lo tanto, este trabajo también clasifica a los convertidores en su aplicación más común, sus ventajas y desventajas, y también señala el dominio de estudio, es decir, simulación o implementación física. Una de las principales conclusiones extraídas de la visión general es una brecha identificada en el estudio de las microrredes de corriente continua / corriente continua a pesar de ser la configuración más simple entre las tres configuraciones analizadas. Esto se debe a que las microrredes híbridas y de corriente alterna son las más utilizadas ya que permiten aprovechar la infraestructura de los sistemas eléctricos actuales

Design and operation of modular microgrids

textMicrogrids are being considered as a solution for implementing more reliable and flexible power systems compared to the conventional power grid. Various factors, such as low system inertia, might make the task of microgrid design and operation to be nontrivial. In order to address the needs for operational flexibility in a simpler manner, this dissertation discusses modular approaches for design and operation of microgrids. This research investigates Active Power Distribution Nodes (APDNs), which is a storage integrated power electronic interface, as an interface block for designing modular microgrids. To perform both voltage/current regulation and energy management of APDNs, two hierarchical control frameworks for APDNs are proposed. The first framework focuses on maintaining the charge level of the embedded energy storage at the highest available level to increase system availability, and the second framework focuses on autonomous power sharing, and storage management. The detailed design process, control performance and stability characteristics are also studied. The performance is also verified by both simulation and experiments. The control approaches enable application of APDNs as a power router realizing distributed energy management. The decentralized configuration also increases modularity and availability of power networks by preventing single point-of-failures. The advantages of using APDNs as a connection interface inside a power network are discussed from an availability perspective by performing a comparison using Markov-based availability models. Furthermore, the operation of APDNs as power buffers is explored and the application of APDNs enabling modular implementation of microgrids is also studied. APDNs enable the system expansion process—i.e. connecting new loads to the original system—to be performed without modifying the configuration of the original system. The analysis results show that a fault-tolerant microgrid with an open architecture can be realized in a modular manner with APDNs. APDNs also enable simplified selectivity planning for system protection. The effect of modular operation on microgrids is also studied by using an inertia index. The index not only provides insights on how system performance is affected by modular operation of modular microgrids, but is also used to develop a simpler operation strategy to mitigate the effect of plug and play operations.Electrical and Computer Engineerin

Telecommunication of stabilizing signals in power systems

Deregulation of the power industry has occurred at a rapid pace, opening some promising competition between suppliers. The result of this competition should be to the benefit of customers.;Telecommunication plays a crucial role in integrating systems and ensuring smooth operation by way of exchanging data and information between various systems that are responsible for monitoring and control of the grid. For example, a Power System Stabilizer (PSS) controller could be placed at one of the generators and requires remote measurements. All the communication schemes within the network generate delays that are characterized in this project using OPNET Modeler. OPNET Modeler is also used to characterize the number of dropped packets.;As a case study, we consider a two-area four-generator (2A4G) and explore the role of communication delay on system stability. Those delays play an important role in the design of a controller that can help the damping of electro-mechanical oscillations between interconnected synchronous generators and therefore maintain the system stability. The network statistics are then imported into Simulink in order to visualize the speed of the shaft w2 as a function of time. Additional communication options to the inter-area oscillation problem are offered at the end of the thesis (use of Virtual Private Network (VPN), use of fiber optic dedicated network, or the use of IPv6 protocol)