Category Power Electronics for Renewable and Distributed Energy Systems

Applications of MAS for Power System Control

Smart-grid control requires flexibility and extensibility, and those are inherent features of MAS. Figure 15.9 shows how MAS enable communication and deci­sion-making for power systems, where agents are associated to sensors, actuators, operators and other physical or virtual entities. MAS have been showing promises

Q = 1 agent

Multi-agent-based
control system
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v

Communication

network

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Sensors / actuators
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Power grid

as an efficient control framework for developing the technology of smart grids, including voltage/VAR control, restoration, energy management, monitoring, and fault analysis (several examples are described in Sect. 15.5). A comprehensive state-of-the-art review can be found in McArthur et al. [4, 5].

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Social Behavior

Agents need to have a social behavior compatible with other fellow agents, expressed under various forms. Their social organization can vary from one system to another and with time, as well as the way they interact with each other and take decisions. In other words, agents can coordinate themselves and cooperate for reaching goals that may not be reachable by a single agent. Agents can influence the actions of others or act as interfaces for negotiations, requests, and contracts, as described in Sect. 15.4.8.

Continuing the previous example on peak demand with storage, before the MAS decides that the battery should absorb the peak, a “discussion” with other agents (such as power system brokers) may happen about whether the load can be taken by another source and maybe a better solution wo...

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Proactivity

Proactive agents have goals which can be local and/or global. A single agent usually has local goals while a group of agents may have global goals. For example, maintaining a voltage steady is mainly a local goal for a power source, while maintaining balance between generation and supply is a global objective and cannot be reached by a single agent, hence requiring cooperation. Such proactivity
might be enabled by autonomous intelligence with information based on knowl­edge about the environment (e. g., the grid), and when appropriate with further information by asking other agents, and knowledge of required actions requested by other agents through communication that may help achieving global goals...

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Distributed Architecture

MAS are distributed by design with three main attributes: (1) local knowledge, (2) flexible interactions, and (3) bottom-up control approach. Local knowledge means that agents’ view of the environment are local, and as a consequence their knowledge is limited to only what they can or need to know. The perception of agents can be limited to their neighbors, which enables reducing data transfer. For example, for a microgrid, an agent for a distributed generator does not need to receive information about a small load, which can be several miles away. There­fore, a distributed MAS architecture contributes to a scalable distribution grid.

Fig. 15.5 When an agent joins an existing MAS, it can announce its name and services to the other agents so that they can interact with him...

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Relevance of MAS for Power Systems

In order to discuss the advantages of MAS-based control versus classical meth­odologies for applications in power systems, it is important to understand how the power grid evolved over the last decades. Classical control methods implemented in SCADAs are fully functional in today’s grid. But the contemporary develop­ments toward the future smart grid will require to integrate millions of devices such as distributed storage, intelligent loads, and distributed energy resources. Control systems will then have to operate efficiently on a large scale system, despite very disperse faults that may occur. In order to analyze practical advan­tages of MAS for tackling these conditions, the following properties (distributed, pro-active, and social) will be discussed in more details.

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MAS for Power Systems

Although MAS have been used for over two decades, their application in power systems have appeared in the last decade. This section explains what are MAS and why they are so important as a distributed paradigm for strategies used in modern power systems control.

15.3.1 Principles of MAS

MAS support a framework of modeling and control of multiple structures that can be decomposed into several interacting entities. Formal definitions for MAS have been proposed by Wooldridge and Weiss [1] and Ferber [2]. The following defi­nition provides a simple overview of the MAS concept:

A multi-agent system is a system composed of a collection of autonomous and interacting entities called agents, evolving in an environment where they can autonomously perceive and act to satisfy their needs and objectiv...

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Distributed Control Systems

The SCADA and associated control systems described in the previous section have been utilized for monitoring and controlling power systems relying on a traditional centralized structure, with a limited number of large power plants used for gen­eration. However, distribution and transmission systems are under transformation toward further incorporation of distributed energy resources, and monitoring and control systems must therefore undertake changes such as:

• Distributing decision making, by moving from centralized analysis and decision systems to distributed approaches, where several components (instead of one) are able to reach a goal through cooperative tasks. This process begun with the
deployment of IEDs, but further features are required due to the evolution of the grid and assoc...

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Modern Architectures for Power Systems Control

Modern control systems used by utilities are based on SCADA systems. SCADAs are information systems used for monitoring and supervising power systems or industrial processes, but without control functionalities. However, with recent popularization of the term, SCADAs are now associated with extensive systems, sometimes performing control actions. Figure 15.2 shows the structure of a basic SCADA, which is a fully centralized architecture, where remote terminal units (RTUs) provide communication interfaces with physical components such as sources, loads, and so on.

With the development of communication interfaces, distributed control systems (DCS) have emerged...

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