Elsevier

Energy Conversion and Management

Volume 75, November 2013, Pages 643-650
Energy Conversion and Management

Multi-agent modeling for the simulation of a simple smart microgrid

https://doi.org/10.1016/j.enconman.2013.07.050Get rights and content

Highlights

  • We created a systemic modular model for a microgrid with a load flow calculation.

  • The model is modular and besides the power devices includes also a communication layer.

  • An agent-based approach allows to include intelligent strategies on every node of the system.

  • First feasibility simulations were run to show the possible outcomes of generator and load management strategies.

Abstract

The smart grid is a highly complex system that is being formed from the traditional power grid, adding new and sophisticated communication and control devices. This will enable integrating new elements for distributed power generation and also achieving an increasingly automated operation so for actions of the utilities as for customers. In order to model such systems, a bottom-up method is followed, using only a few basic elements which are structured into two layers: a physical layer for the electrical power transmission and one logical layer for element communication. A simple case study is presented to analyze the possibilities of simulation. It shows a microgrid model with dynamic load management and an integrated approach that can process both electrical and communication flows.

Introduction

In the last years, energy systems are moving away from a centralized and hierarchical structure, under strict control of the electricity supply companies, toward a new system where distributed actors influence the energy supply. Production is no longer limited to large energy providers, as small decentralized producers in the form of distributed generation (DG) enter the network and are able to inject energy at much lower voltage levels than before.

This paradigm shift involves new challenges for the modeling and simulation of energy systems for which decentralized models are needed. Among the presented in a review in [1], there are, for example, several commercial tools used in power engineering, such as Eurostag or PSS/E. Further, a number of non-proprietary tools exist, such as several toolboxes based on Matlab/Simulink, for example Matpower or PSAT.

Since some years, the term smart grid has become widespread in the energy sector. The introduction of smart grids involves a change from manual operations toward an intelligent, ICT based and controlled network. These changes will especially affect the distribution grid [2], and in this way, microgrids.

A number of models have been developed to analyze and understand the behavior of microgrids. Some of them focused on decentralized control strategies, usually using Matlab/Simulink and similar classic tools, are of special interest [3], [4], [5]. Particularly relevant is the work on demand side management, using virtual powers plants [6] and on multi-agent platforms [7]. And also worth mentioned as significant the recently extended idea, discussed in some conferences [8] and accepted very well in some countries, of using microgrids as building blocks of the future smart grid [9].

Here, we recall that traditional methods used for analysis of electrical networks are based on static power flow calculations [10]. But these methods are not suitable for computing the system response to special events (such as power changes in generators fed by renewable energies, sudden connection and disconnection of loads and sources, or even when the network structure changes after a disaster occurs), because in these cases, the values of the variables have to be updated in a short time, as they are used for the network control or simulation, and therefore, a new “steady” state computation is required each time one of such special event occurs, which is not efficient at all.

Trying to give a solution to this problem the authors designed a decentralized power flow algorithm for this kind of models (see below). This method provides a more flexible and dynamic way than traditional methods and is able to cope with sudden changes and disasters. The method is described in [11] and was successfully validated against the Matlab PSAT Toolbox [12].

In [11], the complexity for modeling smart grids was identified. A first smart grid model was developed, which represents the system on the physical layer, by integrating a distributed load flow algorithm. The model was tested by running different simulations, letting interact a wind generation unit, a photovoltaic panel, a battery, two loads and a diesel generator. By modeling the individual elements as agents, a modular and flexible approach was used, where the agents can be programmed to have different behaviors such as the charging and discharging times for the battery system, or the integration of variable wind speeds by adding a wind speed simulator module which directly interacts with the turbines. On the logical layer, a first approach was made.

This approach is extended in the current work by adding real-time communications to the simulation, which represent one of the main features of the logical layer. Because of their scarce resources, microgrids need a flexible demand side [13], so introducing communication is essential as it allows performing monitoring, control [14] and demand side management, among others.

As some specific aspects of the author’s work in this area were presented in some conferences [11], [15], [16], [11], [17], in a rather informal manner, here we intend to offer a more understandable and reproducible description of them, by using some elements from the ODD protocol [18].

Section snippets

Overview

An agent-based approach was chosen for modeling a simple microgrid, trying to represent a minimalistic smart grid (or smart-microgrid). The implementation was done in the multi-paradigm modeling environment AnyLogic.

Design concepts

As mentioned before, two kind of interactions occur in the model. At the physical layer, these interactions are intended to perform the electrical behavior of the network, by implementing a power flow algorithm, and therefore, they do a completely deterministic, imposed, process. But at the logical layer, interactions are as result of agent communications and so agent behaviors can became rather complex, because they use specific rules which possibly depend of a number of environmental, most of

Elements of the microgrid

The microgrid model aims to include most of the aspects of future smart grids: distributed generation, renewable energy sources and communication flows are represented. The model consists of the following elements:

  • 1 Point of Common Coupling (PCC) – bus 1

  • 1 Diesel generator – bus 2

  • 2 Load (consumers) – buses 3 and 4

  • 1 Wind turbine – bus 5

  • 1 Photovoltaic panel, linked to

  • 1 Battery storage system – bus 6

The load model includes the necessary elements to allow its management through a smart meter device.

Load modeling

Simulation results

The simulation main window appears in Fig. 7. It shows the model structure, including the logical layer and the physical layer, with the bus index and type, the voltage magnitude and angle, and the active and reactive powers, at each bus. Note that the connections in both layers are the same as in Fig. 2. The figure also shows the icons of the main instances in the model: the environment, the agents and the Excel file where the data to build the example are written.

The PCC includes a control

Further considerations

There are two parallel networks, which are however closely related to each other. The logical layer represents the information transfer, based on ICT [23]. The electrical flows and phenomena can be influenced by decisions obtained with the information of the communication network. Therefore, communication and inter-layer devices are needed.

Because AnyLogic gives facilities to easily implement communications between agents, the user only have to instantiate and use them, by calling the

Conclusion and outlook

The given example model implements a very simple load management algorithm, to show feasibility of the simulation model. The communication mechanism between the PCC and the consumers allows monitoring powers and send signals to the consumers, which leads to a load management.

The combination of several approaches allows the creation of models that might abstract some details from the single unit models, but all in all create a much more realistic representation at the system level. The inclusion

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