Microgrids in Distribution

Abstract

According to CIGRE WG C6.21Microgrids are electricity distribution systems containing loads and distributed energy resources (DERs) (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded. The different parts of the microgrid can be interconnected via an AC link forming AC microgrids or via a DC link forming DC microgrids. The notion of control is critical in the definition of microgrids. In fact, what differentiates microgrids from Distribution Grids with distributed energy sources and loads lies in the capabilities to manage and coordinate the available resources, so that they appear to the upstream network as a single coordinated unit. The developments in power electronics that are used for the interconnection of inverter‐based generation and storage units, such as photovoltaics and batteries, within microgrids have provided the possibility of incorporating advanced functionalities in the control of the distributed resources. Droop curves such as active power – frequency (P–f) and reactive power – voltage (Q–V), similar to the ones of traditional rotating machines and together with the capability of remotely controlling them, allow the application of advanced control strategies for microgrid operation. Advanced Information and Communications Technology (ICT) provides further opportunities for the application of intelligent techniques in microgrids decentralized control.This chapter deals with microgrid control and operation, including both primary and secondary voltage and frequency control and optimal dispatch among the DERs. Centralized and decentralized approaches are discussed, and typical results are displayed, obtained from laboratory setups at the Electric Energy Systems Laboratory of the National Technical University of Athens.

A SEPIC-Cuk converter combination for bipolar DC microgrid applications

“…Value DC Voltage Source 96 V L 1 1 m H L 2 , L 3 1 0 0 μ H C1, C2 4 7 μ F C 3 , C 4 4 7 0 0 μ F The different loads, along with the external generation system considered, allow studying the behaviour of the proposed system in a DC microgrid. This MG is designed considering the Thevenin equivalent of a real system.…”

“…The distribution system should be more flexible and configurable, allowing efficient energy management in the presence of new distributed generation units. So, MG have proved to be very attractive structures that meet these premises [1]. They allow the integration of Distributed Generation (DG) based on Renewable Energy Units (RES) [2][3][4][5] A MG allows operation in two basic modes: isolated and connected to the utility grid [6].…”

Intelligent Fault Detection System for Microgrids

“…The algorithm has built-in DC-offset suppression capability as well as recursive least square error filter for current phasor estimation to provide input to the overcurrent fault detector. Nevertheless, this method does not consider alternative operating modes, such as grid-connected versus islanded mode [6]. Table 1 highlights the main aspects considered by FD state-of-the-art techniques and the proposed FD system and challenges that have not been faced.From Table 1, it is possible to remark that the main challenges that have not yet been fully addressed in terms of microgrid protection are the imbalance, dynamic topology, consideration of non-robust communication systems, adaptive coordination, and high-impedance faults occurrence.…”

“…The algorithm has built-in DC-offset suppression capability as well as recursive least square error filter for current phasor estimation to provide input to the overcurrent fault detector. Nevertheless, this method does not consider alternative operating modes, such as grid-connected versus islanded mode [6]. Table 1 highlights the main aspects considered by FD state-of-the-art techniques and the proposed FD system and challenges that have not been faced.…”

A Robust Suboptimal Current Control of an Interlink Converter for a Hybrid AC/DC Microgrid

“…Microgrid must be able to maintain the voltage and frequency stability in both modes and the switching time [3,4]. When microgrid is in grid-connected mode, frequency stability is guaranteed by the utility grid as it performs as the primary source in the AC sub-grid.…”