Control and Coordination of multiple BESS in a Low Voltage Distribution Network

Abstract

The rapidly growing number of renewable energy technologies has started changing the infrastructure of the conventional energy sector, which was based on one-directional power flow. Bidirectional flows are created in the network with the integration of renewable technologies. The electricity network and system operators face many new challenges created due to renewable energy sources. Renewable energy sources are characterized by an intermittent and stochastic character which affects the power production from renewable energy technologies. Thus, the produced energy may pose challenges to the grid when it is higher than demand since the excess power is injected into the grid and it causes overvoltage problems.
BESS can contribute in facing the problems created by renewable energy technologies. They offer environmental benefits, they contribute to the integration of renewable technologies and they enhance grid’s reliability. These factors have as a result an increase in the integration of batteries in the electricity network. This research has as a goal to develop a control and coordination method for multiple BESS in a low voltage distribution network in order to address overvoltage and undervoltage issues caused by high penetration of PV units. There are many control strategies used in order to control the increasing number of batteries so that normal operation of the energy system is sustained. The main control strategies are centralized control, decentralized control and distributed control.
In this thesis study, a coordination control strategy of multiple BESS was developed to address the network's voltage violation issues caused by the high penetration of PV units. The coordination control strategy is based on a consensus algorithm that determines each battery's contribution to the network. The goal of this control strategy is to maintain the voltage within the limits. When a battery is not available due to a state of charge limit violation or maintenance, the amount of power that this battery would contribute under normal operation is distributed equally from the neighboring batteries until the battery becomes available again. This control strategy is a combination of distributed control, as it entails communication between neighboring batteries which share information together, and local control. The developed coordination control strategy is compared to a decentralized control strategy, which is widely used in distribution networks in order to control the contribution of batteries. Moreover, one of the batteries is emulated in the laboratory in order to examine the behavior and contribution of the battery, with the coordination control strategy implemented, in real-time application in comparison to the simulation.
The findings of this thesis study contribute to the research of mitigating voltage limit violations caused by renewable energy technologies by demonstrating the effectiveness and benefits of the proposed control and by providing a comparison of the proposed control to a decentralized control strategy, commonly used in distribution networks for controlling the contribution of BESS, for voltage regulation. Furthermore, the laboratory results contribute in the potential implementation of the proposed control in real distribution networks.