Energy management of a battery energy storage system for renewable energy DC micro-grid

Abstract

This research presents a regime for energy management of a battery energy storage system in a renewable DC micro-grid. The increase in world electricity demand is one of the principal drives to the exhaustion of fossil fuels and expanded greenhouse gas emissions. To solve these problems, several countries have adopted actions for large deployment renewable energy sources, which includes wind energy, solar power, biomass power, tidal and hydropower. These sources are considered as significant in delivering clean energy and reducing greenhouse gas emissions for sustainable improvement. These renewable energy sources are often connected to the conventional power system through the distribution network near consumer loads, thus no extensive transmission system is needed. In such a case, these are referred to as distributed generation systems. Distributed generation can impact negatively the performance of the distribution network as the distribution network will no longer operate with a unidirectional power flow pattern. Some of the known issues are known to affect voltage quality, protection equipment settings, desensitised relays, augmented fault currents, increased maintenance of equipment used, and even a landing portions of the distribution network. To address these issues, micro-grids are used as a platform to integrate distributed generation systems, as they provide significant benefits to end-users and to the distribution network. The utilization of energy storage systems is necessary in renewable micro-grids as they can ensure the reliability of the supplied power. Battery energy storage systems are the types of energy storage widely utilized in renewable micro-grids. Comparatively to Li-ion battery, most of the technologies present some issues (the relation between the charge / discharge rate on their operating conditions, unbalance SoC conditions), which can impact on the battery lifetime as well as the average of energy stored in the battery. In case of battery bank, the deep discharge or the premature charge of battery can lead to a reduced lifetime of the storage system. The problem of this research was the lack of a proper battery management system in a renewable DC micro-grid. The DC micro-grid and energy management system algorithm was implemented and developed using MATLAB/Simulink software, which used a physical modelling approach. The aim of this research was to develop a battery management system algorithm to control the charging / discharging of a battery bank and to keep its state of charge (SoC) in the admissible limits to avoid the deep charging / discharging of the battery within a DC micro-grid. Moreover, in a micro-grid, given that several power sources are connected, an energy management system needs to be implemented to ensure their proper operation. The objectives of this research were to develop DC micro-grid component models to be used in the simulation model; to design and develop function block logic to be used for the simulation using State-Flow logical programming environment in MATLAB/Simulink software; to develop a control system schemes for the DC micro-grid; to develop an energy management system (EMS) algorithm for the DC micro-grid and to develop a battery management system (BMS) algorithm and to design and develop a simulation of a DC micro-grid with battery energy storage using MATLAB/Simulink software. The results of the scenarios of the developed energy management system (EMS) algorithm have successfully shown that this developed algorithm will be able to ensure the reliability, the resiliency, the robustness and the proper operation of the battery systems in micro-grids. The principal advantage of this developed algorithm will be that it will ensure the proper relation between the charge / discharge rate of battery energy storage systems on their operating conditions and will allow to keep its SoC in the admissible limits according to the input power conditions from the EMS flow chart, to avoid the deep charge / discharge of the battery bank, which in return will significantly impact on their lifespan and on the reliability in a DC micro-grid. The results demonstrated that the battery bank was able to handle the load demands for different scenarios studied. Moreover, the developed software model presents another advantage, which enables the users to access and to change any control parameter within the DC micro-grid. In addition, this developed algorithm will provide a low overall cost and degradation impact on the battery. The SoC of the battery operation will directly affect its achievable lifetime positively and the battery degradation costs will significantly decrease. This algorithm offered a proper operation of the entire developed DC micro-grid system, which could result in reduced battery degradation and improve battery life as well as the energy stored in the battery. The results have shown that the initial investment cost will comparatively be lower and will decrease the economic analyse in terms of LCOE.