Improved EPS functionality for AC-coupled battery storage systems

Abstract

With the growing demand for installations of renewable energy systems (RES), the integration of photovoltaic (PV) systems with energy storage systems (ESS) has become essential for maintaining grid stability and ensuring reliable power supply. This project addresses a critical limitation in AC-coupled ESS configurations, which traditionally do not allow PV generation during grid failures, thereby relying solely on stored battery energy. This project proposes a solution that introduces a controller to enable PV generation in emergency power supply (EPS) mode, enhancing system resilience and efficiency. The research begins with a comprehensive analysis of AC and DC coupling ESS configurations, highlighting the advantages and limitations of each. A software simulation was developed to compare the already established frequency shifting method with the proposed controller-based solution. The controller, designed and implemented as part of this project, enables communication between the PV inverter and battery inverter as well as controlling the PV inverter maximum power generation. This ensures seamless PV generation during grid outages. Practical tests confirmed that the new system configuration significantly improves power capability and stability in EPS mode. The controller not only allows for the use of PV inverters with higher power capacities than battery inverters but also supports retrofit applications, making it a versatile solution for various installations. Additionally, the project explored future enhancements, including improved communication protocols and expanded functionality to support demand response operations. This innovative approach offers a robust solution to enhance the functionality and reliability of residential and commercial AC-coupled ESS, paving the way for more resilient and sustainable energy systems.