Integrated power converters for optimal operation of hybrid battery packs

This work demonstrates a method to build and operate hybrid battery systems, which can serve the need for Long-Duration Energy Storage (LDES). LDES systems have to provide energy at different timescales to compensate for the intermittency of renewable resources, supply peak power, support black-start, and serve loads with variable power factor. It is cost prohibitive to use a single battery technology to provide both high power and energy services. Therefore, integration of hybrid technologies is essential. Here, a scalable and flexible method is proposed to build such a hybrid system, where DC-DC converters are integrated between battery packs and a DC-AC converter. The DC-DC converters implement battery-specific charging/discharging protocols, and the DC-AC converter establishes the DC bus voltage and synchronizes with the grid. A hardware-software testbed has been built for operating Lead-Acid battery cells by integrating a commercial DC-AC power conversion system (PCS) with a custom-built Dual Active Bridge (DAB) DC-DC converter. The results validate this method's effectiveness in controlling hybrid battery strings and preventing battery degradation. The authors plan to make the software and hardware design available to the power electronics and battery community, and add support for other DC-DC converter topologies and battery technologies.