A Concept for Improving Battery Energy Storage System Performance in a Redundant DC Microgrid without SoC-Based Droop

The redundancy strategy enhances the reliability of applications such as medical centers, shipboard microgrids (MGs), and aircraft systems. This paper proposes a redundancy-based dc MG integrating two modules: a cascaded bidirectional Cuk converter (CBC) and a cascaded bidirectional Boost converter (CBB), each supported by battery energy storage systems (BESS), improving the reliability in case of module failure. Additionally, a Boost converter integrates the Fuel Cell (FC) through the CBC dc-link, employing a droop controller to regulate power production. In this context, the energy management system (EMS) balances the state of charge (SoC) among BESS units using a Fuzzy-based method, avoiding SoC-based droop control and addressing nonlinearities in SoC equalization. The EMS also mitigates rapid transients due to load maneuvers on the dc-link by using BESS units, and reduces stress on the FC membranes. Considering the CBB, the reliability of the BESS units is improved through battery-to-battery (B2B) equalization, enabled by the Fuzzy-based method able to provide current references, thereby increasing power sharing accuracy. Therefore, the proposed solution performs improvement in the BESS equalization process, with redundancy ensuring stable dc-link voltage even during faults. Finally, infinity norm and Lyapunov's indirect method confirm the MG stability, while lab-scale prototype demonstrates experimentally effectiveness.