Energy flow optimization for a hybrid DC-microgrid integrating hydrogen production via a PEM electrolyzer and fuel cell backup

This paper proposes an advanced nonlinear control strategy coupled with energy flow optimization (EFO) for a hybrid DC-microgrid integrating a photovoltaic (PV) generator, a lithium-ion battery energy storage system (BESS), a proton exchange membrane (PEM) electrolyzer for hydrogen production, and a PEM fuel cell for backup power. All subsystems are interconnected, via power electronic converters, to a common DC-bus supplying diverse loads. The proposed control strategy ensures five key objectives: tight DC-bus voltage regulation, optimal power extraction from PV (MPPT/APPT), intelligent battery operation in constant current/voltage (CC/CV) modes, and specified hydrogen production tracking, and secure fuel cell activation under power deficit. An integrated energy-management algorithm dynamically manages power sharing among sources and storage based on renewable availability and battery state-of-charge (SoC). Nonlinear backstepping controllers are designed for all converters (PV-side DC/DC boost, bidirectional BESS DC/DC buck-boost, electrolyzer DC/DC buck, and fuel-cell DC/DC buck) to guarantee stability and fast dynamics. Simulation results across multiple operating scenarios show smooth mode transitions, reduced battery charge/discharge cycling, accurate hydrogen-production tracking, tight DC-bus regulation, and reliable continuity of supply, confirming the effectiveness and robustness of the proposed control and EFO framework.