Multi-level control for shared hydrogen storage system based offshore DC microgrid cluster involving adaptive barrier function

This paper proposes a hydrogen-powered, shared energy storage system within an offshore multi-microgrid structure. This framework is designed to ensure power balance among individual microgrids in the cluster. During power deficit, the hydrogen system delivers power using fuel cell system to the microgrid. Conversely, in the event of a power surplus, the system receives power and generates hydrogen using its electrolyzer system. Additionally, the hydrogen system has also been connected to the utility grid to provide frequency support and to purchase power when the hydrogen storage system is low. To achieve these objectives, this research proposes a two-stage control system comprising system and local level control system. The system level control optimizes the overall cost of the microgrid and hydrogen system as well as ensure the system constraints are met. To regulate power according to the system level generated references, a barrier function-based adaptive global terminal sliding mode control has been employed at local level. The stability of the control framework is ensured using Lyapunov stability criteria. A case study of a four-microgrid cluster (600 V, varying 400 kW loads) demonstrates a 29% cost reduction with the proposed methodology compared to systems without shared hydrogen storage. The system maintains DC bus voltage stability within ±0.5 V deviations, achieving a rise time of 60 ms and a settling time of under 100 ms. The proposed control framework is further validated through hardware-in-the-loop simulations using OPAL-RT OP5707XG, confirming its real-time effectiveness in offshore renewable energy applications.