Voltage Hierarchical Control for a DC Microgrid Considering Multiple Fuel Cell Efficiency Optimization

Renewable energy in DC microgrids is characterized by randomness and volatility. Integrating fuel cells and energy storage units can improve the utilization of distributed energy resources and enhance power supply quality. However, existing hierarchical control based on DC bus voltage signals does not fully consider the efficiency characteristics of fuel cells, coordination among multiple fuel cell units, and unified control during both grid-connected and islanded operations. Therefore, this paper proposes a unified control strategy for grid-connected and islanded operation of DC microgrids, considering multiple fuel cell efficiency optimization. First, the voltage hierarchical operation modes are analyzed based on the characteristics of different units and the efficiency curve of fuel cells under grid-connected conditions and islanded conditions. In both grid-connected and islanded conditions, the proposed hierarchical control can maintain voltage stability at each mode and ensure a seamless transition between the mode while keeping the fuel cells operating within the medium-to-high efficiency range. Then, an improved fuzzy control combined droop control based on the efficiency characteristics of fuel cell units is proposed to achieve multiple fuel cells adaptive regulation and efficiency balancing. For adaptive allocation of charging and discharging power and SOC balancing among multiple energy storage units, an improved droop control strategy associated with SOC is adopted. Finally, case studies verify the effectiveness and feasibility of the proposed method are verified through case studies.