**4. Conclusions**

Seven control topologies are identified based on the three ways (inputs) to regulate the FC power: via the FC boost converter, and via the fueling regulators. One of these inputs will control the generated FC net power, ensuring the DC power flow balance under variable load. The other two or only one are used for optimization the FC system in order to minimize the fuel consumption. Thus, seven strategies are analyzed for an FC system under constant and variable load demand.

The conclusions of the analysis performed for all strategies are as follows:


The next work will be focused on comparative analysis of fuel economy for the four switching strategies identified, using the RTO6 strategy as reference. Besides the RTO6 strategy (which uses two GES controllers), the RTO4 strategy (which uses only one GES controller) can become a possible strategy in the low range of load demand, due to simple implementation and minor differences in fuel economy compared to RTO6 strategy under constant load. The cases of strategies SW2 and SW4 remain to be further analyzed in order to decide which strategy is best from different points of view: performance, cost, complexity of implementation. For example, the cost and complexity of implementation is lower for the SW4 strategy compared to strategies SW1, SW2, and SW3 due to the use of one GES controller instead of two GES controllers. The threshold of the load demand (which will be used in switching strategies to split the loading range) will be set after a sensitivity analysis for all switching strategies using a threshold in the range of 4 kW to 6 kW.

**Author Contributions:** Conceptualization, Methodology, and Validation: N.B., V.A.S., A.C.C.; Writing—Review & Editing: V.A.S.; A.C.C., N.B.

**Acknowledgments:** This work was supported by a grant of the CNCS/CCCDI-UEFISCDI within "Brancusi" European and international cooperation, PN-III P3-3.1, project "Global Maximum Power Point Tracking algorithms for Photovoltaic Systems under rapid changes in climatic conditions".

**Conflicts of Interest:** The authors declare no conflict of interest.
