## 5 Conclusions  
This paper performed a systematic evaluation of the strategies referred to as air/fuel-PFC, air-PFC, fuel-PFC, and sFF, with the latter being a commercial benchmark used in the analysis of the obtained results. The following findings resulted for FC system (FC/ESS/RES HPS with \(P_{RES}=0\)):  
* The four strategies mentioned above were analyzed as the performance and safe operation of the FC system and battery pack using indicators such as fuel economy and OER. * Following the analysis, the fuel economy strategies for the FC system were ordered starting with the best strategy: air/fuel-PFC, air-PFC, fuel-PFC, and sFF. * The percentage of hydrogen economy for an air/fuel-PFC strategy compared to the strategies sFF, air-PFC, and fuel-PFC is 6.60%, 7.53%, and 12.60% of the total hydrogen consumption of these strategies (see Table 2). * FC net power is generated based on the power flow balance (2) and on a PFC-based strategy to operate the battery in charge-sustained mode (see the 3 rd plot in Figures 4-8), increasing their lifespan. * OER varies within the safe limits (see Figure 9). The results obtained for the FC system and battery pack were validated for an FC/ESS/RES HPS with \(P_{RES}>0\), producing the following findings:  
* From point of view of the hydrogen economy, the same order of the strategies were obtained for an FC/renewable HPS: air/fuel-PFC, air-PFC, fuel-PFC, and sFF. * The integration of the FC system into a renewable HPS will increase with 0.7% of the fuel economy of the air/fuel-PFC strategy for the FC/renewable HPS compared to the FC system (see last row of Table 6) due to the FC system operating at lower power when the renewable energy is available. * PFC-based strategies still operate the battery pack in the charge-sustained mode (see the 4 th plot in Figures 10-13) even under variable RES power, increasing battery lifespan. * OER still varies within the safe limits (see Figure 15). Thus, the novelty and contribution of this paper can be summarized as follows:  
* The use of a PFC-based strategy will establish the FC-system fueling flows so that FC net power compensates the balance of power flows on the DC bus using a battery stack with lower capacity than in other strategies proposed in the literature due to the battery pack operating in charge-sustained mode. The next work will analyze whether only the ultracapacitors pack can dynamically compensate the power flow balance via a bidirectional DC-DC power converter. * The maximization of the fuel economy was obtained by using a real-time optimal control of the boost power converter. * The operation of FC system under a PFC-based strategy and optimal fuel economy control is done in safe operating conditions, maintaining OER within the safe limits. However, before implementing the air/fuel-PFC strategy, these findings should be validated by several future studies using different profiles of charging demand and renewable energy. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter [unit]** & **strategy** & **Air-PFC** & **Fuel-PFC** \\ \hline \(\
icefrac{{\psi_{Fuel}}}{{T_{(strategy)}}}\) [\%] & 6.60 & 7.53 & 12.60 \\ \(\
icefrac{{\psi_{Fuel}}}{{T_{(strategy)}}}\) [\%] & 7.28 & 8.23 & 13.43 \\ \(\
icefrac{{\psi_{Fuel}}}{{T_{(strategy)}}}-\
icefrac{{\psi_{Fuel}}}{{T_{( strategy)}}}\) [\%] & 0.68 & 0.70 & 0.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Fuel economy of the FC system and FC/renewable HPS using the strategy air/fuel-PFC compared to the strategies sFF, air-PFC, and fuel-PFC. **Author Contributions:** Conceptualization, methodology, and writing--Original draft preparation: N.B. and P.T. ; validation: M.C., M.I., and M.O. ; supervision: M.V. and E.C. ; formal analysis: N.B. and P.T. ; writing--Review and editing: N.B., M.S.R., and I.S.S.S. All authors have read and agreed to the published version of the manuscript.