## 6 Conclusions  
In this work, the development of a scaled test bench for the emulation of a hybrid fuel cell/battery powertrain was presented. The realization of this test bench was motivated by the need for proper instruments with easy implementation and component availability and with the ability to emulate the behaviour of the powertrain under certain external load profiles and with different EMSs. The paper focused on the design process and on the main practical challenges that can occur during the realization of the test bench. The topology under investigation was composed of a battery pack directly connected to the DC bus and an emulated FC connected to the DC bus through a DC-DC converter. As for the battery pack, two 12 V series-connected lead acid batteries were adopted, mainly because of their low cost and easy integration with the system. The fuel cell was emulated through a programmable power supply, while the external load was simulated using an  
Figure 21: Estimated hydrogen flow and total consumption for the FCS-C300 during the work cycles with attached implements. Figure 20: Estimated hydrogen flow and total consumption for the FCS-C300 during the handling of a trailer work scenarios. electronic load and an additional power supply for the regenerative phases. The power conditioning unit was represented by the DC-DC converter, which was controlled by an Arduino microcontroller according to a PI-based energy management strategy. The microcontroller also had to programme the PS for the emulation of the FC so that it followed a real FC V-I curve to communicate with a PC for data logging, for determining the external load power demand and to control the electronic load. Instead, the load unit power supply was controlled by the PC through USB communication since it did not have the possibility to be analogically controlled. To monitor the main operating parameters of the test bench, voltage and current transducers were adopted, the signals of which were collected and translated by the microcontroller. To experimentally evaluate the behaviour of the system, a few tests were performed. Firstly, the FC emulation was validated by comparing the emulated FC curve with the real reference FC curve. Secondly, the DC-DC converter and diode assembly efficiency were evaluated. The results showed a peak efficiency of around 93%; however, the efficiency was greater than 88% over almost the entire load spectrum. Moreover, a thermal analysis was performed to monitor the temperatures reached by the components. The highest temperature recorded was approximately 67.5 \({}^{\circ}\)C and was reached with 300 W of power flow from the emulated FC, which corresponded to its nominal power. To calibrate the PI controller gains, a step-load system response test was exploited and a dynamic stress test was used to evaluate the behaviour of the system under discrete power level variations. Finally, two tests were conducted based on real work scenarios obtained by monitoring a real agricultural tractor with a 73 kW diesel engine. The results showed that the load unit successfully managed to perform the external load profile, and the power conditioning unit was able to split the power between the FC and the battery pack according to the EMS strategy and within the constraints regarding the low-dynamic behaviour of the fuel cell. Moreover, an estimation of the hydrogen consumed in the case of the implementation of the real FCS-C300 was performed, showing in the proposed test scenarios a peak virtual consumption of 4.2 \(\times\) 10\({}^{-3}\) g/s. Thus, it is possible to assert that the system successfully emulated the powertrain according to the following aspects:  
* The load unit was able to reproduce the power absorption with a good level of accuracy;
* The power conditioning unit was able to perform the proposed EMS;
* The control unit managed to monitor the main operational parameter of the system and to communicate with each subsystem.