## 1 Introduction
As for the power sources, the experimental setup consisted of a 1.2 kW air-cooled proton-exchange membrane fuel cell system, two series-connected valve-regulated lead acid (VRLA) batteries and four series-connected ultracapacitor modules. To simulate the power demand, a DC load was used, while for emulating the braking operation, a motor/generator unit was exploited. [PERSON] et al. [39] developed an experimental setup to evaluate the behaviour of a battery/fuel cell hybrid powertrain and a battery/supercapacitor/fuel cell hybrid powertrain, applying an EMS based on a finite state machine. [PERSON] et al. [40] experimentally investigated the behaviour of a fuel cell/supercapacitor hybrid system under an adaptive power split control strategy. [PERSON] et al. [41] explored a composite cost-optimal energy management strategy based on a load-following control for a fuel cell/battery powertrain. The EMS principle was to split the power among the two power sources such that the lower frequency part of the power demand was handled by the FC, while the higher frequency part was followed by the battery pack. Moreover, the EMS took into account both hydrogen consumption and source ageing to optimize the power distribution. For the experimental tests, a test bench was developed. In this case, the fuel cell was emulated by a programmable DC power supply, while on the load side, an electronic load was employed. An Arduino was used to collect data from the sensors in the power stage, to communicate with a personal computer and to control the DC-DC converter according to the EMS. [PERSON] et al. [42] developed a laboratory test setup for the emulation of a direct hybrid electric powertrain. In this work, both the fuel cell and the batteries were emulated by programmable DC power sources, whose control was based on a database of their characteristic voltage-current curves. Moreover, both of the power sources were connected without DC-DC converters. It can be stated that in the literature there are many papers that have investigated the topologies and the energy management strategies of hybrid fuel cell powertrains through experimental test benches. However, little attention has been dedicated to the development of software and hardware tools for the realization of the experimental setup. As a matter of fact, most of the existing studies do not provide significant information about the realization of the experimental setups for powertrain testing. Thus, the novelty of this paper lies in providing a simple design procedure for the development of a scaled test bench for the emulation of a fuel cell/battery powertrain. In the proposed setup, the FC is connected to the DC bus through a DC-DC converter, while the batteries are directly connected. The external load is emulated using a DC electronic load and a power supply, which are both programmable. The fuel cell is emulated by another programmable DC power supply controlled so that it reproduces the realistic voltage-current (V-I) curve of a real fuel cell. The power conditioning unit is represented by the DC-DC connection, which is controlled by two signals: a voltage reference signal and a current reference signal. In order to collect data from the power stage, current and voltage transducers are exploited. An Arduino is used as control unit of the test bench due to its easy programming. After defining a simple PI-based control strategy, the system is experimentally validated. The advantages of the proposed experimental setup are the simplicity and easy availability of the required components, the safety and the modularity. In particular, since the FC is emulated using a programmable power supply, all the issues related to the use of a real fuel cell system are not present. Going into detail, the paper is organized as follows: Section 2 briefly introduces the case study and the reference powertrain considered for the bench development. Section 3 describes the test bench layout and its main components. Section 4 explains the proposed PI-based control strategy.