Environmental Engineering Reference
In-Depth Information
Table 6.3 Technical
specifications of the DC-DC
converter
Type of converter
DC-DC
Nominal power
2.8 kW
Maximum input voltage
36 V
Minimum input voltage
16 V
Nominal input voltage
24 V
Nominal output voltage
48 V
Output current
1-50 A
Table 6.4 Technical
specifications of the lead-acid
battery pack
Type of battery
Lead-acid
Nominal voltage of the pack
48 V
Nominal voltage of each battery
12 V
Number of batteries
4
Battery capacity
38 Ah
Downstream of the converter, a DC bus connects this device in electric parallel
with the battery pack to supply the electric drive. Voltage and current sensors are
installed on batteries and upstream-downstream the DC-DC converter, as shown
in Fig.
6.2
, to monitor the electric energy flows between the different components
of the propulsion system. The DC-DC converter allows the stack output power to
be varied according to the selected control strategy. Furthermore, some security
switches are adopted, in order to instantaneously disconnect the electric load from
battery pack and/or stack. An I/O laboratory board is used for data acquisition and
setting of the electrical parameter affecting the DC-DC converter behavior.
A lead-acid battery pack is used as electrical energy storage system, constituted
by 4 units, each one of 12 V and 38 Ah. The choice of using lead-acid batteries is
essentially motivated by its low cost and good efficiency [
2
]. The technical
specifications of the battery pack are reported in Table
6.4
.
A dedicated acquisition system is connected to the single cells of the stack to
monitor and save data of cell voltages during the different runs. Moreover, a d-
Space board was dedicated to acquire and control all the signals of the fuel cell
power train.
The control strategies are programmed in Matlab-Simulink, compiled in C++
and then downloaded into the DSP processor of the d-Space board. The controlled
management of the fuel cell system during the dynamic tests operates on hydrogen
purge, air flow rate regulation (stoichiometric ratio), external humidification, and
stack temperature.
6.2 Efficiency Calculations
In this paragraph, the efficiency calculations to evaluate both the fuel cell system
alone and the overall propulsion system are reported starting from the parameters
