Comparing different electrical architectures for a parallel PEMFC-battery hybrid electric lightweight vehicle

In the field of hybrid powertrains for sustainable mobility, fuel cells are a promising solution to improve the performance of battery electric vehicles by implementing PEMFCs as REx. The selection of proper power electronics, such as converters, is fundamental to guarantee tight control and electrical stability. In this paper, a comparison between different electrical architectures of an electric hybrid PEMFC/battery vehicle is proposed: a light battery electric quadricycle (EU L6e) with four in-wheel motors is hybridized with a 3 kW open-cathode PEMFC as REx in parallel layout. The battery accounts for a bi-directional DC/DC converter to stabilize the voltage at 48V, needed by EMGs. A passive architecture is firstly considered, with the PEMFC stack connected to the battery poles; the second architecture is a semi-active one, with the PEMFC connected after the battery DC/DC converter; the last considered layout is active, with a unidirectional DC/DC converter between PEMFC and electrical system. In the first case, the lack of a dissipative component improves the energy efficiency of the powertrain; however, the stack cannot be directly controlled, following instead the battery voltage. The semi-active layout is similar to the passive one, with a constant voltage set by the battery converter. Active architecture offers an additional degree of freedom: the PEMFC stack can work around optimal operating points, while guaranteeing the power requested by control strategy; on the other hand, the additional converter is a passive element that absorbs energy from the system, worsening powertrain final efficiency. Results show that passive architecture is preferrable when no optimal control strategies are considered, reaching a fuel consumption of 0.24 kg/100 km; the semi-active layout shows little worsening of 1%. The active layout shows best performances implementing optimal control strategies, reducing fuel consumption down to 4% and increasing the final powertrain efficiency by 1%.