**5. Conclusions**

Several studies have shown that classical APU plays an important role in pollution emissions. This has led to the search for new cleaner technologies, so fuel cells have great potential. Major aircraft manufacturers have shown great interest in replacing conventional auxiliary power sources with auxiliary power sources based on fuel cells. In this paper, an auxiliary power source based on the PEM-type fuel cell is proposed. This hybrid source contains fuel cells, batteries, converters, and source management system. The results obtained from the numerical simulation of the proposed auxiliary power source show that it offers a higher peak power than each individual component while maintaining a power density, which is vital for an aircraft. It is also observed on time variations of the battery and battery output currents that the power flow is well managed between the fuel cell and the battery. Another advantage of the hybrid power source is that during the process of starting and transient charging of the system the battery will reliably support the electrical network of the aircraft. The slow performance of the PEM fuel cell during start-up/charge/discharge operations is offset by the fast battery dynamics. If the charging power is subject to sudden changes, the battery is the one that responds immediately so that the electrical system remains in normal operating conditions.

The energy management system proposed in this paper can be used successfully for the applications with high pulsed loads and transient power requirements.
