T. Kut

Fuel Cell System Optimization Using Bypass Converters

The reduction of CO2 emissions, and therefore the increase of ecoefficiency, is one of the most important challenges for the aircraft industry. An approach could be the more electric aircraft concept. Within this concept, the traditional auxiliary power unit could be replaced by a multifunctional fuel cell system. For integration into the ±270 Vdc grid, it is necessary to convert the load-dependent fuel cell output voltage using a direct current-to-direct current converter. The converter usually is designed for the maximum available fuel cell power. This paper deals with an adaption of the fuel cell output voltage to achieve downsizing of the converter. The proposed converter structure with an additional bypass has weight-saving effects and improves overall system efficiency.

Integration scenarios to improve fuel cell dynamics for modern aircraft application

An approach to achieve a high efficiency for energy transfer in modern aircraft could be the More Electric Aircraft concept. According to this, the replacement of the conventional auxiliary power unit by a multi functional fuel cell system reduces the emission of carbondioxide significantly and can increase the efficiency. However, requirements on the electrical system dynamics are higher than currently available fuel cell systems can provide. To improve the electrical dynamics of the fuel cell especially during high peak power demands different methods are considered. This paper compares four possible integration scenarios to improve the system dynamic. Special characteristics as the additional system weight, the stored available energy, the complexity as well as the feasibility under the required conditions are considered. For supplementing the theoretical concepts, a prototype of a super capacitor short-time energy storage was built and integrated into an existing fuel cell test bench. Therefore, a voltage balancing as well as an overvoltage protection is implemented. Measurements show the improved dynamic of the hybrid fuel cell system.

Concept analysis of an electrical fuel cell integration in modern aircraft

The reduction of pollutant emissions and hence the increasing of the eco efficiency of future aircraft is one of the major challenges for the aviation industry. Executing the More Electric Aircraft concept can be one approach to achieve these high targets. One idea in this context is to substitute the traditional Auxiliary Power Unit by a Multifunctional Fuel Cell System. It is necessary to transform the load-dependent fuel cell stack output voltage to the intended electrical onboard grid voltage level. To increase the efficiency and reduce the system weight an optimized electrical integration is presented. Measurement results on a test bench confirm the theoretical concepts.