Design and protection of a high voltage DC onboard grid with integrated fuel cell system on more electric aircraft

A major demand of the aviation industry is the reduction of emissions in combination with cost efficiency improvement. One possible approach to face this challenge is the replacement of the conventional auxiliary power unit by a fuel cell system within a “more electric aircraft” design. In order to integrate a fuel cell system into the grid architecture of modern aircraft new protection arrangements have to be developed. For availability and redundancy the fuel cell system has to be split into two subsystems. Furthermore the two subsystems have to be connected in parallel to bundle the power delivery and to balance the power. This complex grid structure requires smart safety arrangements to protect the grid in case of failures. In this contribution two safety concepts for doubly fed ring structures are introduced and analyzed. The directional stepped-curve distance-time protection and the impedance protection are illustrated and simulated. Concluding the results of the two concepts are compared.