Control Scheme of a Solid Oxide Fuel Cell System for Regional Aircraft

Abstract

In this work, the control scheme of the hydrogen solid oxide fuel cell (SOFC) propulsion system of the DLR-internal project H2EAT is presented. The application of this system is planned for a regional aircraft with an entry-into-service in the year 2050. For the operation of the fuel cell, it is necessary to control multiple variables such as the pressure, the mass flow and the electric power output. Additionally, the temperature gradient, both spatially and temporally, is of paramount importance. Strict temperature gradients have to be complied in order not to damage the fuel cell. The control system is realized by implementing PI controllers as they are favorable for an integrated system due to their low computational effort. The considered fuel cell system operates a pressurized fuel cell stack together with a combustion chamber after the SOFC to burn the excess hydrogen. A turbine then partly recuperates the heat energy by relaxing the exhaust gas stream to ambient conditions. Dynamic simulations over an aircraft mission are performed within the framework of Modelica and the in-house, open source ThermoFluidStream (TFS) library. The control scheme presented in this work is well suitable to operate the fuel cell system over the complete mission. Although small improvements can be made to the control of the temperature gradients and the control of the pressure level.