Baum, Lukas

Der Luftfahrt stehen in naher Zukunft einige notwendige Veränderungen bevor. Während die Flugkilometer voraussichtlich weiter steigen werden, müssen die Emissionen global drastisch gesenkt werden. Neben Antriebssystemen, die die Emissionen reduzieren, scheint das Ziel des emissionsfreien Fliegens nur durch elektrische Antriebe realisierbar zu sein. Eine hier untersuchte Möglichkeit stellt das Fliegen mittels Wasserstoff-Brennstoffzellen dar. Mithilfe von Wasserstoff aus erneuerbaren Energien kann ein Antriebssystem ohne CO₂ oder NOₓ Emissionen verwirklicht werden. Dazu wird ein neuartiges Antriebssystem nach dem H₂-to-Torque-Konzept vorgestellt, wodurch auf eine vereinfachte Elektronik ohne Gleichspannungswandler zurückgegriffen werden kann. Durch ein Multisegment-System enthält das Antriebssystem eine inhärente Redundanz, die im Fehlerfall den sicheren Betrieb weiterhin gewährleistet. Die elektronische Architektur beinhaltet Motor String Power Control Units, welche den hybriden elektrischen Energiefluss aus Brennstoffzelle und Batterie regeln. Nachgeschaltet sind jeweils Motor Control Units, die die Gleichspannung in eine Wechselspannung umwandeln, um den Elektromotor anzutreiben.

To increase the service life or durability of PEM fuel cells, no-load operation at open circuit voltage has to be avoided to reduce destructive electrochemical effects. This paper shows two approaches to realize a regulated base-load with a fuel cell protection unit for application in aircraft multi-powertrain-concepts. Firstly, a clocked MOSFET in the form of a chopper circuit, and secondly, a MOSFET in linear operation as current source. This contribution describes the design concept of both approaches and the validation of prototypes in a laboratory pHiL-environment. Both approaches are proven to be viable solutions, with the current source approach resulting in smoother operation.

Hydrogen fuel cells have become one of the most viable power sources for electric aircraft. Models representing the electrical behavior of the fuel cell stack over the full dynamic operation region are essential for the development of power electronic energy systems powered by fuel cell stacks. This work presents an electrical equivalent circuit model for PEM fuel cell stacks representing the static and dynamic electrical behavior of the fuel cell stack under pulsed loads up to frequencies of 10 kHz. Dynamic phenomena on time scales slower than the considered timescale of power-electronic switching, such as reactant flow, membrane hydration, and temperature effects, are considered stationary. The parameterization method proposed is developed on measured data from a 110 W PEM fuel cell stack and validated with a set of measured data from a 2 kW stack. The time-domain simulated behavior of the parameterized model shows an accurate representation of the measured behavior: the parameterized model reproduces both the static polarization behavior and the behavior under high-frequency pulsed loading with errors of less than 1% with respect to the nominal stack voltage. The model is suitable for dynamic simulation of power electronic systems directly connected to fuel cell stacks and can be parameterized without special electrochemical impedance spectroscopy measurements.

This work presents the development and parameterization of a dynamic equivalent circuit model of proton exchange membrane (PEM) fuel cell stacks. The model represents the static and dynamic behavior of the fuel cell stack under pulsed ohmic loading up to switching frequencies of 10 kHz. The model is developed using established mathematical descriptions of fuel cell processes. The model is then parameterized and validated using measurement data obtained from an 11 cell, 110 W PEM fuel cell stack.