Regelung und Optimierung eines Brennstoffzellensystems für die Hausenergieversorgung

Eide, Björn

kassel university press, ISBN: 978-3-89958-696-1, 2009
(Erneuerbare Energien und Energieeffizienz - Renewable Energies and Energy Efficiency 12)

URN: urn:nbn:de:0002-6976

Zugl.: Kassel, Univ., Diss. 2008

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Content: The objective of this thesis was the development of a control concept as well as the optimisation of the system integration and the overall efficiency of a fuel cell system for residential application for the cogeneration of heat and power. For this purpose a laboratory version of a heat integrated 1 kWel fuel cell system on the basis of PEM fuel cells including the hydrogen generation by steam reforming was designed.

An important aspect of optimising the system integration was the modification of the system for the recirculation of the anode off-gas to the reformer burner to increase the electric system efficiency. Moreover the cooling of the preferential oxidation reactor and the reformer product gas cooling were integrated in the fuel cell cooling circuit to improve the heat integration as well as to reduce the system complexity.
For system analysis and control development a dynamic zero-dimensional model based on energy and material balances was developed in MATLAB®/Simulink®. For optimising the operating performance as well as the overall efficiency the system integration and operating parameters were varied with the simulation model. Parameters with the highest potential regarding the electric system efficiency are the reformer temperature and the fuel utilisation of the fuel cell stack.

To ensure a stable and energy efficient operation and to avoid critical operating conditions a control concept was developed to keep operating parameters constant for steady state and dynamic operation. The control development was supported by simulations with the dynamic system model. The central control of the system is the control of excess hydrogen providing for a constant fuel utilisation in the fuel cell stack. This control is the basis for the power led system control.

The control concept which was implemented in LabVIEW™ was validated by dynamic measurements. During a load change the maximum rate of change for the electric power is 5 W/s whereas the fuel utilisation of the fuel cell stack as well as other operating parameters are kept constant. Thereby operating ranges of the reformer-shift reactor, the preferential oxidation reactor and the fuel cell stack are maintained even during dynamic operation.

The characterisation of the fuel cell system regarding time constants and efficiencies was carried out by dynamic and steady state measurements. The time from cold start-up to steady state operation adds up to less than one hour. The maximum DC net efficiency (without inverter losses) of the laboratory version reaches 24 %. In the upper load range values of 55 % were measured for the thermal efficiency. The sum of thermal efficiency and electrical DC net efficiency yields the overall efficiency which can reach up to 80 % depending on the operating state.

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