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Optimal Design and Operation of Microfabricated Fuel Cell Systems

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Abstract:
Batteries are the predominant technology for the power supply of portable electric and electronic devices up to 50 W. However, batteries have relatively low energy densities, are costly and have a large life-cycle environmental impact. Out of the alternatives that are available, we focus on micro-scale power generation devices based on the electrochemical conversion of common fuels and chemicals in fuel cells. These micro processes have the potential to yield much higher energy densities than state-of-the-art batteries. In this presentation, procedures for the optimal design and operation of micro power generation employing fuel cells are described. Because the underlying physico-chemical phenomena are complicated and intrinsically coupled, one cannot rely on engineering intuition only to determine the optimal design and operation. The use of mathematical models along with systematic optimization methods based on mathematical programming is clearly warranted. Optimal design and steady-state operation is addressed in the rst part of the presentation. For a given power demand, this problem is to determine values of the design and operational variables so as to maximize the system energy density subject to safety and reliability constraints. It yields a constrained optimization formulation with multi-stage DAEs embedded. The solution and post-optimal sensitivity analysis of this problem is presented in light of recent developments on adjoint sensitivity analysis for multi-stage DAE systems. Transient operation is considered in the second part of the presentation. For start-up purpose, the devices will most likely be coupled with a small battery (or ultra-capacitor). The objective of the start-up problem is then to bring the system to a desired operating point with a minimal total mass of the system (battery and fuels), while meeting the nominal power demand at any time and satisfying the operational restrictions. The model for the fuel cell stack consists of PDAEs with multiple time scales and numerical techniques that exploit a separation of these time scales are used for ecient and reliable solution of the optimal control problem.

Type of Seminar:
Public Seminar
Speaker:
Dr. Benoit Chachuat
Laboratoire d'Automatique, Ecole Polytechnique Federale de Lausanne (EPFL), Station 9
Date/Time:
Jun 05, 2008   9:30 /
Location:

ETH Zentrum, Building ETL , Room K 25
Contact Person:

Prof. Manfred Morari
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Biographical Sketch:
Benoit Chachuat is a Research Associate and Lecturer at the Ecole Polytechnique Federale in Lausanne (EPFL), Switzerland, since September 2005. He received his Ph.D. in Chemical Engineering, in 2001, from the Institut National Polytechnique de Lorraine (INPL), Nancy. Before joining EPFL, he worked as a Postdoctoral Associate at INRIA, Sophia-Antipolis, for 1 year in bioprocess control, then at MIT, Cambridge, for 2 years in process systems engineering. His main research interests are in the area of dynamic optimization and control, with emphasis on real-time optimization and global optimization. Application interests range from chemical process design and operation to systems biology.