Simultaneous estimation of states and inputs in a planar solid oxide fuel cell using nonlinear adaptive observer design

In this paper we design an observer for online estimation of species concentrations in a steam reformer based Solid Oxide Fuel Cell (SOFC) system with anode recirculation and with methane as fuel. Since in SOFCs steam reforming occurs both in the reformer and in the fuel cell, a large number of concentration sensors are necessary for accurate control of critical performance variables such as utilization and steam-to-carbon-ratio. The purpose of the observer is to reduce the number of sensors required for control. In contrast to existing observers which are either designed for chemical reactors or for fuel cells exclusively, our design considers the coupled dynamics of the reformer and the fuel cell. We design an adaptive observer where the rates of reforming reactions are treated as slowly varying unknown parameters. Using a few concentration sensors we show that all other species concentrations, molar flow rates, and reaction rates in the fuel path can be dynamically estimated. Simulation results are provided in support of the proposed design.

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An Adaptive Observer for Recirculation-Based Solid Oxide Fuel Cells

Journal of Dynamic Systems Measurement and Control ◽

10.1115/1.4033271 ◽

2016 ◽

Vol 138 (8) ◽

Cited By ~ 2

Author(s):

Singith Abeysiriwardena ◽

Tuhin Das

Keyword(s):

Fuel Cell ◽

Species Interactions ◽

Cell Damage ◽

Observer Design ◽

Solid Oxide ◽

Adaptive Observer ◽

Oxide Fuel ◽

Computationally Efficient ◽

State Equations ◽

Reduced Order Observer

In this paper, we present an observer design for online estimation of species concentrations in recirculation-based solid oxide fuel cell (SOFC) systems with integrated reformers. For the system considered, on-board reforming of methane results in mixture of several species of different concentrations along the fuel path. The presence of a fuel reformer gives way to coupling of system equations, in turn, increasing species interactions and complexity of the state equations. The knowledge of concentration of species at key locations in the fuel cell can help prevent cell damage and improve longevity. In this regard, the use of sensors to determine species concentration is an invasive process which is expensive to both utilize and maintain. While existing observers are designed either for chemical reactors or for a fuel cell exclusively, the proposed strategy aims to improve on that by considering a combined reformer and fuel cell and designing a nonlinear adaptive observer using readily measured concentrations and selected variables. For estimating certain critical indicators, such as fuel utilization, state transformations have been used in the design to obtain a more versatile and computationally efficient reduced order observer. The study develops detailed stability analysis of the observers and quantifies the effect of uncertainties on observer performance.

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