Abstract
Several methods to prevent fuel starvation in solid oxide fuel cells are developed and investigated. Fuel starvation can occur during transients, if fuel is consumed in the fuel cell faster than it can be supplied by the fuel processing and delivery system. It is demonstrated through simulation that fuel depletion can occur in the fuel cell if no corrective action is employed. Fuel starvation can be prevented by the use of rate limiters, reference governors, and modifications to the fuel-flow controller. The various methods to prevent fuel depletion within the fuel cell are developed and compared. Analysis indicates that reference governors can avoid hydrogen depletion with much less of an impact on transient load following capability than rate limiters. Hence, various reference governors ranging in level of fidelity were developed and compared for performance. It was further demonstrated that with knowledge of the fuel preprocessor response, it is possible to manipulate the fuel flow to minimize reformer flow dynamics, minimizing the need to govern the fuel cell transient capability.
Highlights
Fuel cell systems with fast load following capabilities offer increased flexibility over systems with limited transient capability
A fast fuel cell system will allow use in a larger number of applications and can limit the undesirable dynamics put onto the utility grid, which often is an important barrier to greater fuel cell adoption [1]
This paper focuses on the fuel starvation constraint since this constraint will affect all solid oxide fuel cell (SOFC) systems regardless of the specific configuration, and is considered a key and fundamental limiting factor in power following [6]
Summary
Fuel cell systems with fast load following capabilities offer increased flexibility over systems with limited transient capability. A fast fuel cell system will allow use in a larger number of applications and can limit the undesirable dynamics put onto the utility grid, which often is an important barrier to greater fuel cell adoption [1]. Various control concepts to prevent hydrogen starvation that result in different transient capabilities are investigated . This investigation identifies methods for implementing advanced controls to improve fuel cell transient capability without making major hardware changes, and provides fuel cell designers a basis to evaluate controller cost benefits and risks in commercial systems. In order to develop load following fuel cells several constraints need to be considered during
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