On control concepts to prevent fuel starvation in solid oxide fuel cells

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.

Dynamic modeling and evaluation of solid oxide fuel cell – combined heat and power system operating strategies

“…cell system modeling methodology previously developed, verified and used for dynamic system modeling and control development [12][13][14][15][16][17]. The previously developed simple-cycle SOFC system includes and physically resolves the dynamic governing equations of a steam reformer, blower, heat exchangers, and combustor in addition to the fuel cell stack.…”

Two-Layered Real-Time Optimization of a Solid Oxide Fuel Cell Stack

“…From a safety standpoint, two of the outputs, U cell and ν, represent key constraints that must be respected so as to avoid fast system degradation (Gaynor et al (2008)). …”

“…As highly integrated chemical systems, they are subject to a number of safety and physical constraints, all of which must be respected in a real environment. Consequently, feedback control is important, and several control studies have been carried out recently in this area (Golbert and Lewin (2004); Gaynor et al (2008); Zhang et al (2008)). On the other hand, research on the optimization of fuel cell processes remains somewhat scarce.…”

Load-following active power filter for a solid oxide fuel cell supported load

“…Hence, the current model implements a more physically-based delay by modeling the fuel flow as the volumetric filling of a plenum volume and a flow restriction as was developed and explored in [29,30] and used to develop SOFC control strategies in [24,25,31]. The change in pressure of a plenum volume can be derived from the ideal gas law and is determined by the following equation:…”

“…2, where r vmin is the minimum voltage setpoint, y v is the voltage measurement, r i is reference current, K v and Sat are feedback gain and saturation, and u i is the input current. This type of governor is explored and discussed in detail in [31]. The voltage feedback current governor provides advantages over the utilization-based governor implemented in [5] that include: (1) eliminating the need to measure fuel flow rate, and (2) allowing fuel stored within the anode compartment to be consumed to maximize the transient load-following capability.…”