Mona Bavarian

Control of a heat-integrated co-ionic-conducting solid oxide fuel cell system

A control study of a heat-integrated solid oxide fuel cell system with a BaCe1-xSmxO3-α. type electrolyte is presented. This type of electrolytes exhibit both proton and oxygen-anion conductivity, and the fuel cell has multiple steady states in some operating regions. A multi-loop control system consisting of four proportional-integral (PI) controllers with two coordination rules is used to adjust four manipulated inputs to control the cell solid temperature and outlet voltage. For the temperature control two secondary PI controllers that adjust the duties of an air and a fuel inlet temperature conditioner are used. The set-points of the secondary PI controllers are set by a primary PI controller. Simulation results show that the control system can operate the cell at all steady states, whether stable or unstable. They also indicate that the control system is capable of tracking step changes in the set-points and rejecting piece-wise constant external load disturbances.

Mathematical modeling and steady-state analysis of a co-ionic-conducting solid oxide fuel cell

A mathematical model of a solid oxide fuel cell (SOFC) with a BaCe1-xSmxO3-α type electrolyte is developed. This class of electrolytes exhibits both proton and oxygen-anion conductivity. To develop the model, heat transfer, mass transfer and electrochemical processes are taken into account. The existence of steady-state multiplicity in this class of fuel cells is investigated under three operation modes: constant ohmic load, potentiostatic and galvanostatic. The cell has up to three steady states under the constant ohmic load and potentiostatic modes, and a unique steady state under the galvanostatic mode. This same steady state behavior has been observed in oxygen-anion conducting and proton conducting SOFCs. Interestingly, this study shows that in this class of SOFCs, thermal and concentration multiplicities can coexist; ignition in the solid temperature is accompanied by extinction in the fuel and oxygen concentrations, and ignition and extinction in concentrations of water in the anode and cathode sides, respectively.

Steady-state multiplicity in a solid oxide fuel cell

Steady-state multiplicity in a solid oxide fuel cell (SOFC) in constant ohmic external load, potentiostatic, and galvanostatic operation modes is studied using a detailed first-principles lumped model. The SOFC model is derived by accounting for heat and mass transfer as well as electrochemical processes taking place inside the fuel cell. Conditions under which the fuel cell exhibits steady-state multiplicity are determined. The effects of operating conditions such as the convection heat transfer coefficient, and the inlet fuel and air temperatures and velocities on the steady state multiplicity regions are studied. Depending on the operating conditions, the cell exhibits one or three steady states. For example, it has three steady states at low external load resistances in the constant ohmic external load mode, and at low cell voltages in the potentiostatic mode.