Dynamic Analysis and Control of a Planar IT-SOFC System

2009 ◽  
Author(s):  
A. Salogni ◽  
P. Iora ◽  
S. Campanari
Keyword(s):  
Steady State ◽  
Fuel Cell ◽  
Dynamic Model ◽  
Characteristic Curve ◽  
Cell System ◽  
Internal Reforming ◽  
Internal Cell ◽  
Layer Region ◽  
Air Channels ◽  
And Control

This paper analyzes the dynamic behaviour of a 5 kW fuel cell system based on planar co-flow Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) stack, with internal reforming. The system is composed by the SOFC stack, a combustor of the cell exhausts, two heat exchangers for fuel and air preheating and the related control valves, where the air temperature at the stack exit and the fuel utilization is controlled by means of a PI (proportional integral) device. The model of the stack is based on a lumped parameters dynamic model of a single cell, which is composed of the fuel and air channels, the electrochemically active three layer region representative of the anode, the cathode and the electrolyte. The stack model is first used here for a qualitative steady-state validation, reproducing the cell characteristic curve. Then it is presented the dynamic model of the system, which has been implemented using an a-causal software based on the open-source Modelica modelling language, which allows for future integration in complex power-plant configurations. After a description of the plant layout and of the dynamic model, we present and discuss the results obtained by applying the PI controls to different load changes and with different tuning of the controller parameters, evidencing the amplitudes of load changes, the extent of the transient phase to the new steady-state conditions, the internal cell temperature distribution and the thermal gradients along the PEN structure, giving the possibilities to adapt the control system to the requirements of specific SOFC technologies.

Performance Evaluation of Dynamic Model of Compact Heat Exchange Reformer for High-Temperature Fuel Cell Systems

2013 ◽  
Vol 11 (1) ◽  
Author(s):  
Jeongpill Ki ◽  
Daejong Kim
Keyword(s):  
Steady State ◽  
Heat Exchanger ◽  
Fuel Cell ◽  
Heat Exchange ◽  
Dynamic Model ◽  
Operating Conditions ◽  
Transfer Model ◽  
Thermal Dynamics ◽  
Internal Reforming ◽  
Experimental Apparatus

Solid oxide fuel cell (SOFC) systems are the most advanced power generation system with the highest thermal efficiency. The current trend of research on the SOFC systems is focused on multikilowatt scale systems, which require either internal reforming within the stack or a compact external reformer. Even if the internal reforming within the SOFC stack allows compact system configuration, it causes significant and complicated temperature gradients within the stack, due to endothermic reforming reactions and exothermic electrochemical reactions. As an alternative solution to the internal reforming, an external compact heat exchange reformer (CHER) is investigated in this work. The CHER is based on a typical plate-fin counterflow or coflow heat exchanger platform, and it can save space without causing large thermal stress and degradation to the SOFC stack (i.e., eventually reducing the overall system cost). In this work, a previously developed transient dynamic model of the CHER is validated by experiments. An experimental apparatus, which comprises the CHER, air heater, gas heater, steam generator, several mass flow controllers, and controller cabinet, was designed to investigate steady state reforming performance of the CHER for various hot air inlet temperatures (thermal energy source) and steam to carbon ratios (SCRs). The transient thermal dynamics of the CHER was also measured and compared with simulations when the CHER is used as a heat exchanger with inert gas. The measured transient dynamics of CHER matches very well with simulations, validating the heat transfer model within the CHER. The measured molar fractions of reformate gases at steady state also agree well with the simulations validating the used reaction kinetics. The transient CHER model can be easily integrated into a total integrated SOFC system, and the model can be also used for optimal design of similar CHERs and provides a guideline to select optimal operating conditions of the CHERs and the integrated SOFC system.

Dynamic Simulation of the Anodic Side of an Integrated Solid Oxide Fuel Cell System

2006 ◽  
Author(s):  
A. Traverso ◽  
F. Trasino ◽  
L. Magistri
Keyword(s):  
Steady State ◽  
Fuel Cell ◽  
Solid Oxide Fuel Cell ◽  
Dynamic Model ◽  
Characteristic Temperature ◽  
Cell System ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
State Tests

A new dynamic SOFC model was integrated with the simulation modules of other system components (i.e.: reformer, anodic off-gas burner, anodic ejector) to construct a system model that could simulate an integrated 250 kW SOFC hybrid system. This work describes the preliminary results obtained for the anodic loop, which was studied in order to obtain a complete time characterization of its time-dependent behavior. The new dynamic model was then compared with an existing model for an integrated planar pressurized Solid Oxide Fuel Cell at the steady state. The two models differed due to their levels of complexity and calculation times: the first one was meant for real-time applications, hence retaining the basic dynamic information but including relevant simplifications in the internal information on fuel cell behavior; the second one was used for more accurate predictions at the steady-state, but required longer simulation times. The unsteady-state tests with the new dynamic model showed that the characteristic voltage transient due to changes in SOFC hydrogen concentration had a time scale that was of the order of fractions of seconds while the characteristic temperature transient was of the order of hours. The frequency characterization of the anodic loop with phased oscillations in the fuel flow and stack current enabled us to correlate the inner SOFC anode features with the anodic loop response, thus providing useful indications for designing robust anodic loop controllers.

On Maximizing the Steady-State Efficiency of a Multi-Stack Fuel Cell System

2018 ◽  
Author(s):  
Neigel Marx ◽  
Daniel Hissel ◽  
Frederic Gustin ◽  
Loic Boulon ◽  
Kodjo Agbossou
Keyword(s):  
Steady State ◽  
Fuel Cell ◽  
Cell System ◽  
Fuel Cell System

Proton Exchange Membrane Fuel Cell System Identification and Control: Part I — System Dynamics, Modeling and Identification

2006 ◽  
Author(s):  
Yee-Pien Yang ◽  
Fu-Cheng Wang ◽  
Hsin-Ping Chang ◽  
Ying-Wei Ma ◽  
Chih-Wei Huang ◽  
...  
Keyword(s):  
Fuel Cell ◽  
System Identification ◽  
Proton Exchange Membrane ◽  
Cell System ◽  
Proton Exchange ◽  
Time Varying ◽  
Fuel Cell System ◽  
And Control ◽  
Exchange Membrane ◽  
Auxiliary Input

This paper consists of two parts to address a systematic method of system identification and control of a proton exchange membrane (PEM) fuel cell. This fuel cell is used for communication devices of small power, involving complex electrochemical reactions of nonlinear and time-varying dynamic properties. From a system point of view, the dynamic model of PEM fuel cell is reduced to a configuration of two inputs, hydrogen and air flow rates, and two outputs, cell voltage and current. The corresponding transfer functions describe linearized subsystem dynamics with finite orders and time-varying parameters, which are expressed as discrete-time auto-regression moving-average with auxiliary input models for system identification by the recursive least square algorithm. In experiments, a pseudo random binary sequence of hydrogen or air flow rate is fed to a single fuel cell device to excite its dynamics. By measuring the corresponding output signals, each subsystem transfer function of reduced order is identified, while the unmodeled, higher-order dynamics and disturbances are described by the auxiliary input term. This provides a basis of adaptive control strategy to improve the fuel cell performance in terms of efficiency, transient and steady state specifications. Simulation shows the adaptive controller is robust to the variation of fuel cell system dynamics.

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