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Title: An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads

Abstract

Development of high-performance and durable solidoxide fuel cells (SOFCs) and a SOFC power-generating system requires knowledge of the feedback effects from the power-conditioning electronics and from application-electrical-power circuits that may pass through or excite the power-electronics subsystem (PES). Therefore, it is important to develop analytical models and methodologies, which can be used to investigate and mitigate the effects of the electrical feedbacks from the PES and the application loads (ALs) on the reliability and performance of SOFC systems for stationary and non-stationary applications. However, any such attempt to resolve the electrical impacts of the PES on the SOFC would be incomplete unless one utilizes a comprehensive analysis, which takes into account the interactions of SOFC, PES, balance-of-plant system (BOPS), and ALs as a whole. SOFCs respond quickly to changes in load and exhibit high part- and full-load efficiencies due to its rapid electrochemistry, which is not true for the thermal and mechanical time constants of the BOPS, where load-following time constants are, typically, several orders of magnitude higher. This dichotomy can affect the lifetime and durability of the SOFCSs and limit the applicability of SOFC systems for load-varying stationary and transportation applications. Furthermore, without validated analytical models and investigative designmore » and optimization methodologies, realizations of cost-effective, reliable, and optimal PESs (and power-management controls), in particular, and SOFC systems, in general, are difficult. On the whole, the research effort can lead to (a) cost-constrained optimal PES design for high-performance SOFCS and high energy efficiency and power density, (b) effective SOFC power-system design, analyses, and optimization, and (c) controllers and modulation schemes for mitigation of electrical impacts and wider-stability margin and enhanced system efficiency.« less

Authors:
Publication Date:
Research Org.:
University Of Illinois
Sponsoring Org.:
USDOE
OSTI Identifier:
899235
DOE Contract Number:
FC26-02NT41574
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; DESIGN; ENERGY EFFICIENCY; FUEL CELLS; PERFORMANCE; POWER DENSITY; SOLID OXIDE FUEL CELLS

Citation Formats

Sudip K. Mazumder. An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads. United States: N. p., 2005. Web. doi:10.2172/899235.
Sudip K. Mazumder. An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads. United States. doi:10.2172/899235.
Sudip K. Mazumder. Sat . "An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads". United States. doi:10.2172/899235. https://www.osti.gov/servlets/purl/899235.
@article{osti_899235,
title = {An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads},
author = {Sudip K. Mazumder},
abstractNote = {Development of high-performance and durable solidoxide fuel cells (SOFCs) and a SOFC power-generating system requires knowledge of the feedback effects from the power-conditioning electronics and from application-electrical-power circuits that may pass through or excite the power-electronics subsystem (PES). Therefore, it is important to develop analytical models and methodologies, which can be used to investigate and mitigate the effects of the electrical feedbacks from the PES and the application loads (ALs) on the reliability and performance of SOFC systems for stationary and non-stationary applications. However, any such attempt to resolve the electrical impacts of the PES on the SOFC would be incomplete unless one utilizes a comprehensive analysis, which takes into account the interactions of SOFC, PES, balance-of-plant system (BOPS), and ALs as a whole. SOFCs respond quickly to changes in load and exhibit high part- and full-load efficiencies due to its rapid electrochemistry, which is not true for the thermal and mechanical time constants of the BOPS, where load-following time constants are, typically, several orders of magnitude higher. This dichotomy can affect the lifetime and durability of the SOFCSs and limit the applicability of SOFC systems for load-varying stationary and transportation applications. Furthermore, without validated analytical models and investigative design and optimization methodologies, realizations of cost-effective, reliable, and optimal PESs (and power-management controls), in particular, and SOFC systems, in general, are difficult. On the whole, the research effort can lead to (a) cost-constrained optimal PES design for high-performance SOFCS and high energy efficiency and power density, (b) effective SOFC power-system design, analyses, and optimization, and (c) controllers and modulation schemes for mitigation of electrical impacts and wider-stability margin and enhanced system efficiency.},
doi = {10.2172/899235},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Dec 31 00:00:00 EST 2005},
month = {Sat Dec 31 00:00:00 EST 2005}
}

Technical Report:

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  • Solid-Oxide Fuel Cell (SOFC) stacks respond quickly to changes in load and exhibit high part- and full-load efficiencies due to its rapid electrochemistry. However, this is not true for the thermal, mechanical, and chemical balance-of-plant subsystem (BOPS), where load-following time constants are, typically, several orders of magnitude higher. This dichotomy diminishes the reliability and performance of the electrode with increasing demand of load. Because these unwanted phenomena are not well understood, the manufacturers of SOFC use conservative schemes (such as, delayed load-following to compensate for slow BOPS response or expensive inductor filtering) to control stack responses to load variations. Thismore » limits the applicability of SOFC systems for load-varying stationary and transportation applications from a cost standpoint. Thus, a need exists for the synthesis of component- and system-level models of SOFC power-conditioning systems and the development of methodologies for investigating the system-interaction issues (which reduce the lifetime and efficiency of a SOFC) and optimizing the responses of each subsystem, leading to optimal designs of power-conditioning electronics and optimal control strategies, which mitigate the electrical-feedback effects. Equally important are ''multiresolution'' finite-element modeling and simulation studies, which can predict the impact of changes in system-level variables (e.g., current ripple and load-transients) on the local current densities, voltages, and temperature (these parameters are very difficult or cumbersome, if not impossible to obtain) within a SOFC cell. Towards that end, for phase I of this project, sponsored by the U.S. DOE (NETL), we investigate the interactions among fuel cell, power-conditioning system, and application loads and their effects on SOFC reliability (durability) and performance. A number of methodologies have been used in Phase I to develop the steady-state and transient nonlinear models of the SOFC stack subsystem (SOFCSS), the power-electronics subsystem (PES), and the BOPS. Such an approach leads to robust and comprehensive electrical, electrochemical, thermodynamic, kinetic, chemical, and geometric models of the SOFSS, PES and application loads, and BOPS. A comprehensive methodology to resolve interactions among SOFCSS, PES and application loads and to investigate the impacts of the fast- and slow-scale dynamics of the power-conditioning system (PCS) on the SOFCSS has been developed by this team. Parametric studies on SOFCSS have been performed and the effects of current ripple and load transients on SOFC material properties are investigated. These results are used to gain insights into the long-term performance and reliability of the SOFCSS. Based on this analysis, a novel, efficient, and reliable PES for SOFC has been developed. Impacts of SOFC PCS control techniques on the transient responses, flow parameters, and current densities have also been studied and a novel nonlinear hybrid controller for single/parallel DC-DC converter has been developed.« less
  • Exxon Enterprises, Inc., at the request of EPRI, has completed an evaluation of Alsthom/Exxon alkaline fuel cell technology for application to utility power generation. The purpose of this study was to determine how close the technology could come to EPRI efficiency, investment, and related targets and to begin to define those limitations which must still be overcome. The program consisted primarily of a systems analysis to explore the effect of major variables such as fuel cell operating temperature, fuel type and degree of carbon oxides preremoval on efficiency and cost. Most of the effort centered around minimizing cost and heatmore » rate by selecting the most appropriate process techniques and by heat integrating the various parts of the process. Two routes were found for meeting the EPRI heat rate targets, 7100 Btu/kWh with methanol and 7500 Btu/kWh with naphtha as starting fuel. The simplest route involved reforming followed by Pressure Swing Absorption yielding a nearly pure hydrogen feed to the fuel cell. Alternatively, carbonate scrubbing could be used but required an increased fuel cell temperature of 393/sup 0/K so that waste heat could be used for carbonate regeneration. The major uncertainty was in the assumed fuel cell performance which while taken from the literature for alkaline fuel cells has not yet been achieved with Alsthom/Exxon components. Investments for a 400 MW plant were between 20 and 30 percent higher than the target of $200/kW in 1974 dollars. Since the estimates contain no allowance for contingencies it would be unrealistic to project lower costs.« less