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RESEARCH PAPERS

Effects of Electrical Feedbacks on Planar Solid Oxide Fuel Cell

[+] Author and Article Information
Sanjaya K. Pradhan

Laboratory for Energy and Switching-Electronics Systems, Department of Electrical and Computer Engineering, University of Illinois at Chicago, 851 S. Morgan Street, MC: 154, 1020 SEO, Chicago, IL 60607-7053spradh1@uic.edu

Sudip K. Mazumder

Laboratory for Energy and Switching-Electronics Systems, Department of Electrical and Computer Engineering, University of Illinois at Chicago, 851 S. Morgan Street, MC: 154, 1020 SEO, Chicago, IL 60607-7053mazumder@ece.uic.edu

Joseph Hartvigsen

SOFC and Hydrogen Technologies, Ceramatec, Inc., Salt Lake City, UTjjh@ceramatec.com

Michele Hollist

SOFC and Hydrogen Technologies, Ceramatec, Inc., Salt Lake City, UTmhollist@ceramatec.com

A PSOFC-based PCS essentially consists of a PSOFC stack, a balance-of-plant subsystem (BOPS), which controls the flow of fuel and air into the stack and as well controls the stack temperature, and power electronics subsystem (PES), which processes the output power from the stack, and provides an interface between the stack and the application load (AL).

J. Fuel Cell Sci. Technol 4(2), 154-166 (Jul 17, 2006) (13 pages) doi:10.1115/1.2713773 History: Received April 19, 2006; Revised July 17, 2006

Planar-solid-oxide-fuel-cell stacks (PSOFCSs), in PSOFC-based power-conditioning systems (PCSs), are subjected to electrical feedbacks due to the switching power electronics and the application loads. These feedbacks (including load transient, current ripple due to load power factor and inverter operation, and load harmonic distortion) affect the electrochemistry and the thermal properties of the planar cells thereby potentially deteriorating the performance and reliability of the cells. In this paper, a detailed study on the impact of these electrical effects on the performance of the PSFOC is conducted. To analyze the impact of such feedbacks, a spatiotemporal numerical system model is developed on a low-cost Simulink modeling platform and the model under transient and steady-state conditions is validated experimentally. Using this validated model, parametric analyses on the impacts of transience, power factor, and distortion of the application load as well as low-frequency current ripple is conducted. Finally, using experimental data, we demonstrate the long-term impact of two most significant electrical feedbacks on the area-specific resistance and the corresponding loss of effective stack power.

Copyright © 2007 by American Society of Mechanical Engineers
Topics: Stress
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References

Figures

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Figure 1

Schematic of a PSOFC based residential power-conditioning system

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Figure 2

Power-electronics induced high- and low-frequency ripples in the fuel cell current

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Figure 3

(a) Voltage-current (V-I) characteristics of AC loads at different power factors and (b) illustration of the circulating reactive power due to nonunity power factor of the load

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Figure 4

(a) Current distortion due to a rectifier load and (b) Fourier analysis of the distorted current

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Figure 5

Spatial homogenous model for the PSOFC providing two-dimensional discretizations; electrolyte region signifies electro-active area of the cell

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Figure 6

One-dimensional homogenous slab model for PSOFC providing discretizations involving finite-difference method; Temperature, current, and molar-flow rates of air and fuel are calculated each time for n=1,…,N

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Figure 7

A simplified architecture of the PES for the residential PCS

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Figure 8

Steady-state I-V characteristics comparison of the planar SOFC stack

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Figure 9

(a) Experimental setup of the 25 cell PSOFC stack with the PES; the flow of air and fuel into the stack is kept constant and (b) The PSOFC stack manifold and the arrangements for air and fuel flow

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Figure 10

(a) Effect of load current transient (2.2–12A) on the voltage of the stack model and (b) the experimental validation of its effect on the planar stack, scope channel 1 (10V∕div) and channel 4 (2A∕div) measures the stack voltage and current, respectively

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Figure 11

(a) Validation of the effect of single load transient (no load (NL) –, full load (FL) –, no load (NL)), and (b) multiple load transient on the stack temperature

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Figure 12

(a) Effect of 40% current ripple on the stack voltage of 1D model and (b) experimental validation of the ripple effect on planar SOFC stack, scope channels A and D show the stack voltage and current, respectively

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Figure 13

Effect of (a) magnitude of load transient, (b) duration of load transient, and (c) the frequency of transients on the increase in the mean stack temperature

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Figure 14

Effect of low frequency ripple on the performance and efficiency of the stack

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Figure 15

Effect of low-frequency ripple on (a) operable fuel utilization (b) achievable efficiency, and (c) mean temperature of the stack

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Figure 16

Effect of power factor of the load on the magnitude of stack current ripple

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Figure 17

Effect of THD on the stack current ripple

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Figure 18

Comparison of long-term ASR degradation due to low-frequency ripple, constant current, and load transient

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