Research Papers

Analysis of Input Current Ripple and Optimum Filter Capacitor for Fuel-Cell-Based Single-Phase Inverter

[+] Author and Article Information
Tirthajyoti Sarkar

Staff Device Engineer
Process Technology Group
Fairchild Semiconductor,
3030 Orchard Parkway,
San Jose, CA 95134
e-mail: tirthajyoti.sarkar@fairchildsemi.com

Sudip K. Mazumder

Laboratory for Energy
and Switching-Electronics Systems,
Department of Electrical
and Computer Engineering,
University of Illinois,
Chicago, IL 60607
e-mail: mazumder@uic.edu

Manuscript received December 13, 2013; final manuscript received November 14, 2015; published online December 15, 2015. Assoc. Editor: Shripad T. Revankar.

J. Fuel Cell Sci. Technol 12(6), 061005 (Dec 15, 2015) (5 pages) Paper No: FC-13-1124; doi: 10.1115/1.4032040 History: Received December 13, 2013; Revised November 14, 2015

Most single-phase inverters, being sourced by fuel cell stacks (FCSs), subject the stacks to reflected low-frequency (120 Hz) current ripples that ride on average dc currents. The ripple current impacts the sizing and efficiency of the FCS. As such and typically, a passive or active filter is required at the input of the inverter (or output of the FCS) to mitigate the ripple current. Toward that end, this paper outlines a guideline to choose the optimum size of a passive input-filter capacitor for a fuel-cell-based power system from the standpoints of the overall system energy density and cost. Detailed case-specific simulation results, based on an analytical approach, are provided to illustrate key issues for both unity power factor as well as harmonic loads.

Copyright © 2015 by ASME
Topics: Stress , Filters , Capacitors , Fuels
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Fig. 1

Current distribution in an FCS-based single-phase single-stage inverter. A typical illustration of such a topology is shown in Ref. [2], which achieves voltage amplification using an embedded step-up high-frequency transformer. It is noted that such a single-stage inverter can be nonisolated as well even though it is normally less practical due to the cost of the stack to support a high voltage. Symbols IOut, IFCS, and ICap represent, respectively, the inverter-output, FCS-output, and filter-capacitor currents. IOut, devoid of high-frequency components (which is absorbed by the output capacitor), represents the load current. The sinusoidal modulation of the inverter results in an inverter input current that has a dc- and a strong ripple-current component.

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Fig. 2

Peak negative FCS current with non-unity power factor load without input-filter capacitor

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Fig. 3

FCS current at 0.6 load power factor, with and without a 50 mF input-filter capacitor

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Fig. 4

FCS current ripple as a function of input-filter capacitor size and load power factor

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Fig. 5

Input-filter capacitor size versus FCS current ripple for different stack nominal voltages at load power factors of (a) 1.0 and (b) 0.8, respectively

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Fig. 8

Input-filter capacitor size versus monetary savings (due to increased FCS efficiency) and total footprint area of the inverter. The zone of optimality is illustrated by dotted ellipse. A curve-fitted equation was used to plot this, however, the nature and coefficients of the equation will vary greatly with FC stack and capacitor technology choice, and therefore, it should not be perceived as a generic equation.

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Fig. 7

FCS efficiency as a function of input-filter capacitor size and (a) stack voltage and (b) stack current ratings

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Fig. 6

THD versus peak-to-peak FCS current ripple for varying fundamental power factor




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