A Novel Method for Electrically Modeling of Fuel Cell Using Frequency Response Technology: Executed on a Direct Methanol Fuel Cell

Abstract

In this paper, a novel semi-empirical modeling method to mathematically derive a nonlinear equivalent circuit from a special group of impedance fuel cell models is proposed. As an example, a 5-cm 2 direct methanol fuel cell (DMFC) was modeled by this method. The derived equivalent circuit is composed of lumped nonlinear resistors, capacitors and an inductor. The nonlinear circuit has an impedance equivalent to the target fuel cell in various operating conditions and provides a good approximation of the static and transient behaviors of the fuel cell. The equivalent circuit fuel cell model was validated by comparing its numerical simulation results with its polarization curve and the dynamic behavior of the target DMFC. These comparisons were performed while the DMFC was operated under square current pulses with different upper and low current levels.

Modeling of Direct Methanol Fuel Cell Using a Resistive-Capacitive-Inductive Transmission-Line Equivalent Circuit

“…The j describes the transformation of proton current density I into electronic current via Faradic processes. In our fuel cell model, the transformer is the RCL circuit element and the nonlinear elements of the RCL circuit have the expressions of (4): [2][3][4][5] in which, ECS Transactions, 6 (13) 63-75 (2007) CT), A, C 0 , R ohm and L 0 are constant parameters. j 0 is a integral constant.…”

“…When the mass transport limitations are excluded, it is believable that the impedance of DMFC cathode at low frequency is much smaller than the large pseudo Faradic impedance of DMFC anode. Based on our previous numerical study (4), the RC component with high cut-off frequency (>10 Hz) can be approximated as a resistor, and it will not affect the dynamic response of the DMFC operating in low frequency (< 0.1 Hz) square pulse current load. Comparing with the catalyst layers, the capacitance of membrane is definitely negligible, and the impedance of the membrane can be approximated as a resistor too.…”

“…The total capacitance C 0 is the sum of C d and C E . The parameters of R L , R ct and L are also obtained from their definition in lumped nonlinear electrical circuit fuel cell model (4). In this study, the possible dependence of electrical elements to the local electrode potential is neglected by assuming the good fuel transportation and gas diffusion of the catalyst layers.…”