A comparison of two equivalent circuits for double-layer capacitors

The double-layer capacitor is a very complex device that is best represented by a distributed parameter system. Many different lumped-parameter equivalent circuits have been proposed for the double-layer capacitor. Presented in this paper is a comparison of the classical equivalent circuit and ladder circuits. Parameters for the classical equivalent circuit are determined from in-situ circuit measurements. AC impedance data is acquired for the capacitor and utilized to determine parameters for the ladder circuits. The performance of the two equivalent circuits is evaluated in slow discharge and pulse load applications. In comparison to the ladder circuits, the classical circuit more accurately calculates the capacitor voltage during a slow discharge. In the pulse load application, the classical circuit and a low order ladder circuit predict approximately the same voltage drop measured in the laboratory.