Evaluating Energy Storage Efficiency by Modeling the Voltage and Temperature Dependency in EDLC Electrical Characteristics

Abstract

This study characterizes and models the temperature and charge voltage dependency in the electrical characteristics of a packed electric double layer capacitor (EDLC). The characterized results indicate that the frequency response of the terminal impedance in a packed EDLC varies with the charge voltage and temperature. The latter can be attributed mainly to the temperature change of the resistive component because the thermal sensitivity of the capacitive component is low, whereas the resistive component increases as the temperature drops. A multistage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> equivalent circuit model is developed, and three stages are determined to be adequate to reduce the model error for the studied EDLC. The charge voltage dependency in the capacitance of the extracted equivalent circuit is modeled by the physics-based Stern's model. The temperature dependency of the internal resistance is modeled by the quadratic function of temperature. The large signal response of the proposed model is verified with charge/discharge experiments at various temperatures. The proposed EDLC model suitably expresses the time response of the terminal voltage and current, can estimate the charged and discharged electrical power and energy of the EDLC, and explains the degradation of energy efficiency at low temperature.