Modeling of a Supercapacitor, Battery, and Hybrid Energy Storage System Using Equivalent Circuits and the Laplace Transform

Abstract

Modeling short-term transients in a hybrid energy storage system (HESS) requires a terminal model that preserves the relationship between the storage-device currents and the DC-bus voltage at moderate computational cost. This study aims to develop a Laplace-domain model of a passive system comprising a battery and an electric double-layer supercapacitor connected in parallel. The supercapacitor is represented by a nonlinear fast-response branch, the battery by a circuit with two polarization RC branches, and the rapidly varying load by a time-varying resistance. Applying the Laplace transform with allowance for the initial conditions yields differential relations and physically admissible solutions for the supercapacitor, Laplace-domain equivalents of both storage devices, and a system of equations for the complete model including the interconnecting-wire resistances. The results are intended for numerical calculation of currents and voltages during separate and joint operation of the storage devices and for subsequent model verification in dynamic simulation environments.