Accurate modelling and analysis of battery–supercapacitor hybrid energy storage system in DC microgrid systems

Battery is considered as the most viable energy storage device for renewable power generation although it possesses slow response and low cycle life. Supercapacitor (SC) is added to improve the battery performance by reducing the stress during the transient period and the combined system is called hybrid energy storage system (HESS). The HESS operation purely depends on the control strategy and the power sharing between energy storage systems. The low pass filter based frequency sharing method is the common strategy used to share the power between the battery and SC. The HESS controller consists of two current controllers for controlling battery current and SC current and a voltage controller for regulating DC bus voltage. The quick regulation of DC bus voltage and current depends on the rapidity of operation of each control loop and the delay imposed by LPF. However, the conventional method considers only the SC characteristics for designing the outer voltage controller which leads to error in the calculated parameters. This work investigates controller design based on accurate modelling of HESS by factoring in battery converter and SC converter characteristics and the low pass filter effect. Further, the system is analyzed and compared in conditions with and without battery current loop. To verify the efficacy of the controller designed for the purpose, simulation studies are conducted in MATLAB/SIMULINK. A system prototype is developed in dSPACE 1104 platform.