Single-Phase Grid-Connected LiFePO$_{\bf 4}$ Battery–Supercapacitor Hybrid Energy Storage System With Interleaved Boost Inverter

AC line integrated energy storage systems are attractive as they increase the system efficiency by reducing the number of required power processing stages. In this paper, operation of a recently proposed battery-supercapacitor hybrid energy storage system (HESS) comprising two DC/AC boost converters, battery, supercapacitors, grid connection, state of charge (SOC) estimation, and associated control systems is experimentally verified and further improved. The improvement is achieved by a phase-shifted interleaved operation of the boost converters. The proposed phase-shifted interleaved operation reduces the switching frequency current ripple component in both the battery and supercapacitor currents. Experimental results show that during the interleaved operation, the HESS operates as expected and allocates all fast current variations to the supercapacitor, while the battery responds to slow varying current demands. At the same time, the control system maintains the supercapacitor voltage at around a predefined value and the battery's SOC, estimated using an extended Kalman filter, is maintained within the specified SOC limits.