Modelling a five-level LLC resonant converter for bidirectional battery application

This study designed and evaluated an integrated cascaded pair of full-bridge LLC resonant bidirectional DC-DC converters usable in varied applications, including in energy storage systems, to function as an interface between two dc voltage buses in a variety of applications. The proposed converter combines an isolated five-level cascaded H-bridge LLC (IFCHB-LLC) resonant circuit with a buck/boost circuit (bidirectional converter BID). In this converter, the inbuilt capabilities of an LLC converter, which function as a current source and a voltage source, were exploited, resulting in the constant current (CC) and constant voltage (CV) charges while CV was implemented in the discharge stage (reverse flow). The modelling of the LLC converter was done following the first harmonic approximation (FHA) approach. Furthermore, to ensure improved efficiency of the proposed system, the passive elements of the resonance tank and isolation transformer ratio were programmed in a manner that the converter can be operated within the zero-voltage switching (ZVS) and zero-current switching (ZCS) regions. The feasibility and validity of the converter were tested using a 500 W prototype converter with an input voltage of 200 V resulting in the highest efficiency level of 94.46%. The design of the proposed converter combines a five-level cascaded H-bridge LLC resonant circuit with a buck/boost bidirectional converter to achieve the constant current (CC) and constant voltage (CV) charges while CV is implemented in the discharge stage (reverse flow). The validity of the converter was tested using a 500 W experimental prototype converter with input voltage of 200 V; the converter achieved the highest efficiency level of 94.46%.image