A Bi-Directional Reconfigurable LLC Converter Design for DC Microgrid Application

Abstract

A DC-microgrid system is an immerging topic of research due to their several advantages compared to the AC grid system and DC-DC converters are an essential part of the DC network. Due to the higher system efficiency and reduced device stress, LLC converter is generally considered to be a better choice over DAB type. However, CLLC type converter with integrated transformer and resonant tank for high power density application (integrated magnetics) has issues for bi-directional operation with high input-output voltage variation range. To address these issues a reconfigurable bi-directional LLC (RC-LLC) converter is proposed. The proposed converter has a bidirectional feature like a CLLC type with a linear output voltage variation range for a wider range of gain variation. Detailed analytical study to calculate the resonant tank gain for both LCC and CLLC type bi-directional configuration is presented in this paper. Results from the analytical study is then used for a detailed system design and simulation studies for a 15 kW, 600V to 600 V RC-LLC system application. The proposed system also helps to reduce the system cost by 27% as compared to the conventional system.