Design and Implementation of CLLLC Bidirectional Converter with Wide Voltage Range on Low Side

The design and implementation of a high-frequency isolated bidirectional resonant converter for efficient energy transfer between the DC bus and the batteries in electric cars are the focal points of this research. To achieve high switching frequency, the converter utilizes a planar transformer and wide bandgap elements. The main circuit comprises a three-level half-bridge structure on the high voltage side, a full bridge structure on the low voltage side, and a CLLLC resonant tank. The circuit control can be simplified by the symmetrical resonant tank of circuit characteristics of bidirectional power flow. This converter enables soft switching, effectively reducing switching losses. The research also includes the derivation of voltage-gain curves, steady-state equivalent models, and an analysis of the operating principles of the bidirectional resonant converter. For energy conversion control, the research employs the DSP TMS320F28379D with a rated power of 1 kW, a DC bus voltage of 800 V, and battery voltages ranging from 200 V and 400 V. The converter achieves a maximum efficiency of 94.2%.