Research on Novel Asymmetric Levels Combination in a Multilevel Bidirectional CLLC Resonant Converter for Wider Voltage Gain

A novel asymmetric level of combination is proposed between the front and rear dc buses in the intermediate link of the energy router (ER) for wider voltage gain. This is achieved by a hybrid modulation strategy via pulse frequency modulation (PFM) and Fixed-Frequency plus Phase shift Hybrid Modulation (FF-PSHM) in a novel bidirectional CLLC resonant converter. On the input and output sides of the CLLC resonant tank module (RTM), the ac total voltage of a five-level coupling cascaded neutral point clamping active bridge (5L-CNPC) can, furthermore, be multilevel through voltage flexible superposition on coupling transformers. Then, an asymmetric passive resonant components parameter design is developed to meet differentiated voltage demands between the front and rear dc buses in the intermediate link of the ER, which also reduces the rms of resonant current and the conduction power loss. Finally, six innovative voltage gain modes have been devised for forward and backward operations, and a novel “left fundamental harmonic five levels” drive method is incorporated in specific modes to make it easier to realize the ZVS of lagging switches. Besides, experimental prototype results corroborate that the attained voltage gains are in alignment with the theoretical design values, and conduction loss optimization is reflected in the efficiency curves and power loss distribution.