A Control Strategy for Wide-Voltage Output CLLC Converter in On-Board Chargers

Isolated DC/DC converters are of importance for on-board chargers (OBCs) in rapidly developed electric vehicles. DC/DC converters with a CLLC resonant tank are widely adopted due to high power density, high efficiency, wide voltage gain, and bidirectional power transfer capability. And the phase-shift modulation is usually applied to increase output gain in some occasions, which make currents in the resonant tank increase as phase-shift angle increases. To cope with this challenge, a control strategy is proposed with three-degrees-of-freedom, i.e., regulation of the dc-bus voltage, frequency, and phase-shift angle for wide-voltage output CLLC converters. The circuit analysis and working principles are first elaborated, considering various operation stages. The proposed control strategy is introduced, including the control structure and loop configuration. The proposed control strategy is validated with simulations.