Isolated Single-Input Dual-Output LLC Converter for a Wide Range of Voltage Gain using Mode Transition

Abstract

In this study, an LLC converter that can achieve a wide range of voltage gain and high efficiency for two loads is proposed. The efficiency of the proposed LLC converter is found to be greater than that of the conventional full-bridge LLC converter. Depending on the ON/OFF state of the five primary switches, the proposed converter offers five modes of operation. These modes enable a squeezed switching frequency span that is close to the resonance frequency. In all operation modes, one load is controlled by the switching frequency, while the other is controlled by the switching frequency and phase-shift angle. The proposed control method provides a wide operating range and seamless transition between different modes. Furthermore, the mode transitions are performed based on the relationship between the switching frequency and phase-shift angle. First, the theoretical characteristics of the proposed converter are analyzed. Next, the gain characteristics of each operation mode and the mode transition method are described. The prototype is designed to convert a constant input voltage of 360V to output voltages ranging from 80-420V and 36-48V. The experimental results confirmed that steady-state waveforms can be achieved in the multiple proposed modes of operation and voltage gains ranging from less than 0.5 to more than 1.0. Moreover, seamless mode transitions can be achieved without large deviations between the outputs. Finally, the efficiency of the proposed converter is evaluated in comparison to that of a conventional converter. The proposed converter achieved high-efficiency operations in the CC2 region of the battery compared to the conventional converter.