Dual bridge LLC resonant converter with frequency adaptive phase-shift modulation control for wide voltage gain range

This paper presents an isolated DB LLC resonant converter with frequency adaptive phase-shift modulation control which overcomes the unity gain problem of conventional DB converter. The proposed control maintains the Zero Voltage Switching (ZVS) to all switches under all operating voltage and load variations. The control proposed for this circuit based on two control variables: switching frequency and phase-shift angle of the secondary switches. The Switching frequency changes with the load in such a way that, it is secured ZVS to the primary side for all phase-shift angles. To do so, the voltage gain becomes independent of the loaded quality factor. On the other hand, the phase-shift angle in between two bridges is used to regulate the output voltage and power flows of the converter. However these two variables control is beneficial for reducing conduction losses and switch turn-on losses throughout the wide voltage and load operation. Experimental results of a 1-kW prototype converter with 200–400V input and 48V output are presented to verify all theoretical analysis and characteristics.