Optimal Phase Shift Control Strategy of Buck-Boost Integrated LLC Converter Achieving Wide Input Voltage Range, MHz-frequency and High Efficiency

Buck-boost integrated LLC converter (BBLLC) is a good candidate for the isolated DC-DC converter with wide input voltage range. However, difficulties of how to control phase shift of BBLLC limit the potential of high frequency and high efficiency performance. In this paper, the mechanism that the currents of the two-stage commutate to cancel out with each other during the conduction period is firstly analyzed. Then, an accurate phase shift control model is derived to realize both Zero-Voltage-Switching (ZVS) and minimum conduction loss. Finally, the control architecture to implement the optimal phase shift is established. To verify the theoretical analysis and performance of the proposed solution, a 1MHz 1kW BBLLC with GaN devices is demonstrated, which achieves a peak efficiency of 96.4% and the input voltage range of 250~420V.