Soft-Start Procedure for Four-Switch Buck-Boost Converter with PCCM ZVS Modulation Scheme

For applications where voltage step-up/down and zero-voltage-switching (ZVS) are both required, the four-switch buck-boost (FSBB) converter with pseudo-continuous conduction mode (PCCM) ZVS modulation scheme is popular and has attracted more and more attention. Moreover, in these applications, the soft-start of the FSBB converter is important to avoid the inrush current during start-up and to eliminate the bulky external pre-charge circuits. However, when with the PCCM ZVS modulation scheme, almost no literature is available on the soft-start procedure of the FSBB converter. In this paper, to facilitate the practical application of the FSBB converter, a soft-start procedure is proposed based on PCCM ZVS modulation scheme and is demonstrated carefully as well. In the FSBB converter where the proposed soft-start procedure is used, there are no inrush current during the start-up and no modulation mode transition at the ending moment of the start-up. Moreover, the output voltage of FSBB converter always follows its reference voltage and increases monotonically without any overshoot. The experimental verification is carried out with a 1500W FSBB prototype to verify the proposed soft-start procedure.