Frequency Adaptive ZVS Control for Four-Switch Buck-Boost Converter with Minimized Inductor Current

Abstract

In recent years, four-switch buck-boost (FSBB) converters have been increasingly used in step-up/down dc-dc applications. Given high-frequency power devices using SiC or GaN, the zero-voltage-switch (ZVS) modulation scheme with quadrilateral inductor current is a preferred choice and has been studied in some recent researches. In order to further minimize the loss of the converter and improve the efficiency, in this work, a control strategy with minimum RMS of inductance current and soft switching of all switches is proposed, which can realize frequency adaptive adjustment when the load increases. Under light-load condition, DCM (Discontinuous Mode) operation at constant switching frequency is adopted. Under heavy loads, it enters CRM (Critical Mode) operation with adaptively decreased frequency achieving ZVS while keeping inductor currents minimized. A simple algorithm is proposed to calculate the optimal power transferring time $(T_{2})$ with the switching period $(T_{\mathrm{s}})$ in an iterative manner. Thus, ZVS control with minimized inductor current is achieved in all working conditions. The correctness and effectiveness of the control method are verified by simulation. Experiments are underway.