Power Loss Model and Efficiency Analysis of the Quasi-Z-Source Isolated Buck-Boost Converter with Wide Input Voltage and Load Range

The galvanically isolated full-bridge series resonant quasi-Z-source dc-dc converter is studied. It features two main operating modes, buck and boost, which correspond to the converter operation above and below the nominal voltage, respectively. Power loss models are developed for both operating modes to identify the mechanism of losses. They consider switching and conduction losses in the input-side switches, core and windings losses in the transformer and the quasi-Z-source inductor, and conduction losses in the voltage doubler rectifier diodes. The developed loss models are verified at three input voltages using a 300 W experimental prototype. The inaccuracy of the developed models does not exceed 2 W, which is acceptable in comparison with the maximum estimated power loss of over 12 W. The experimental and the estimated efficiency follow the same trend. Also, the estimated efficiency exceeds the measured by no more than 1% at full power.