Light-Load Efficiency Improvement of Galvanically Isolated Quasi-Z-Source DC-DC Converter for Photovoltaic Applications

This paper evaluates the light-load efficiency optimization of the multi-mode quasi-Z-source series resonant DC-DC converter operating in the boost mode. The photovoltaic (PV) microconverters are typically designed for wide input voltage and load variations for ensuring the best possible energy harvest from the PV modules in different operating conditions. The efficient operation at part- and light-load is the most challenging design target that can negatively impact the weighted efficiency of a PV microconverter. The cycle skipping modulation and frequency reduction techniques are used to improve the efficiency of the converter at light load. The operation principle of the converter is explained for both approaches. They are compared against each other, and their shortcomings and advantages are discussed. The effects of their implementation on the power losses are investigated by theoretical analysis. An experimental prototype rated for 300 W was used to validate all the findings.