Multiphase Quasi-Z-Source DC-DC Converters for Residential Distributed Generation Systems

A multiphase quasi-Z-source (qZS) dc-dc converter was proposed for distributed energy generation applications. It contains single-switch qZS isolated dc-dc cells with a voltage doubler rectifier. These cells are connected in parallel at the input side and in series at the output side to increase the dc voltage gain. A dc voltage blocking capacitor in series with the isolation transformer results in resonance that could be utilized for soft-switching. Two design approaches were proposed: considering phase shedding dependent on the input voltage and without it. The former targets wide input voltage range applications, while the latter is better suited for high input current applications. An experimental prototype rated for 300 W was tested with two types of isolation transformers designed according to the two presented approaches. It could be used as a PV module integrated converter with wide input voltage regulation range. The experimental results prove efficiency improvement from the phase shedding. Resonance frequency variations caused by the utilization of the multilayer ceramic capacitors and their possible influence on switching losses are discussed.