Quasi-resonant DC-link H5 PV inverter

By removing transformer from PV inverters, they become more attractive for distributed power generation systems. Regardless of their some extra leakage currents, transformer-less inverters would be more advantageous regarding their higher efficiency. However, using traditionally hard-switching converters still causes to drastic switching losses, high di/dt and electromagnetic interference. Quasi-resonant DC-link techniques have promising features to provide zero-voltage switching (ZVS) condition for full bridge inverters, but they are not suitable for transformer-less PV inverters due to consequent high leakage current. In this study, a transformer-less PV inverter is proposed by adapting a proper quasi-resonant DC-link technique to the H5 topology. Using only two auxiliary switches, ZVS turn on and turn off for high-frequency bus switch and ZCS turn on and ZVS turn off for high-frequency switches of the bridge as well as ZVS turn on and turn off of the antiparallel diodes of main switches are realised. Zero current switching (ZCS) turn on and ZVS turn off for auxiliary switches and ZVS turn on and ZCS turn off for antiparallel diodes are also provided. To verify the proposed circuit operation, a 20kHz 1kW quasi-resonant DC-link H5 PV inverter prototype is implemented and operation characteristics, soft switching conditions and design rules are confirmed.