Design of Photovoltaic Microinverter for Off-Grid and Grid-Parallel Applications

The design and construction of a 500VA microinverter for photovoltaic applications is presented. The developed microinverter is capable of operating as a standalone AC voltage source for small loads or, alternatively, as a grid-parallel system. Possible applications are therefore small off-grid installations as well as installations where space constraints do not allow enough modules to be combined to use string inverters. The design of the microinverter is based on a two stage concept. Two alternative topologies for the DC-DC converter stage have been considered. A prototype using a current-fed push-pull converter and a full-bridge output stage has been built and was shown to be operational. The prototype has achieved a maximum overall efficiency of 93.9 %, which includes all sensing, control and driving losses. SiC MOSFETs have been utilized to illustrate the capability of wide-band-gap devices.