Single Stage Quasi-Z-Source Push-Pull based Microinverter for On-Grid PV Applications

In recent years, Microinverters have gained much attention since the direct connection of PV modules to the grid can increase the amount of harvested energy when compared to traditional string inverters. In addition, the use of microinverters results in a modular system which can grow over time, with increased reliability. Key aspects for the implementation of a microinverter are that the selected power converter topology is required to have high voltage gain to interface the low voltage PV input to the grid, and to have high efficiency. Usually, microinverters are implemented in a two-stage approach which impacts overall power conversion efficiency. Further, a fly-back converter is commonly used as input stage, which has several disadvantages such as high EM noise, high semiconductor voltage stress, and that a highly discontinuous current is drawn from the PV module. To cope with these issues, a single stage microinverter topology based on a push-pull converter integrated with a quasi-Z source network and coupled with a voltage unfolder is presented in this paper. The proposed topology results in reduced component count, low voltage stress and reduced EM noise.