Dual Polarity DC-DC Converter Integrated Grid-tied Single-Phase Transformer Less Inverter for Solar Application

Abstract

This study proposes a novel single-phase transformer-less inverter, using the principle of combined Cuk SEPIC (CCS) converter for grid-connected photovoltaic (PV) systems. The new inverter has a common ground between the grid and the PV source, which helps to eliminate the leakage current for the grid-connected PV application. Unlike common ground-type charge-pump-based transformer-less inverter, this topology eliminates inrush current and hence reduces the current stress on the components. The CCS allows voltage control with both step-up and step-down abilities, along with more robustness against solar panel side fault. Further, application of wide band-gap devices, such as SiC MOSFETs allows higher switching frequency to be achieved, and thus reduction of the passive components. A novel switching strategy, proposed here allows current in both directions, positive and negative (to the load/grid or from the load/grid, for reactive loads), making the converter suitable for grid connection (unity power factor), as well as stand-alone operation. The proposed concept has been discussed in detail, along with simulation results. Finally, a prototype hardware has been fabricated and the experimental results are reported.