An Improved Power Electronic Controller with Unity Power Factor for a Single-Stage Grid-Tied PV System

A single-stage PV system using Z-source inverter (ZSI) capable of operating in grid-connected mode or stand-alone mode has been developed for extracting power from PV array. For feeding the extracted power to the grid, an analog current controller adjusting the modulation index of ZSI combined with the shoot-through duty ratio has been designed and developed. The proposed system has the advantage of using less number of power converters and can be built with simple controllers. Experiments have been conducted on a PV array consisting of seven PV panels (each rated for 21.2V, 5.17A) connected in series, feeding a 110V single-phase utility grid through ZSI. A hysteresis current controller for varying the modulation index of ZSI has been built using analog ICs. Using MATLAB/Simulink, the complete system has been simulated and the simulation results closely correlate with experimental ones. The efficacy of the proposed scheme with the power being fed to the grid at unity power factor is indicated by the results. It is also proved that the total harmonic distortion of both voltage and current waveforms fed to the grid terminals is less than 5%.