Designing smart inverter with unified controller and smooth transition between grid-connected and islanding modes for microgrid application

A three-phase smart grid-connected inverter (SGCI) for grid integration of PV system is designed where an appropriate controller for grid-connected (GC) operation is developed to avoid transients and distortion usually caused by switching internal current/voltage controllers. The presented control technique uses d-q decoupled electrical axis and after the controller detects any impeding fault in the grid voltage, a unified control allows a very smooth transition between the grid-connected and islanded modes of operation. In addition, a floating interleaved boost converter (FIBC) is implemented in this system for photovoltaic array energy conversion and energy storage has an optimized lifetime algorithm, used to increase the power handling capability of the PV-modules. Analysis and results verify the effectiveness of the proposed control framework under different operating conditions.