Improved Cascaded SOGI Control for Islanding-Synchronization in Photovoltaic System

Abstract

This work presents an improved cascaded second-order generalized integrator (I-CSOGI) controlled photovoltaic system (PVS), which functions as an islanded system during grid interruption without energy storage. Here, a single-stage PVS structure is used, simplifying the control by automatically regulating the PV array operating point and dc-link voltage during the grid outage. The I-CDSOGI algorithm is exercised to determine the sensed voltages angle, frequency, and harmonics free positive sequence components of the sensed voltages and load currents. The advantage of the presented I-CDSOGI over the existing CDSOGI algorithm is that the gain of its frequency-locked loop is changed adaptively. It reduces the spurious change in the frequency during the sudden phase jump, which is experienced by the load voltages during synchronization. Hence, the repeated tripping of the power electronics switches, which isolates the PVS from the local grid, is reduced, and smooth synchronization is achieved. Furthermore, the cascading of two second order generalized integrator (SOGI) blocks eliminates the dc offset from the sensed signals and boosts the overall harmonics rejection capability, which enhances the angle and frequency estimation performance. A comparison is made to showcase the benefits of I-CSOGI compared with the existing SOGI-based methods in the PVS.