Nonlinear control and stability analysis of single stage grid-connected photovoltaic systems

This work presents the control development of a single stage grid-connected photovoltaic (PV) system. The topology used by the PV system consists of two PV panels, a single-phase half-bridge inverter using two DC link capacitors, and an LCL filter in the grid side. The aim is to design a nonlinear controller to ensure simultaneously the following three objectives: (i) PV panels to provide their maximum power, (ii) balanced power exchange by regulating the DC link voltage, and (iii) power factor correction, i.e. grid current in phase with grid voltage. In order to fulfill these objectives, a multi-loop controller is designed by using back-stepping and Lyapunov approaches for the power factor correction objective and a filtered PI regulator to ensure the power balance between the grid and the PV panels. The controller performances are formally analyzed using an average large signal model. The performance of the proposed controller is shown by means of simulation results in MATLAB/SimPowerSystems environment.