Nonlinear control for MPPT and UPF of PV system connected to the grid

Abstract

In this paper a nonlinear control for a single-phase photovoltaic (PV) system connected to the grid is proposed. The system consists of a PV array, DC-DC converter and a DC-AC inverter coupled to the grid network. Our goal is the achievement of three control objectives i) regulating the DC voltage to a desired value (Vdc*) ii) supply a current with sinusoidal form and in phase with the grid voltage by controlling DC/AC converter (Unite Power Factor: UPF) iii) extracting the maximum power from the PV array by acting on the DC/DC converter (MPPT). The control strategy is based on the robust integral Backstepping control design to be applied to the DC_DC converter and the DC_AC inverter in order to optimize the PV energy extraction and to achieve unity power factor. In order to improve the robustness of the nonlinear control, an integral action is introduced. The stability of the nonlinear control is demonstrated by means of Lyapunov analysis. Representative computer simulations demonstrate the performances of the control strategy to track the maximum power point of the photovoltaic array panel and synchronization of grid current with grid voltage under various climatic conditions.