Advanced sensorless nonlinear control strategy for grid connected photovoltaic systems via the two-time scale singular perturbation technique

This paper presents a new control strategy for grid connected photovoltaic (PV) system. The system consists of a solar panel, a boost converter, and a full-bridge inverter with L-filter connected to the grid. The control objectives are threefold: 1) tracking the maximum power point of the PV panel; 2) balancing the power exchange by regulating the DC link voltage; 3) ensuring a unity power factor in the grid. To achieve these objectives, a multi-loop controller is synthesised using a high-gain output feedback controller and the singular perturbation technique. The addressed control problem involves several difficulties including the existence of a number of state variables that are inaccessible to measurement. To address this problem, two-time-scale sliding mode observers are added which allow estimating, simultaneously, the solar panel current and the grid voltage. It is formally shown that all control objectives are asymptotically accomplished. This theoretical result is confirmed by numerical simulation tests.