Nonlinear control of multicellular single stage grid connected photovoltaic systems with shunt active power filtering capability

This work deals with the nonlinear control of grid connected photovoltaic (PV) systems with shunt active power filtering functionality. The Proposed power plant consists of two PV generators, a single-phase power grid connected to non-linear loads at point of common coupling (PCC) and a multicellular inverter that will play a dual role, on one hand, compensating harmonic currents and reactive power caused by non-linear loads, and on the other hand, injecting active power provided by the PV generators into the electrical grid. The proposed nonlinear controller is designed in order to achieve the following objectives: i) guarantee a balanced distribution of the input voltage over the power switching devices, ii) ensure a unity power factor in the grid by compensating harmonic currents and reactive power, iii) operate the PV panels in their optimal operating points by extracting the maximum power despite the climatic variations. In order to achieve these objectives, a cascaded non-linear controller, consisting of two loops is designed, an outer loop based on a filtered PI controller for the regulation of PV panels voltages and, an inner loop developed based on Lyapunov approach for power factor correction as well as flying capacitors voltages regulation. Furthermore, a state observer is combined with the non-linear controller to perform the grid voltage estimation. The proposed power plant and control strategies are verified and validated by numerical simulation using Matlab/SimPowerSystems environment to assess their performance.