Nonlinear control of single-phase grid-connected photovoltaic systems via singular perturbation

This paper focuses on the problem of controlling a single-phase grid connected to the photovoltaic system with L filter. In this system the DC/AC converter is constituted by two stages: a boost power converter and a single phase inverter. The main control objective is threefold: (i) extracting maximum possible power from photovoltaic module MPPT (ii) tight regulation of the DC link voltage (iii) the power factor correction requirement must be satisfactorily realized. The proposed strategy combines two cascaded nonlinear proportional-integral controllers under pulse-width modulation feedback. The design methodology is developed by using the singular perturbation technique where two time-scale dynamics are artificially induced in the closed-loop system. The Filippov's average model is applied in order to reduce the DC/AC controller design to the continuous-time controller design. It is formally demonstrated, through theoretical analysis and simulation results in MATLAB/SIMULINK that the proposed design methodology achieves desired objectives and it validates the performance of controllers.