Nonlinear Control of Double Stage Three-phase Grid-Connected Photovoltaic Systems

This study concerns the control law design for a three-phase grid-connected photovoltaic (PV) system. The proposed control approach consists of a cascaded structure to deal with the following objectives: (i) Operate the PV panels at their maximum power point (MPP); (ii) Regulating the intermediate voltage to ensure convenient operation of the inverter: (iii) Power factor correction (PFC) at the grid-filter connection point. To meet these aims: On the DC side, a control loop is designed to monitor the PV voltage to track its optimal reference generated by the MPPT algorithm. On the AC side, two nested loops have been designed, the outer voltage loop is made by using a filtered PI regulator for the DC bus voltage regulation, while the inner loop is developed using the Backstepping-sliding mode technique to deal with power factor correction (PFC). The performance of the proposed controller under operating conditions is evaluated by simulating it on MATLAB/Simulink, the results obtained show that this controller presents a good response.