A Grid-Connected PV Multilevel Cascaded Inverter System Based on Single and Three-Phase Two-Level Inverters

In this paper it is presented a new multilevel-cascaded inverter (MCI) based grid connected photovoltaic system. To avoid a dispersed PV structure the proposed multilevel topology uses a combination of three and single-phase classical two-level inverters. The multilevel topology consists in a conventional three-phase VSI inverter, connected to the PV generator DC/DC converters, and three single-phase inverters connected to the AC grid. The DC side of the single-phase inverters will use floating capacitors. The output levels voltage are maximized through the asymmetry that will be used between the DC voltages of the single and three-phase bridge inverters. A control strategy for this three-phase MCI is also presented. This strategy is based on a sliding mode and proportional-integral (PI) linear controllers. Their design is made to obtain the SPWM modulator parameters. The algorithm of this controller also ensures the DC voltage balancing of the single phase inverters floating capacitors. Simulation results are presented in order to confirm the proposed topology and the control adopted.