Multilevel power conditioner for grid-connected photovoltaic applications

A novel scheme for three-phase grid-connected photovoltaic (PV) generation systems is presented in this paper. The proposed scheme is based on two insulated strings of PV panels, each one feeding a standard two-level three-phase voltage source inverter (VSI). Inverters are connected to grid by a three-phase transformer with the open winding configuration on inverters side. The resulting conversion structure performs as a multilevel power active filter, doubling the power capability of a single VSI with given current rating. An original control method has been introduced to regulate the dc-link voltages of each VSI. The proposed algorithm has been verified by numerical simulations with reference to different operating conditions. The results confirm the effectiveness of the whole conversion structure.