Space vector modulated cascaded H-bridge multilevel converter for grid integration of large scale photovoltaic power plants

The increasing power rating of large scale grid connected photovoltaic (PV) power plants has opened new opportunities for research in the suitable converter and control techniques considering the existing grid codes. In this paper, a medium voltage multilevel converter is considered based on a three-phase cascaded H-bridge (CHB) multilevel converter and multiple string dc-dc converters. Multilevel converters have reduced switching frequency, good power quality with less THD thus reducing filter requirements. The need of several sources on the dc side of the CHB makes this multilevel technology attractive for photovoltaic applications. Moreover, the converter structure is very flexible and modular. The main challenge of this configuration is to handle the power imbalances among the different cells of one phase of the converter as well as among the three phases. A control strategy based on space vector modulation(SVM) to deal with these imbalances is proposed in this paper. Simulation results of a 5-level CHB for a multistring PV system in MATLAB/Simulink are presented to prove the effectiveness of the proposed control method.