Integration of a large-scale photovoltaic plant using a multilevel converter topology and virtual synchronous generator control

This work investigates the integration of large-scale photovoltaic (PV) plants to the grid. In particular it presents a case study where a cascaded H-bridge topology based on single-phase current-source inverters (CHB-CSI) is used as the grid interface of the PV plant and a control technique named virtual synchronous generator (VSG) is used in order to contribute to the stability of the grid by providing inertial response and primary frequency control to the PV plant. For all the three simulated cases the proposed control strategy for the PV plant was always capable to perform the VSG functions (inertial response and damping), even when one of the PV arrays output power went down to 10 %. However, simulation results also showed that in some cases the voltage variations were close to 100 % and even 300 % of its nominal value. Even though the execution of the VSG was always successful, the obtained results indicate that voltage loops are needed in order to keep the output voltages at a safe level.