On the control of a grid-connected photovoltaic plant under non-uniform insolation

This work presents a case study of a modular photovoltaic (PV) plant where PV panel arrays are connected to the grid through cascaded single-phase current-source inverters. It is shown that, under non-uniform insolation conditions of the PV arrays, the output voltages of the cascaded inverters become unbalanced. Therefore, a dc voltage elimination control loop is proposed to balance the output voltage of the H bridges. Additionally a control technique called virtual synchronous generator (VSG) is applied to the PV plant in order to support the control of the grid frequency emulating an inertial response and providing damping and droop power. For the simulated cases the PV plant was always capable of performing the VSG functions, in spite of the unbalance condition of the output voltages of the H bridges. However, when the proposed dc voltage elimination control loop was in operation the maximum peak output voltage and the amplitude of its fundamental component were reduced in 13.3 % and 27 % respectively.