Model Predictive Control of Dual Three-Phase Four-Leg Multilevel Inverter Supplying Photovoltaic Energy to Low-Voltage Unbalanced Grids

In this paper, a new control system is proposed for a grid-connected photovoltaic (PV) generation system based on a dual three-phase four leg multilevel inverter. This power converter topology, built using two four-leg two-level three-phase inverters, connects two PV arrays in the DC side to three open-end-windings of a three-phase transformer on the AC side. This arrangement is controlled to inject the PV generated power into the low voltage (LV) grid allowing support for unbalanced loads. The proposed control system is based in the model predictive control (MPC). It allows the control of the injected grid currents in balanced/unbalanced conditions while ensuring the balance of the capacitor DC voltages. Several simulation tests are made to validate the effectiveness of the control strategy applied to the proposed PV generation system.