Control of three-phase stand-alone photovoltaic systems with unbalanced loads

Three-phase four-wire supply with a neutral point is often required in stand-alone photovoltaic systems. In general, the neutral point is achieved in three-phase systems by using three H-bridge inverters, with a high number of semiconductors, or from the dc-bus medium point, which is affected by loads consuming dc currents. In photovoltaic systems, many regulations demand the use of a transformer. Then, the configuration consisting of a three-leg inverter and a delta-wye transformer is very interesting. This system presents a natural coupling between the variables. In order to control it, this paper proposes a double-loop strategy with new inner current and outer voltage control loops that include feed-forward and feedback compensations. Simulation results show that the proposed control strategy achieves an accurate and robust behavior.