Control technique to solve the imbalance problem in photovoltaic grid connected power systems

This paper presents a control strategy applied to a three-phase Cascaded Cell Multilevel Inverter (CCMLI) feeded by photovoltaic panels and connected to power grid, able to compensate imbalances between cells and phases. The technique consists in indirectly obtaining common mode voltage and adding a control loop power control in the conventional structure. Following in this analysis, it will be presented a method for determining the operational limits of a photovoltaic system to support the most diverse conditions of imbalances. Finally, simulation results of a seven levels CCMLI are presented, with string topology without boost stage to demonstrate and validate the proposed technique.