Model of three level neutral point clamped converter (NPC) for grid connected photovoltaic systems

Photovoltaic modules as direct converters of solar energy into electrical energy are typically connected to the power grid trough standard two level converters. A photovoltaics system can be connected to the power grid if it can satisfy the IEEE standardized conditions set by the power grid operator. The conditions include limitations of THD factor and current harmonics. Multilevel converters which have a lower THD factor than two level converters can satisfy these conditions and in the same time work at higher switching frequencies lowering the losses and the size of the output filter. The model implemented in Simulink® MATLAB consists of a photovoltaic array, boost dc-dc converter with MPPT control and three level neutral point clamped converter connected to the power grid. The simulation results are presented, analyzed and compared to the standard model with a two level converter to validate the benefits of the usage of multilevel converters for grid connected photovoltaic systems.