Modeling and control of the modular multilevel cascade converter based on chopper-cells for grid-connected photovoltaic systems

This paper presents a modular multilevel cascade converter (MMCC) based on chopper-cells for a grid-connected photovoltaic (PV) application suitable to medium and high voltage systems without line-frequency transformers. This converter is characterized by a modular arm structure composed by cascaded chopper-cells with floating dc capacitors, each one connected to a photovoltaic panel. This paper proposes a continuous model and a control method to achieve independent voltage control of all the floating dc capacitors, enabling the tracking of the maximum power point for each photovoltaic panel. The validity of the theory is confirmed by simulation and experiment.