Internal Energy Balance of a Modular Multilevel Cascade Converter Based on Chopper-Cells With Distributed Energy Resources for Grid-Connected Photovoltaic Systems

Abstract

This paper presents the internal energy balance of a modular multilevel cascade converter with photovoltaic arrays as distributed energy resources. This converter is characterized by a modular arm structure composed of bidirectional cascaded chopper cells with floating DC capacitors, where each cell is connected to a photovoltaic array through a DC/DC converter. A continuous model and a control method are proposed to maintain the internal energy balance and achieve independent voltage control of all the floating DC capacitors, allowing the tracking of the maximum power point for each photovoltaic array. The operation with asymmetric energy generation at different levels of irradiance is discussed to maintain the internal energy balance without distortions in the DC link and AC output currents, focusing on the operation with individual cells with zero energy generated from PV array. This topology and control method is suitable for hybrid multi-terminal high voltage DC systems and hybrid generation systems, such as wind-solar energy systems. Experiments are presented to validate the proposed model and control method.