A multi-port MMC topology with reduced capacitor size for use in grid-connected PV systems

Abstract

In this article, a novel multi-port modular multilevel inverter topology is presented for grid-connected photovoltaic systems, which feature a smaller capacitor size compared with its counterparts. In the proposed MMC topology, each submodule is an individual input port being fed by an independent PV array through a boost converter. This allows modularity of the proposed topology, easing its maintenance and facilitating its expansion for PV integration. Individual maximum power point tracking controllers are used to operate the boost converters in each submodule to extract maximum energy from their PV arrays under different radiation conditions. A model-predictive control scheme is designed for regulating the proposed multi-port MMC topology to inject the harvested solar power to the grid. This controller enables minimized circulating currents in the MMC arms and balanced capacitor voltages in the MMC submodules, while total harmonic distortion (THD) of injected current to the grid is kept within the limits. The proposed multi-port MMC topology with model-predictive control is validated under different radiation conditions for a grid-connected PV system to indicate that the proposed topology has a desirable performance under different radiation conditions.