Comprehensive assessment of voltage and current source PV-based modular multilevel converters

Recently, modular multilevel converters (MMCs) gained popularity for the grid integration of photovoltaic (PV), due to their many advantages, including low total harmonic distortion, high control flexibility, and distributed maximum power point (MPP) tracking capability. Two distinguished families of MMCs exist: voltage source and current source. Voltage source MMCs are mostly studied, but current source MMCs offer advantages under certain operating conditions. This article compares voltage and current source MMCs, for PV integration. To this aim, several key indicators are identified: number of components, energy stored in passive elements, semiconductor power rating, and the number of MPP trackers. The results of the analysis, performed in MATLAB©, show that for a fixed number of output voltage levels, power rating, and switching frequency, voltage source MMCs have simpler control and higher number of MPP trackers. In contrast, current source MMCs minimize the semiconductor power rating, the number of components and the energy stored in passive elements. Regarding efficiency, in the analyzed case study, voltage source MMCs perform better under both homogeneous and non-homogenous irradiance conditions. This article provides a tool to select the optimal solution based on the required target (e.g. efficiency, energy storage etc.), given the specific characteristics of the application.