Modular Multilevel Converters for Large-Scale Grid-Connected Photovoltaic Systems: A Review

Abstract

The use of photovoltaic (PV) systems as the energy source of electrical distributed generators (DG) is gaining popularity, due to the progress of power electronics devices and technologies. Large-scale solar PV power plants are becoming the preferable solution to meet the fast growth of electrical energy demand, as they can be installed in less than one year, as compared to around four years in the case of conventional power plants. Modular multilevel inverters (MMIs) are the best solution to connect these large-scale PV plants to the medium-voltage (MV) grid, due to their numerous merits, such as providing better power quality, having higher efficiency, providing better reliability, and their scalability. However, MMIs are still progressing and need some improvement before they can be implemented safely in the industrial, medium, and high voltage networks. The main purpose of this paper is to review the present MMIs topologies when used in PV applications. The review aims to present a comprehensive study of the various recent submodule circuits associated with MMI topologies. Maximum power point tracking (MPPT) control schemes for PV inverters will be explored extensively. Then, the different control strategies of PV MMIs will be presented and compared to give a holistic overview of the submodules balancing techniques, ranges, and capabilities under balanced and unbalanced grid conditions. In addition, the paper will discuss the future of PV MMIs systems in electricity networks.