A New Submodule for Capacitor Voltage Ripple Reduction with Fewer Semiconductor Components in Modular Multilevel Converters

Abstract

The size of energy storage resources has a vital role in the cost, size, and weight of power electronics converters. Multilevel converters usually operate at low switching frequencies to prevent high switching loss. Since modular multilevel converters are constructed of a series connection of some submodules, a lower switching frequency causes a higher capacitor voltage ripple. To deal with this issue, the size of converter capacitors has to be increased. This paper presents a new submodule (SM) that enables the parallel connection of capacitors. This SM decreases the ripple of the capacitors and offers three-level voltage at its terminals. In addition, it uses fewer switching devices and gate driver circuits in comparison with other submodules presented in the literature. Also, the number of capacitor voltage sensors is reduced by half due to the parallel connection of SM capacitors. The simulation and experimental results verify the performance of the proposed submodule.