Reduction of capacitor voltage ripple in a modular multilevel converter employed in adjustable speed drive application

Abstract

Nowadays modular multilevel converters (MMCs) are widely used due to their excellent performance and high modularity. However, in the variable speed drive application, there is a challenge to control the voltage ripple of submodules at the low frequency operating points. This challenge is even more critical during the startup procedure of electrical drives. In this paper, the main reasons of voltage ripple generation are explained. Then a method to control the amount of voltage ripple at the low frequency applications is introduced. In fact, the trapezoidal voltage waveform is injected at the reference of phase voltage to reduce the voltage ripple. Next, the proposed method is compared with existing methods to show its better performance. Finally, MATLAB/Simulink software is used to evaluate the performance of proposed and already existing methods.