Effects of phase leg reactor, submodule capacitor, number of submodules and switching frequency on harmonics in modular multilevel converters

Abstract

The modular multilevel converter (M2C) will play an important role in the future especially for high-voltage and high-power applications where controllability is a key factor. Although a lot of research has been carried out on this topic, little has been done to understand how different system parameters, like the arm reactor, the submodule capacitor, number of submodules and switching frequency, influence the performance of the converter. In this study, a robust model of a M2C was presented and used to perform an extensive parametric sweep versus the variables mentioned above. It has been shown that by implementing an anti-windup scheme, the model remains stable over a large range of parameters. It has also been shown that an optimum knee point exists in all total harmonic distortion (THD) graphs versus inductance, capacitance, number of submodules and switching frequency. Finally, it has been shown that to decrease THD, the number of submodules can be increased while making sure the effective arm capacitance is maintained constant.

Keywords

• power capacitors
• harmonic distortion
• voltage-source convertors
• capacitance
• inductance
• submodule capacitor
• switching frequency
• modular multilevel converter
• high-power applications
• arm capacitance
• inductance
• THD graphs
• total harmonic distortion
• anti-windup scheme
• phase leg reactor