Number Of Levels, Arm Inductance And Modulation Trade-Offs For High Power Medium Voltage Grid-Connected Modular Multilevel Converters

There is an increasing focus on integrating flexible dc links for bulk power routing in medium voltage distribution grids. In such applications, the ac-dc Modular Multilevel Converter (MMC) devised for medium voltage and high-power ratings can be an interesting choice. This paper highlights some less explored design trade-offs arising due to the limitation on N in relation to modulation frequency and arm inductance. Specifically, the study intends to describe the interdependent influence of each degree of freedom on several aspects such as capacitor voltage balancing, circulating currents and harmonic performance. Finally, the importance of considering inter-harmonies in the performance assessment of the MMC instead of the conventional interpretation of distortion calculation is highlighted.