Influence of modulation and voltage balancing on spectral emission of modular multilevel converters

Modular Multilevel Converters (MMC) are a common VSC topology for high power applications like HVDC. Different modulation techniques are being used with this converter topology. Low excitation of harmonics is considered an important advantage of multilevel VSCs, but the generation of a high frequency spectrum above 2 kHz due to the high number of switching devices has not yet been sufficiently investigated. This paper analyses the influence of the modulation strategy and voltage balancing algorithms on the voltage spectrum of the MMC. This is done by simulations of a MMC model using MATLAB / Simulink. Multi-Carrier Pulse Width Modulation strategies and Nearest Level Control are compared. Voltage balancing is analysed by a comparison of different variations of the sorting technique. Simulation results show that modulation affects general composition of the voltage spectrum while voltage balancing influences excitation of high frequency spectral components.