Improving the System Dynamic Stability of MMCs by Insertion Indices Compensation with Capacitor Voltages Feedforward

Due to the significant coupling impacts of the internal multiharmonic dynamics on the ac terminal in a modular multilevel converter (MMC), its terminal characteristics is quite different from a two-level voltage-source converters (VSCs). Thus the complex modeling methods, e.g. the harmonic state-space modeling approach, are required to analyze the stability of MMC-based system. In this paper, the internal dynamics of MMCs are decoupled in the differential-mode (DM) circuit using insertion indices compensating method by feedforwarding the capacitor voltage. Therefore, the ac-side characteristics is the same as that of the two-level VSCs, and the stability and controller parameters can be design-oriented by the simple averaged small-signal model.