Internal Faults Analysis of MMC using State-Space Modeling

The modular multilevel converter (MMC) has gained significant attention due to its potential usage in high-voltage direct current (HVDC) grids. Simulation study of MMCs can become cumbersome since they are made up of a large number of series connected sub-modules (SMs). In this paper, a state-space model of switching function-based representation of MMC is developed to ease the analysis of internal faults. The proposed model combines multiple SMs into a single switching function, making analysis more straightforward. The switching functions reported in the literature are static and cannot be used to analyze internal SM faults. Case studies are performed using the proposed and detailed switching model for a 21-level MMC for normal and fault conditions. Further, the simulation execution time is compared for both models.