Proposal and Verification of Modular Multilevel Converter Circuit Model for RMS Analysis

HVDC with modular multilevel converters (MMC) is being considered for the point-to-point transmission system. RMS analysis is used for efficient analysis of the impact of HVDC on the existing AC system. However, conventional MMC models are not suitable for RMS analysis because they represent complex circuits and controls of MMC in detail. We have developed a simplified MMC model suitable for RMS analysis by extracting the features of MMC. This model reduces the cell capacitors of the MMC to a single capacitor, and only the DC modulation function is added to the conventional 2-level converter model. To verify the developed model, we compared the results between XTAP and CPAT. The waveforms of the RMS and instantaneous value analyses are in good agreement. The accuracy of the developed model was verified by comparing the behavior during change of active power order and system disturbance.