An Efficient Unified-Structure Modeling Method for Hybrid MMCs Based on Subdivision States

Hybrid modular multilevel converters (MMCs), which integrate multiple types of submodules (SMs), exhibit complex switching behaviors and diverse operational states. These characteristics substantially increase the computational burden in electromagnetic transient (EMT) simulation and pose significant challenges for real-time implementation. While existing Thevenin-equivalent models strike a reasonable balance between accuracy and efficiency, their coarse representation of SM states limits further gains in computational performance and hinders extension to new SM topologies, as each requires a topology-specific companion circuit. To address these limitations, this paper proposes an efficient, unified-structure EMT modeling method for hybrid MMCs based on refined SM state decomposition. The proposed approach simplifies the internal equivalent circuits while preserving detailed switching characteristics, enabling a unified mathematical formulation applicable to arbitrary SM types without reconstructing companion circuits. Comparative studies against detailed models in PSCAD demonstrate that the proposed method achieves an accuracy higher than 99.9% while significantly reducing computation time. Furthermore, real-time hybrid digital-physical simulation experiments are conducted on a multi-core CPU platform, benchmarked against the Chongqing-Hubei MMC-HVDC project. Both steady-state power transmission tests and transient power-step experiments confirm that the proposed model completes simulations within a 50μs time step without overruns, while maintaining deviations within approximately 5% compared to field-recorded waveforms.