Universal terminal model suitable for various modular multilevel converter topologies for power-system-level simulation application

Modular multilevel converters (MMCs) have extensive applications and increasing power occupancy in power systems, and various improved topologies with dc fault blocking capability have been developed. The control, dynamic behaviour, and topology of MMCs require significant consideration when building MMC models for power-system-level simulation. In this study, a universal terminal model (UTM) that is suitable for various MMC topologies and can be renewed by simply setting two indexes without changing the circuit structure is proposed. The complicated arm circuit structure can be simplified with the aid of auxiliary components, such as diodes, ideal switches, and controlled voltage sources. Arm dynamics, including cumbersome sub-module switching actions, can be averaged by disregarding the differences among sub-modules and the effect of modulation and capacitor voltage balancing. The proposed UTM exhibits high accuracy and efficiency and thus beneficial for investigating power-system-level issues. In addition, UTM can avoid repetitive and duplicate modelling efforts when the MMC topology changes. The UTMs of MMC based on half-bridge, clamp-double, and full-bridge sub-module are built. Simulation results of comparisons between detailed models and UTMs validate the accuracy and efficiency of the proposed models.