Average Model of Hybrid Modular Multilevel Converter Considering Overmodulation

The Half-Bridge Full-Bridge Hybrid Modular Multilevel Converter (MMC) commonly leverages the negative voltage output capability of full-bridge submodules and operates in an overmodulation state during DC transient processes. However, the electromagnetic model that takes into account the switch states of the submodules tends to simulate at a slow pace, which is not conducive to system-level simulation analysis. To address this issue, this paper proposes a hybrid MMC average value modeling approach that incorporates the overmodulation process. This model considers the external characteristics of both the alternating current (AC) and direct current (DC) sides, as well as the dynamic characteristics of the DC capacitor voltage. The paper first introduces the typical hybrid MMC topology and the overmodulation process in engineering applications. It then presents a hybrid MMC average value model that accounts for the overmodulation process. Finally, the effectiveness of this model is verified in scenarios involving faults at the sending end of the converter station, faults at the receiving end, and DC faults. The results show that the average model proposed in this paper has a high degree of agreement with the detailed model and can greatly improve the simulation efficiency.