Transient Voltage Stress Modeling for Submodules of Modular Multilevel Converters under Grid Voltage Sags

The trend for the model-based design of modular multilevel converters (MMC) demands a better estimation of the submodule (SM) voltage stress. The transient voltage stresses of MMC SMs are important for the SM capacitor dimensioning and the robustness of power modules. This paper proposes an analytical model of the SM transient voltage stress under grid voltage sags. It is based on a simplified analysis of the MMC current control and circulating current control schemes. A case study reveals that a sufficient accuracy level can be achieved with the proposed model to estimate the transient voltage stress.