Short-circuit analytical model for modular multilevel converters considering DC cable capacitance

Abstract

Developing analytical short-circuit models for Modular Multilevel Converters (MMC) is not straightforward due to their switching and blocking characteristics. Short-circuit models for MMCs have been developed previously in the literature. However, there is a lack of understanding regarding the dynamics in the short-circuit model when the DC cable capacitance is taken into account. Therefore, this work proposes an analytical pole-to-pole short-circuit model for half-bridge MMCs that considers the cable capacitance and terminal capacitors and accounts their contribution to fault dynamics. An approximated analytical model has been derived separating the system solutions in different natural frequencies. The proposed model provides an excellent approximation for a vast range of realistic system parameters. The analytical model reproduced the behaviour of the variables in the time domain and provided a clear basis for interpreting the dynamics of the voltages and currents involved.