Impact of System Inherent Characteristics on Initial-Stage Short-Circuit Current of MMC-Based MTDC Transmission Systems

This paper studies the impact of the inherent characteristics on the initial-stage short-circuit current of modular multilevel converter based multi-terminal direct current (MMC-based MTDC) transmission system. A short-circuit current calculation method based on input-output characteristics is proposed. The MMC's input-output characteristics are factorized into a series combination of a linear and a nonlinear part through the operator approach. The inherent characteristics of the system represent the inherent properties of the MMC-based MTDC system, which are unrelated to the short-circuit fault. Therefore, short-circuit currents are decoupled and quantitative indices are proposed to measure the impact of the system inherent characteristics on the initial-stage short-circuit current. The proposed decoupled short-circuit current calculation method and the quantitative indices are verified in a typical MMC-based MTDC transmission system under different system parameters and structures. The proposed quantitative indices can effectively evaluate the short-circuit current of the MMC-based MTDC system without calculating the short-circuit current, which indicates that they can provide guidance for the planning of DC system structure, determination of operational modes, and selection of system parameters from the perspective of short-circuit current.