Computation of Transient Short-Circuit Currents Analytically in Multiport Flexible DC Transmission System

After a fault occurs on the direct current (DC) side of a flexible DC transmission system, the short-circuit current rises rapidly and the fault develops extremely quickly. Therefore, accurate fault current calculation is the basis for fault characterization of DC networks. To accurately carry out the calculation of fault current, this paper establishes a system fault equivalent network model based on a modular multilevel converter high voltage direct current system (MMC-HVDC). First, the topology and fault characteristics of the MMC-HVDC system are analyzed in detail, and then a fault current equivalent analysis model of the multi-terminal ring network is established. Finally, the established fault equivalent network model is simulated and verified based on PSCAD/EMTDC to verify the accuracy of the proposed method.