Equivalent Method of IGCT-MMC Submodule Snubber Parameter for VSC-HVDC System Study

Recently, much attention has been paid to the investigations on IGCT based modular multilevel converter (IGCT-MMC). However, the time constant of additional snubber in IGCT-MMC submodule is quite small (orders in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{s}$</tex>), leading to a smaller simulation solution time step around <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1 0 0}$</tex> ns to accurately represent the operation characteristics of snubber. Consequently, such a smaller time step is not suitable for VSC-HVDC system study since the required simulation time is much longer. To handle this issue, analytical aspect of IGCT-MMC submodule is firstly described, including the topology, operation analysis and parameter calculation of the snubber. Then the equivalent method of snubber parameter is proposed to utilize a larger time step for system study. The principles as well as the determination of the scaling coefficient are illustrated. Finally, simulation results of double pulse test and system operation are shown, and the correctness of the proposed method is verified.