Maximum Value Calculation and Linear Approximation of DC Fault Current of a Single MMC Before Blocking

The calculation of the DC fault current of a single MMC before blocking is of great significance for practical engineering. For example, the maximum value calculation of the DC fault current before blocking is important for the selection of the inductance of the smoothing reactor. Therefore, this paper mainly studies the calculation of the DC fault current of a single MMC before blocking. Firstly, the analytical expression of the DC fault current before blocking is derived. Secondly, the approximate value of the maximum DC fault current before blocking is obtained by merging and simplifying the expression. Compared with the approximate value calculated by an existing method, it highlights that the maximum value calculation before blocking in this paper is more reasonable. Finally, the feasibility of linear approximation of the DC fault current before blocking is qualitatively analyzed, and the linear approximation analytic expression of the DC fault current is given based on the Taylor formula. By analyzing the error of the linear approximation calculation, its applicability is discussed with 5% and 10% as examples. The feasibility and correctness of the linear approximation calculation are verified by building an electromagnetic transient simulation model in PSCAD/EMTDC.