Modified Fault Current Calculation Scheme Combined With MMC Control for AC/DC Distribution Networks

The existing fault current analysis in distribution networks tend to ignore the impact of the control dynamics arising from AC/DC converters. In response to the abovementioned challenge, this paper introduces a novel fault current estimation calculation approach tailored for AC/DC distribution networks, specifically considering the control dynamics of Modular Multilevel Converters (MMC). The methodology commences with the simplified model of the AC/DC distribution networks. Subsequently, on the basis of the analysis for the control structure of MMC, the impact of various control dynamics on fault current is quantified. Then, the branch currents and node voltages are obtained through a set of voltage-current differential equations. To validate the proposed method, simulation verification is conducted using PSCAD/EMTDC. The calculation results of main branch currents demonstrate that the accuracy of the improved method is about 90%, which shows the effectiveness of the proposed method. Furthermore, the robustness of the presented method against the variations of voltage level, breaker delay, and transition resistance is validated, where its accuracy is over 80%.