Research on Influence Factors in MMC-HVDC Short-Circuit Current Based on Improved Calculation Method

The short-circuit current in MMC-HVDC power grids increases rapidly and is hard to cut off. And there are many factors that affect the development of short-circuit current. Therefore, it is necessary to research the impact mechanism of short-circuit current in DC power grids. An improved calculation method is proposed for short-circuit current based on the transient energy exchange process after a fault. Based on the improved calculation method of short-circuit current, the influence of electrical parameters such as DC line reactance and resistance, bridge arm effect reactance and resistance, and submodule capacitance on short-circuit power is studied. And the mechanism of different grounding methods on short-circuit current is investigated. The two-terminal MMC-HVDC transmission model is built in PSCAD/EMTDC. The results indicate that the DC inductance has the strongest influence on the short-circuit current, the resistance has less influence, and different grounding modes have obvious impact on the short-circuit current. Moreover, the improved calculation method can accurately describe the evolution of the short-circuit current after a fault, providing an important basis for DC protection setting and system planning and design.