Analytical Calculation of Valve-Side Short-Circuit Current of Bipolar MMC-HVDC System Considering Feeding AC Current

The bipolar MMC-HVDC system has unique superiority of large transmission capacity and high dependability, and has become the first choice for onshore new energy delivery methods. Compared to an AC line fault, the short-circuit grounding point is closer to the converter with occurrence of a valve-side short-circuit fault, the coupling discharge between the sub-module capacitor(SMC) and the grounding point is more violent, and the short-circuit current rises rapidly, which may cause serious damage to the converter and the line. Therefore, this paper investigates the valve-side AC symmetrical short-circuit fault of the converter station, analyzes the discharge mechanism of SMC and fault current path, and calculates the discharge current of SMC in non-faulty converters(NFC) and the discharge current of SMC in fault converters(FC) analytically, considering feeding AC current. The PSCAD/EMTDC simulation model verifies that the short-circuit current calculation curve considering feeding AC current is in better agreement with the simulation curve and the error is smaller than that without considering feeding AC current, thus verifying the rationality of the theoretical analysis.