Improved Accuracy in Calculation of Initial Fault Current in Converter-based Power Systems

Initial short-circuit current is an important characteristic parameter (operational and planning) for the classical power system and is calculated as per the VDE/IEC 60909 standard. However, with synchronous generators being replaced with converter-interfaced generators, the short-circuit current profile is changing. Therefore, the question is: How to update the static modeling of generating units to calculate initial fault current with high penetration of converter-interfaced generators in the power system? This paper contributes by investigating the accuracy of currently valid VDE/IEC standard with respect to the assumptions made and modeling of fault contributing units. Then an extended approach is proposed for the calculation of initial fault current for better accuracy. This is achieved by characterizing the initial fault response of converters and then considering the complex contribution instead of scalar contribution as in the existing norm. This extended approach is further investigated and sensitivity analysis with respect to system impedance, fault location, and proportion of synchronous generators is presented.