Load-Flow-Based Calculation of Initial Short-Circuit Currents for Converter-Based Power System

Short-circuit current is a key characteristic value for synchronous generator-based power systems. It is employed for different applications during the planning and operation phases. The proportion of converter-interfaced units is increasing in order to integrate more renewable energy sources into the system. These units have different fault current characteristics due to their physical properties and operation strategies. Consequently, the network’s short-circuit current profile is changing, both in terms of magnitude and injection time. Therefore, accurately estimating fault currents is crucial for reliable power system planning and operation. Traditionally, two calculation methods are employed: the equivalent voltage source (IEC 60909/VDE 0102) and the superimposition (complete) method. In this work, the assumptions, simplifications, and limitations from both types of methods are addressed. As a result, a new load-flow-based method is presented, improving the static modeling of generating units and the accuracy in the estimation of short-circuit currents. The method is tested for mixed generation types comprising of synchronous generators, and grid-following (current source) and grid-forming (voltage source before and current source after the current limit) converters. All methods are compared against detailed time-domain RMS simulations using a modified IEEE-39 bus system and a real network from ENTSO-E. It is shown that the proposed method provides the best accuracy in the calculation of initial short-circuit currents for converter-based power systems.