A Short-Circuit Calculation Method for Distribution Networks With 100% Converter-Based Generators Based on Outer-Layer Voltage Approximation and Inner-Layer Spectral Gradient Iteration

With the continuous advancement of power electronic equipment and the widespread integration of distributed generation, distribution networks composed entirely of converter-based generators have become one of the key development approaches for low-carbon and flexible modern distribution systems. This paper investigates a short-circuit calculation method for 100% converter-based generator distribution networks with system voltage established by V/f-controlled converters and multi-point grid-following distributed generation integration. The limitations of the widely used fixed-point iteration method in short-circuit calculations for active distribution networks are analyzed. The intrinsic relationships between the capacity of V/f-controlled generators, the capacity and connection locations of grid-following distributed generators, the magnitude of fault resistance, and the convergence behavior of the fixed-point iteration sequence are revealed. To address the convergence issues of traditional iterative algorithms caused by the capacity of converter-based generators and fault conditions, a short-circuit calculation method based on outer-layer voltage approximation and inner-layer spectral gradient iteration is proposed. The global convergence of the proposed method is mathematically proven. A case study involving a 100% converter -based generator distribution network with five converter-based generator nodes is conducted. A simulation model is built in PSCAD/EMTDC to simulate fault scenarios. The effectiveness and superiority of the proposed method are validated by comparing the short-circuit calculation results with simulation results and benchmarking against fixed-point iteration methods.