Modeling of Three-Winding Transformer Based on Root Matching and Shifted Frequency Analysis

When simulating the transient process of a power system, the traditional shifted frequency-based electromagnetic transient (SFEMT) simulation method, based on the trapezoidal rule for numerical integration, is affected by the cumulative truncation errors of the Taylor series, leading to numerical oscillations. To address this issue, a root-matching-based SFEMT simulation (RM-SFEMT) algorithm has been proposed. The RM algorithm achieves precise transfer functions by matching zeros and poles, eliminating truncation errors. This effectively avoids the issue of reduced simulation accuracy during fault transients in traditional SFEMT simulations and enhances the stability of the simulation process. However, there is currently a lack of RM-SFEMT models specifically for three-winding transformers, limiting the application of SFEMT simulations in large-scale AC power grids. This paper presents an RM-SFEMT model for three-winding transformers. First, the principles of SFEMT modeling and simulation are introduced. Based on this, the SFEMT simulation method utilizing RM algorithm is proposed. Then, an RM-SFEMT model for three-winding transformers is developed. Finally, the proposed model is tested on both small-scale and large-scale systems, demonstrating its accuracy and stability.