A simplified static frequency converter model for electromechanical transient stability studies of 16 2 3 Hz railways John Laury 1 , Lars Abrahamsson 1 , and Math H.J. Bollen 1 1 Lule˚ a University of Technology, Electric Power Engineering Group, Skellefte˚ a Abstract With increased share of Static Frequency Converters (SFCs) in 16 2 3 Hz railway grids concerns about stability have increased. Stability studies for such low-frequency railway grids are few, and models that describe SFC dynamics are especially few. This paper presents an open SFC model for electromechanical stability studies in the phasor domain, suited for 16 2 3 Hz synchronous railway grids. The developed and proposed SFC model is implemented in MatLab Simulink, together with grid and loads. Numerical studies are made, in which the proposed SFC model is validated against both measured RMS-phasor amplitude of voltage and current at the railway grid side of an SFC. The SFC model developed is able to reproduce the measured RMS voltage and current with an acceptable accuracy. 1 Introduction Low-frequency railway grids exist in Austria, Germany, Norway, Sweden, Switzerland and in some parts of the North Eastern U.S. [1]. Because the frequency in the railway grid differs from the one in the public power grid, conversion of frequency is needed. This conversion can either be done by using a Rotary Frequency Converter (RFC) or a Static Frequency Converter (SFC) [2, 3, 4, 5]. The RFC is essentially a three-phase motor and a single phase generator mounted on the same mechanical shaft. The motor is either an asynchronous motor or a synchronous motor, depending on if the railway grid is synchronous to the public grid or asynchronous to the public grid. Therefore, two different types of low-frequency grids can be distinguished. If the motor of the RFC is of synchronous type, the railway grid is synchronously coupled with the public grid. This type of RFC are called synchronous-synchronous RFC. The pole ratio between the synchronous motor and synchronous generator is 3 (Norway, Sweden) or 2.4 (U.S.). Therefore, the induced frequency in the single-phase generator stator will be 16 2 3 Hz in Norway and Sweden, and 25 Hz in the U.S. Using a three-phase induction motor on an RFC results that the railway grid is asynchronous to the public grid. This type of RFC are called asynchronous-synchronous RFC. The pole ratio between the induction motor and single-phase generator is three. The induction motor is a doubly-fed one and the slip is controlled, which results that the frequency of railway grid is controlled. As the railway grid of Norway and Sweden are synchronously to the public grid, the frequency on the railway grid is determined by the frequency in the public grid (the ratio being exactly three). There- 1 arXiv:1811.04962v4 [eess.SP] 30 Jan 2019