Converter Modelling Aspects at the Boundary between EMT and RMS Domain

The main distinction between Electromagnetic Transients (EMT) and Root Mean Square (RMS) simulation is the constant power system frequency assumption in the RMS domain. This paper highlights the insufficiencies of RMS simulation in a converter-dominated power system traced back to an elementary mathematical model. A new variable called ‘Transient Voltage Difference’ is introduced to quantify the modeling error of inductively coupled converters in RMS domain with respect to EMT domain. The proposed index is calculated analytically and verified simulatively in a basic inductive network highlighting the coupling impedance effects. This quantity measures the transient output voltage capacity and is vital in Voltage Source Converter (VSC) design and planning studies. ‘Transient Voltage Difference’ emphasizes the hidden assumption on the converter’s output voltage rating, as current sources consider only the limitation in current. It can be used to assess the viability of the RMS domain modelling approach. This work highlights the basic design requirements for typical VSC in stability analysis.