Frequency Stability and Fast Frequency Response in Hybrid AC-DC Transmission Grids: A Comparative Study of EMT and RMS Modelling Approaches

As inverter-based generation and HVDC systems continue to be integrated into power systems, the system dynamics are becoming faster and more complex, posing new challenges for maintaining system stability and reliability. Consequently, determining the appropriate modelling approach for power system simulations – electromagnetic transient (EMT) or phasor (RMS) modelling in the context of hybrid AC-DC networks, is becoming more essential. This paper provides a comparison of the RMS and EMT modelling approaches based on a comparative study to evaluate the frequency dynamics of an AC-DC network. A model of the modified 4-machine-2-area transmission system is implemented to investigate both modelling approaches. A fast frequency response for the HVDC converters is implemented to reduce the frequency nadir and limit the rate of change of frequency (RoCoF). Various scenarios are studied to represent different dynamic phenomenon in the network. The suitability of RMS models for these various scenarios is investigated.