Investigating small-disturbance stability in power systems with grid-following and grid-forming VSCs using hybrid modelling approaches

The mass integration of power electronics-based devices is changing small-disturbance stability issues in power systems from primarily interactions between synchronous generators to include interactions between power electronic devices and the AC network. However, modelling of AC networks for small-disturbance stability assessment in large power systems generally do not include the transmission network dynamics and, therefore, fails to identify these newly emerging power phenomena. A suggested solution is the hybrid modelling approach which models the vicinity around the power electronics with network dynamics while representing the remainder of the network with a steady-state model. This paper identifies the most appropriate selection of dynamic AC network modelling in accordance with different scenarios including different power electronic control schemes, different power electronic operation modes, and different locations of power electronic devices. It is shown that more of the network must be modelled dynamically when VSCs are located in low SCR regions, operating in inverting mode, and using grid following or grid-forming control with inner current control explicitly modelled. Contrastingly, less dynamic detail is required for high SCR regions, rectifying mode, and when modelling grid forming control without explicit representation of the inner current controllers. Investigations are performed using the IEEE 39-bus test system.