May 2021

Featured Speaker: Tim Green, Professor, Co-Director of the Energy Futures Laboratory (EFL), Imperial College London

The replacement of electro-mechanical machines by inverter-based resources (IBR) is fundamentally changing the dynamics and stability properties of grids. A review will be made of the needs a grid system has in order that it is stable and secure. The needs in terms of voltage strength, frequency regulation and synchronisation will be discussed in term of how they are met by synchronous machines, grid-following converters and grid-forming converters. A case will be made that there is advantage in not all resources being obliged to provide all system services and that new services can replace some traditional services. Thus, strictly following a virtual synchronous machine (VSM) approach may not yield the best solution.

Approaches to ensuring system-wide dynamic stability will also be explored noting that IBR have overlapping sets of dynamics but with details often hidden in black-box models. A method for identifying root-causes of poorly damped modes in black-box models will be illustrated. This analytical grey-box method avoids exhaustive transient simulation. A toolbox for compiling models of composite grids with IBR and synchronous machines will be introduced. The talk will conclude with some thoughts on modelling and analysis challenges that remain for IBR dominated grids.

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