A Modal Contribution Metric for Quantifying Small-Signal Variability in Power Systems With Converter-Interfaced Generation

Power system dynamic behaviour is changing drastically with the disconnection of synchronous generation and increasing connection of converter-interfaced units, which is not necessarily captured by traditional static grid strength metrics. This paper uses the modal superposition concept to derive metrics and information with respect to locational variability, defined in terms of the maximum deviation of system variables in different network locations. Going beyond typical grid strength metrics, the analysis considers voltage magnitude and frequency variability separately, reflecting the complexities arising from the transition to power electronic control dominated power system dynamics. A further benefit of the approach is the derivation of a clear relationship between the variability of output variables and specific modal interactions via their contribution to the response. The Kundur two-area, four-generator system is utilised and investigations are performed with the integration of grid-following and grid-forming converters to compare with the standard synchronous generator case. The methodology and suggested metric reflects the independent voltage and frequency variability trends across different locations of disturbance and observation across the network. Also exhibited is the use of the proposed method to focus on the characteristics and causes of variability at different timescales.