Model order reduction of converter-based ac power systems based on interaction modes identification

The considerable integration of renewable energy sources into modern power systems has led to the widespread application of power-electronics devices. Fast-acting controllers of voltage source converters (VSCs) that are employed in many applications can potentially interact mutually, as well as with the resonances of the ac grid, giving rise to new stability problems commonly named converter-driven or harmonic stability. New stability issues require modeling guidelines redefinition for proper analysis. Phasor-based ac grid modeling is adequate for the study of conventional stability phenomena. However, it becomes insufficient for the analysis of converter-related stability issues. Electromagnetic (EMT) ac line modeling is therefore required for modeling the parts of the network in the vicinity of power electronics devices. This paper presents the model order reduction methodology of the ac grid model that determines the boundary between the phasor- and EMT-based grid model, including the complexity level of the EMT part of the model. The methodology is established on the eigenvalues analysis and the interaction modes identification between VSC and ac grid state variables, and it is demonstrated on the IEEE 39 bus grid.