Investigation on interactions between AC and DC grids

In this paper, interactions between AC and DC systems are investigated with theoretical proof. Results are assessed by modal analysis, using participation factor to retrieve the eigenvalues origin among system states. A simple system is studied to present basics of AC/DC interaction studies. Such an example allows an in depth analysis, a very helpful step for understanding more complex systems. Observations were confirmed by time domain simulations comparison with EMT models. The DC part is a Multi-terminal HVDC grid controlled by the voltage droop method. Finally, a case with grid side Voltage Source Converters participating to the primary frequency control is considered.