Investigating Sub- and Super-Synchronous interaction between static VAR compensators and a weak AC grid

Static VAR compensators (SVCs) are widely used to improve the dynamic performance of power systems. This paper explores the vulnerability of SVCs to triggering emerging sub- and super-synchronous interaction (S²SI) when connected to weak AC grids. The mechanism and characteristics of the interaction phenomenon are investigated through frequency impedance modelling (FCIM) and reactance-crossover based stability criterion. The analysis results show strong frequency coupling between sub- and super-synchronous frequencies. In addition, the impact of controller parameters on the mechanism and features of the interaction phenomenon have also been investigated. Finally, the stability results are validated through electromagnetic transient (EMT) time domain simulations using PSCAD/EMTDC.