Sub- and Super-Synchronous Interaction Caused by Static Var Compensators in a Weak AC Grid Aanlysis and Oscillation Suppression

[Objective] With the increase in the proportion of new energy connected to the grid， issues with power system stability associated with weak grids are becoming increasingly prominent. Static var compensator （SVC）， an important device for improving the dynamic response of power systems， may trigger sub-synchronous and super-synchronous interaction （S²SI） in weak power grids， causing system oscillation. This paper aims to study the mechanism of sub- and super-synchronous interactions induced by SVC in a weak current network and proposes an effective oscillation suppression strategy. [Methods] First， a frequency-coupled impedance model （FCIM） was used to analyze the frequency coupling characteristics between the SVC and weak grid， revealing a strong coupling relationship between the sub-synchronous and super-synchronous frequencies. Second， based on the stability criterion of impedance crossing， the influence of the controller parameters on the oscillation mode is studied， and a supplementary sub-synchronous damping controller （SSDC） is proposed. Finally， an electromagnetic transient time-domain simulation was performed using the PSCAD/EMTDC platform to verify the correctness of the theoretical analysis and effectiveness of the control strategy. [Results] The results show that SVC can cause S²SI in a weak power network， with the oscillation frequency closely related to the controller parameters. The oscillation phenomenon can be effectively suppressed by optimizing the controller parameters. The simulation results show that the proposed SSDC control strategy can significantly reduce the amplitude of sub-super-synchronous oscillation and improve system stability. [Conclusions] The results reveal the mechanism of S²SI triggered by SVCs in a weak power grid at the frequency-domain impedance level. The proposed control strategy improves the oscillation suppression effect while ensuring the regulation rate of the SVC， thus highlighting significant engineering application value.