Review of oscillations in VSC-HVDC systems caused by control interactions

Owing to the fast control response and distinct characteristics of the voltage source converter (VSC), various types of oscillation incidents related to the VSC-HVDC systems have been observed around the world. However, the causes of such oscillations are complex due to the interactions among the components of the transmission system and the various control methods of the converter station, and yet not systematically comprehended and summarised. Therefore, this study reviews several typical VSC-HVDC oscillation incidents and focuses on the root causes of the oscillation phenomenon. The analysis indicates that the oscillations in the VSC-HVDC system can occur either in subsynchronous frequency or in high-frequency range, up to 1.2kHz. The modelling methods, including the conventional detailed model, equivalent detailed model, and average equivalent model, are also affecting the accuracy of describing the oscillations. The control methods, including adding active control scheme, passive filter at oscillation frequency, and temporary power plant disconnections, are also discussed. The advantages and drawbacks of these modelling methods, analysis methods, and control methods are summarised based on the various system conditions. In the end, the future research perspectives and key challenges are provided for further research references.