Sub-synchronous oscillation analysis of converter and SVG interactive system

Although the SVG (Static Var Generator) can improve the voltage characteristics of grid-connected converter, it will sometimes deteriorate the stability of the system. In this paper, the influence of SVG on sub-synchronous oscillation of grid-connected converter is modeled and analyzed. Firstly, a symmetric impedance model and the equivalent complex circuit of converter and SVG interactive system are constructed. The system is simplified into SISO (Single-Input Single-Output) model. The impact of SVG on the original system can be measured by the additional impedance of SVG in equivalent complex circuit. Secondly, the analytic expression, which is used as the influence factor index, of SVG additional impedance on sub-synchronous oscillation modes are derived based on the complex circuit modal power analysis. Finally, the influence of SVG on the stability of the system is analyzed based on the influence factor index. The effectiveness of the modeling and analysis method is verified by Nyquist criterion and time domain.