Impedance based stability analysis of VSC-based HVDC system

With increasing activities in development of Voltage Source Converter (VSC) based High Voltage dc (HVDC) transmission system, it is necessary to pre-asses their impact on system stability before connecting to the main ac grid. Existing approaches to study such instability are mainly based on converter control models and do not include the effects of grid impedance. This paper presents the stability analysis of VSC- based HVDC system which includes controller dynamics and also main ac grid impedance. It is shown that the system will remain stable as longs as the ratio of dc system impedance and HVDC converter dc input impedance satisfies the Nyquist stability criterion. An analytical linearized model of a point-to-point connection HVDC system is developed to demonstrate the application of this method and the result is compared with nonlinear model developed in matlab/simulink association with simpower system.