DC Impedance Modeling, Stability Analysis and Active Stabilization of the VSC-HVDC System

In the VSC-HVDC system supplying power to passive network, the dc-side of the system is prone to oscillation and even instability, which is resulted from the constant power characteristic of the inverter station and the interactions of the dc impedance between converter stations. In view of this, firstly, the output impedance model of the rectifier station, dc cable impedance model and the input impedance model of the inverter station are built in this paper. Then, the effect on system stability caused by the length of the dc cable, and the output impedance of the rectifier station is examined by the impedance-based Nyquist stability criterion. And the reason why the rectifier station fails to mitigate oscillation on the dc-side of the VSC-HVDC system using traditional virtual resistance stability control method is revealed. Based on the virtual resistance stability control method, a resistive-inductive impedance active stabilization method aiming at rectifier station is proposed. This method can effectively mitigate the oscillation on the dc-side of the VSC-HVDC system without affecting the load performance of the inverter station. Finally, simulation results validate the proposed method and analysis in this paper.