Impedance Analysis and Stabilization of Point-to-Point HVDC Systems Based on a Hybrid AC-DC Impedance Model

Stability analysis of the point-to-point high-voltage dc (HVdc) transmission systems is crucial for planning and operational purposes. However, due to the protection of trade secret and user privacy, it is difficult to have access to detailed information of the converters of an HVdc system. To avoid detailed information of the converters during system stability assessment, this article adopts a hybrid ac-dc impedance model along with a new network partitioning method to assess stability of the point-to-point HVdc system. The proposed method has the following advantages. First, in contrast to the conventional stability analysis methods, the number of right half-plane poles of the system minor-loop gain is not required. Second, different from the conventional impedance models, the hybrid ac-dc impedance excludes the impacts of the impedances of the ac grid and dc networks, to which the converter is connected. Accordingly, the hybrid ac-dc impedance model solely depends on the converter itself. In addition to the proposed method, this article demonstrates that the power flow direction of a point-to-point HVdc system has no impact on selection of different system minor-loop gains. Accuracy and effectiveness of the proposed method are evaluated and validated by time-domain and frequency-domain simulations in the MATLAB/Simulink environment.