Frequency-dependent cable modelling for small-signal stability analysis of VSC-HVDC systems

Abstract

State-of-the-art time-domain models of power cables account for the frequency dependency of physical parameters to enable accurate transient simulations of high-voltage transmission schemes. Owing to their formulation, these models cannot be directly converted into a state-space form as required for small-signal eigenvalue analysis. Thus, dc cables are commonly represented in high-voltage direct current (HVDC) power system stability studies by cascaded pi-section equivalents that neglect the frequency-dependent effects. This study demonstrates how the conventional cascaded pi-section model is unable to accurately represent the damping characteristic of the cable and how this can lead to incorrect stability assessments. Furthermore, an alternative model consisting of cascaded pi-sections with multiple parallel branches is explored, which allows for a state-space representation while accounting for the frequency dependency of the cable parameters. The performance of the proposed model is benchmarked against state-of-the-art cable models both in the frequency domain and in the time domain. Finally, the study provides a comparative example of the impact of the cable modelling on the small-signal dynamics of a point-to-point voltage-source converter (VSC) HVDC transmission scheme.