Stability of two-terminal high-voltage direct-current power transmission systems: Nexus between parameters and controls

The stability of high-voltage direct-current (HVDC) power systems is determined by both parameter variables (e.g., proportional-integral parameters) and control variables (e.g., control references). However, the two decision variables are separately addressed in the literature, ignoring their nexus. To this end, this study investigates the interdependence of stability between two decision spaces for two-terminal line-commutated converter (LCC) HVDC transmission systems. Therein, we formulate concise closed-form eigenvalues for HVDC systems, yielding HVDC stability regions that satisfy given stability margins. Then, the HVDC eigenvalues are intuitively characterized as butterfly-like shapes in the control space but valley-like shapes in the parameter space. This elucidates the co-existence of two situations of non-smoothness in the dominant eigenvalue. More importantly, the variations of these geometric shapes reveal the interdependent eigenvalue mechanism from an inter-stakeholder and inter-timestage perspective. This indicates how prior parameters (or posterior controls) determine the HVDC stability in the operation stage (or planning stage). In particular, this leads to a zero eigenvalue in one decision space, while the solution is located in the other decision space. Finally, the proposed interdependent stability properties of HVDC systems are verified in a Real Time Digital Simulator (RTDS)-based testbed. • Closed-form eigenvalues reveal HVDC stability boundaries in two decision spaces. • Interdependent HVDC eigenvalue mechanism across planning and operation stages. • Co-existence of two switch-induced non-smoothness in the dominant eigenvalue. • Stability properties validated via a RTDS testbed and visualized in attached videos.