Assessing Interaction Strength between Synchronous Generator and LCC-HVDC in AC/DC Systems

In AC/DC systems, unit interaction factor (UIF) has been developed based on engineering experience to quantify the strength of interactions between generators and LCC-HVDC ties. However, there is no theoretical justification for UIF, which is deemed necessary for the application and further development of UIF. In this paper, we present theoretical proof for UIF by the small signal stability analysis of AC/DC systems. On this basis, critical UIF (CUIF) is further proposed to characterize the stability boundary of AC/DC systems so that UIF along with CUIF can be used to assess the interaction strength and analyze system stability. The theoretical results are verified by eigenvalue analysis and time-domain simulations.