Modeling of VSCs Considering Input and Output Active Power Dynamics for Multi-Terminal HVDC Interaction Analysis in DC Voltage Control Timescale

Multi-terminal high-voltage direct current (MTDC) systems based on voltage source converters (VSCs) are increasingly utilized. In such a case, dynamic interactions among different VSCs of each terminal become one of the leading problems for the ac/dc interconnected system. This paper presents a frequency-domain small-signal model of MTDC-linked VSCs in dc voltage control (DVC) timescale based on the motion equation concept. Control schemes, including two typical dc voltage-droop control, phase-locked loop, and vector control in DVC timescale are taken into account adequately. By considering the dynamics of both input and output active powers across the dc capacitor, the proposed model aims to describe the external characteristics of MTDC-linked VSCs independent of grid conditions, which makes it easy to extend in various types of MTDC systems. Interaction analysis of a typical four-terminal HVdc system was conducted to validate the feasibility of the presented model.