Interaction analysis of MTDC systems based on self-/en-stabilizing coefficients in weak AC grid conditions in DC voltage control timescale

Multi-terminal HVDC systems based on voltage source converters (VSCs) are widely used to integrate and transmit large-scale renewable generations. Small signal stability problem of such systems caused by the interactions among different VSCs seriously threaten the security and stability of modern power systems. This paper quantified the interactions among VSCs analytically based on self-/en-stabilizing coefficients in weak AC grid conditions in DC voltage control timescale. Based on the analytic expressions, this paper finds the devices and interaction paths that causes the oscillations. Moreover, it analyzes how controller parameters of PLL and reactive power control affect the stability of the system in weak AC grid conditions. The analytic quantification of the interactions among VSCs in this paper provides a way to explain the dynamic stability mechanism of an MTDC system.