Research on a z-domain impedance criterion for wideband oscillation of the VSC-HVDC transmission system

Abstract

To delve into the mechanism behind wideband oscillation instability in voltage source converter based high voltage direct current （VSC-HVDC） transmission system and swiftly assess system stability with precision， a modeling method and a stability criterion based on z-domain impedance are proposed. Firstly， employing precise discretization techniques， a z-domain impedance model is established for voltage-source converters considering phase-locked loops （PLLs）， inner-current loop， and voltage feedforward control， along with a z-domain impedance model for AC grids in a global coordinate system. Subsequently， a criterion for generalized forbidden zone is proposed using Gershgorin circle theorem to analyze the impact of phase-locked loops and line impedances on system stability. Finally， simulation analysis is conducted on the VSC-HVDC system to demonstrate the effectiveness of the proposed generalized impedance criterion.

Keywords

• wideband oscillation
• vsc-hvdc
• stability analysis
• impedance model
• discretization