Impedance-Based Resonance Analysis in a VSC-HVDC System

Resonances can limit power transfer in a voltage-source converter-high voltage dc (VSC-HVDC) system. The objective of this paper is to develop impedance models for the rectifier ac system and the inverter ac system for a VSC-HVDC system. Resonance stability will be examined using Nyquist stability criterion and impedance frequency responses. The impedance models consider the outer control loop and the inner current control loops of VSCs. Impacting factors are then examined. Stability analysis demonstrates that the feedforward filter, line length, and power transfer level have a significant impact on resonances. Time-domain simulation results obtained by Matlab SimPowerSystems are used to validate the analysis.