Sub-/Super-SCI Influencing Factors Analysis of VSC-HVDC and PMSG-Wind Farm System by Impedance Bode Criterion

A sub-/super-synchronous interaction (sub-/super-SCI) can occur between a voltage source converter-based high-voltage direct current (VSC-HVDC) and the permanent magnet synchronous generator (PMSG)-based wind farms with long AC transmission lines. However, the influencing factors have not been properly analyzed. In this paper, these are deconstructed and mathematically analyzed from detailed small-signal impedance equations in the dq-frame and the corresponding Bode stability criterion. Distinguishing conclusions from existing papers are obtained by studying the controllers' bandwidths instead of their coefficients. The impacts of AC line impedance on system stability are also investigated. From the analysis of their compositions in impedance structure, the VSC-HVDC bandwidths and the wind farm phase-locked loop (PLL) bandwidth and power ratio, and the AC line impedance have various influences on the system stability. Meanwhile, the wind farm outer DC voltage and inner current control bandwidths have little impact on system stability. The results of these studies show that the magnitude in the axes q-axes impedance interaction is the essential factor for system instability. Our studies also show system stability is more sensitive to the HVDC bandwidths than the wind converter PLL bandwidth. The simulation results verify our theory conclusions.

Automated summary

This paper analyzes the sub-/super-synchronous interaction between VSC-HVDC and PMSG-based wind farms, focusing on the impacts of VSC-HVDC bandwidths, wind converter PLL bandwidth, and AC line impedance on system stability. The study shows that the magnitude in the q-axes impedance interaction is the essential factor for system instability, and system stability is more sensitive to the HVDC bandwidths than the wind converter PLL bandwidth. Simulation results confirm the theoretical conclusions.