Studying and damping the sub-synchronous resonance in the VSC-based high-voltage direct current power transmission system

This article has studied the sub-synchronous resonance (SSR) phenomenon in the high-voltage direct current power transmission systems which are based on voltage-source converters (VSC HVDC), to find a method to limit it by the use of VSC HVDC controllers. The VSC-HVDC converters act like active filters, so we can use secondary controls to absorb low harmonic currents, and we can compensate the harmonic current with sub-synchronous frequency through generator-side inverter. Inverter controls power, but it can also absorb SSR current and limit the sub-synchronous oscillations. The proposed solution reduces the torque applied to the generator shaft, which ultimately reduces shaft fatigue and increases its life span. SSR creates the possibility of severe damages such as shaft failure; but the proposed method not only absorbed this risk, but also provided the system with the benefits of series capacitors and consequently improved the reliability of network performance. The results of the simulation conducted by MATLAB / SIMULINK software indicated the capability Of proposed method in damping sub-synchronous oscillations