Steady-State Stability Analysis of Shaft Torsional Oscillation in AC-DC Interconnected System with Self-Commutated Converters

Abstract

Recent progress of power electronics technology makes it possible that self-commutated converter using GTOs (Gate Turn-Off thyristors) is considered to be applied to HVDC transmission systems. Since the self-commutated converter can be operated stably without depending on ac-side voltage, the magnitude and the phase angle of the converter output voltage can be controlled independently. Therefore, this type of converter will improve the voltage stability at its ac side. On the other hand, shaft-torsional oscillation of a thermal power plant caused by the interaction between shaft-generator system and control system of the self-commutated converter is still an open problem. In this paper, a linearized model for eigenvalue analysis of a power system including HVDC interconnection with self-commutated converters is described to analyze the effect of the self-commutated converter on the shaft-torsional oscillation of a thermal power plant. Then, numerical results from the eigenvalue analysis of the shaft-torsional oscillation are presented. Results obtained by frequency response method are also reported. The numerical results make it clear that there exist the parameter regions of DC-AVR and ACR control systems of the self-commutated converter where the shaft-torsional oscillation may be caused.