1227

In China, line-commuted converter (LCC) based ultra-high voltage direct current (UHVDC) transmission projects are main technical means for power transmission from west to east. However, due to high voltage level and large capacity of LCC-UHVDC projects, commutation failures of LCCs have seriously threatened power system stability. The commutation failure of a LCC-UHVDC system will lead to large-scale power flow transfer of the sending end grid, which will cause the power angle of two clusters to pull apart and threaten the power angle stability of the weak sending end grid. Based on a simple sending end power grid model composed of two generators, this paper analyzes the influence factors of the peak value and the damping ratio of the power angle, and reveals the mechanism of power angle instability caused by commutation failures. Finally, based on the electromechanical simulation software PSS/E, the correctness of the theoretical analysis is verified in a modified two-area four-machine system.