After the asynchronous interconnection of Yunnan and South China Power Grid, a long period of ultra-low frequency oscillation occurred, which seriously affected the safe and stable operation of the system. In this paper, a typical asynchronous interconnected system with high hydropower proportion is established. When entering the asynchronous interconnection mode, the frequency oscillation of the system occurs. The frequency regulation characteristics of steam turbine and hydro-generator are compared and analyzed. The analysis shows that the ultra-low frequency oscillation is caused by the counter-regulation of half cycle of the turbine. On the other hand, the frequency regulation performance of the system can be improved to a certain extent by installing frequency limit control of DC control system. The dead zone of FLC is not too small, so it can be adjusted jointly by referring to the primary frequency regulation dead zone configuration of the unit speed control system.

DC,ultra-low frequency oscillation,asynchronous networking,frequency limitation control