Research On Identification And Control Of Key Units For Ultra-low Frequency Oscillation In Southwest Power Grid

The rapid development of the power industry has promoted the social economy and people's lives.In order to meet the growing demand for electricity and the sustainable development of the power industry,modern power systems are developing in the direction of large capacity,long distance and high voltage.The interconnected power grid came into being.The interconnected power grid has a long distance and a large transmission power,which makes the electrical connection between the generators extremely weak.The long-distance heavy-duty working conditions easily lead to various types of oscillation accidents in the interconnected power grid.Before the end of 2018,the Southwest Power Grid will be completed and put into operation,and the southwest main network and the Central China Power Grid will be connected to each other through the back-to-back asynchronous interconnection.The AC-DC hybrid will become a pure DC asynchronous interconnection pattern,and the frequency adjustment capability of the Southwest Power Grid will decline.The grid frequency will change greatly,and the frequency limit and the risk of instability increase.In the asynchronous networking system test,70%of N-2 faults will cause long-term ultra-low frequency oscillations in the Southwest grid.For this problem,the main work of this paper is as follows:Firstly,the mechanism of ultra-low frequency oscillation of Southwest Power Grid is analyzed from the damping angle.One of the reasons for the ultra-low frequency oscillation of Southwest Power Grid is the negative damping effect of hydropower unit.The negative damping effect of hydropower unit is the main factor that causes the ultra-low frequency oscillation of Southwest Power Grid.Then,a comprehensive identification method for key units of ultra-low frequency oscillation is proposed.The amplitude-phase analysis is used to study the clustering phenomenon of the ultra-low frequency oscillating unit of the Southwest Power Grid.The key units of the ultra-low frequency oscillation are selected according to the oscillation amplitude and oscillation energy of the unit,and then the equipment level of the ultra-low frequency oscillation key unit is positioned.Finally,based on the parameter adjustment and frequency limit controller of the speed control system,two measures to suppress the ultra-low frequency oscillation of the southwest power grid are proposed,which solves the ultra-low frequency oscillation of the southwest power grid,ensures the southwest hydropower transmission,and improves the stability of the AC/DC system..