Research On Stability Analysis And Control Measures Of Power Sending System With High DC Penetration Level And Asynchronous Interconnection

The flexible HVDC transmission technology has been gradually getting matured,and the Chongqing-Hubei Flexible DC back-to-back transmission project with the highest voltage level and the largest transmission capacity in the world will soon be put into commission in China.After the commission,the Southwest Grid will implement asynchronous interconnection with the North China-Central power network.Southwest Power Grid has rich hydropower resources and is a typical power grid of exporting electricity by DC circuits to transmit clean energy.After the asynchronous interconnection,due to the further increase in the proportion of hydropower units in the Southwest Grid,system stability problems such as ultra-low frequency oscillations are more likely to happen.It is necessary to study the stability characteristics and instability modes of asynchronous networks after high penetration of DC transmission and to figure out feasible countermeasures,in order to provide reference to the stable operation and control strategy of the regional power grid after the flexible DC project going into operation.Firstly,an asynchronous networked simulation system for high penetration of DC transmission is modeled in this paper,based on the research of Chongqing-Hubei flexible DC back-to-back transmission project and the practical power grid simulation analysis data.Secondly,based on the stability analysis of the Chongqing-Hubei project integrated with the southwestern power grid,a series of fault types including AC line N-l and N-2 faults,DC lines,blocking,and commutation failures are studied.Dominant instability modes and simulation results are analyzed.Thirdly,starting from the dominant instability mode in the Southwest Power Grid,this paper studies the emergency control strategy after DC fault and the adaptability of the Three Defense Lines.It compares,analyzes and improves the schemes of cutting machine and proposed the high cutting machine measures.The configuration scheme to effectively prevent the continuous high-frequency risks of the DC-blocked faults in the southwest network after the security control fails is optimized.Finally,targeting at the failure of DC commutation failure and locking,this paper studies the adaptability of system emergency control measures.It proposes an optimization control strategy that minimizes the amount of generation being curtailed,and proposes a defense measure against the failure to improved DC system reliability.