Research On Key Section Search Of AC/DC Hybrid Power Grid Considering Operation Mode

Under the background of AC/DC hybrid power grid,the scale of power grid continues to expand.Key section is the weak links of power system and can realize the dimension reduction controlling of the system.Key section identification is the basis of the calculation of the available transmission capacity and the stability control of the key section.With the rapid development of power grid technology,a large number of direct current projects have been put into use,and the operation mode of power system changes more frequently.The traditional key section is AC transmission section.Nowadays,the transmission capacity of power system is affected not only by AC lines,but also by DC lines.Therefore,it is of great significance to study the key section identification of AC/DC hybrid power grid considering the operation mode of power system.Key sections affect the safe and stable operation of power system.There are some deficiencies in the existing research.The influence of the change of operation mode on the position of section is less discussed.Research on the relation between key section and security attributes is less discussed.Research on identification method ofkey sections in AC/DC power grid is less discussed.In view ofthe above problems,this paper proposes a power grid partition method considering operation mode,designs the search procedure of key sections for transient safety,and improves the search method of key sections on this basis to make it suitable for AC/DC hybrid systems.The specific content is studied as folows:Firstly,based on the definition of impedance electrical distance,a calculation method of active power sensitivity electrical distance is proposed as the basis of electrical connection in power grid partition considering operation mode.Based on clustering algorithm,an improved K-means partition method is proposed,and the number of partitions is determined by defining the comprehensive partition performance index.This method can divide the power grid into several regions which are relatively closely connected,where the interconnection of lines between regions is weak and the power direction of lines between regions is identical.Taking IEE39 as an example,it is verified that the change of operation mode will lead to the change of power grid partition,and compared with the existing methods.Secondly,in the search of key sections of transient security,the cut-set algorithm of directed graph is used to find the cut-set transmission section,and the cut-off distribution factor is used to screen the section to get the transmission section with close electrical connection.In the field of specified operation mode,a large number of operation modes are generated for transient simulation calculation.Based on the two-variable theory in statistical analysis,the relationship between the power of transmission section and the maximum power angle difference of system transient is analyzed.The correlation coefficient between transmission section and transient maximum power angle difference is taken as the key measure index.Taking EEEE39 generators as an exaple,the correlation between transmission section power and transient maximum power angle difference is verified,and the key sections of transient power angle stability are found out,and compared with the existing methods.Finally,in the key section identification of AC/DC system,based on the transient safety of AC key section,AC section in the power system is found first.Based on the multivariable complex theory,the complex correlation coefficients between transient maximum power angle difference and AC section and one or more DC lines are analyzed.The composite section with high complex correlation coefficient is regarded as the key section of transient safety for AC/DC system.Taking the simplified model of Shandong power grid as an example,the results show that this section identification method can search out the reasonable AC/DC key sections.