Transient Stability Analysis Of Southwest Grid After Asynchronous Network

With the development of the power grid,in order to strengthen the grid structure of the strong grid,more and more power grids are interconnected by asynchronous interconnection.In order to making full use of the hydropower resources of the southwest power grid,the national Power Grid plans to build the back to back direct current network project of Chongqing Hubei,which uses VSC-HVDC transmission to connect the central and Southwestern power grid.After the construction of the project,the south-west power grid and central China changed from the AC network mode to the asynchronous network mode.The fundamental changes of the power grid structure,the emergence of various problems,and the profound changes of the power grid structure and operation characteristics,therefore,we need to study the impact of the project’s operation on the transient stability of Southwest power grid.In this paper,the steady-state mathematical model of flexible direct current is established for the asynchronous networking of the Southwest Power Grid.Study the influence of the asynchronous networking of Southwest and Central China on the trend of the Southwest Grid is studied.The comparative analysis of the trend,focusing on changes in the trend of key cross-sections,obtained the conclusion that the equilibrium distribution of the trend of the Sichuan-Chongqing section after the asynchronous network connection was improved.Then,the transient mathematical model of flexible HVDC transmission is established.Based on this,the transient stability calculation is performed to classify faults into N-1 faults and N-2 faults.The changes in transient stability after the asynchronous networking of Southwest China Central Power Grid are studied and compared.The transient characteristics of synchronous networking and asynchronous networking are synchronized.The results show that the transient stability of the southwestern power grid after asynchronous networking is reduced.At the same time,the influence of the flexible DC asynchronous connection and DC asynchronous connection on the transient stability is studied.It is concluded that the flexible DC asynchronous connection is beneficial to the stability of the system.After asynchronous networking,when the DC line of the Southwest Power Grid is locked by a double pole,the frequency of the system fluctuates and the transient stability decreases.Therefore,effective measures must be taken to improve the transient stability of the system after DC blocking.For this phenomenon,VSC-HVDC emergency control measures are selected to improve the system stability.However,in a multiple DC system,when the DC system has a blocking fault,it can rely on several other DCs for support.Since each DC has different supportive effects for a certain fault,it is very important to select an appropriate line for emergency power support.Therefore,this paper proposes a DC emergency power support strategy for selecting the optimal DC line for emergency power support.Finally,the correctness of the strategy is verified by the actual power grid.