Research On The Pattern And Propagation Path Of AC-DC Chain Reactions In The Receiving AC Power Grid

As the load level of the receiving AC power grid increases,HVDC connecting points are becoming more and more crowded.Therefore,the HVDC system plays an increasingly profound role in the dynamic response of the receiving power grid.In the AC/DC hybrid receiving power grid,system disturbances and even normal equipment operation may cause multiple HVDC commutation failures or blocking,causing a chain reaction between AC and DC systems and generating huge transient energy shocks which can spread across the regional power grid.So it is necessary to analyze the specific propagation path of power or energy when the chain reaction occurs at the receiving power grid and describe the propagation mechanism and process of the chain reaction in the actual large-scale AC/DC hybrid power grid more accurately.Based on the above,this paper focuses on AC-DC system interaction characteristics and chain reaction pattern,power/energy shock propagation mechanism and process,and AC-DC chain reaction propagation path of AC/DC hybrid receiving power grid.The main content is as follows:(1)The interaction characteristics of AC-DC systems in large-scale hybrid power grid and chain reaction pattern considering three defense lines is studied.First of all,this paper summarize the changes in the structure of the power grid brought by the development of the actual UHV AC/DC hybrid power grid,as well as the new characteristics of the power flow and system stability.Secondly,the mathematical model of the HVDC transmission system is established in the electromechanical transient simulation software to study the new operating characteristics presented by the receiving power grid,and to study the interaction characteristics of the AC system and the HVDC system.Finally,the typical AC-DC chain reaction pattern of a large-scale receiving power grid considering three defense lines are proposed.(2)The propagation mechanism and propagation process of power/energy shocks caused by AC system and DC system faults in the large-scale receiving power grid is studied.First,for the HVDC blocking,in the short-term the initial value of power shock redistribution and power peak estimation are taken as the research objects,and the derived transient energy or frequency is taken as the research object in the medium and long-term.Based on the three-stage theory of power distribution after power disturbance,combined with the power angle instability,frequency instability and thermal instability mechanism,the propagation mechanism and propagation process of power/energy shock caused by DC blocking are obtained.Secondly,considering the electrical structure characteristics of the main network of the large-scale receiving power grid,the redistribution mechanism and state transition conduction process of power shocks caused by source and load transformations of HVDC system after AC/DC faults are studied.(3)The propagation path of AC-DC chain reaction in receiving AC power grid is studied.For DC blocking caused by a DC fault,the active power redistribution is selected as the propagation object;for commutation failure caused by the AC fault,the transient energy of the generator is selected as the propagation object.Based on the actual receiving power grid,the chain reaction propagation diagram caused by AC/DC system fault is drawn.Taking Jiangsu Power Grid as an example,the chain reaction propagation path is plotted and its transmission characteristics are obtained.