Study On HVDC Systems Participating In The Process Of Power System Restoration

Due to the increase of the power system complexity,it is still an important subject of power system safety prevention to implement fast and effective restoration measures after power failure and to realize the restoration of system safety and stability.Establishing the rapid self-healing power system is an inevitable choice to ensure both complexity and security of the grid.Therefore,it is of great technical and economic significance to study the theory and practice of power system restoration for preventing large-scale power failure in AC/DC system.In view of the characteristics of high transmission power,fast start-up and adjustment speed as well as strong controllability,the application of high voltage direct current transmission(HVDC)systems can possibly help the power grid to return to normal in the shortest time.Therefore,this study aims to comprehensively consider the basic methods and rules of restoration control,combine the traditional black-start and restoration control technology,and incorporate the start-up and restoration control characteristics of HVDC systems,to finally propose a better restoration strategy for the AC/DC system.The related problems of HVDC systems in the process of power system restoration are studied in this paper.The main work is as follows:the problems related to the current black-start and recovery process are summarized,including the traditional black-start problems and restoration strategy,etc.,and the general recovery control mode,the relevant modeling and application of recovery control methods are briefly described.the role of HVDC systems in the restoration process is discussed and analyzed,including realizing fast networking and improving the stability of power grid.The start-up process of HVDC system is studied.Four general control modes and two unlocking modes of DC system are briefly analyzed.Based on the analysis of voltage and frequency fluctuation,the necessary conditions for AC system are proposed.And above all,the start-up process of HVDC system is proposed.the power recovery process of HVDC system is studied and analyzed.From the aspect of ensuring voltage stability,the conditions for DC power lifting speed to be satisfied are proposed.Considering that the HVDC systems consume a large amount of reactive power,the speed of DC voltage rise needs to be controlled.In order to ensure that the system can withstand the supporting DC power,the constraint of the effective short circuit ratio and the control method of gradually increasing the DC power during the restoration are proposed.Considering that HVDC systems are involved in the black-start process,the priority sequence for HVDC systems is proposed.Based on the traditional black-start and recovery optimization process,an improved restoration optimization model considering HVDC is established.And a solution strategy for HVDC systems participating in the process is proposed,which can play a guiding role in the formulation of black-start scheme for AC/DC system.Finally,a typical AC/DC power system in China(the Guangdong power grid)is set as an example calculation analysis.Several regions in that the system,which have HVDC placement areas,are selected for concrete analysis.Comparing with the traditional restoration strategy,the effectiveness of the proposed strategy considering HVDC systems is verified.