Research On Restoration Strategies For Receiving-end AC Systems Considering Power Support From VSC-HVDC

With the rapid development of high voltage direct current(HVDC)transmission in recent years,cross-regional AC-DC hybrid power grids are gradually estblished in China.After a major blackout occurs in the receiving-end system connected to HVDC transmission,using HVDC rationally can help in the system restoration.Voltage source converter based high voltage direct current(VSC-HVDC)systems can be used as black-start power sources.However,the control strategies of VSC-HVDCs participating in the restoration process and optimization decisions of the receiving-end system restoration are still lack of in-depth research.This thesis focuses on the restoration research of the receiving-end AC system with VSC-HVDC connected.The restoration process and strategies of the receiving-end AC system considering the connected VSC-HVDC are studied in depth.The main works of this thesis include:(1)BPA-NETOMAC data conversion software is developed,which can quickly convert the AC systems simulation data in BPA format to the data in NEMOMAC format,laying the AC system models and data foundation for subsequent simulation research.The electromagnetic transient model of VSC-HVDC is developed in NETOMAC,which shows the simulation advantages of NETOMAC.Data conversion and DC modeling work provide the foundation for the hybrid simulation analysis and verification of AC-DC systems restoration strategies in NETOMAC.(2)By analyzing the characteristics of VSC-HVDC control strategies during receiving-end system restoration with VSC-HVDC connected,the division method for the restoration process of the receiving-end AC system is proposed.The restoration process can be divided into power supply passive network stage,power supply weak AC system stage,and power supply strong AC system stage,which can provide theoretical support for subsequent system restoration strategy study.(3)The constraints of VSC-HVDC as the black-start power during supplying passive network stage are proposed.Considering the objectives of unit restoration time,ramp-rate and charging reactive power of restoration path,a multi-objective restoration optimization model of the power supply passive network stage is developed.A step-by-step solution is proposed to select the units to be restored during the power supply passive network stage.An AC/DC hybrid simulation model based on the IEEE39-node test system is developed in NETOMAC.The simulation results verified the feasibility of the proposed restoration scheme and the superiority of VSC-HVDC as a black start power supply in preventing voltage rise.(4)The constraints of the VSC-HVDC inverter-side station during the weak AC system restoration stage are proposed.Considering the objectives of unit restoration efficiency,charging reactive power of restoration path and system strength,a multi-objective restoration optimization model of the power supply weak AC system stage is developed.A step-by-step solution is proposed to formulate the restoration schemes of the units to be restored during power supply weak AC system stage.An AC/DC hybrid simulation model based on the IEEE39-node test system is developed in NETOMAC,the feasibility of the proposed restoration strategy is verified.Compared with the restoration schemes of traditional unit as black start,the efficiency and practicability of VSC-HVDC participating in system restoration are illustrated.In summary,this thsis focuses on the restoration methods of the receiving-end AC system with VSC-HVDC connected,and the restoration schemes are verified using NETOMAC’s hybrid simulation function.These studies on the AC-DC power system restoration are of great importance for theoretical research and have some reference value for the AC system restoration schemes considering VSC-HVDC connected.