Research On Synchronous Compensator For Terminal Voltage Support Of UHVDC System

In China,the western part of China has more energy resources and less load,and the east has less energy and more load.In order to comply with the policy and solve this problem,China's UHV DC transmission technology has developed rapidly.As the transmission capacity and voltage level continue to increase,there will be a problem of insufficient dynamic reactive compensation,which may cause the grid to collapse.Therefore,we should pay close attention to the link between reactive power compensation and voltage support,study the voltage support strategy of the weak end,to ensure the stability and reliability of the receiving power grid,and improve the dynamic performance and safety and stability of the UHV DC transmission system.A compensator is one such device that provides reactive power compensation to the grid in transient,transient,and steady state ranges.According to the above background,this paper takes ±800kV Jiuquan-Hunan UHV DC transmission system as the research object,and selects the dynamic control and stability of the new generation large-capacity compensator and its excitation system in UHV DC transmission system as the main research content.Firstly,the status quo of transmission technology and the relationship between synchronous compensator and DC transmission system are introduced in detail,and then the advantages of compensator adjustment in reactive power support are pointed out.According to the actual needs of the project,the operating principle and main structure of the new generation of hidden-pole type compensator are analyzed,and the excitation control strategy of the compensator(mainly voltage closed-loop control)is analyzed.Try to study the startup and grid-connecting process of the compensator with fast adjustment and controllability,and analyze the action characteristics und er typical faults of the compensator,and give the simulation operation characteristics under the fault of the terminal.According to the actual engineering parameters,the simulation model of Jiuquan-Hunan UHV DC transmission system and its control system was built in PSCAD/EMTDC,and then the simulation model of the new synchronous compensator was built according to the requirements of the operating characteristics of the compensator.The flow bus is set up with asymmetrical faults and other conditions for simulation experiments.Finally,this paper analyzes the voltage stability characteristics of the UHVDC system receiving converter busbar when the strength of the fed-in AC system is different and the DC-positive grounding fault is used to make the reactive power compensation.It is pointed out that UHVDC is connected to the weak AC system.There are many problems in the system that the DC power fluctuations are easy to cause the bus voltage to be unstable,and the addition of the compensator can improve the strength of the AC system.Compared with other reactive power compensation devices such as SVC,synchronous compensator has a significant advantage,which can send a large amount of reactive power to suppress the occurrence of commutation failure in the transient.In the transient process,its strong excitation provides reactive power.Output to increase the voltage recovery speed of the system after a fault.In steady operation,the compensator can perform continuous reactive power adjustment,resulting in capacitive or inductive reactive power.Therefore,in a "strong and weak" system,the synchronous compensator enhances the stability of the grid voltage better than other reactive power compensation devices.