Study On Operation Characteristics Of Multi-infeed HVDC Transmission Systems With Different Hybrid Structures

With the development of power electronic devices,the types of HVDC systems have evolved in many forms.Owning to China's electricity production center and the main consumptive Center shows reverse distribution,the demand for electricity in the developed cities of the eastern and southern coastal areas is increasing gradually.The number and capacity of the existing transmission systems have been unable to meet their needs.Many HVDC transmission lines supply to the same load center at the same time,which has become a reality.In order to make full use of each DC line for the multi infeed HVDC system,it is necessary to study the multi infeed HVDC system with different hybrid structures,in particular,the new hybrid Multi infeed HVDC system composed of LCC-HVDC and VSC-HVDC or H-HVDC.The paper was based on the study done by forefathers for HVDC,and took the effects on the LCC-HVDC after VSC-HVDC or H-HVDC infeed in for example.Based on PSCAD/EMTDC simulation software,a multi infeed transmission system with H-HVDC was established,In the same case,LCC-HVDC multi infeed transmission system and multi infeed transmission system with VSC-HVDC were also established for comparison with the previous one.Through connected to weak AC system at the receiving end,the influence of different types of HVDC transmission into LCC-HVDC transmission system on its operation characteristics was simulated and analyzed.Result showed that H-HVDC containing subsystems combine the advantages of both LCC-HVDC and VSC-HVDC,which effectively improves the ability of withstanding commutation failures for LCC-HVDC transmission systems and the transient operation characteristics of LCC-HVDC.The commutation failure immune factor(CFII)and the system transient overvoltage(TOV)index were introduced to evaluate the influence of the H-HVDC transmission system of two topologies on the transient performance of LCC-HVDC transmission system quantitatively,and calculation results showed that the feed of VSC-LCC HVDC increase the CFII of LCC-HVDC,and reduce the transient overvoltage of the system.The simulation experiment of three-phase and single-phase grounding fault carried out to explore the influence of the feed in two topologies of H-HVDC on the transient characteristics of LCC-HVDC transmission system.Simulation results showed that the feed of VSC-LCC HVDC effectively improve the stable operation capability of LCC-HVDC,and to a certain extent,which also improved the fault recovery characteristics.