Analysis Of Performance Of Synchronous Condenser In Weak Sending System In HVDC

Nowadays,in order to promote the absorption of' new energy and the optimal allocation of resources,high voltage direct current(HVDC)transmission with high voltage level and long distance is developing rapidly in China.Due to the reverse distribution of energy and load centers in China,a large number of HVDC transmission systems exist in China,forming a "strong direct and weak AC" grid structure.The existence of weak AC HVDC will reduce the reactive power reserve and deteriorate the reactive power dynamic characteristics and voltage stability of the system.Therefore,it is proposed to install a large capacity synchronous condenser(SC)at the bus of the converter station as a reactive power compensation device,which provides reactive power support to the system through fast and forced excitation when the system fails,improves the bus voltage regulation ability and enhances the coupling between AC and DC systems.Based on the background of installing synchronous condenser in HVDC converter station,this paper studies the effect of synchronous condenser on system voltage recovery after HVDC faults at weak system.Firstly,the definition of "weak AC" in AC/DC hybrid system is defined,and the potential security and stability hazards of HVDC with weak system at sending end are analyzed.On the basis of the analysis of HVDC system composition and mathematical model,the relationship between reactive power consumption and reactive power balance of HVDC system is elaborated.Secondly,the composition,working principle and mathematical model of synchronous condenser system are elaborated.Based on the theory of motor and circuit analysis,the analytic expression of dynamic reactive power characteristics of synchronous condenser is established when terminal voltage suddenly changes.The influence of parameters of synchronous condenser on reactive power output in steady,transient and sub-transient dynamic processes is analyzed.Finally,the simulation model of HVDC synchronous condenser connected with weak system is built under PSCAD simulation software.By comparing whether to add synchronous condenser or not,and adding SVC and STATCOM respectively,the dynamic reactive compensation performance of synchronous condenser is demonstrated,and the influence of key parameters of synchronous condenser on reactive power output performance is determined,which is the reactive power configuration and synchronization of HVDC.The performance optimization of the camera provides reference and basis.