Research On The Application Of Saturated Iron-Core Fault Current Limiters In The VSC-HVDC System

The high-voltage direct-current transmission based on voltage source converter(VSC-HVDC)has been widely used in many fields such as renewable energy integretion,asynchronous AC power grids connection and power supply of urban grids.However,the DC side fault current has the characteristics of high peak value and fast rising speed.Large fault current,which seriously threatens the safety of the VSC-HVDC system,can easily damage converter components,yet is difficult to eliminate immediately.In this context,the fault current limiter(FCL)is introduced to limit the fault current to a relatively low level.With excellent current-limiting ability,the FCL can avoid the damage to equipment and plays an irreplaceable role in enhancing the security of the VSC-HVDC system.This paper mainly studies the application of the saturated iron-core fault current limiter(SI-FCL)in VSC-HVDC systems and the cooperation between the SI-FCL and DC circuit breaker.Firstly,the current-limiting performance of passive SI-FCLs in the VSC-HVDC system is analyzed,and the calculation method of the equivalent inductance also is given.Taking the typical two-level VSC-HVDC transmission system as an example,the maximum current and the drop velocity of DC capacitor voltage are presented according to the parameter of the SI-FCL.After researching electromagnetic characteristics of the active SI-FCL,a transient analysis model of the active SI-SFCL is proposed,which considers the influence of the dc-biased source circuit.Supposing a DC fault occurs,this paper works out the VSC-HVDC system equivalent circuit with the active SI-SFCL applied.Moreover,the numerical method of solving the state equations of the equivalent circuit is obtained.On this basis,the influence of the parameter of the metal oxide arrester(MOA)on the current-limiting performance is studied.Finally,the coordination between the active SI-FCL and the DC circuit breaker in the VSC-HVDC system is studied.When considering the breaking request,the conditions that the parameters of the active SI-FCL should satisfy are analyzed.Meanwhile,the fault current clearing process of the VSC-HVDC system with the action SI-FCL and circuit breaker is analyzed.Based on the simplified equivalent of SI-FCL and circuit breaker,a simplified calculation method for calculating the clearing time of DC side fault current is given.The working principle and electrical properties of the passive type and active type SI-FCL are discussed,and the current limiting performance of the SI-FCL in the fault transient process and the cooperation between the active type SI-FCL and DC circuit breaker are mainly studied in this paper.