Aiming at the open-circuit failure of power switch in voltage sourced converters high voltage direct current（VSC-HVDC）system

the operating characteristic of IGBT open-circuit failure is analyzed and the variation law of AC fault current is studied.The reason of power grid alternating current containing direct current component is proved when open-circuit fault occurs.A fault diagnosis method based on current characteristics is put forward.According to the value of slipping calculation near-zero current samples named as ‘zero sign’in a period

the fault phase is determined at first.The fault power switch is located based on the DC components of fault phase current being positive or negative.The results of simulation example show that the method presented in this paper can locate the faults in real time accurately and diagnosis results are not affected by transmitted power.