Analysis and solution of UHVDC current oscillation caused by DC line fault restart

It is analyzed that DC current oscillation and protection action of single bridge multiple commutation failure caused by simulating DC line fault in the initial operation stage of ±800kV Ximeng-Taizhou(XT for short) 10GW UHVDC pilot project. It is determined that the current fluctuation is mainly caused by the weak sending terminal(Ximeng) weak AC system. In the initial operation of Xitai UHVDC project, the AC power grid at the sending end is weak, and the DC current oscillation will be caused during the restart of the DC line. Moreover, the commutation failure at the receiving end exacerbates the current oscillation. The commutation failure at the receiving terminal is mainly caused by the shift the zero crossing of AC voltage caused by harmonics, resulting in the failure of VBE(Valve Base Electronics) to incorrectly identify the TCE(Thyristor Control Electronics) negative voltage establishment signal after the trigger pulse is sent to the thyristor, and resulting in the DC pole blocking of the inverter side commutation failure protection action. Through in-depth analysis and the solution is given, the delay detection of the negative voltage signal sent by VBE to TCE is cancelled, and the correctness is verified by the field simulation DC line restart test and DC line ground fault test.