Mechanism analysis and solutions to tap-changers frequent action problem of Gaoling back-to-back HVDC

In the Gaoling back-to-back HVDC, there are frequent actions of the converter transformer tap-changer during the power adjustment period. The number of tap-changer actions is significantly higher than the normal design value, and there is invalid reciprocating adjustment of the tap-changer, which brings serious challenge to safe operation of equipment. This paper first studies the principle of tap-changer control of a back-to-back HVDC, and further analyzes the frequent action mechanism of the tap-changer based on the actual operating data of the Gaoling back-to-back HVDC. The RTDS simulation test reproduces the frequent action of the tap-changer, and a solution to control the dead zone reference value by changing the firing angle of the tap-changer on the rectifier side according to the power change state is proposed. Finally, the effectiveness of the solution is verified by the RTDS simulation test.