Analysis and Suppression of Sending-End Transient Overvoltage in A Wind Power Integrated LCC-HVDC System under Commutation Failure

Receiving-end AC faults in line-commutated-converter-based high-voltage direct-current (LCC-HVDC) systems may trigger commutation failures (CFs) and cause sending-end transient overvoltage (TOV) during recovery. Existing work emphasizes rectifier reactive power control and DC current recovery, but the DC current undershoot from constant current controller over-regulation and its effect on sending-end TOV are not well studied. This paper analyzes the coupling among DC current, rectifier reactive consumption, AC filter reactive output, wind farm reactive response, and sending-end bus voltage during CFs. It reveals that the current undershoot reduces rectifier reactive consumption, aggravating the sending-end reactive surplus and elevating the peak TOV. A TOV assessment method incorporating the dynamic reactive response of wind farms is developed, along with a voltage-threshold-constrained DC current undershoot suppression strategy (VTC-DUS). The VTC-DUS calculates a current lower limit from a preset voltage threshold to form a modified DC current order, and adjusts the voltage-dependent current order limiter characteristic by the deviation between the modified and actual currents to suppress the excessive current drop. PSCAD/EMTDC simulations indicate that the peak TOV errors of the proposed method are below 0.01 pu for three-phase-to-ground faults and 0.03 pu for single-phase-to-ground faults, and that VTC-DUS effectively reduces the sending-end peak TOV under various fault conditions.