Receiving-end AC system fault ride-through control strategy of LCC-FHMMC hybrid HVDC transmission system

When the LCC-FHMMC hybrid HVDC transmission system，in which the sending end adopts line commutated converter（LCC） and the receiving end adopts full and half bridge submodule hybrid modular multi-level converter（FHMMC），has a fault at the receiving-end AC system，the AC voltage at the receiving end drops，and the power transmission at the receiving end is impeded. The surplus power leads to the overvoltage of the sub-module capacitor，and may even cause serious damage to the equipment. A receiving-end AC system fault ride-through control strategy based on the DC voltage step-down operation of FHMMC is proposed，which always sets the DC voltage of FHMMC to be lower than the root mean square value（RMS）of AC bus voltage at the inverter side. Meanwhile，the rectifier-side LCC adopts the constant DC current control to ensure that the inverter-side DC current is near the rated value，thereby achieving the balance between the active power injecting into the DC system and the active power output by the inverter to the receiving-end AC system. The symmetric faults and asymmetric faults occurred on the receiving-end AC system of LCC-FHMMC hybrid HVDC transmission system are simulated and analyzed on PSCAD／EMTDC platform finally. The simulative results verify that the proposed control strategy can rapidly and effectively ride through receiving-end AC system faults，as well as suppress the overvoltage of sub-module capacitors. © 2023 Electric Power Automation Equipment Press. All rights reserved.