Aiming at the problem that AC faults at the sending end of the offshore wind power through modular multilevel converter based high voltage direct current (MMC-HVDC) system can easily cause power transmission interruption and threaten the frequency security and stability of the receiving end grid

this paper proposes an AC fault ride-through strategy at the sending end considering transient frequency support. Firstly

by revealing the dynamic coupling mechanism between the sending end AC voltage and the transmission power

the control requirements of MMC-HVDC system under different fault degrees are clarified. An inertia support control strategy based on the regulation margin of the extended sub-module capacitor energy is presented. By reconstructing the sub-module switching logic and designing the parameters

the rate of change of the receiving end grid frequency can be rapidly suppressed while fully utilizing the capacitor energy margin. Then

a fault ride-through control strategy based on the adaptive optimization of the AC voltage at sending-end MMC is proposed

and its start-up criterion and implementation process are designed. Under different disturbance conditions

the power transmission can be maintained to the maximum extent

effectively alleviating the impact of large power deficiency on the receiving end grid frequency and significantly enhancing the transient frequency support capability of MMC-HVDC system. Finally

based on real-time digital simulation platform

the simulation model of the offshore wind power system through MMC-HVDC system is built to verify the effectiveness of the proposed control strategy.