During shore-side grid faults

the rapid absorption of surplus power from offshore wind farms connected to modular multilevel converter-based high voltage direct current (MMC-HVDC) is crucial for ensuring reliable system operation. Addressing the issues of high cost

energy waste

and large required storage capacity associated with existing fault ride-through (FRT) technologies

this paper introduces an energy storage-based modular multilevel converter with grid-forming and grid-following capabilities. Configuring energy storage within the internal submodules of the grid-side converter and combining regulation of the number of submodules to enhance the flexibility of submodule energy control. Additionally

the turbine-side converter without energy storage integrates wind turbine speed control and regulation of the number of submodules. It proposes a control strategy that coordinates wind turbine speed control

submodule energy control

and energy storage. Based on relevant offshore wind farm standards

we analyze submodule energy constraints and turbine speed constraints to design the maximum power capacity of the energy storage system. This approach not only ensures FRT performance but also reduces the required capacity of the energy storage system. Finally

the effectiveness of the proposed control method is verified through simulations of different fault types using a typical offshore wind farm connected to a flexible DC grid system model built in Simulink.