Smooth AC Fault Ride-Through Control Technique for Offshore Wind VSC-HVDC System Based on AIED-SM

The arm in energy dissipation-submodule (AIED-SM) is the essential device used for AC short-circuit fault ride-through (FRT) in offshore wind voltage source converter based high voltage direct current (VSC-HVDC) systems. Its function is to absorb the surplus power injected by the wind farm during AC short-circuit faults at the onshore converter station. However, directly activating and deactivating the AIED-SM after AC short-circuit fault occurrence can lead huge fluctuation in DC bus voltage, triggering protective measures and causing the wind power system to disconnect from the grid. To solve this problem, the paper proposes a control technique to achieve smooth AC short-circuit fault ride-through in offshore wind power systems. Firstly, the fault circuit during the steady-state activation process of the AIED-SM is analyzed. The analysis includes a quantitative assessment of the voltage during the operation of the energy dissipation. Moreover, a coordinated control strategy is designed for the AIED-SM and submodules of modular multilevel converter (MMC) during AC short-circuit fault conditions to achieve smooth fault ride-through. Finally, the simulation results of ±320kV/1000MW VSC-HVDC system verify the effectiveness of the proposed AC short-circuit fault ride-through control technique.