Coordinated Control Strategy of Offshore Wind Farm and MMC-HVDC to Improve the Inertia Level of Power System

The offshore wind farm is connected to the onshore power grid via a modular multilevel converter based high voltage direct current (MMC-HVDC) transmission, which results in decreasing of total rotary inertia of the power system. The frequency stability of the power grid will faces bigger challenges. This paper proposes a coordinated control strategy utilizing both the capacitor energy of the MMC-HVDC submodule and the over-speed reserve capacity of the wind turbine (WT). The strategy can provide fast frequency support for the power grid within the range of DC voltage and the reserve capacity WT. It further improves system inertia and avoids secondary impact on the grid frequency in the process of rotor speed recovery. Finally, the effectiveness of the proposed coordinated control strategy is verified by time domain simulation.