This paper addresses the issue of insufficient active frequency support and regulation capabilities at the receiving converter stations of flexible direct current transmission systems. A control strategy based on model predictive control (MPC) for grid-forming modular multilevel converters (MMC) is proposed. Firstly
the paper introduces the principle of frequency support for grid-forming MMCs. Subsequently
the MPC algorithm is integrated into the traditional droop control to overcome the inherent limitations of secondary frequency regulation in conventional droop control. This control method generates real-time optimal control functions that indirectly enable the dynamic adjustment of the droop coefficient
thus allowing the system frequency to stably track the setpoint and achieve the effect of secondary frequency regulation. Finally
time-domain simulations conducted on the Matlab/Simulink software platform validate the feasibility and effectiveness of the proposed control strategy.
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