Converter control strategy optimization research on new energy access multi-terminal flexible HVDC system

The multi-terminal flexible HVDC transmission system based on a modular multilevel converter (MMC-MTDC) has become a research hotspot of new energy grid connections due to its flexibility and economy. Aiming at the randomness of new energy generation, this paper proposes a multi-level, multi-objective, and multi-time scale coordinated control strategy to ensure the safe and economic operation of the system. Firstly, the unified controller model of the converter station is established, the soft switching control strategy is proposed to achieve seamless switching, and two-factor adaptive sag control is introduced to quickly respond to new energy output fluctuations. Secondly, a coordinated control strategy based on model predictive control (MPC) is designed to optimize the transient control coefficient, reduce the DC voltage deviation, and improve the system stability. On this basis, aiming at minimum network loss and system stability, the NSGA-III algorithm is used to solve the problem and adjust the parameters regularly to ensure the optimal operation of the DC power grid. Finally, a multi-objective, multi-level, and multi-time scale coordinated control strategy is proposed to solve the contradiction between complex scheduling and fast control in the MTDC system and enhance the robustness of the system.