Adaptive droop-based hierarchical optimal control strategy for VSC-MTDC grids with large-scale wind farm integration

Achieving net-zero emissions requires transitioning from a fossil fuel-based energy system to one dominated by renewable energy sources. VSC-MTDC systems play a crucial role in this transition by efficiently integrating renewable energy, particularly offshore wind farms. In this paper, a novel hierarchical optimal control strategy without additional PFCs is proposed to achieve cost-effective control of wind farm-integrated MTDC grids after contingencies. Two objectives are considered in the proposed hierarchical control strategy: maintaining effective power line sharing and providing frequency support for AC areas without enough power reserve. A multi-objective optimal control algorithm is implemented in the secondary control layer to optimise the adaptive droop control parameters and determine the voltage reference parameter of VSCs. Adaptive droop control is implemented in the primary layer based on the obtained control solution. A five-terminal MTDC connected with offshore wind farms and AC grids is employed as the test system. The effectiveness of the proposed hierarchical control strategy is verified through system analysis and simulation results carried out using OPAL-RT RT-LAB libraries and MATLAB/Simulink Simscape Blockset.