Abstract:

Facing the challenge of large-scale access to offshore wind power, multi-terminal direct current (MTDC) system has become an important solution for grid-connection of wind power by virtue of its highly efficient power transfer capability and flexible control characteristics. However, the strong volatility of wind power output makes the cooperative control of power distribution and voltage stability of MTDC system face severe challenges. To this end, a cooperative control method of MTDC system power and voltage based on fluctuation interval division is proposed. First, a multi-objective optimization framework with comprehensive consideration of economy, reliability and flexibility is constructed, and a three-zone division criterion for wind power fluctuation is innovatively proposed to match the system regulation and control needs under different fluctuation intensities. On this basis, an interval-adaptive co-optimization strategy is developed to dynamically adapt the system operation mode to the wind power fluctuation characteristics. Further, a multi-objective coordinated control method based on variable voltage reference value is proposed to realize the cooperative optimization of optimal utilization of converter station capacity, line load balancing and voltage stability. For this complex optimization problem, the marine predator algorithm (MPA) is adopted to effectively improve the search capability and convergence performance of the solution space. The test results based on MATLAB/Simulink and OPAL-RT simulation platform show that the proposed method has significant advantages in improving the operating economy and safety stability of the MTDC system, and provides feasible technical support for the grid integration of a high proportion of renewable energy sources.

Key words: offshore wind farm(OWF), voltage source converter(VSC), droop control, multi-terminal DC(MTDC), marine predator algorithm(MPA)