Adaptive coordinated control strategy for multi-terminal flexible DC transmission systems with deviation control

Abstract

Due to the advantages of multiple power supply points and multiple power receiving points, the multi-terminal direct current (MTDC) technology has gradually become the main trend in the future development of DC power grids. The coordinated control of a MTDC system is one of the key technologies to realize the stable operation of power systems. Droop control is an effective coordinated control method to maintain the power and voltage balance of a DC transmission system. However, improper selection of the droop coefficient leads to an imbalance of the power and voltage distribution. An improved coordinated control strategy based on an adaptive droop coefficient is proposed to realize a faster dynamic response and a more reasonable power distribution, which is applicable to all of the topologies of MTDC systems. The power and voltage deviation controls are added to prevent the output power and voltage from exceeding the range that a converter can bear. In addition, a lagging link is added in the current loop to compensate for the delay caused by the current loop and to improve the response speed of the system. Taking the MMC topology as an example, the dynamic characteristics of the proposed control strategy are analyzed, and a four-terminal MTDC simulation model based on the MATLAB/Simulink simulation platform has been established to verify the superiority of the proposed strategy under different disturbances.