With the continuous increase in the proportion of wind power in the power system, improving the inertia support and frequency response capability of wind farms has become a research hotspot. This article applies the inertia synchronization control strategy and proposes a coordinated control strategy for DC networking and flexible DC systems. And a small signal model of the direct drive wind turbines grid connected system based on inertial synchronization control is established. Through eigenvalue analysis, it is found that introducing inertial synchronization control would reduce system stability. And using the "complex torque coefficient method", the mechanism of inertia synchronization control reducing the stability of the system operation from the perspective of damping characteristics is revealed, providing guidance for the improvement of inertia synchronization control method. The effectiveness and theoretical analysis of the proposed strategy were verified through PSCAD and Matlab platforms.

Grid type direct drive wind turbines; Inertial synchronous control; Coordination control; Eigenvalue analysis; Complex torque coefficient method