An active damping control method for direct-drive wind farm with flexible DC transmission system based on the remodeling of dynamic energy branches

Abstract

In view of the sub-synchronous oscillation in direct-drive wind farm caused by its connection to flexible DC transmission system, an active damping control method based on the remodeling of dynamic energy branches is proposed. First, a dynamic energy model of direct-drive wind farm with flexible DC transmission system is constructed, which contains the interaction energy, dissipation energy and stored energy. The energy model depicts the energy interaction between the control links and the energy transmission process. By analyzing the role of each control link in the transmission system (whether it emits, absorbs or transmits the dynamic energy), the control link that induces the oscillation is found. Thus the source of the energy flows in the whole system is revealed, and the application locations of the compensation branches are determined. On this basis, a parameter optimization strategy for the compensation branches considering both the sub/super synchronous oscillation scenes and the fundamental-frequency characteristics is established, so that the energy distribution can be optimized under sub/super synchronous oscillations. Finally, hardware-in-loop tests are conducted on the RT-LAB platform using the parameters of a real direct-drive wind farm. Simulation results verify that, the proposed strategy can optimize the overall energy distribution in the system through coordinated optimization control. It can quickly suppress the oscillations in both sub and super synchronous frequency bands, without affecting the LVRT capability of the wind generators and the fundamental-frequency characteristics of the system.