Frequency Response Strategy for Grid-Forming Wind Turbine Systems Considering DC Side Dynamics

With the decreasing inertia level and frequency response (FR) capability of power systems, the grid-forming wind turbine systems (GFM WTSs) have attracted much attention due to their active frequency support characteristics. However, most of the existing FR strategies focus on the AC side of WT, with little consideration of the effect of the dynamic characteristics of the DC side on the frequency response of the system. For this reason, this paper proposes a frequency control strategy based on energy transfer from the AC and DC sides. Firstly, the grid-forming wind turbine's FR model considering the DC side's dynamics is established, and its response mechanism is analyzed. Based on the energy flow relationship of a GFM WTS, two energy transfer paths from the DC side to the AC side are designed to enhance the active frequency support performance of the grid-side converter. The active power reference value of the turbine is corrected according to the new power balance point during the steady state of FR, thus improving the steady-state frequency characteristics of grids. Finally, simulations verify that the proposed strategy can effectively improve the grid frequency stability.