Transient Frequency Interaction Between Grid-Following and Grid-Forming Sources in Windfarm Under Severe Grid Faults

To address the issues of transient stability in heterogeneous wind farms with grid-forming energy storage, a transient analysis model of the heterogeneous system is developed, which incorporates both grid-following wind turbine units and grid-forming energy storage sources. The mechanism of frequency interaction among heterogeneous power sources during severe grid short-circuit faults is revealed by the model. It is discovered that grid-forming energy sources with slower rotor angle dynamics exhibits a frequency pinning effect on those with faster rotor angle dynamics, and the latter has a rotor angle co-driving effect on the former under the condition of frequency pinning. By solving the critical d-axis current, the impacts of wind power integration rate, the proportion of energy storage installation, and other parameters on frequency interaction are analyzed. The effects of wind turbine unit reactive power injection and the current limiting strategy of grid-forming energy storage sources are also discussed. Finally, the proposed mechanisms are comprehensively validated by simulations using MATLAB/Simulink platform.