Equivalent Modeling of Wind Farms considering Wake Effects and Analysis of Probability of Sub-synchronous Oscillations

Characteristics of sub-synchronous oscillation of direct-drive permanent magnet synchronous generator(D-PMSG)-based wind farm are closely related with the number of operating D-PMSGs and active power. Therefore, above changes in operating conditions caused by random wind conditions should be considered in the oscillation risk assessment. The wake effect of D-PMSGs causes obvious differences in the active power of each D-PMSG. It is a key issue that needs attention in equivalent modeling of wind farms, and the randomness of wind conditions makes this problem more complicated. Therefore, this article considers the randomness of wind speed and direction, conducts detailed simulation and establishes equivalent models of wind farms, and analyzes the probabilistic stability of the grid-connected system in the sub-synchronous frequency range. Firstly, a calculation model of the D-PMSGs' wind speed of a wind farm is established which takes the wake effect into account, and a wind farm equivalent method based on the K-means algorithm is studied, and a state space model of the grid-connected system is formed. Secondly, based on the theoretical model of wind speed probability and taking the influence of wind direction into account, a probabilistic analysis method of sub-synchronous oscillation is proposed. Finally, a typical example system is built, and based on methods above, this article studies the typical probability characteristics of sub-synchronous oscillation of grid-connected D-PMSGs.