Damping torque analysis for open-loop modal resonance as a cause of torsional sub-synchronous oscillations excited by grid-connected wind farms

Incidents of sub-synchronous oscillations (SSOs) reported in the Hami power network of western China indicate that the torsional dynamics of a synchronous generator (SG) can be excited by a grid-connected wind farm and trigger torsional SSOs. The concept of open-loop modal resonance (OLMR) reveals the excitation mechanism from the standpoint of system modal condition. This paper proposes a novel damping torque analysis (DTA) for detecting and assessing the risk of OLMR exciting torsional SSOs in a complex power system with multiple grid-connected wind farms. The proposed analysis is modal-computational free and can also accurately identify the grid-connected wind farm responsible for the excitation of the torsional SSOs. Moreover, the proposed DTA provides a physical insight into the OLMR to facilitate an understanding of the essential reasons that the OLMR may excite torsional SSOs. The effectiveness of the proposed DTA is demonstrated and evaluated in an example power system with multiple grid-connected wind farms.