Drivetrain torsional vibration analysis and mitigation of grid-forming DFIG-based wind turbine generators
You Ying, Xiaotian Yang, Zhihao Wang, Xuesong Gao, Haoan Yu, Jia‐Zhuang Xu, Weiyu Bao, Lei Ding
Abstract
Insufficient drivetrain damping can cause torsional vibrations of doubly-fed induction generator (DFIG)-based wind turbine generators (WTGs), affecting their stability and safety. Typically, virtual damping control is employed in grid-following WTGs to increase equivalent damping. However, it may not perform effectively in the rapid developing grid-forming (GFM) WTGs when connected to weak grids, which has not been recognized and resolved essentially. To address this issue, the mechanical and electrical characteristics are integrated for unified analysis in this paper, revealing the coupling between GFM control and damping control. It shows that the root cause for the weakened damping control effects is the active power response delay caused by the long internal voltage phase adjustment process in weak grid condition, which is a basic characteristic for WTG to exhibit GFM capability. Accelerating power synchronization loop to speed up the internal voltage phase adjustment can alleviate the issue, but it also impairs the GFM capability. Therefore, a phase angle feedforward control scheme is proposed. It only accelerates the active power response speed but does not alter the internal voltage phase adjustment process following a grid disturbance. Simulation studies demonstrate that the proposed control scheme enables the GFM DFIG-based WTG to maintain drivetrain stable under the conditions of short-circuit ratio equaling 1.3, while not affecting the GFM capability.