Power Coupling Mechanism Analysis and Hierarchical Adaptive Decoupling Control for Wind Farm Connected to Weak Grid

Active frequency and voltage support from wind turbine generators (WTGs) improves grid stability. However, when connected to weak grid, phase-locked loop (PLL) tracking inaccuracies can cause inadequate power decoupling in WTGs. This issue is further aggravated by uneven wind speeds and spatial structure within wind farm (WF), ultimately undermining overall support capability. To address this problem, this paper firstly systematically investigates the influence of multiple factors on the coupling power from the unit, farm, to grid levels. Specifically, PLL bandwidth and grid strength affect the tracking performance of the PLL, while wind speed distribution and spatial structure influence the operating points of WTGs and the coupling transmission between nodes, respectively. On the basis, the Hierarchical Adaptive Decoupling Control (HADC) strategy for WF is proposed, which mitigate the coupling power by introducing quantified power coupling components into the power outer-loop control of rotor-side converter. To improve the applicability and robustness, the main parameters of HADC adaptively vary according to load changes and wind speed distribution. It enables to reduce the power coupling degree and improve frequency and voltage support capability of WF. Finally, case studies are conducted on a real WF project in Bazhou, Xinjiang, China. Simulation results verify the effectiveness of the proposed control method.