Impedance-based sensitivity analysis of wind turbine generator

With increasing penetration of converter-based systems such as HVDC, inverter-based resources (IBRs) and FACTs, harmonic stability of interconnected networks has gained significant attention from transmission system operators and stakeholders. This attention stems from potential multi-scale interactions among interconnected systems that can lead to poorly damped oscillations and resonances. Impedance-based stability analysis is one of the preferred methods for harmonic stability studies due to its clearly defined metrics and ability to obtain impedance characteristics from black-box models. However, a critical limitation is the inability to identify root causes of potential instability and determine control parameter mitigation measures due to limited parameter knowledge in black-box models. This study addresses this limitation by performing impedance-based sensitivity analysis on control parameters and setpoints of an 8 MW Type-IV wind turbine generator (WTG) using a detailed WTG model and EMT-based impedance measurement tool. The sensitivity of various parameters in outer and inner control loops and power set-points is investigated to identify the most impactful ones. Results demonstrate that different control gains significantly impact the impedance in varying degrees and frequency ranges. Adjusting these influential control parameters facilitates reshaping the WTG impedance profile, improving system-level marginal stability, facilitating root-cause analysis, and enhancing operational stability.