As the penetration of inverter-based resources (IBRs) and systems such as Wind Power Plants (WPP) and HVDC increases, the harmonic stability of the interconnected networks has gained special attention from transmission system operators (TSOs) and stakeholders. This increased attention arises due to the potential multi-scale interactions among the interconnected IBRs and systems which can lead to poorly damped oscillations and resonances. Currently, the impedance-based stability analysis is one of the preferred methods for harmonic stability studies due to its clearly defined metrics and the capability to obtain impedance characteristics from black-box models. However, a critical limitation of this method is its inability to identify the root causes of potential instability cases and determine how control parameters could mitigate these issues due to the limited knowledge of black-box model parameters. This study addresses this limitation by conducting an impedance-based sensitivity analysis on control parameters and setpoints of an 8 MW Type-IV wind turbine generator (WTG) to identify their impacts on output impedance. The analysis employed a detailed WTG model and utilized an EMT-based impedance measurement tool.

The sensitivity of different parameters of the outer and inner control loops and power set-points are investigated and most impactful ones are identified. The results demonstrate that different control gains significantly affect the impedance in varying degrees and frequency ranges. Moreover, the analysis clearly distinguishes between frequency ranges predominantly influenced by inner-loop (current-control) gains and outer-loop (voltage/power-control) gains, enabling estimation of bandwidth for each control loop. Adjusting these influential control parameters facilitates reshaping of the WTG impedance profile, thus improving system-level marginal stability, enabling root-cause analysis and enhancing operational stability.