Stability analysis of power electronic converters in an offshore wind farm: A case study of the Princess Elisabeth energy island

Details

Supervisors

De Jaeger, Emmanuel

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

enThe accelerating integration of Inverter-Based Resources (IBRs) into the European electrical grid raises new stability concerns that the classical angle/voltage/frequency framework no longer captures on its own. Interactions between grid-following power-electronic converters and the resonances of the surrounding network are a recurrent issue in modern offshore wind power plants and have been recognised in the most recent CIGRE classification as a standalone class of stability phenomena. This thesis investigates the small-signal stability and robustness of the Princess Elisabeth Energy Island, an offshore wind project under construction in the Belgian North Sea equipped with 14 MW Type-4 wind turbines. An impedance-based framework is adopted, in which every subsystem --- wind turbines, transformers, array cables, the HVAC export cable, the grid Thevenin equivalent and the planned onshore synchronous condenser --- is represented as a frequency-dependent dq impedance/admittance. The analytical wind-turbine admittance is validated against a detailed EMT model in MATLAB/Simulink through perturbation-based frequency scans, and the small-signal stability and robustness of the full plant at the Point of Common Coupling are assessed over the band 100 Hz--2.5 kHz through four indicators: the Generalized Nyquist Criterion, the passivity index, the vector margin and the disk margin. The baseline configuration is shown to be small-signal stable and globally passive, yet only marginally robust, with a worst-case vector margin of 0.10 and a disk margin of 0.096 at f ≈ 242 Hz; the GSC's LC filter resonance, combined with its transformer leakage inductance, is identified as the dominant source of fragility. A three-step converter-side mitigation strategy --- LC filter re-sizing, capacitor-current-feedback active damping and a notch filter retuned on the dominant mode of the aggregated wind-farm/grid network --- raises the worst-case vector margin to 0.63 and the disk margin above 0.5, and a short-circuit-ratio sweep that includes the planned synchronous condenser confirms that the final design remains robustly stable across the full range of expected grid strengths. The thesis thereby demonstrates, on a publicly documented case study, that distinguishing between systems that are merely stable and systems that are robustly stable is both feasible and essential in the design of the next generation of offshore wind connections.