ADVANCED OFFSHORE WIND ENERGY HYBRID DAMPING CONTROL OF MODULAR MULTILEVEL CONVERTERS USING WIDE-AREA MEASUREMENT SYSTEMS TO MITIGATE SUB-SYNCHRONOUS OSCILLATIONS

Abstract

This study investigates the performance of a Hybrid Damping Control strategy applied to a
Modular Multilevel Converter (MMC)-based HVDC offshore wind farm to mitigate sub-synchronous oscillations (SSOs) and enhance system stability. The primary problem addressed is the insufficient damping of high-frequency oscillatory modes under conventional local control, which can compromise dynamic performance and grid reliability. The methodology integrates fast local damping using resonant current injection with a supervisory wide-area measurement system (WAMS) employing Prony analysis for mode estimation. The hybrid current reference combines local and wide-area damping signals with delay compensation to ensure phase-aligned control.
Simulation results demonstrate significant performance improvements: the d-axis current
oscillation amplitude is reduced from ±50 A to ±30 A, and the q-axis from ±30 A to ±15 A,
achieving full settling within 4 s and 3 s, respectively. The damping ratios for critical modes
increase from 0.05 and 0.03 under local control to 0.11 and 0.10 with hybrid control, representing approximately 7% absolute improvement. Oscillation energy is drastically reduced, with cumulative energy falling from 1260 A²·s to 90 A²·s (≈93% reduction) in one scenario and from 760 A²·s to 25 A²·s (≈97% reduction) in another, confirming robust energy mitigation. Settling times and overshoot percentages are also significantly improved, demonstrating faster, more stable responses. These quantitative results validate the effectiveness of the Hybrid Damping strategy in enhancing dynamic stability, minimizing oscillatory energy, and ensuring reliable operation of offshore wind integration, providing actionable insights for grid operators and policymakers in the deployment of advanced damping controls in MMC-HVDC systems.