Recursive orthogonal signal decoupling for improving weak fault observability in wind turbine drivetrains

Strong operational excitations in wind turbine drivetrains often mask the weak vibration signatures associated with incipient faults. Under high interference conditions, conventional frequency-domain suppression strategies may become counterproductive. Indiscriminate removal of frequency bands disrupts signal continuity and distorts phase information. This study introduces a recursive orthogonal signal decoupling framework based on a time-domain peeling strategy. The proposed approach sequentially identifies dominant resonance modes and removes their contributions through orthogonal projection. The waveform integrity of the residual signal is preserved. By dynamically tracking the 1X rotational speed reference, the framework maintains high robustness against non-stationary conditions, restricting kinematic extraction errors to 0.33% under severe noise masking at a signal-to-noise ratio of −15 dB. Validation using operational data from a commercial wind farm demonstrates effective decoupling of composite drivetrain faults and system-level damage induced by shaft currents. Crucially, the extracted features successfully captured the natural macro-kinematic slip of approximately 2.9% in high-speed bearings, aligning with the elastohydrodynamic lubrication regime under fluctuating loads. These results confirm that the proposed framework provides a physically interpretable solution for monitoring complex electromechanical systems with enhanced fault observability.