A co-designed on-rotor sensing and tacholess order tracking framework for robust fault diagnosis in marine electric propulsion systems

Fault diagnosis of marine electric propulsion systems (MEPS) is significantly challenged by non-stationary operating conditions, where varying speeds and loads cause severe spectral smearing that obscures fault signatures. Conventional methods, reliant on housing-mounted sensors and often impractical encoders, are further limited by signal attenuation. To address these issues, this study introduces an integrated hardware-algorithm framework that combines a novel wireless OnRotor Sensing (ORS) system with a computationally efficient algorithm. The ORS system captures high-fidelity vibration signals directly from the rotating shaft, bypassing structural transmission paths to achieve an average signal-to-noise ratio (SNR) improvement of 90.3% over conventional sensors. It also enables real-time, tacholess speed estimation via centrifugal acceleration. Leveraging this data, we propose the Zero-Crossing Tacholess Order Tracking (ZC-TOT) algorithm. Unlike methods based on complex time-frequency transformations, ZC-TOT employs an event-driven zerocr ossing strategy to extract instantaneous frequency with high efficiency. Benchmarked on a standard laptop, ZC- TOT processes 500,000-point datasets across varying speeds 25.9 times faster than the Short-Time Fourier Transform (STFT), effectively eliminating spectral blurring. Experimental validation on a dedicated MEPS test bench, involving realistic speed and load transients with over ten repeated fault trials per component, demonstrates the framework's transformative performance. The results show average SNR improvements of 92.6% for bearing outer race faults, 242% for inner race faults, 186.9% for gear faults, and 121.8% for propeller faults. This integrated solution establishes a single-sensor paradigm capable of simultaneous high-fidelity acquisition, tacholess order tracking, and real-time diagnosis for multiple MEPS components, demonstrating robust performance under hydrodynamic disturbances and representing a significant advance in marine propulsion diagnostics.