Fault Diagnosis of a Marine Electric Propulsion System Based on Order Tracking Motor Current Signature Analysis

In marine electric propulsion systems (MEPS) driven by variable frequency drives, motor current signals often exhibit not only complex modulation components, but also ambiguous spectra and severe noise interference, making it challenging to extract fault-related modulation components. To address this, a zero-crossing tacholess order tracking (ZC-TLOT) method based on motor current signals is proposed. This method utilizes zero-crossing estimation of instantaneous frequency to perform angular resampling of stator current signals and demodulates the envelope spectrum to extract fault characteristic spectra, thereby diagnosing mechanical faults in MEPS. Given the synchronization of the synchronous motor speed with the inverter fundamental frequency, this method estimates instantaneous frequencies (IFs) in the time domain without requiring integration or time-frequency representation. being simple and computationally efficient. Data validation on a small-scale marine electric propulsion test platform demonstrates that the method exhibits good robustness under variable speed conditions, effectively detecting imbalance faults caused by propeller breakages and gear faults due to bevel gear tooth defects. This further expands the application of the method in diagnosing faults in downstream mechanical equipment driven by motors.