Improved Order Tracking in Vibration Data Utilizing Variable Frequency Drive Signature

Area of Science:

• Mechanical Engineering
• Signal Processing
• Condition Monitoring

Background:

• Variable frequency drives (VFDs) control AC motor speed by altering supply frequency.
• VFDs induce unique sideband signatures in motor vibration signals.
• These signatures offer a potential for deriving motor speed without external sensors.

Purpose of the Study:

• To develop and validate a signal processing technique for extracting a pseudo tachometer from VFD signatures.
• To assess the accuracy of speed estimation and order tracking using VFD signatures.
• To demonstrate the utility of this method for identifying mechanical faults.

Main Methods:

• A signal processing algorithm was designed to detect and isolate VFD-induced sidebands in vibration data.
• The algorithm extracts a pseudo tachometer signal from the VFD signature.
• The method was tested on vibration data from a gearbox test rig with seeded bearing faults under variable-speed conditions.

Main Results:

• The developed technique successfully extracted a pseudo tachometer from VFD signatures.
• Accurate speed profiles were obtained with a root mean square error (RMSE) below 2.5%.
• Effective order tracking was achieved, facilitating the identification of bearing faults.

Conclusions:

• VFD signatures in vibration signals provide a reliable method for estimating motor speed and performing order tracking.
• This approach offers a cost-effective and non-invasive tool for condition monitoring of AC motor systems.
• Limitations include potential inaccuracies at higher motor slip levels, requiring further research.