Analysis of Harmonic and Noise Influence on Temporal Envelope Estimation for Detecting Broken Rotor Bars in Asynchronous Machines

This research investigates the impact of harmonics generated by inverters and different level of Signal-to-Noise Ratio (SNR) measurement, on diagnostic methods used to identify damaged rotor bars in induction machines. The purpose of this study is to assess the efficiency of envelope estimation techniques, namely peak detection, in power supply networks that are affected by inverter harmonics. The investigation integrates both time domain envelope estimation and frequency domain analyses of signals obtained through stator current measurements. Initially, the methodology and theoretical background of the proposed technique are explained. Subsequently, the study validates spectral analysis of the modulated signal through practical testing under two power supply conditions: signals sourced from inverters and network sources. Furthermore, the research examines the impact of different SNR levels on stator current measurements and their implications for the sensitivity and precision of envelope extraction in the diagnostic method. Spectrum analysis of the stator current envelope demonstrates successful defect detection across various SNR levels, even amidst the presence of inverter-induced harmonics, provided an appropriate filter is employed.