Quad Demodulation: A Time Domain Diagnostic Method for Induction Machines

This paper introduces the use of a full time-domain based method for the quantitative evaluation of electrical faults. It relies on stator current measurements, thus it is compliant with switching power converter drives, provided that a proper current measurement techniques is available, that mitigates the ripple intrinsically produced. Moreover it allows an accurate quantification of faults without requiring spectrum analysis, hence it achieves high resolution even with low time acquisition periods. The advantages are perfectly suited to time varying signals. The proposed technique, referred to as quad demodulation, is pretty general and can be applied to any electrical or mechanical faults provided that a dedicated frequency signature exists on the current spectrum. Here the quad demodulation method is presented and validated for rotor faults.