Monitoring of Static and Dynamic Air Gap Eccentricity of Inverter Fed Induction Machine Drives

The detection of eccentricity in modern ac drives is difficult under mains operation. At high dynamic inverter-fed operation it then becomes extremely challenging. The only industrially accepted method so far is the usage of the vibration spectrum obtained from extensive measurements. In this paper the influence of airgap asymmetry on the transient reactance of the machine is investigated. It is shown how the transient stimulation of the machine by the inverter can be used to determine even small changes of the transient reactances. Besides the stimulation of the machine with a specific switching sequence of the inverter, methods for a sophisticated excitation integrated into a PWM are described. Measurements of static as well as dynamic eccentricity are given to show not only the accuracy of the method, but especially the dynamic performance in tracking the time trace of the position of the eccentricity. Using the described method tracking is also possible at standstill of the drive where spectrum based methods deteriorate in their performance