Detection of Torsional Oscillations in Line-Start IPM Motor Drives Using Motor Current Signature Analysis

Line-start interior permanent magnet (LSIPM) motors are vulnerable to limit cycles and often experience severe torsional oscillations. This paper presents a technique for detection of torsional oscillations in LSIPM motors based on stator current signatures. Rotor speed variations associated with torsional oscillations in a LSIPM motor influences the electrical supply, and introduces variable amplitude lower and upper sidebands in the stator current. In this paper, frequency domain analysis of the nonstationary current signals is carried out for detection of the sideband frequency components superimposed on the fundamental. The proposed technique is validated by performing finite element analysis (FEA) of a 3-phase 4-pole 1HP LSIPM motor drive. Experimental investigations have been carried out for the same motor drive in order to validate the performance of the proposed method under various practical operating conditions. Based on FEA and experimental results, the proposed technique can successfully detect the onset of torsional oscillations in the drive system without any vibration sensor.