The influence of closed loop control on the monitoring of induction motors faults

Abstract

The paper deals with the impact of closed loop control on characteristic frequencies of broken bar and mixed air-gap eccentricity of three-phase induction motor. The study is based on the analysis of direct stator current isd of indirect control field due to its independence from torque. The analytical expression of the measured direct stator current at faulty conditions is developed using the transfer function of current loop. To confirm the analytical development, the simulation and experimental results are presented. The results show that the current control loop comports as low-pass filter and can attenuate the fault signature amplitudes. This influence can lead to an erroneous assessment fault severity. Using the analytical of measured direct stator current an original way based on the analysis a new approach is proposed to overcame the influence of current loop.