Investigation of motor current signature analysis to detect motor resistance imbalances

The trend to use inverter drives in industry is well established. It is desirable to monitor the condition of the motor/drive combination with the minimum of system intervention and at the same time retaining compatibility with the latest generation of AC PWM vector drives. This paper studies the effect that an increase in motor stator resistance has on the motor performance, efficiency and voltage/current characteristics during operation of a latest-generation unmodified AC PWM drive under varying speed conditions. The increased resistance is intended to simulate the onset of a failing connection between drive and motor but one that is non-critical and will remain undetected in use because the resistance increase is small and does not appear to affect the motor operation. Performance of the motor/drive combination is measured against baseline motor data for the resistance increase. Measurements are also taken following an autotune on the drive to observe the effects that motor stator resistance imbalance has on the sensorless vector control algorithms. All data collection signals are post-processed using data analysis methods developed for MATLAB. Initial results from the motor tests clearly show a difference in values measured from the motor current and voltage signals post-processed under MATLAB and the asymmetry values equally show the 0.1Ω resistance increase. The test results are presented herein and future research work is identified.