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Sensorless fault detection of induction motor with inverter output filter

The paper presents the problem of monitoring and fault detection of a sensorless voltage inverter fed squirrel cage induction motor with LC filter. The detection is based on load torque estimation of the investigated torque transmission system. The load torque is calculated besides the computation of other variables that are mandatory for sensorless drive operation such as rotor flux and speed. The implemented LC filter smooths the voltage inverter output voltage to a close sinusoidal shape and improves the efficiency and faultless operation time of the motor. Nevertheless, this additional elements have to be considered in the control structure whereby the control will become more complicated. The properties of an observer system will be compared with focus on disturbance detection in a torque transmission system. The tests are done on a drive system which consists of two coupled 5.5 kW squirrel cage induction motors, where one machine serves as disturbance generator of different amplitudes and frequencies. The second machine represents the investigated object with LC filter and is equipped with a disturbance detection procedure. The paper includes theoretical background as well as the experimental results of the proposed solution.