Active Broken Rotor Bar Diagnosis in Induction Motor Drives

A new active fault diagnosis strategy for broken rotor bars (BRBs) in induction motor (IM) drives is proposed. The active scheme consists of injecting a zero-sequence signal online with a standard space vector pulsewidth modulation (PWM). The injected signal is obtained by applying the null vectors of the PWM, when the star point of the IM is connected to the dc-link midpoint. The response to the injected signal is acquired by using current derivative sensors, from which the diagnostic signals are obtained. BRB faults produce new components in the spectral distribution of the diagnostic signals, which are used as a fault indicator. These components are extracted by using a proposed algorithm, based on a simple reference frame transformation. Experimental results demonstrate the validity of our proposal not only at steady state, but also at transient conditions of speed and load. This is possible because a methodology to convert the diagnostic signals to a stationary ones by resampling it as a function of the rotor position is proposed.