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.

I. Introduction

Broken rotor bars (BRBs) in induction motors (IM) have been one of the most studied faults in literature in the past few decades [1], [2]. This fault can be caused by thermal, magnetic, environmental, and mechanical stress conditions, as a consequence of overloads, unbalance, electromagnetic noises, vibrations, contamination, and manufacturing problems. When a BRB occurs, adjacent bars take currents greater than their design value, producing an increase in the local temperature and a degradation in the performance of the IM, which can lead to the complete failure of the machine [1], [3]–[5]. In addition, the use of pulsewidth modulation (PWM) inverters for feeding the IM increases these stress conditions. Sudden changes in the load torque at any rotor speed, even for very low speed, produce high thermal and mechanical stress in the rotor of the machine [6]–[9]. Therefore, early diagnosis of this fault is imperative in order to avoid catastrophic conditions of the IM.