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Rotor eccentricity is one of the common failures that can happen to a motor. In recent years, considerable amount of researches for rotor eccentricity fault diagnosis have been presented. However, no attention is given to the case of 'eccentricity fault tolerant control'. The necessity of 'eccentricity fault tolerant control' is the importance of motor continuous operation during fault in sensitive industries with the best possible performance. Applying conventional control methods during eccentricity fault is not efficient. Since, these methods do not consider eccentricity fault effects such as distortion in flux linkage distribution and motor back-electro-motive force (EMF) waveform, as well as phase inductances changes which may lead to undesirable torque ripples. Hence, a new control strategy for improving motor performance is advantageous. In this study, a control method for brushless direct current (BLDC) motor in presence of static rotor eccentricity is proposed. On-line estimation of phase inductances and phase-to-phase flux linkages during eccentricity is the basis of the proposed control method. In the proposed strategy, the controller adjusts motor terminal voltages considering changes in motor specifications because of eccentricity, without using phase current control loop. Experimental results verify performance of the proposed method in reducing electromagnetic torque pulsations during fault.

In conventional control methods of brushless DC (BLDC) motor drives, back-electromotive force (EMF) is assumed to be in ideal form and the controller injects rectangular phase current commands to produce the desired constant torque. However, real back-EMF waveform might not be exactly trapezoidal because of non-ideality of magnetic material, design considerations and manufacturing limitations. This makes the generated electromagnetic torque contain ripples in its waveform which is not desirable in motor operation performance especially, in sensitive industries. Moreover, commutation states affect the quality of generated torque by producing torque pulsations because of changes of conducting phases. In this study a control strategy for a four-phase BLDC motor with non-ideal back-EMF to reduce electromagnetic torque ripples is presented. Basis of the proposed method is to inject phase currents considering back-EMF instantaneous magnitude. For this purpose, an on-line back-EMF estimation technique is used to inject appropriate phase currents to compensate non-ideality of back-EMF waveform. Moreover, the estimated back-EMF is also used for commutation torque ripple reduction. The experimental results indicate performance of the proposed control strategy in torque pulsations reduction compared with conventional control method.

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