Torque ripple reduction with modified torque comparator in direct torque-controlled induction motor

The torque ripple (TR) causes vibration in induction motor's shaft. This TR should be reduced to operate the induction motor drive safely. In this paper the modified torque comparator in direct torque control (DTC) scheme for three-phase induction motor is proposed to reduce the TR. The induction motor is fed with three-level neutral-point clamped (TLNPC) inverter so that the inverter gives more voltage vectors (VVs) as that of two level inverter. Due to the availability of more VVs, the DTC scheme can be implemented with modified five-level torque comparator (MFLTC). The MFLTC modifies the selection of VVs in a comparator both during incrementing and decrementing TR. The selection of VVs through MFLTC restricts the TR near the reference electromagnetic torque. The proposed DTC scheme also balances the dc link neutral point through alternately selection of positive and negative half VVs through MFLTC. To validate the proposed DTC method the simulation and experimental results are provided.