Line current harmonic reduction in adjustable-speed induction motor drives by harmonic current injection

Modern adjustable-speed, induction motor drives are responsible for contaminating electric networks with undesirable harmonics. Most of the speed controllers developed for induction motors employ a rectifier-inverter arrangement. In this arrangement, the alternating current drawn by the rectifier contains many undesirable harmonics. These harmonics may be reduced by third-harmonic current injection into the neutral point of the DC windings of the rectifier transformer. In this paper, the third-harmonic injection technique is applied to an induction motor driven by a voltage-source inverter. Experimental results shows that the presented scheme is capable of reducing the undesirable line current harmonics generated by the drive system. Harmonic reduction is maintained during wide variations of the motor load. The presented scheme does not affect the high performance of the induction motor