Induction machines with two three-phase windings in convertor applications

A method for reducing the influence of current harmonics in variable-speed drives on electrodynamic torque has been analyzed with experiments and calculations. An 11 kW 380 V induction motor was rewound with two three-phase systems displaced 30 electrical degrees. Measurements were made with quasi-square-wave supply generated by two voltage source inverters. The induction machine was coupled via a torque transducer to a DC machine. The voltage, two phase currents, and the torque were measured with a transient recorder connected to a computer. In the computer the data were processed with a fast Fourier transform program in order to determine the harmonics. Calculations were also made on a transient computer model of the drive. It is shown that, by designing an induction machine with an extra set of three-phase winding, displaced 30 electrical degrees from the ordinary winding, the influence of the 5, 7, 17, 19, . . . current harmonics on the torque is eliminated. Only the 11, 13, 23, 25, . . . harmonics still produce pulsating torques. The drawback is the extra inverter and winding