Improvement in Performance of Short Chorded Three-Phase Induction Motors With Variable PWM Switching Frequency

The harmonic voltage components and efficiency of four different chorded motors fed from a pulsewidth modulation inverter voltage supply were investigated at different loads and were measured with three different switching frequencies. Total harmonic distortion voltage due to the third, fifth, and ninth harmonics were lowest in a motor with a 120deg coil pitch at 16- and 8-kHz switching frequencies and a motor with a 160deg coil pitch at a 4-kHz switching frequency. The efficiency of the motor with the shortest chorded winding was as much as 22% higher than that of the full-pitched motor at 16-kHz switching frequency due to harmonic cancellation