An improved direct AC-AC converter and its application to three phase induction motor drive

The authors propose a direct AC-AC converter with an improved modulating technique which uses a clipped sine wave as reference instead of a pure sine wave or a square wave. The switching function derived gives rise to an output voltage with a very low harmonic content. The performance of an induction motor fed by a direct AC-AC converter is analyzed using its equivalent circuit. The harmonic components of the stator current as well as the stator current waveform are computed for various modulating schemes using digital simulation. It is seen that the current waveform for the case of clipped-sine modulation contains a lower percentage of harmonics. The harmonic torques and rotor losses are very small.<>