The application of three-level pulsewidth modulation (PWM) to voltage source inverters feeding three-phase induction motors is considered. A subharmonic modulation method using two modulating waves is introduced. It is particularly well adapted to the elimination of specific harmonic bands. Systematic optimization of precalculated waveforms with respect to loss factor, shows that three-level PWM is very well suited to harmonic reduction. Transient behavior is discussed. It is concluded that three-level PWM yields significant improvements compared with two-level PWM, especially in high-power (gate-turn-off) GTO applications where the high DC link voltage requires a series connection of the switches.
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