Harmonic imbalance in asynchronous PWM schemes

The harmonic content (both integral and nonintegral) of an asynchronous three-phase PWM (pulse width modulated) scheme is analyzed. It is shown that in a three-phase inverter with asynchronous modulation the nonintegral line currents produced form unbalanced sets. The percentage imbalance for a particular order is a function of the harmonic order only. No attempt has been made here to analyze the effect of harmonic imbalance in a load such as an induction motor. However, for practical frequency ratios the absolute amplitude of the current imbalance is small due to the small amplitude of the nonintegral components. More significant changes occur in the balanced integral orders due to small changes in frequency ratio.<
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