Harmonic Cancellation under Interleaved PWM with Harmonic Injection

This paper presents a general analysis of interleaved operation of three-phase voltage-sourced converters (VSC). Both the conventional symmetric interleaving and the more general, asymmetric interleaving with unequal carrier phase shifts are studied. For each case, previously reported analytical phase voltage spectral models are generalized to include the effects of harmonic injection into the reference (modulation) signals. The spectral models are then used to determine and quantify harmonic cancellation effects in the phase current, common-mode voltage, as well as dc-link current. The analyses will prove that harmonic injection doesn't affect harmonic cancellation in any of the variables mentioned above under symmetric interleaving. For asymmetric interleaving, a scaling factor is defined to model the effects of variable interleaving angles on individual harmonics. Examples are provided to demonstrate the potential benefits of asymmetric interleaving, such as minimization of EMI filter size. The analyses are further extended to regular-sampling PWM where complete harmonic cancellation usually doesn't happen to all sideband harmonics simultaneously. Numerical results are included to validate the analytical models.