A comprehensive study of harmonic cancellation effects in interleaved three-phase VSCs

This paper presents a systematic study of the effects of interleaving on three-phase voltage-sourced converters (VSC). Analytical results are developed for the spectra of converter phase currents, common-mode voltages, and dc-link currents for the general case of interleaving N parallel modules with a common dc link. It will be shown, both analytically and numerically, that ripple cancellation effects similar to what have been widely observed in buck dc-dc converters, that is, the elimination of harmonic sidehands other than those centered at N multiples of the carrier frequency, can also be achieved by proper interleaved operation of N three-phase VSC modules. This will be shown to be true not only for the ac phase currents, as previously known, but also for the common-mode voltage as well as the dc-link current. Analytical results are also presented for the circulating current among parallel modules. Additionally, a relationship between interleaved VSCs and capacitor-clamped multilevel converters is established and used to extend the analytical results developed for interleaved VSCs to multilevel converters.