Bandwidth considerations for multilevel converters

摘要

Multilevel converters can achieve an overall effective switchnfrequency multiplication and consequent ripple reduction through thencancellation of the lowest order switch frequency terms. This paperninvestigates the harmonic content and the frequency response of thesenmultimodulator converters. It is shown that the transfer function ofnuniformly sampled modulators is a bessel function associated with theninherent sampling process. Naturally sampled modulators have a flatntransfer function, but multiple switchings per switch cycle will occurnunless the input is slew-rate limited. Lower sideband harmonics of theneffective carrier frequency and, in uniform converters, harmonics of theninput signal also limit the useful bandwidth. Observations about theneffect of the number of converters, their type (naturally or uniformlynsampled), and the ratio of modulating frequency and switch frequency arenmade