Suppression of harmonics of multi-level converter applied for back-to-back HVDC link

Multilevel converter is suitable for high power application and is able to reduce harmonics while keeping switching frequency at the fundamental frequency. We propose to apply multilevel converter configuration for back-to-back HVDC link to suppress harmonics without multi-pulse PWM method which introduces large switching loss. In this paper, 9, 11 and 13 level converters are described and compared from the point of harmonic reduction. Theoretically, 9-level can suppress 5th, 7th and 11th harmonics, however 11-level cannot suppress 5th, 7th, 11th and 13th harmonics and 13-level is required.