Cascaded Transformer Multilevel Inverters With Asymmetrical Turns Ratios Based on NPC

In this article, three cascaded transformer multilevel inverters (CTMIs) are proposed. One of the topologies employs cascaded transformers coupled to three-level (3L) neutral-point clamped (NPC) legs, of which one is shared between the transformers. The other two are based on cascaded transformers associated to 3L NPC and two-level (2L) legs, where one 2L leg is shared between the transformers. The proposed topologies use transformers with asymmetrical turns ratios, which allows for synthesizing the maximum number of output voltage levels, significantly reducing the total harmonic distortion. Compared to other conventional CTMIs, the proposed configurations can produce a greater number of levels using the same number of transformers, so that it is possible to have a higher levels-per-switch ratio. In addition, the proposed systems have a natural balancing that self-regulates the dc-link capacitor voltages. Simulations and experimental results confirm the feasibility of the proposed configurations.