Cascaded Transformer Multilevel Inverter With Shared Leg Based on Neutral-Point Clamped

In this paper, the basic structure and generalization of a cascaded transformer multilevel inverter (CTMI) is proposed. Such a topology is based on cascaded symmetrical transformers associated to three-level (3L) neutral-point clamped (NPC) and two-level (2L) legs, of which one 2L leg is shared between the transformers. Also, it is presented a generalized modulation technique based on duty-cycle functions that is readily implementable on a digital signal processor (DSP). Compared to two conventional CTMIs, the proposed configuration can generate almost the double of levels using equal number of transformers or the same number of levels using half of the transformers, in such a way that a higher levels-per-switch ratio can be offered. In addition, the proposed system offer a natural balancing property that can self-regulate the dc-link capacitor voltages. Simulations and experimental tests are presented in order to demonstrate the performance and feasibility of the proposed configuration.