A Novel Tapped Transformer Multilevel Inverter

Abstract

This work proposes a novel tapped transformer multilevel inverter (TTMLI) to address the issues of MLIs that require multiple DC sources or use cascaded transformers. The proposed topology replaces multiple cascaded transformers with a single transformer having taps at the primary winding. The taps of the primary winding are energized by a single DC source through semiconductor switches to produce a stair-case sinusoidal voltage output at the secondary winding. The proposed idea is explained with the help of switching waveforms followed by detailed calculations of the transformer design and voltage/current ratings of the semiconductor switches. The proposed topology is initially tested and verified through simulations, and then validated through a 1 kVA hardware setup with a 12 V input and a 220 V output. The simulation and hardware results of the proposed topology demonstrate huge potential for future research and development in this area. Unlike several other MLI topologies that require multiple DC sources or multiple transformers, the proposed topology uses a single DC source and a single transformer, and hence it is compact. Only a pair of switches conducts at any given time instant resulting in low conduction loss. Energizing a particular tap of the primary winding results in a specific voltage step at the secondary winding. For \(N-\)level MLI N taps on the primary winding and the same number of switches are required. Hence, the proposed topology is generic to realize \(N-\)level MLI with \(N>1\). The hardware complexity increases linearly with an increase in N. Moreover, the proposed topology is equally suited for the implementation of MLIs with symmetric and asymmetric step-sized outputs by adjusting the turn ratios.