June-Seok Lee, Hyun-Woo Sim, Juyong Kim, and Kyo-Beum Lee, "Combination Analysis and Switching Method of a Cascaded H-Bridge Multilevel Inverter Based on Transformers with the Different Turns-Ratio for Increasing the Voltage Level," IEEE Transactions on I > Paper

This paper analyzes the combination in a cascaded H-bridge multilevel inverter (CHBI) based on transformers with the different turn

ratios for increasing the voltage level and proposes the switching method for achieving the output voltage distribution among H-

bridge cells (HBCs). The transformers used in this paper are connected to the output of the respective HBCs, and the secondary sides

of all the transformers are connected in series for generating the final output voltage. Only one of the transformers, in particular,

has a different turn ratio for increasing the output voltage level. In this paper, the possible turn ratio of the special transformer with

a different turn ratio is discussed in detail, and a switching method based on the level-shifted switching method for the topology

used in this paper is proposed. To verify the effectiveness of the proposed method, a three-phase 21-level CHBI is experimentally

tested.