Cascaded H-bridge Multilevel Inverter
  A cascaded H-bridge multilevel inverter (CHMI) is one of the popular converter topologies used in high-power medium-voltage drives. It is composed of a multiple units of single-phase H-bridge power cells. Generally, the H-bridge cells are connected in cascaded on their ac side to achieve medium-voltage operation and low harmonic distortion. The use of identical power cells leads to a modular structure, which is an effective means for cost reduction. On the other hand, in the proposed topology, each output terminal of H-bridge cells is connected with transformers and secondary sides are connected in series to synthesize output voltage. It can make a 21-level output voltage by selecting proper turn ratio of transformer. Therefore, the output voltage waveform is very similar to a sinusoidal form without output filter.

Block diagram of the Cascaded H-bridge Multilevel Inverter

Cascaded H-bridge Multilevel Inverter Experimental Set