Understanding the Staircase Modulation Strategy and its Application in Asymmetric Cascaded H-Bridge Multilevel Inverter

The staircase modulation strategy is the best choice for Asymmetric Cascaded H-bridge Multilevel Inverter (ACMI) because it makes the output voltage to present a high number of levels and makes one of the ACMI modules to operate at low frequency. However, the staircase modulation is usually employed without giving its deserved attention. This paper presents a clear understanding of the staircase modulation strategy and its applications in an ACMI. The principle of operation is carefully described, also indicating how to command the ACMI transistors. The output voltage of the two superior modules is evaluated for different value of iterations. Special attention is given to the power distribution among the ACMI modules when the staircase modulation is applied. It is demonstrated how the power is processed in each module considering an ACMI with three modules. Experimental results clarify and show the efficacy of the concepts presented in this paper.