Scalable Bidirectional Switched-Capacitor Multilevel Inverter With Enhanced Voltage Gain

In this paper, a novel switched-capacitor basic cell is introduced as the building block of a multilevel power-electronic inverter. Two distinct modulation strategies are proposed that control how the capacitors are charged. The two modulation strategies enable different utilization of capacitor voltages, number of voltage levels, and dc-to-ac voltage gains. The operations of the two-cell and three-cell topologies, yielding 4 and 5 ac voltage levels, and 7 and 8 ac voltage levels, respectively, are analyzed. The concept and analysis are experimentally validated through a 1-kW prototype, exhibiting superior maximum voltage gains, competitive levels of efficiency across a large power throughput range, high peak efficiencies, and low total harmonic distortions (THD) for the ac-side variables. The featured prototype exhibits peak efficiencies of about 97%, across-the-board efficiencies in excess of 94% for the majority of the power throughput range, and voltage THDs of the unfiltered ac voltage better than about 13%. This paper aims to present an original basic cell, the modular development of topologies using this cell, two modulation options for these topologies that modify their gain characteristics and the number of output voltage levels, thus demonstrating a versatility not normally found in conventional topologies. This work is not intended to cover all the issues related to these topologies, such as closed-loop control, experimental optimization, capacitor voltage balancing when in closed loop; these issues will be discussed in future work. As shown in the paper, the proposed inverter topology demonstrates superior software and hardware configurability and modularity, as compared with a number of well-known multilevel inverter topologies.