A Series-AC-Link ISOP AC-AC Converter with Two Power Cells

Power converters used in shipboard power systems and industrial motor drives typically need to handle voltages and/or currents beyond the voltage/current ratings of the commercially available switches. A common solution is to employ multilevel converters. Most of the existing multilevel topologies are based on dc-link converters, and require a large number of switches and capacitors with high capacitances. This paper proposes a new three-phase ac-ac converter, the power cells of which are derived from a new class of highly reliable three-phase series-ac-link ac-ac converters. Using three-phase series-ac-link ac-ac converters as power cells minimizes the number of required components. A diode is placed between the two power cells to realize the series connection of power cells to accomplish the voltage sharing at the input side. Moreover, each power cell in the proposed configuration requires only a small film capacitor for transferring the power. This eliminates the need for electrolytic capacitors, which have high failure rates. The proposed ac-ac converter is evaluated in this paper, and the simulation results verify its promising features.