Investigation on the Expansion of Output Voltage Range Using a 9-level DAB Converter with Pulse Amplitude Control

The efficiency of dual active bridge (DAB) converters decreases further as the input/output voltage ratio deviates from the transformer turn ratio of one. A 5-level DAB converter that replaces the primary circuit with an FC-type 3-level circuit has been used to solve this limitation so far. However, the optimization of the staircase voltage waveform is required and is complicated in such converters. In this paper, a DAB converter with an FC-type 9-level converter leg in the primary circuit is proposed. It uses multilevel squared voltage waveforms to expand a high-efficiency operation range and eliminate any waveform optimization. Experimental results show that the proposed converter can maintain a high efficiency on a wider operation range compared with the conventional converter.