Development of Flying Capacitor Dual Active Bridge Converter using Multi-mode Operation depending on Output Power

Abstract

This paper proposes a multi-mode operation for a five-level dual active bridge (DAB) converter using a flying capacitor (FC) topology in order to achieve a wide-load-range high efficiency over a wide output voltage range. The FC inverter alternates between three types of operations: five-level waveform operation, square wave operation, and operation of square waveform with half of the input voltage. In the multi-mode operation, the output voltage waveforms of the FC inverter are changed depending on the output power. By using multi-mode operation, zero voltage switching (ZVS) is achieved at light load against the change of the output voltage. In addition, the circulating current is also reduced compared to that of a two-level DAB converter. Therefore, the efficiency is improved by the proposed method. The experimental results show that the maximum efficiency is 96.4%. At 75% of the nominal voltage, the converter loss is reduced by 24.4% compared to that in the conventional two-level DAB converter operation.