Output Capacitor Current Reduction with T-type Dual Active Bridge Converter for Wide Output Voltage Condition

Abstract:
This paper presents a capacitor ripple current evaluation of a bidirectional isolated DC/DC converter with a one-leg T-type dual active bridge (DAB) converter for energy storage system applications. The DAB converter transfers the power with the high efficiency when the input and output voltage ratio is close to turn-ratio of the high frequency transformer. However, the other condition such as the output voltage fluctuation decays the performance of the DAB converter. However, the conversion efficiency decreases due to increasing the inductor rms current, and the limitation of the Zero Voltage Switching (ZVS) range. Moreover, the DC-bus capacitor rms current also increases due to increasing the inductor rms current. In this case, the capacitor will be bulky because a high allowable ripple current devices or a lot of parallel connection of the capacitor is required in order to satisfy the current rating for each capacitor. In this paper, the capacitor rms current reduction by the one-leg T-type DAB converter which has the half and full bridge operation mode is revealed. This converter generates the two-level transformer voltage by each operation modes, and the operating condition of the DAB converter is shifted by widely output voltage condition in order to reduce the inductor and the capacitor rms current. As the simulation result, the capacitor rms current was reduced by 51% when the output voltage is decreased by 50% from the nominal voltage condition. Finally, the experimental results are demonstrated including the inductor and capacitor current reduction by one-leg T-type DAB converter. From the experimental result, the capacitor rms current was reduced by 60% when the output voltage becomes half of the nominal value.