Combined Operation of CCM and DCM for an Active Buffer DAB AC-DC Converter

This paper proposes a combined control method of continuous-current-mode (CCM) and discontinuous-current-mode (DCM) for an active butter dual-active-bridge (DAB) AC-DC converter. CCM of the DAB converter requests a high switching frequency at light-load condition to realize CCM, therefore, it is difficult to operate the converter with CCM in this condition. The proposed control method of the DAB converter establishes a limit of the switching frequency in CCM, then, DCM with a constant switching frequency is applied when the requested switching frequency of CCM is higher than the limit. Thus, the DAB converter can partially apply CCM by the proposed control method to improve the power conversion efficiency from middle to light load conditions compared to DCM alone. Experimental results verify the combine operation of CCM and DCM with smooth transition at the timing of the operation mode change. As a result, the power conversion efficiency is improved as high as 93.7% at the 230-V, 3.9-kW output.