High step‐up/step‐down non‐isolated BDC with built‐in DC‐transformer for energy storage systems

Abstract

A non-isolated bidirectional DC-DC converter (BDC) is proposed for high step-up/step-down bidirectional power conversion applications. A DC-transformer is integrated into a conventional non-isolated buck-boost BDC to achieve high-voltage conversion ratio and wide voltage/power range regulation simultaneously. The switches are shared by the buck-boost BDC and the DC-transformer. Voltage stresses of switches are reduced by connecting the input and output of the DC-transformer in-series. The duty cycles of switches are used to make sure that the voltages on the two sides of the DC-transformer are matched. As a result, the DC-transformer always operates under the highest-efficiency condition. The phase-shift angle between the switching bridges is employed to achieve the power flow regulation. Soft-switching of all the switches is achieved by adopting the pulse-width modulation plus phase-shift control strategy. Operation principles, characteristics and design considerations of the proposed BDC are analysed in detail. Experimental results from a 48 V/400 V-1 kW prototype verify the effectiveness of the proposed converter. The efficiency is demonstrated to peak at 96.6% for both the step-up and step-down modes.