Circulating Current Analysis and Suppression in Bipolar DC-DC Converters

Bipolar dc-dc converters, which are widely used in the battery testing equipment, have many advantages such as simple structure, wide range of output voltages and high conversion efficiency. However, the traditional synchronous carrier modulation method leads to a circulating current in the ground wire connected between filtering capacitors and the negative dc input bus. The circulating current results in enlarged power loss of switching devices and low conversion efficiency of the converter. This paper presents an asynchronous carrier modulation method which makes a half cycle phase-shift to the carrier wave. Thus, the bipolar output currents could be identical in amplitude and opposite in directions to eliminate the circulating current and its influence on the converter. The simulation results validate the feasibility of the asynchronous carrier modulation on suppressing the circulating current of the bipolar dc-dc converter and the effect on increasing conversion efficiency under light loads.