A Control Method Based on Minimum Conduction Losses for High Efficiency Isolated Dual-bridge Series Resonant Converters

Abstract

As it is known, dual-bridge series resonant converters (DBSRCs) can achieve a relatively high efficiency by reducing the switching losses. In order to further improve the performance of DBSRCs, it is significant to minimize the losses of MOSFET and wire losses in coil winding and PCB. Hence, reducing root-mean-square of current conducted in resonant tank deserves consideration. In this paper, time-domain analysis is applied to obtain the accurate root-mean-square of resonant tank current ( $\boldsymbol{i_{rms}}$ ). From the perspective of control, phase shift modulation (PSM) and variable frequency modulation (VFM) are combined to realize the minimum $\boldsymbol{i_{rms}}$ under different output current and gain conditions. The possible influences caused by parameters of resonant tank, input voltage and transformer ratio are all taken into consideration, aiming at adapting different applications. For the purpose of simplifying the complexity of control, a fitted formula is produced, and with this method, high efficiency can be guaranteed when the output voltage varies in a wide range. The analysis and method are validated via experimental test on a 3.3kW DBSRC prototype, the efficiency can rise to 98% in a wide range, and the peak efficiency at rated operation point can reach up to 99%.