Common-Duty-Ratio Control of Input-Series Output-Parallel Connected Phase-shift Full-Bridge DC–DC Converter Modules

Input-series output-parallel (ISOP)-connected converters allow the use of low-voltage and low-power converter modules for high input-voltage and high-power applications. Further, the use of high-frequency, low-voltage MOSFETs, which are optimized for very low on-resistance, is enabled, resulting in lower conduction losses and higher power density. In this paper, a common-duty-ratio control scheme is proposed for an ISOP converter consisting of multiple phase-shift full-bridge (PS-FB) converter modules. The proposed control method achieves stable sharing of the input voltage and load current by applying a common duty ratio to all converter modules, without a dedicated input-voltage sharing controller. The control method is analyzed by using both a small-signal averaged model and a steady-state dc model of the ISOP converter, and it is concluded that the equal sharing of input voltage and load current among converter modules can be achieved through reducing the mismatches in various module parameters, which is practically achievable. The stability and performance of the control scheme are verified by Saber simulation and a 500 W experimental prototype consisting of two PS-FB converter modules.