| In a fuel cell power generation system,the front-end DC/DC converter needs to meet the following requirements: wide range input voltage adaptability; high voltage gain; power isolation and wide range soft switching. In this thesis, a hybrid phase-shift controlled full-bridge converter is designed in order to fit for such situation.A full bridge converter with new three level rectifier and auxiliary current source circuit is designed to improve the voltage gain, reduce the voltage stress of the switch and achieve soft switching in a wide output range. It can work in Boost mode with second-side phase-shift control and Buck mode with dual phase-shift control which extend the voltage gain range of the converter by hybrid phase-shift control strategy. What’s more, there is no current circulaion loss and second side voltage spike. The efficiency of the converter is enhanced.By analysising the steady-state characteristic of each mode, a detailed description of the relationship among the output characteristic, soft-switching characteristic and the circuit parameters is illustrated. It provides the design idea for the parameters and control stratagy of the circuit. Generalized Average Model and equivalent circuit model are established and compared in this thesis. Following that, PI correction for closed-loop compensation of the converter is used to ensure the steady-state characteristic and dynamic characteristic of the system. Finally, the simulation results prove the correctness of the theoretical analysis in different working modes.An experimental prototype is designed in this thesis with input voltage 40V-80 V, output voltage 300 V, switching frequency 100 k Hz and output Power 300 W. DSP is used as the control core to complete the closed-loop of the converter. The experiment results show that the converter not only can maintain a stable output voltage within a wide voltage input range and achieve soft switching of all switches, but also has good dynamic characteristics. |
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