The Study Of SiC MOSFET Based Shift-phase Full-bridge Converter

With the development of power electronics technology, the DC/DC power supply has being more and more widely applied in various fields, such as aerospace, communications power, new energy and other applications. However, the demand of higher efficiency, higher power density and higher temperature endurance are more and more eager. Meanwhile the electromagnetic interference during the switching process also has many bad effects on the system. To solve these problems, soft switching technology is proposed, by realizing zero-voltage switch(ZVS) or zero current turn-off(ZCS), the system can significantly reduce its switching losses、its heat sink and its electromagnetic interference. Then its power efficiency and power density can increase. Among all kinds of the soft switching circuit, the phase-shifted full-bridge converter structure is widely used in the high power devices because of its simple structure and easilycontrolled scheme and its switch stress will also not increase. Nowadays, the performance of the semiconductor material power device based on silicon(Silicon, Si) has already being reach its theoretical limit of the material, and it is difficult to make significant difference through technological innovation and process improvement in the aspects of on-state resistance, parasitic parameters, switching frequency, voltage endurance and temperature endurance. Therefore, the application of SiC materials on the power devices has made great progress in commercial usage, the studies are widely developed.In this paper, firstly, the SiC-MOSFET is utilized in the isolated converter, whose primary side is phase shifted full bridge ZVS(PS-FB-ZVS) topology and its secondary side is full wave rectifier topology with synchronous rectification technology being applied. Then the soft switching process and its inherent problems in the structure have being analyzed and the main circuit parameters were designed by taking the problems into consideration. In the paper, the small signal model of PS-FB-ZVS has being built by modifying the Buck’s and the transport function has being deduced. Then the double-loop controller was designed according to the Bode diagrams and the system step response diagrams. The Saber SiC-MOSFET model was built by its datasheet and MATLAB/Simulink s-Function, who has included the initialization, sampling, closed-loop control, PWM pulse generation and system protection, was programmed based on DSP TMS32028335. The main circuit simulation model was built in the Saber and the control circuit simulation model was built in the MATLAB/Simulink, they can work coordinately by the interface between Saber and MATLAB/Simulink. At last, by the steadystate and dynamic simulations, it can be concluded that the response time and steady precision are in line with the design requirements. And the above work lays foundation for the experiments.