Research On Performance Of Push-pull DC/DC Converter Based On Silicon Carbide Device

With the increasingly serious exhaustion of fossil energy and the increasing rise of reasonable and efficient use of renewable energy,the research on electrical energy routers has been widely concerned.As a vital part of the energy router,the isolated DC/DC converter has also been widely studied.At present,silicon devices have basically reached the limit in terms of high voltage due to their physical material properties.Silicon carbide devices have been valued and studied because they can withstand severe working conditions such as high temperature,high voltage,and high frequency.Due to the application in the field of power routers,this paper studies the characteristics of SiC MOSFET devices and the working mode of push-pull isolated DC/DC converters.Combining the advantages of SiC MOSFET and push-pull DC/DC converter,a push-pull isolated DC/DC converter based on SiC MOSFET is designed.First,the working principle of the push-pull isolated DC/DC converter is analyzed.Aiming at the problem of establishing an equivalent model in the analysis of soft switching of converter,a switching transient equivalent circuit of push-pull isolated DC/DC converter is established.The relationship between the transmission inductance and the parasitic capacitance under soft switching conditions is obtained.Through the analysis of soft switching in each mode,the difficult working mode of soft switching is obtained.The power transmission relationship is derived according to the symmetry theory of power transmission in the cycle in the working mode;The theoretical analysis of the transmission inductance results in the transmission inductor current relationship;The PWM matching method is used to match the voltage on both sides of the transmission inductor to prevent current overshoot;And the converter is simulated and verified by simulation software.Secondly,the dynamic and static characteristics of SiC MOSFETs in push-pull isolated DC/DC converters are analyzed.Aiming at the problem of voltage oscillation between the drain and the source when the MOSFET is turned off in the dynamic characteristics,the method of increasing the gate resistance to suppress the voltage oscillation is adopted.The static characteristics of the SiC MOSFET are analyzed through the static characteristics: low threshold voltage,low on-resistance,and small parasitic capacitance.According to the dynamic characteristics analysis,the switching time of SiC MOSFET is short and the switching loss is small.By analyzing the dynamic and static characteristics,the parasitic capacitance of the SiC MOSFET is lower than that of the Si MOSFET,and it is easier to realize the soft switching of the push-pull isolated DC/DC converter.Then,aiming at the characteristics of low threshold voltage and small parasitic capacitance in the characteristics of SiC MOSFET,the drive circuit is designed.The gate-source voltage clamping circuit is designed to prevent the bridge arm from short-circuiting fault;The improved drive signal amplifier circuit is designed to increase the driving capacity;The overcurrent protection circuit is designed to prevent SiC MOSFET overcurrent damage.Finally,the theoretical analysis and simulation of push-pull DC/DC converters are combined with the characteristics of SiC MOSFETs to build a 1k W push-pull DC/DC converter experimental platform.The experimental results verify the correctness of the theoretical analysis.