Research On High Frequency And High Voltage Gain SEPIC Based DC/DC Converter

Since switch-mode power supplies are expected to have smaller volume,higher operating frequency and higher power density in the recent years,wide bandgap power devices such as Ga N and Si C have gained a growing population thanks to their low on-resistance and good high-frequency performance.A high voltage gain converter based on SEPIC topology and Ga N HEMT is proposed in this paper,which can realize soft switching of main switches and is capable of operating under high switching frequency.By implementing planar magnetics and the resonant gate driver,working efficiency of the system is further improved.Compared to the traditional SEPIC topology,the converter proposed in this project has two additional voltage multipliers,which increases voltage step-up ratio of this topology and reduces devices' voltage stress.In addition,by introducing the resonant tanks,capacitors connected in parallel with the switches will resonate with inductors in the circuit,so that drain-source voltage of the switches can drop to zero before their drive signals arrive,and therefore,zero voltage turn-on is achieved.Parameter design methods and the critical conditions for zero voltage switching within a wide input and output voltage regulation range under these fixed parameters are also introduced in detail in this article.Increase of the switching frequency reduces the inductance in the system,thus,windings can be integrated on the PCB and planar magnetic cores can also be applied,which will effectively reduce converter volume.In this paper,two magnetic integration schemes are also designed and compared,which further optimizes system structure and magnetic losses,finally improves system power density.In order to enhance the reliability of gate driver at high frequency and reduce losses,this paper uses an isolated resonant drive circuit to accelerate switching by resonant charging and discharging between the inductance and the intrinsic capacitance between gate and source of the switch.Isolation and dual-channel synchronized drive signals are achieved by a transformer: the primary side uses a bridge structure;considering the characteristics of Ga N HEMTs,two level shift circuits are added to the secondary side,so the output drive signals may let the switches work under best performance.Regarding to loss analysis of the driving circuit,methods for parameter optimization is further proposed.In this paper,the generalized state-space averaging modeling method is used to establish a small-signal model of the converter,then a compensator is designed according to the Bode diagram of open-loop system,which improves system's dynamic performance.Digital control method is designed based on conditions for soft switching.Through implementing the PWM and PFM hybrid control,the system could ensure soft switching characteristics under different loadings and meanwhile realize constant current output.This project verified the above theoretical research by designing and building a 36 W output experimental prototype.The converter can achieve a voltage conversion of 12 V ? 120 V at full load,1MHz operating frequency,while its output current is 300 m A.Experimental waveforms and results are consistent with theoretical and simulation analysis,which verifies the validity of the contents in this article.Efficiency of this system under full load can reach 91.6%.