Research On Bidirectional Full-bridge DC-DC Converter Based On GaN Device

Lithium batteries need to be formed into equipment to activate the active materials in the battery before leaving the factory.Traditional lithium battery formation equipment mostly uses IGBTs and MOSFETs as power tubes,which have problems such as large heat generation,low efficiency,poor reliability and large footprint.At the same time,because the equipment does not support energy recovery,there is a problem of serious power consumption.The performance of silicon(Si)devices has reached a bottleneck.The appearance of gallium nitride(Ga N)devices provides new possibilities for performance improvement and enhancement.Compared with Si devices,Ga N devices have high frequency,high efficiency,high junction temperature and high temperature.With excellent performance such as withstand voltage,the application of Ga N devices in lithium battery formation bidirectional DC-DC converters can not only realize energy recovery but also improve the performance of traditional formation equipment,which has certain engineering value and research significance.First,the research background and significance of lithium battery formation equipment are introduced.The research status of bidirectional full-bridge DC-DC converters is analyzed from the circuit topology and control strategy,and the research status of Ga N devices in DC-DC converters is analyzed.to sum up.Then,the circuit topology of the bidirectional full-bridge DC-DC converter is given,and the working mode of the converter under three control strategies of phase shift control,extended phase shift control and double phase shift control is analyzed,and the mathematical model of transmission power is established.,And then draw the transmission power vs.shift phase curve,analyze the return power of the three phase shift control strategies,establish a mathematical model of the return power,and verify the working waveform through Simulink simulation.Theoretical analysis shows that the dual phase shift control method is more flexible,the transmission power adjustment range is larger,and the return power can be optimized.Next,the soft switching process of the three phase-shifting control strategies is analyzed in detail,the zero voltage switching(ZVS)inequality constraint mathematical model is established,and the ideal ZVS range curve is drawn.Theoretical analysis shows that in the dual phase shift control,the resonant energy of the switch tube to achieve ZVS is smaller,and it is easier to achieve soft switching.Next,the key parameters of Ga N devices and Si MOSFETs were compared and analyzed,and the actual ZVS range curves of Ga N devices and MOSFETs were drawn,and simulated and verified by PSIM.Theoretical analysis and simulation results show that,compared with MOSFETs,the smaller equivalent output capacitance of Ga N devices can improve the ZVS characteristics of the converter.Finally,based on the bidirectional DC-DC converter in the lithium battery formation equipment,the hardware circuit was selected and designed,and the volume of the magnetic components under different switching frequencies was compared,and a bidirectional full bridge based on Ga N devices and MOSFET devices was fabricated.The DC-DC converter experimental prototype has carried out two-way power transmission experiments at 200 k Hz and50 k Hz switching frequencies.Using the equivalent output capacitance of Ga N devices and MOSFETs and the equivalent resonant inductance in the circuit,the ZVS of the switching tube is realized,and analyze the waveforms in the switching process of the switching tube,and test the efficiency of the two converters.The experimental results show that Ga N devices still have good ZVS characteristics while increasing the converter switching frequency and reducing the volume of magnetic devices.The application of Ga N devices in bidirectional full-bridge DC-DC converters can reduce converter losses and improve Converter transmission efficiency.