Research On Design And Control Method Of CLLC Resonant Isolated Bidirectional DC/DC Converter

Bidirectional isolated dc-dc converter has the functions of voltage conversion,energy bidirectional transmission and electrical isolation,and is the key link of power electronic systems such as switching power supply and power electronic transformer.In recent years,a variety of circuit topologies with various characteristics have been introduced.The relationship between the excitation inductance of the high-frequency transformer and the dead time of the switch under the condition of resonant soft switching is analyzed.The design basis of the magnetizing inductance is pointed out.Considering that the converter voltage gain is affected by the change of the operating mode and the resonance parameters,an optimization design method of the resonance parameters is given for the requirement of constant voltage gain in some applications such as DC transformers.At the same time,the influence of the deviation of the switching frequency and the resonant frequency on the voltage gain is studied.A fixed frequency synchronous open-loop control strategy for CLLC resonant bidirectional isolated DC-DC converter is proposed for the application of constant voltage gain of converter.That is,the dual active bridge switch operates in the same frequency in-phase control and the switching frequency is selected at the designed resonant frequency,without the need for feedback adjustment.When the resonant parameters vary within a limited range,the constant frequency synchronous open loop control strategy can maintain the voltage gain substantially constant under optimized design parameters.In order to meet the requirements of high-voltage gain or fine-tuning of output voltage,a frequency adjustment control strategy is proposed to fine-tune the switching frequency according to the change of output voltage to ensure that the converter operates in a resonant state and improve the efficiency of the converter.Designed and developed a CLLC resonant bidirectional DC-DC converter with a rated power of 6kW and using SiC MOSFET devices.Two control strategies were carried out under different working conditions and different parameters.The experimental results verify the correctness and effectiveness of the parameter optimization design method and control strategy of the CLLC resonant converter.