Reserch On 220V Ac-dc Bidirectional Transfor-Mation Power Supply For Dc Distribution Network

AC-DC bidirectional converter is the key equipment for energy exchange in AC-DC hybrid microgrid.It has different topologies for different application requirements.The two-stage AC-DC bidirectional converter witch is applied to 220 V DC voltage level is studied in this thesis.This thesis focuses on the problems of secondary ripple of DC output voltage and the increasing of output voltage gain under light load condition.The circuit topology and working principle of two-stage AC-DC bidirectional converter is introduced.The single phase full bridge circuit topology is used in the first stage and the CLLC DC converter is used in the second stage.The mathematical model of the former AC-DC converter is derived,and the double closed-loop control is used to realize the stable output of DC side and the unit power factor control of AC side.This thesis analyzes the mechanism of double frequency pulsation produced by the former stage and the adverse effect of double frequency pulsation on the system to solve problem of the secondary ripple voltage.The Buck active filter circuit is adapted to suppress the secondary ripple voltage and puts forward the corresponding control strategy.In order to solve the problem of output voltage gain increase of isolated CLLC DC converter under light load,the gain model of post isolated CLLC DC converter is established by using fundamental equivalent analysis method.The influence of inductance coefficient k and quality factor Q on the gain is deeply analyzed.What's more,an optimal design method of resonance parameters is proposed to make the isolated CLLC DC converter work with the fixed swiching frequency.It can run stably near the fixted switching frequency.This thesis analyzes the problem of output voltage gain rise of resonant converter under light load condition.This problem is solved by using double side control.The simulated results show that the voltage gain is kept at 1 in the full load range.An experimental prototype of two-stage AC-DC bidirectional converter with 1500W power is designed and developed.The experimental results show that the design method and control strategy proposed in this thesis could effectively solve the secondary ripple voltage and the increase of output voltage gain under light load condition.