Research On Bidirectional LLC Resonant Converter For DC Microgrid Energy Storage

In recent years,with the development of the microgrid,the dc switching power supply which can realize bidirectional power transfer can transfer the excess renewable energy to batteries,and it can also provide energy to the load from the battery when the renewable energy cannot fully meet the load demand.So,it has attracted great attention.This thesis studies the bidirectional LLC resonant converter with an inductance in parallel with a resonant cavity and researches about the selection of the DC switching power supply's hardware topology optimization of control method and so on.Firstly,this thesis analyzes the working principle of bidirectional LLC resonant converter in each mode.The steady-state model is established based on FHA(first harmonic approximation).Then,we can obtain the equivalent AC circuit and the voltage gain,and analyze the main influence factors of the voltage gain.The result shows that the converter can obtain a larger variation range of controllable gain with soft switching operation when the converter works near the first resonance working point.In addition,The parameter should be designed from the trade-off between the quality factor Q and inductance k because the voltage gain is very sensitive to these two parameters.For the hardware design of the bidirectional LLC resonant converter,in consideration of the requirement of the DC microgrid for the converter,this thesis researches the the cavity device selection and magnetic component design.In terms of control method,the pulse frequency modulation method is selected to realize the drive control because the bidirectional LLC resonant converter has a problem of energy reflow in the sub-resonant region when the synchronous rectification control strategy is adopted.The MATLAB simulation model is built for verification,and a 1.5kW experimental prototype was designed and manufactured.Based on the simulation model and experimental prototype,the voltage,current waveform and the efficiency of the converter are simulated and tested.The experimental results show that the bidirectional LLC resonant converter proposed in this thesis can realize soft-switching and complete the power conversion of DC400V/DC48V,which is reasonable and feasible.Figures:64,Tables:5,References:75.