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Design And Control Strategy Of LLC Resonant DC-DC Converter Based On MMC

Posted on:2024-02-08Degree:MasterType:Thesis
Country:ChinaCandidate:J P QiFull Text:PDF
GTID:2542307118972949Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
In order to alleviate excessive exploitation of fossil and environmental pollution,our country constantly promotes the development of renewable energy,realized leapfrog development in the field of renewable energy,ranked first in the world installed capacity of renewable energy.In order to realize stable grid-connected of renewable energy,the operation of DC power grid is indispensable.DC converter is the core equipment of grid-connected renewable energy,voltage level conversion and other fields.Therefore,this thesis focuses on the grid-connection of renewable energy and proposes a DC converter which can realize wide range of output voltage changes.Firstly,this thesis studies the traditional Modular Multilevel Converter(MMC)and LLC resonant converter,based on the characteristics of both,this thesis designs a new LLC resonant DC converter based on MMC: Isolated Modular Multilevel Resonant Converter.In order to facilitate the analysis,the full-bridge MMC part of Isolated Modular Multilevel Resonant Converter is analyzed first,include the quasisquare wave modulation strategy,pre-charging strategy and submodule capacitor voltage equalization strategy.These control strategies enable the full-bridge MMC to achieve a large ratio voltage boost without relying on the transformer.By changing its working mode,the output voltage can be changed,a wide range of output voltage can be roughly adjusted,and the capacitor voltage balance of each submodule can be maintained.Further,the LLC resonator part of Isolated Modular Multilevel Resonant Converter is analyzed in this thesis.The working frequency of Isolated Modular Multilevel Resonant Converter is divided into three working regions according to the two resonant frequencies.Then analyzed the advantages and disadvantages of the three working regions,and selected the optimal working region to realize the Zero Current Switching of the output rectifier circuit.In the selected working region,the voltage gain of the LLC resonator is greater than 1,and the voltage gain of the LLC resonator can be changed by frequency conversion control,so that the voltage amplitude of the AC side of the full-bridge MMC can be fine-tuned to meet the requirements of the output reference voltage.In addition,this thesis derived the mathematical model of Isolated Modular Multilevel Resonant Converter.According to the mathematical model,we can control the LLC resonator by frequency conversion control,and the wide range of Isolated Modular Multilevel Resonant Converter output voltage can be adjusted with the full-bridge MMC,so as to meet the grid connection demand of renewable energy.Finally,the circuit structure and control strategy of Isolated Modular Multilevel Resonant Converter are simulated and verified by Matlab/Simulink software,and the hardware-in-the-loop experiment is designed by RT-LAB platform.This thesis analyzed the simulation and experimental results,and the results show that the converter can achieve a wide range of output voltage smooth adjustment and it has good steady-state performance.There are 73 figures,5 tables and 81 references in this thesis.
Keywords/Search Tags:DC/DC converter, Resonant converter, Modular structure, Wide output voltage range, Quasi square wave modulation
PDF Full Text Request
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