Study Of Three-port DC/DC Converter For Optical Storage System

In recent years,under the background of global energy reform,renewable energy has been vigorously developed and utilized,and the photovoltaic plus energy storage formation of renewable energy distributed power generation has been widely studied by scholars at home and abroad.Compared with the traditional two-port converter with a single function,the three-port converter has more voltage levels,and a single converter can realize the balance between input source,energy storage device and load in the optical storage system,which greatly simplifies the structure of the power generation system and improves the stability of the distributed power supply,and the three-port converter has received extensive attention from scholars.By comparing the existing three-port converter,a three-port converter based on Dual Active Bridge(DAB)topology using multiplexing of power devices not only reduces the number of switching tubes,but also has the advantages of DAB to realize soft switching and bi-directional energy flow,which is suitable for light storage power generation system.A new three-port converter studied in this thesis is a combination of DAB-based topology and bi-directional Buck-Boost by means of power device multiplexing,which not only has the above advantages of DAB but also includes the flexible ramp-up and ramp-down capability of bi-directional Buck-Boost converter.The thesis firstly introduces the composition of the converter topology in detail,analyzes the voltage mode and the detailed operation process of the converter under the PWM+phase shift control strategy,and derives the expressions for the phase shift inductor,the DC filter inductor current and the transferred power.The soft-switching characteristics of the converter are analyzed,and the conditions for soft-switching of all switching tubes are derived.The backflow power(BP)characteristics of the converter are analyzed,and a way of modeling the BP of the three-port converter is given to find out the region where the BP of the converter is zero in the whole power transmission range.Secondly,in order to achieve the maximum power output at the PV side,the charge/discharge control at the battery side and the stability of the output voltage in the optical storage system,a control strategy with competing output variables of the primary side controller of the converter is adopted,in which the maximum power point tracking control is adopted at the PV side and the constant voltage control is adopted at the battery side,and the specific implementation process of the PWM+phase shift control strategy is refined,based on the above control strategy,a simulation platform is built in MATLAB/Simulink software,and the control strategy,soft switching characteristics,and BP characteristics of the converter are simulated and verified.Finally,the design parameters as well as the control strategy are verified through experiments.The component parameters section containing the prototype is designed,the hardware circuit design scheme such as the driver and sampling conditioning circuit in the control circuit and the main software design flow based on TMS320F28335 are given,and the experimental platform of the 300W optical storage system is built.The power transfer,soft switching and BP experimental waveforms of the converter are given and analyzed,and the experimental results verify the feasibility of the proposed converter and the correctness of the BP theory analysis and optimization method.