Research On Bi-directional DC/DC Energy Storage Converterand Its Control Strategy For Dc Micro Grid

Along with the development of the progress of human society and economy,the environmental pollution and energy shortage are becoming more serious,we are facing the severe challenge of adjusting energy structure strategically in the domestic and overseas.As a consequence,more and more countries vigorously support the photovoltaic DC micro grid system based on solar energywhich is attracting more and more attention.In consideration of the flexibility and sensitivity of the power system,there needs anenergy storage device with reasonable control strategy to realize the construction of new and intelligent micro grid system.As the interface of energy storage device and the micro grid system,the bidirectional DC/DC Converter(BDC)accounts for the optimization of charging and discharging the storage battery and undertakes the task of energy management and control.By further applying soft switching technology to BDC,the system volume and loss can be reduced effectively and the overall energy conversion is improved.Thus the BDC applies to photovoltaic DC micro grid has very important research and application value.The dissertation discusses the topology and control strategy of the half bridge soft switching BDC in the application of photovoltaic DC micro grid background.Firstly the working principle in different operating modes of the micro grid system is analyzed,and then the parameter calculation of main and auxiliary circuit is conducted on soft switching condition.The control strategy of the studied BDC is discussed,and its small signal dynamic model is built using state-space averaging method under each operating mode,thedouble closed-loops framework is applied and the corresponding PI parameter of voltage and current loop controller is designed.The integrated system design of the half bridge soft switching BDC is achieved on the basis of theoretical analysis,including the hardware and software design.We use DSP TMS320F28335 as the core controller to accomplish digital control for the system,which at the same time can communicate with the host computer,and LABVIEW software is applied to human-computer interface design.The simulation model of the studied energy storage BDC is established in PSIM,and the working state of the converter under island-charging,island-discharging,grid-connected mode and the dynamic switch-over between two of the running modes are simulated.The simulation results demonstrate the correction and rationality of the previous working principle analysis and control strategy design.The designed BDC is able to achieve soft-switching working state under various operating modes of the DC micro grid system.In the end,a 100 W prototype is made to build the experimental platform,the testing result shows that the designed energy storage BDC can realizetwo way flows of power and change the power direction smoothly,and it can control the charging and discharging process of the battery effectively and maintain the stability of the DC bus voltage.