Research And Design Of Multi-port Converter For Dc Microgrid

Compared with AC microgrids,DC microgrids eliminate multiple DC/AC or AC/DC links.It has no problems of synchronization,reactive power,frequency control,skin effects,and harmonics.Moreover,it provides high levels of renewable energy and DC loads with better performance in efficiency,reliability,and cost.In addition,it requires simpler control scheme and can provide more efficient power quality.It has become a research hotspot for scholars consequently.As a new type of converter that has appeared in recent years,multi-port converters have the advantages of reducing system size,reducing the number of switching tubes,improving converter efficiency,reducing losses,and saving costs in contrast to traditional converters.This paper focuses on the researches of multi-port converter topology and control technology in DC microgrid.The main works are as follows:Firstly,comparisons are made between DC microgrids and AC microgrids.The topology and control scheme of existing multi-port converter are analyzed.Based on the characters of DC microgrids,partially isolated multiport converters are analyzed in detail.As the conventional multi-port converter has disadvantages of more quantity of switches,complex system and low power density,a new type of multi-port converter is analyzed in this paper.The switches of bi-direction Buck/Boost converter and two arms of phase-shifted full-bridge converter are multiplexed.As a result,two input ports are obtained,the number of switches is reduced and the power density is improved.The secondary side of the converter is combined with the synchronous Buck converter to realize two output ports with different voltage.It can better adapt to various electrical equipment consequently.The working state and switching mode of the proposed converter are analyzed in detail.The relationship between the input and output of the converter and the ZVS implementation conditions are derived in detail as well.The converter is analyzed by Matlab/Simulink.The construction and simulation analysis of the simulation model are presented.Secondly,based on the characteristics of DC microgrid,a control strategy suitable for multi-port converters of DC microgrids is studied considering the maximum utilization of photovoltaic input ports,protection control of energy storage ports,and voltage stabilization control of output ports.This control strategy uses the minimum selector to determine the control mode of each port by selecting the output duty cycle of the converter according to the current operating mode of the multi-port converter.When the control strategy of each port is switched and the duty cycle changes suddenly,it keeps stable.PWM plus phase-shift control is used to achieve target control of each port.Small signal modeling and analysis of the converter are made to determine its stability.The control strategy of the converter is simulated and analyzed in Matlab / Simulink.Finally,the hardware circuit and software part of the proposed multi-port converter are designed.A 1000 W DC microgrid multi-port converter experimental prototype based on TMS320F2808 is designed.The experimental results prove the effectiveness and feasibility of the multi-port converter proposed in this paper.