Research On Topology And Control Of Three-port Converter With Wide Operation Range

With the depletion of fossil energy,renewable energies such as solar,wind,thermoelectric generator and so on are becoming more and more popular.However,energy storage components such as batteries and supercapacitors are mandatory to repair the power mismatch between the renewable sources which feature intermittent power supply and loads which need constant and stable power delivery.Several converters,with the disadvantage of large size,high cost and complex control strategy,are employed to connect renewable source,energy storage component and load in conventional solution.Then,three ports converters(TPCs),which can simultaneously connect the renewable source,the energy storage component and the load,with the merits of compact packaging,fewer components and unified power management,show large potential to be applied in low power renewable system,which is sensitive to cost and volume.Based on the problems the non-isolated TPCs faced when applied in low power renewable applications,research contents in this thesis are as follows:Without transformers,non-isolated TPCs always suffer tight ports voltage restrictions,which limit the operation range of the non-isolated TPCs.To solve this problem,based on the convertional two switch Buck/Boost converter,by inserting one switch and one diode to connect the energy storage component,the variable structure TPCs with compact size are generated.In variable structure TPCs,structures between ports can vary among Buck,Buck/Boost and Boost,and thus the ports voltage restrictions are loosen and the operation range is extended.Without transformers,non-isolated TPCs cannot utilize magnetic coupling to supply energy to or absorb energy from multiple ports simultaneously.And as the battery port is usually in parallel with the renewable source and the load,time-sharing concept is always introduced,which negatively impacts the dynamic response of the TPCs.To solve this problem,based on conventional two-port non-isolated converters,by inserting two switches and two diodes to connect the energy storage component,a family of TPCs,in which ports can absorb or supply energy simultaneously,is generated.In these TPCs,the load mutation can be responded immediately,and thus the operation range is further extended.Based on overal analysis and summary of working modes of the former proposed TPCs,rules of synthesizing TPCs is concluded,inner relation of topology restriciton and working modes and a systematic methods of generating TPCs which can realize all the working modes is proposed.Moreover,a method of supplementing working modes which the TPC cannot realize is given.With this method employed in flyback converter,a flyback TPC which can feedback the energy in the leakage inductor is generated.In the above work,TPCs with variable structures among ports,serial battery port and full working modes are generated to realize wide operation range.However,multiple working states of these TPCs complicate the control strategy design.In this thesis,these working modes are divided into three levels based on time scale: modulation optimization,working modes switch and variable structure switch.With control strategy designed in these three levels,the TPCs working performance is further optimized and smooth switching among different working modes and variable structures is realized.At last,the complete process of applying TPCs is given.