Research On Wide Range Output Combined Multi-resonant Converter

In the "14th Five-Year Plan" and the long-term goal of 2035,the state once again made it clear that new energy vehicles will be a strategically developed emerging industry for my country,and the development of electric vehicles has entered a highway.At present,most of the on-board batteries of electric vehicles are lithium batteries.The battery charging is divided into two processes: constant current(CC)charging and constant voltage(CV)charging,which determines that the DC/DC converter used for charging needs to meet wide voltage gain,high efficiency and high power density requirements.In response to the above requirements,two combined converter topologies are proposed,using fixed frequency control to achieve constant current and constant voltage output of the converter while ensuring high efficiency and wide voltage gain.Firstly,based on the analysis of the current research status of DC/DC converters for electric vehicle charging at home and abroad,two combined topologies are constructed:dual LCLCL combined resonant converters and LCLCL-LLC combined resonant converters.The construction principle of the converter is: The construction principle of the two converters is: the two resonant networks on the primary side share the main switches in parallel,and the secondary side has a series structure.With a simple control method,constant voltage or constant current output characteristics can be obtained by adopting fixed frequency control,so as to better meet the charging requirements of electric vehicle lithium batteries.Secondly,the fundamental analysis method is used to analyze the characteristics of single LCLCL resonant network and single LLC resonant network,and the constant voltage frequencies and constant current frequencies of the two networks are found out respectively.In CC mode,the combined converter uses the constant voltage frequency of one resonant network and the constant current frequency of the other network to make the circuit equivalent to a constant voltage source and a constant current source in series;in CV mode,the combined converter uses the constant voltage frequency of two resonant networks to make the circuit equivalent to two constant voltage sources in series.The converter only needs to change the working frequency to realize the switching between the two working modes;the use of fixed frequency control can realize soft switching in the entire load range,which can improve the low efficiency problem under light load conditions,which also relaxes the design requirements of the magnetizing inductance of the combined converter.Finally,combining the setting of operating frequencies and power capacity requirements,the design of the combined resonant network parameters and the construction of a prototype experimental platform with 3.3k W,400 V input and 250-450 V output are completed.And the system hardware and software design process are given.The experimental data is used to verify the working principle of the combined topology and the rationality of the parameter design.Analyze and compare the experimental data of the two sets of converters,and provide their respective efficiency curves in CC and CV modes.The two frequencies set by the dual LCLCL combined resonant converter are respectively 50 k Hz and 120 k Hz.The highest efficiency is 97.29%,and the overall efficiency is above 95.5%.The two frequencies set by the LCLCL-LLC combined converter are respectively 50 k Hz and 90 k Hz,the highest efficiency is 97.0%,and the overall efficiency is above 96.5%.And the converter can realize soft switching in the full load range.