Research On Current Sharing Technology Of Interleaved LLC Resonant Converter Based On Compensation Capacitor

LLC resonant converter has obvious advantages in the future energy development strategy because of its good soft switching characteristics and easy integration.It is widely used in new energy power generation system,especially in high-power photovoltaic and high-power wind power generation system.In high-power applications,the traditional LLC resonant converter will have the problem of capacity expansion.The interleaved parallel technology is often introduced to realize the uniform transmission of each phase power,so as to reduce the current stress of the power components of the converter.Due to the different parameters of the resonant components among the three-phase converters,the resonant cavity is inconsistent,which leads to the uneven current distribution among the three-phase converters and reduces the reliability of the converter.Therefore,in the parallel operation of the multi-phase converter,one of the key problems of the parallel LLC resonant converter is to ensure the balanced output of the current among the three-phase converters.In this paper,two interleaved LLC resonant converters are studied,and an automatic current sharing method based on compensation capacitor is proposed.In this paper,starting from the working principle and characteristics of full bridge LLC resonant converter,the mathematical model of single-phase LLC resonant converter is established by using the fundamental equivalent analysis method,and the mathematical expressions and equivalent relations of voltage gain and equivalent resistance are obtained.Taking the two-phase parallel LLC converter as an example,the main working process of the two-phase converter is described,and the working modes of the two-phase LLC resonant converter are introduced.The influence of single parameter error of resonant inductor,resonant capacitor and excitation inductor and combined parameter error on the current sharing characteristics of the converter are analyzed respectively,The fundamental reason of serious current imbalance caused by different resonance parameters is deduced theoretically.Secondly,an interleaved LLC Resonant Converter Based on compensation capacitor is proposed.Taking two phases as an example,the automatic current sharing is realized through the resonant cavity composed of compensation capacitor and resonant capacitor.The basic principle of current sharing can be realized by compensation capacitor is introduced,and the relationship curve between unbalance degree and compensation capacitor is drawn.Finally,the relationship formula of compensation capacitor is calculated through theoretical derivation,It is proved theoretically that this method has good current sharing effect.Finally,PSIM simulation is used to verify that the LLC resonant converter with compensation capacitor can achieve better current sharing effect between phases in the case of the most serious combination error.An experimental prototype of two-phase interleaved LLC resonant converter with compensation capacitor is built to verify the correctness of the design of compensation capacitor and resonant parameters and the effectiveness of current sharing scheme of compensation capacitor.The efficiency of the prototype is tested,and the efficiency curve of the prototype with compensation capacitor is compared with that without compensation measure,It is concluded that the converter can keep high efficiency after adding compensation capacitor.This paper has 49 pictures,5 tables and 51 references.