Design And Control Of CLLC Resonant Converter

With the rapid development of microgrid technology,energy storage technology,and two-way interaction between grid and electric vehicles,With a series of advantages such as electrical isolation,flexible control mode,wide range of soft switches,high power density,low power loss,bidirectional energy transmission and voltage conversion,bidirectional isolation DC-DC converter has gradually emerged in these technical fields and shown great application prospects.Therefore,this thesis takes CLLC resonant bi-directional full-bridge DC-DC converter as the research object to explore and study its design method and control strategy.Firstly,the background significance,development history and research status of DC-DC converter are introduced,and the topology structure and working modes of CLLC resonant converter under three different frequency modes are analyzed in detail.The equivalent model of the converter is established by using the fundamental wave equivalent analysis method,and the relationship between the voltage gain of the converter and the switching frequency and resonance parameters is found.The influence of the power transmission characteristics,voltage gain characteristics and dead time on the transmission power of the converter is analyzed.Then,under the conditions of zero voltage on and zero current off,the relationship between the excitation inductance and switch dead time is analyzed,and the excitation inductance is designed based on this.Because the voltage gain of the converter is affected by the resonant parameters and the operating mode,it is hoped that the converter can keep the voltage gain constant in some applications.In order to keep the voltage gain constant,the resonant parameter design method is optimized in this thesis.At the same time,the influence of the deviation between resonant frequency and switching frequency on voltage gain is also studied.Then,in order to make the converter run well,the open-loop control strategy of CLLC bidirectional full-bridge DC-DC converter is proposed.At this time,the switching frequency and the resonant frequency are equal,and there is no need for feedback adjustment.Because the resonant parameters of the converter are optimized,when the resonant parameters change little,the deviation between switching frequency and resonant frequency is small.The open-loop control strategy allows the converter to keep the voltage gain basically constant.For some need to fine-tune the output voltage or high voltage gain requirements,the open-loop control strategy can not meet the application requirements.Therefore,a control strategy of frequency modulation voltage stabilization is proposed in this thesis,that is,using PI closed loop to fine-tune the switching frequency according to the output voltage transformation,so that the switching frequency is always equal to the resonant frequency,so as to ensure that the converter works in the resonant state.The proposed frequency modulation voltage regulator strategy broadens the application of the converter.Finally,each working state of CLLC resonant converter is simulated and analyzed by Simulink,and an experimental platform is designed and built for experimental verification.The simulation results are in good agreement with the experimental results,which verifies the correctness of the control strategy and parameter design method proposed in this thesis.