Research On Isolated Bidirectional AC/DC Converter Based On CLLLC Resonance

In the context of carbon neutral development,the power industry needs to accelerate the supply of clean energy and low-carbon.Solar energy and wind energy will further develop and become important power sources in China.Electric vehicles will also become an important direction for the development of new energy vehicles,The interface converter between AC transmission bus and new renewable energy power generation system and new electric vehicle needs to have the function of two-way energy flow.There are various problems in the traditional bidirectional AC/DC converter.It is of great significance to study the new bidirectional AC/DC converter.Firstly,the isolated AC/DC converter with the first stage of Swiss rectifier and the second stage of CLLLC resonant converter is selected as the research object.The topology has the advantages of effective isolation of DC/AC measurement,high power factor,good switching characteristics,strong load protection ability,strong output regulation ability,strong stability and small application limitations.Secondly,several IGBT switches are used to replace some diodes in Swiss rectifier to realize the two-way flow of energy.Through the analysis of the switching state and conduction mode of the bidirectional Swiss rectifier in different working areas and the equivalent treatment of the step-down chopper circuit,the control strategy of the bidirectional Swiss rectifier is deduced.The simulation results show that under this control strategy,the converter can realize two-way energy flow,power factor correction in both forward and reverse modes,the power factor is close to 1,and has good dynamic response ability in case of disturbance.Then,the main working principle of CLLLC resonant converter based on phase-shifting control is analyzed.In order to solve the problem that the maximum equivalent gain of phase-shifting control is 1,the single phase-shifting control is applied to CLLLC resonant converter,and the voltage output is controlled by controlling the phase-shifting angle of the primary and secondary driving pulse signal.The simulation results show that the output voltage ripple of CLLLC resonant converter is far less than 1% in both forward and reverse modes,and has soft switching characteristics in a wide range.Finally,in view of the slow dynamic response of the CLLLC resonant converter system when disturbed and the more disturbance of the system when connected with the front stage,a flattening controller suitable for the CLLLC resonant converter is deduced and designed based on the differential flattening theory and combined with the single-phase shift control.The flat controller includes two parts: expected trajectory generation and output trajectory tracking.Better dynamic performance is achieved by planning the trajectory of state variables and correcting the output.According to the simulation results,compared with the traditional PI control,the CLLLC resonant converter under differential flat control has less time to enter the steady state.In case of load fluctuation,the voltage overshoot,time to enter the steady state again and error are reduced,and the dynamic performance is greatly improved.