Research On LLC Resonant Converter System And Control Strategy

With the continuous development of science and technology,the production life of the power of technology demand is higher and higher,switching power supply are advancing towards high efficiency high power density,high power density is bound to have a great relationship with the frequency of the switching devices,and as the device switching frequency increasing,hard switching loss will increase sharply,leading to low efficiency,so current hard switching power supply can no longer meet our daily needs.Resonant converter using soft switching technology means to greatly reduce the switching loss,can make the switching frequency up a level,improve the efficiency and power density,has been widely concerned and applied.LLC resonant converter,because of its good soft switching characteristics,has been applied to new energy,aerospace systems,electric vehicles,data centers and other fields.At present,the common operating mode of LLC resonator is variable frequency mode and phase shift mode,both modes of operation are based on pi controller control methods,but PI controller itself does not have a good dynamic response,if the system needs faster response speed,then PI controller can not meet the needs of the system.In this thesis,the active disturbance rejection controller(ADRC)of LLC resonant converter,including nonlinear ADRC and linear ADRC,has a faster dynamic response speed,which can solve the problem of slow dynamic response well while meeting the steady state effect,so this thesis will focus on the advantages of nonlinear ADRC.In order to highlight the advantages of nonlinear ADRC controllers,this thesis analyzes and compares the basic characteristics of LLC systems based on three controllers(nonlinear ADRC,PI controller,linear ADRC).Firstly,the working principle of the full-bridge LLC resonant converter in two operating modes is discussed in detail,and the steady-state characteristics of the LLC system in the variable frequency mode are analyzed by the base wave analysis method,and the steady-state characteristics of the LLC system in the phase-shifting mode are analyzed by using the time domain analysis method.For the variable frequency operating mode,the small signal model of the whole bridge LLC system is deduced,and the PI compensation link is designed according to the small signal model.For the two modes of operation,the simulation based on PI controller is established and the steady state and dynamic performance are analyzed.Then the basic principles of nonlinear ADRC and linear ADRC are introduced,and based on the ADRC controller,the simulation of the two operating modes is established,and the superior dynamic performance index of nonlinear ADRC is analyzed by simulation.Finally,the design of experimental parameters and the design of hardware circuits are completed,and a prototype of a fullbridge LLC resonant converter is produced,The result proves that the nonlinear ADRC control method has better dynamic performance under the premise of meeting the steady state performance of the system.