Research On High Performance LED Lighting Circuit And Its Control

With the development of LED driving technology,medium and high power LED driving power supply has been paid more and more attention.The half-bridge LLC resonant converter commonly used in the medium and high power LED driving circuit,can realize the soft switching of switches and zero current turn off on rectifier diodes to some extent,thus having the advantages of high efficiency and low electromagnetic interference.Therefore,it has more and more applications in the LED lighting circuit.In order to meet the characteristics of LED lamp load,and to solve the shortcomings of slow dynamic response and poor dynamic performance of control parameters on traditional PID control,an adaptive dimming driving power supply of high reliability and high efficiency is studied in this paper,which can not only improve the life of LED,but also can reduce pollution,save energy.and is of great significance to the application and popularization of LED.In this paper,the working principles and control method of the LLC circuit are studied based on the half-bridge LLC resonant converter,which is applied to the LED lighting driving power supply.And the large signal model of LLC resonant converter is deduced by extended describing function method.On this basis,the nonlinear system can be transformed into a linear system effectively by using the large signal model of the LLC resonant converter.The traditional PID control method,fuzzy PID control method and fixed switching frequency sliding mode control strategy are studied in this paper,focusing on the design of the sliding surface and stability analysis.In order to solve the problem of large output voltage ripple in the dimming of the LLC circuit using the sliding mode control with fixed switching frequency switching,a strategy for controlling the dimming using the fuzzy frequency selective sliding mode control based on fixed switching frequency sliding mode control is presented in this paper,thus improving the dynamic response speed of dimming,and ensuring the low output voltage ripple on half-bridge LLC resonant converter.In this paper,the design method of the main parameters of the half-bridge LLC circuit is given,including the design of the resonant parameters and the design method of the high frequency magnetic components,and the selection of the power device.In the software design,the main program and the interrupt service subprogram are mainly designed.In order to obtain constant current characteristics,the full load operating frequency is designed at the frequency of resonance.Therefore,the switching frequency of the circuit will be above the resonant frequency when dimming.In order to improve the efficiency of power supply,the secondary side of the half-bridge LLC resonant circuit adopts the synchronous rectificaation technology to reduce the circuit loss.Combined with the specific 240W LED driving power supply,this paper also gives the method of loss analysis of half-bridge LLC resonant converter.PSIM simulation software is used in this paper to simulate on the main circuit of the half-bridge LLC resonant converter and on the above control methods.On this basis,a 240W all-digital dimming power prototype platform is built.The simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the fuzzy frequency selective sliding mode control scheme.