Design And Implementation Of An Improved Flyback Converter With Double Closed Loop Control

With the miniaturization and intelligent development of electronic products,flyback with the trend of miniaturization and intelligence in electronic products,flyback converters are highly favored in small and medium-sized power applications due to their advantages such as flexible inductance values of high-frequency transformers,electrical isolation function,and convenience in achieving multi-channel output.The design of highperformance switching power supplies with flyback converters as the main circuit topology has gradually become an important research branch in the field of power supply.This thesis focuses on the research and improvement of traditional flyback converter systems.The main work of the thesis is as follows:(1)Several basic non-isolated and isolated converters are introduced,and the working modes and commonly used modulation techniques of flyback converters are analyzed;Then,the high-frequency transformer parameters,power transistor selection and output filtering circuit in the main circuit topology are designed.In order to absorb the peak pulses of the power switch,an RCD clamping circuit is designed in the main circuit topology.(2)The control strategy of the flyback converter is analyzed and designed in detail.Firstly,an overview of loop control methods for flyback converters is presented,and the characteristics of single closed-loop and double closed-loop control strategies are compared and analyzed.Then,a voltage loop and a current loop feedback loop are designed based on the dual closed-loop control chip UC3842.Finally,in order to further reduce power loss,the control chip UC3842 was designed with a power on reset circuit to improve the efficiency of the flyback converter.(3)The dual closed-loop control system of the flyback converter is optimized and improved.In order to overcome the system instability and poor dynamic performance problems caused by the zero poles introduced by the filter circuit and optical coupler in the traditional flyback converter circuit,mathematical models of the main circuit,PWM module and current sampling loop of the flyback converter are established,and the small-signal modeling of the flyback converter is constructed.Furthermore,the parameters of the compensation network using a single zero and single pole compensation network are design and calculated.(4)In order to further improve the output accuracy and anti-interference ability of the flyback converter,a dual closed-loop variable universe fuzzy PI control strategy is applied to the control circuit of the flyback converter based on the improvement of zero pole control.Due to the introduction of scaling factors,the control process is more refined,and the control system has stronger fault tolerance and adaptive ability.The simulation verification results of Simulink show that the zero pole correction control mode effectively improves the dynamic performance and stability of the system.Moreover,the application of dual closedloop variable universe fuzzy PI control to the flyback converter results in a smaller steadystate error of output voltage and shorter dynamic adjustment time compared to traditional control methods,which improves the robustness of the system.(5)A simulation model of flyback converter with dual closed-loop control was built and debugged in the Saber simulation environment,and the simulation results meet the design requirements preferably.Then,the principle diagram,PCB diagram,component layout and wiring of the dual loop control flyback converter system are drawn using Altium Designer software.Finally,an experimental prototype of the dual closed-loop controlled flyback converter is made,and test results are analyzed.