| With the development of power electronics technology and microwave technology,the research of magnetron and magnetron power supply is deepening gradually.The traditional magnetron power supply uses magnetic leakage transformer,which has the problems of high loss and low efficiency.It can only adjust the output power by relay absorption,and can not achieve continuous output regulation,resulting in uneven microwave heating.In this thesis,a magnetron power supply with LLC resonant conversion topology as the main circuit is studied.The output power is continuously adjusted by frequency conversion control.The power supply has the advantages of good reliability and high power density.Firstly,the working principle and volt-ampere characteristics of magnetron are analyzed,and the requirements of magnetron for power supply are defined.Through the analysis and comparison of various resonant converters,half-bridge LLC resonant converter is selected as the main circuit of magnetron power supply.The working process of resonant network in different frequency range is analyzed.The main circuit of LLC is modeled by fundamental wave analysis method.The relationship between DC gain,input impedance and voltage gain is deduced.The conditions of zero voltage switching on(ZVS)are analyzed.Secondly,according to the design requirements of magnetron power supply,the main circuit parameters of LLC resonant converter are designed,and the relevant components are selected.Through the finite element simulation software Jmag,the electromagnetic and thermal fields of transformers with different shapes of magnetic cores are simulated.According to the temperature distribution,the selection of magnetic cores is made clear,and the geometric parameters and winding mode of transformers are designed.Considering the stability of the analog chip and the flexibility of the single chip computer,a control method based on the analog chip L6599 and supplemented by the single chip PIC16F1828 is adopted to control the circuit.The analog chip L6599 directly drives the switch tube to control the switching frequency,detect the current size and realize soft start.The single chip PIC16F1828 assists to realize the output voltage continuous adjustment,complete the power setting and other functions.At the same time,a two-way output auxiliary power supply is designed to supply power for the control system.Finally,the magnetron power supply is simulated and experimented.The simulation results verify the feasibility of the designed magnetron power supply.The energy conversion efficiency and power factor at different output power are tested experimentally,and the relevant experimental waveforms are obtained.The simulation and experimental results show that the designed LLC resonant half-bridge magnetron power supply meets the design requirements. |
