Research On Series Resonant Medium Frequency Induction Heating Power Supply Based On DsPIC

With the development of power electronics technology,induction heating has been widely used in industrial fields.The requirements for the reliability and efficiency of induction heating power supply are raised continuously.And digital control is an important technique to improve the performance of induction heating power supply.In this thesis,dsPIC is used as the core controller to study the intelligent and digital control mode of series resonant medium frequenc y induction heating power supply.This thesis introduces the basic principle,application and advantages,development status and trend of induction heating.Based on the analysis and comparison of several common main circuit structures and control schemes of induction heating power supply,the system structure of series resonant medium frequency induction heating power is determined with rectifier circuit using three-phase uncontrolled mode and inverter circuit adopting the structure of single-phase full-bridge.The working characteristics of the series resonant load,the phase shift PWM function and the working mode and process of the inverter circuit are studied.The working principle of phase-locked loop in frequency tracking technology and the methods for phase difference measurement are described.And the commonly used methods of power supply startup are analyzed.After analying for the defects of conventional digital PID control to apply in induction heating power system in this thesis,two compound strategies,FUZZY-DPLL and FUZZY-PI,are adopted based on the fuzzy control principle.In the process of realizing the frequency tracking,the FUZZY-DPLL segmentation control method is utilized for frequency correction and phase correction according to the measured phase difference,which is obtained through the input signal capture module of dsPIC and the function of the FFT.In the process of realizing the power adjusting,the FUZZY-PI segmentation control is used to calculate the phase angle with the principle of phase shift PWM for power adjustment and fuzzy adaptive PID tuning control is used to adjust the control parameters in digital PI control.According to the detection value of the load current and the technology of DDS,the problem of power supply startup is solved by the sweep program.Design of hardware and software for the series resonant medium frequency induction heating power supply is completed based on dsPIC33EP32MC202.The simulation model and the experimental platform are established according to the design contents.The control strategy to solve the key problems such as system frequency tracking and power regulation is analyzed and debugged.The results show that the control system design is correctness and feasibility and has laid a good foundation for further digital study of induction heating power supply.