Design And Analysis Of Digital Control System For Induction Heating Power Supply

Compared with traditional direct heating technology,induction heating technology has the advantages of fast heating speed,high heating efficiency,more uniform heating,safety and reliability,and low pollution.It is widely used in industrial fields such as metallurgy,machining,and national defense.Traditional induction heating power sources are mostly controlled by analog circuits,which have a number of limitations such as complicated control methods,poor flexibility,and low system stability.With the advent of high-speed digital processors,digital control methods can not only effectively solve the problems in analog control circuits,but also improve the working performance and efficiency of the power supply,making it easier to adjust,safe and more reliable.This thesis focuses on the digital control system of induction heating power supply.Based on FPGA(Field Programmable Gate Array),the digital phase locked loop of the induction heating power system is designed to realize the synchronous tracking of the operating frequency of the induction heating power inverter to the resonance frequency of the load,so that the switch tube works at quasi-resonance.In the state,the switching loss is reduced,and the working efficiency of the power supply is improved.First,by investigating the structure and power regulation of an induction heating power system,the thesis analyzes and compares the topology and characteristics of series and parallel resonant inverters,and determines the series resonant inverter power supply as the research object.The power modulation methods of DC side and inverter side are compared and analyzed.Finally,a dual closed-loop pulse frequency power control scheme is proposed.Then,based on the research on the digital control system of induction heating power,this thesis designs a digital phase locked loop based on FPGA to realize the frequency tracking technology of digital control in induction heating power system.First,the working principle of the phase-locked loop is theoretically analyzed,and then by comparing the advantages and disadvantages of analog chip control frequency tracking technology and digital chip control,a digital phase-locked loop based on FPGA control frequency tracking is proposed,and its performance and implementation of each module are discussed,analysis and introduction.In this thesis,a digital phase-locked loop is designed based on the traditional digital phase-locked loop.The mode-change control module and the frequency measurement module are added.The real-time control of the digital loop filter’s modulo value and the divider’s modulo value in the PLL is improved.The frequency-locking range and phaselocking speed of the digital phase-locked loop are simulated in Matlab to verify the influence of the digital loop filter’s modulus on the digital phase-locked loop.The design of digital phase-locked loop is completed in Quartus II software,and the logic function is verified by simulation.In addition,the thesis also completes the overall design of the digital control system for induction heating power supply,including the design of a separate-excitation start circuit,a separate-excitation self-excitation circuit,a drive circuit,a PWM generation circuit,a signal acquisition processing circuit,and a fault detection and protection circuit,and digital phase-locked loop together form a complete closed-loop control system.The output signal of the digital phase-locked loop outputs two driving signals with adjustable dead time through the PWM generating circuit,and then outputs four driving signals through the driving circuit to drive the full-bridge inverter to ensure that the switch can abide by the principle of first turning off and then turning on.Finally,by modeling and simulating the induction heating power system in Matlab / Simulink,it is verified that the designed control scheme can realize the synchronous tracking function of the inverter operating frequency to the load resonance frequency,and ensure that the inverter works in a quasi-resonant state.The overall design and simulation of the closed-loop control system is completed in the Quartus II software.The simulation results verify that the designed closed-loop control system can achieve frequency tracking of the resonant frequency of different loads of the induction heating power supply.Based on this result,an experimental prototype with a power of 2k W and an output oscillation frequency about 20 k Hz is designed and built.Through experiments and sampling waveform analysis,the digital control system designed in this thesis can accurately complete the induction heating power frequency tracking.