Research And Design Of Digital Control Technology For Induction Heating Power Supply

With the increasingly serious environmental pollution problem,traditional industries are gradually developing in the direction of energy saving,high efficiency and pollution-free.In the field of metal heat treatment,green and environmentally friendly induction heating technology has been widely promoted and used.At present,most of the existing induction heating power supplies are controlled by analog circuits,which has the problems of low tracking accuracy of load resonant frequency and slow response of power and current.Therefore,this thesis studies the digital control technology and corresponding digital control system of induction heating power supply in detail,and deeply studies the control algorithms such as load frequency tracking and power and current loop controller.During the induction heating process,the load resonance frequency will vary widely,while the traditional induction heating power supply uses an analog phase-locked loop to track the load frequency,which has problems such as narrow phase-locked frequency band,fixed center frequency,and complicated design.The conventional digital induction heating power supply uses the previous digital phase-locked loop for frequency tracking,and the above-mentioned problems are alleviated,but there is the problem of inaccurate phase tracking.For this reason,this thesis designs an automatic variable modulus all-digital phaselocked loop based on CPLD for load frequency tracking.The phase-locked loop adopts an automatic variable modulus controller,which reduces the phase jitter during frequency tracking by automatically adjusting the modulus of the digital filter,and designs a numerically controlled oscillator based on a finite state machine to improve phase-lock accuracy and speed.The program is simulated by Modelsim software,and the results show that the phase jitter is suppressed,and the phase accuracy and phase lock speed are greatly improved.The improvement of the load frequency tracking accuracy directly improves the control accuracy and heating performance of the induction heating power supply,but the traditional PI controller cannot meet the current high-performance induction heating power control requirements.During the equipment startup stage,the power output has a large overshoot.It is very dangerous in high-power equipment,which may cause the temperature of the heated workpiece to be too high or even damage.For this reason,this thesis designs a variable parameter segmented integral separation PI controller according to the characteristics of power changes,and adjusts the power output value in a targeted manner,and adjusts the controller parameters in time according to the characteristics of power changes.It is verified by Matlab/Simulink simulation that the scheme can effectively suppress the power overshoot and speed up the dynamic response.Finally,in order to verify the feasibility of the above algorithm,an experimental prototype of a digital induction heating power supply is built,and an LCD display screen is designed to make up for the blind area of human-computer interaction.In the hardware design part,according to the experimental conditions and personal design experience,the working current and working voltage of the main circuit device are calculated in detail to provide a reference for device selection.On this basis,the control circuit parameters are designed accordingly.In the software design part,the main program is to program the automatic variable mode all-digital phase-locked loop and variable parameter segmented integral separation PI controller.In addition,the PWM phase shift power adjustment program and the clock cycle,phase angle,Parameters such as dead zone,power startup procedure,ADC sampling procedure,etc.Experimental results show that the power supply can continuously adjust the power of the power supply by phase shifting power adjustment;the improved phase-locked loop can track the load frequency change in time,so that the load resonance frequency is consistent with the power supply operating frequency,and the inverter circuit switching device can work in the soft switching state,the switching loss is reduced.The above experimental results verify that the digital control strategy proposed in this thesis is effective and feasible.