Research On High Frequency Induction Heating Power Supply Based On LLC Resonant Load

Induction heating is a new type of non-contact heating technology.It uses modern electronic technology to realize the conversion of electric energy to thermal energy.Compared to traditional heating mode,It has the advantages of high efficiency,energy saving,easy control and environmental protection,which makes it widely used in quenching,melting,heating,welding and forging as a key technology in heating field.Induction heating power supply is an important application of this technology.But induction heating power supply has low capacity,low accuracy and low digitization degree.Therefore,it is of great significance to improve its performance by studying its topological structure and control strategy.In this thesis,the high frequency induction heating power supply for LLC resonant load is studied as follows:Firstly,by comparing and analyzing the characteristics of LC series resonance,LC parallel resonance and LLC resonant load,the LLC resonant load with current conversion function is determined.In view of the difficulty of LLC parameter tuning and the problem of the poor reliability of the parameter design scheme,an improved Q value(quality factor)estimation method is proposed.The values of each matching parameter are obtained by the estimated Q value.Secondly,based on the analysis of the basic principle of PLL,a mathematical model of phase locked loop is established.Aiming at the problem of the poor reliability and dead time of analog phase-locked circuit,we need to study the digital phase-locked loop based on DSP to track the variation of LLC load resonant frequency.Then,by comparing the advantages and disadvantages of different power adjustment strategies,the Buck chopper circuit is selected to achieve power regulation.Aiming at the shortcomings of traditional power adjustment algorithm,the Buck closed loop control system based on fuzzy control algorithm is studied.Finally,a closed loop simulation model of the whole power system(including load matching,phase lock control and power regulation)is built in MATLAB.The simulation results show that at the resonant frequency,the load operates on the small sensibility,the inverter can output the maximum power,and the output voltage of the Buck converter is stable and adjustable.