Research On The High-frequency Resonant Inverter Pulse Density Modulation Control Technology

As an important heating tool in industrial production,induction heating power supply has obvious advantages in environmental protection,energy saving and controllability.Its main circuit structure is high-frequency resonant inverter.According to the resonant load connection form,it can be divided into two types: series type and parallel type.As an important part of induction heating power supply,series type high-frequency resonant inverter uses pulse density modulation technology,which can realize full power range load matching and has high flexibility in the industrial production process.In view of the current research hotspots and problems of pulse density power regulation control technology for series-type high-frequency induction heating power supplies,this paper conducts an in-depth study on the power device commutation method,power regulation method,digital phase-locked control method and silicon carbide device main circuit design method for series-type high-frequency resonant inverters,and the main research results and conclusions are as follows.1.The improved pulse density power regulation control method is proposed,and the pulse distribution adopts ΔΣ modulation method,which can realize the uniform distribution of inverter pulses under any inverter power regulation period without ROM memory and look-up table,reduce the output current fluctuation,and improve the power control accuracy and device performance.2.An improved pulse density power device commutation control method is proposed.By adjusting the trigger timing of inverter pulses,the output voltage spikes of high-frequency resonant inverters are avoided,and the switching frequency of power devices is reduced,so that the switching and conduction losses of power devices of different bridge arms converge.3.A fully digital phase-locked loop(ADPLL)control method for pulse density power regulation of series resonant inverters is proposed.The inverter output voltage and resonant capacitor voltage are used as the input and feedback signals of the phase-locked loop,which improves the anti-interference performance and adaptability to different frequencies and ensures that the inverter always works in the best condition.4.The MATLAB SIMULINK simulation model of the main loop of the series-type high-frequency induction heating system is built,and the pulse density power regulation algorithm of the inverter and the working state of the main loop are simulated and verified.the pulse density power regulation control program in Verilog HDL language is programmed using the FPGA chip as the main controller,and the designed control program is simulated and functionally verified using Model Sim software.5.A prototype 50 k W/300 k Hz series induction heating power supply was built using SIC MOSFET power module,and the designed controller function was tested under load,and the control method described in the paper was verified experimentally.