Research On Control Strategy Of Series Induction Heating Power-supply

Because of its unique advantages of high efficiency,environmental protection and safety,series induction heating power supply is widely used in industrial heating fields such as heat treatment,thermal processing,welding and smelting.However,its control system has the characteristics of nonlinearity,strong coupling,small time delay and sudden change of equivalent model.When using conventional control methods to control the output current and inverter phase angle,there are problems such as large overshoot,slow response time,and difficult control parameter setting,resulting in low heating efficiency and high failure rate of equipment.To solve the above problems,this paper designs a series induction heating power supply control system based on ARM and FPGA,and optimizes the control methods and strategies of the system to improve the overall performance of the equipment.The main research contents of this paper include:(1)By analyzing the design requirements of series induction heating power supply,this paper determines the topology and control method of the power supply.The uncontrolled rectification technology is used to convert the AC input power supply into DC,and then output high-frequency AC after series resonant inversion.The phase-shift PWM method is used to control the output current and adjust the operating frequency of the inverter to ensure that the power supply works in a weak inductive state.(2)According to the control characteristics of the system,this paper adopts a double closed loop control strategy combining the output current outer loop and the inverter phase angle inner loop to precisely control the output.In order to solve the problem of large overshoot and slow response time of output current control,this paper applies fuzzy control to the current outer loop control,and adjusts the parameters of PID controller in real time according to the current deviation and deviation change rate to meet the requirements of controller parameters under different working conditions.In view of the large change range of inverter phase angle during heating process,poor real-time performance and narrow dynamic range of analog phase lock,the inverter phase angle inner loop uses a variable parameter PI controller based on FPGA to change the parameters of the controller according to the phase angle deviation,which improves the control accuracy and speed.(3)Based on ARM and FPGA embedded control technology,the control system of series induction heating power supply is designed and implemented.In terms of hardware,this paper designs sampling,protection,drive,communication circuits,completes the schematic and PCB drawing,and makes and debugs the circuit board.In terms of software,this paper develops and debugs the control program of ARM and FPGA,and completes the design of human-computer interface.Finally,this paper builds an experimental test platform to verify the system function and control performance.The experimental results show that the output current control accuracy of the power supply system is better than 0.3% and the inverter angle control accuracy is better than ±0.05°.Under the step response,the output current overshoot is zero,and the adjustment time is within 200 ms.When the load changes dramatically,the output current overshoot is controlled within 6%.Therefore,the control system of the series induction heating power supply designed in this paper can realize the precise control of output,has the advantages of short adjustment time and small overshoot,improves the control performance of the system,and meets the design requirements.