Research And Design Of The Resonant Medium Frequency Induction Heating Power Supply

The output of resonant medium frequency induction heating power supply is a single-phase alternating electric energy which frequency range from 400Hz to 20kHz and which voltage is up to thousands of volts. It belongs to a kind of special power supply. The medium frequency induction heating supply has many advantages like high efficiency, small size, light weight and so on. So it is widely used in melting , welding, heat treatment, forging extension processing and any other hot-working processes. The medium frequency power works in the resonant or quasi-resonant condition by using the series characteristic of RLC load's equivalent circuit.This article focuses on the series resonant Full-Bridge Inverter in the medium frequency induction heating power supply. The parameters of main circuit's devices are given for the design object of this paper which is a power supply in 20kHz/5kW. First of all, a detailed analysis on the load's equivalent circuit of induction heating is carried out. It obtained the calculation formula of quiescent point of series resonance. The analysis of the three working modes of inverter, capacitive mode, inductive mode and resonant mode, are aimed to the soft-switching state of MOSFET. And the optimal designs of absorption circuit, driver circuit and dead-time of the MOSFET are obtained on the basis of the switching characteristics. The topology of series resonant Full-Bridge is ascertained. The DPLL (Digital Phase Locked Loop) of control system based on ATmega128 and CD4046 achieved the frequency closed-loop control of power in steady condition. Power control use the method of PS-PWM (Phase Shift PWM). Accroding to the detal theoretical analysis of PS-PWM, the separated PI-P (Proportional Integral-Proportional) control algorithm is realized for power control in ATmega128. So the output power is constant,and the PS-PWM power closed-loop control is obtained. Starting method of power is proposed that can realize the starting from separate excitation to self-excitation.The close loop simulink model of phase-shift PWM series resonant Full-Bridge medium frequency induction heating power supply was established under MATLAB/Simulink environment, and the system simulation research was implemented with the established model.