All-digital Design Of Induction Heating Power Supply

Direct current side power modulation is usually used today in our country. One way is controllable rectifier of thyristors, this power has a low power factor when it worked in deep control, and the efficiency is also lower because of big current harmonic of net. The other is DC chopper, this power has a big switching loss and poor efficiency, because the power device of Buck circuit works in hard switch. The phase-shifted soft switch has a shortcoming that the power modulation range is narrow. So, we design a new-style serial resonant main circuit topology, the converter circuit is diode rectifier, the inverter circuit adopts bridge structure which consists two parts, which is the leading arms and the lagging arms. The leading arms are paralleled with capacitor and works on the mode of PWM, the lagging arms with nothing and don't do PWM modulate, the two arms work alternately. The output power depends on duty circle of the leading arms and the lagging arms are not regulated.The characteristic, primary principle, history, actuality and foreground of the induction heating are introduced in the first part of this paper, next, tell the develop character of the semiconductor devices and the important factors of the induction heating power. This paper compares the differences between the current source inverter and the voltage source inverter used in induction heating power, then sum up several normal power regulation methods of the series resonant inverter and compares the characteristic of these methods, and our design scheme is decided on this base.This paper designs a main circuit of the series resonance induction heating with IGBT switch device, proposed a way to realize switch device working on soft-switching, and analyze the relations of the output power, load frequency and drive pulse width, meanwhile, this paper analyze the shutdown current of the leading arms. Aiming at the request of frequency tracing for the voltage sourced induction heating supply, a novel control strategy is proposed in the paper, and a kind of PWM and PFM hybrid control method for voltage fed series resonance inductive heating is described, which has the advantages such as wide areas of power modulation and little changes of frequency, this method can be used in induction heating of any power.Based on analyzing the math model of PLL, the paper analyzes the stability of the whole system. We do the system's simulation with MATLAB/SMULINK, and the control methods which we choose are reasonable and effective, and give the calculation, design techniques and technology of inductive part such as high-frequency isolating transformer, induction coil are provided. At last, described the whole control circuit thinking, and an induction heating power supply is made with its output measured and wave tested when the system is heated in different load.We use VHDL language on Quarturs II to realize our software design. According to the startup question of the induction heating power, we design software scanning frequency to realize self-excitation. According to the disadvantage of the analog PLL which were used in the traditional induction heating power, we design digital PLL based on 74LS297 in Quartus II, compensate the disadvantage of the analog PLL, and realize frequency tracing.The main circuit and control system of the paper's induction heating power are simple. The induction heating power not only saves the energy sources but also is difficult to be disturbed, the power factor can reach 0.95. The control strategy is simple, it is easy to realize soft-switching and power modulation range is wide.