Research On Power Control Of The High-frequency Induction Heating Voltage-fed Inverter

Induction heating power supply has been widely applied in the areas of industrial heating on account of its advantages, such as high efficiency, no pollution, flexible control and fast heating speed. To satisfy the different requirements for heating various work-pieces, the output power of an induction heating power supply must be regulated and controlled flexibly according to the load changing. Focusing on the existing power regulation modes of induction heating power supply inverter, this paper makes an intensive research on power control for the voltage-fed inverter of high-frequency induction heating power supply using the phase shift control, pulse density mode control, and through load matching. The main works and innovative achievements are as following:1. A kind of phase shift control multi-phase LLC voltage-fed inverter parallel method is proposed. The output power of the parallel inverters is modulated by controlling the phase shift between multi-inverters, and the inverter capacity is enhanced by the parallel connection of multi-phase LLC voltage-fed resonant inverters. The equations of each phase inverter output current, output power, load current and efficiency are derived using the analysis of fundamental steady state. A 0~360°phase shift control circuit is designed. In addition, the simulation and prototype experiments are carried out and verified.2. The topology, output power, output current ratio and output voltage ratio of LCCL load matching circuit are explored, a kind of power control approach employing LCCL load matching is proposed and the simulation and prototype experiments are verified. The results presented that the LCCL circuit not only has the characteristics of the circuit current transformation of CCL load matching circuit, but also can regulate the inverter's output power by changing the series capacitor.3. An improved symmetrical pulse density control approach is proposed. The impact of quality factor to load current and the relationship between quality factor and the minimum pulse density are analyzed. Compared with symmetrical pulse density control approach for LC series load resonant circuit, using this method can make the control pulse distribute more evenly and reduce the fluctuation of the load current, implement reliable load resonant frequency tracking, and improve the resonant inverter precision of power control when the voltage-fed inverter is in the condition of deep power control.4. High frequency induction heating power supply test system is established. The experiments were accomplished using the above mentioned control methods and different load forms. The correctness of theoretical analysis and the feasibility of the approaches are validated.