Research On Induction Heatimg Power Supply For Feebly Magnetic Materials

Induction heating is a method that converts electric energy into heat energy based on the law of electromagnetic induction.Compaed with traditional heating ethodslike coal and petroleum,induction heating has a series of advantages,such as high heating speed,high efficiency,easy to control,energy conservation and environment protection,so it is widely used in various fields.Induction heating is mainly realized by Joule-heat generated by induced eddy current in workpiece.But for workpieces of feebly magnetic materials like aluminum and copper,it is not easy to produce eddy current because of low permeability.The induction heating power supply has to offer higher frequency output to increase the eddy current.However,increasing the frequency of power supply will increase the switching loss and reduce circuit efficiency.In addition,induction heating power supply needs to achieve load matching,but if high frequency transformer is used for load matching,the power supply volume will increase and the high-frequency transformer is difficult to design.Dual class-E inverter’s structure is simple,and can keep high efficiency when working with high frequency because of soft switch.It is suitable for high frequency applications.Therefore,the power supply designed in this paper adopts the dual class-E inverter.Based on the detailed analysis of the working principle of the dual classs-E inverter and the characteristics of the LLC resonant circuit,the third order LLC resonant circuit is applied to dual classs-E inverter in this paper.The circuit characteristics and parameter design method of dual classs-E inverter based on LLC resonant circuit are studied.ln addition,the relationship between the circuit characteristic parameters and the load of the inverter in any working state is deduced,and the circuit characteristics of the inverter with load variation are studied.Through theoretical research,it is concluded that:the LLC resonant circuit can transform the larger load variation to a smaller range,which can reduce the sensitivity of the dual class-E inverter to the load change and expand the soft switching range.At the same time,the LLC resonant circuit realizes the load matching of the dual class-E inverter by electrostatic coupling which can remove the high frequency transformer.Finally,on the basis of theoretical analysis,the simulation model is established,and the hardware experimental circuit of induction heating power supply is built.The correctness of the theoretical research and the feasibility of the scheme are verified through the results of simulation and experiment.