Research On Induction Heating Power Supply With Dual Mode Operation

Induction heating technology is widely used in many heating occasions for safety,health,efficiency,accuracy and other advantages.Its application in the civil field is known as the induction cooker.At present,a large part of induction cookers on the market at home and abroad are made of class D inverters,among which the pulse frequency modulated(PFM)and pulse density modulated(PDM)are widely used.For induction heating with a low load quality factor and a wide output power range,the working frequency of the low power stage is larger in PFM and the switching loss is obvious.When the operating frequency deviates from the resonant frequency of the load,the on-state loss of the anti-parallel diode is obvious,too.In this paper,PFM power regulation is applied in the high power stage and PDM power regulation is applied in the low power stage to keep the operating frequency constant.When voltage flicker is considered,PDM power regulation with a small power range makes the power regulation period easy to design.In addition,due to the high working frequency of class D inverter used at low power stage,the switching loss of switch tube and the on-state loss of anti-parallel diode are obvious,so the circuit at low power stage is switched to the mode of class DE inverter to solve this problem.When resonant,the maximum output power of class DE inverter is less than that of class D inverter and class DE inverter satisfies the soft switching characteristics of ZVS and ZDS.Firstly,this paper theoretically analyzes the on-state loss and switching loss of the circuit in the process of PFM power regulation,explains the reasons for the low efficiency of power supply in the low-power stage of PFM power regulation and the advantages of the method combining PFM power regulation with PDM power regulation.Secondly,based on IEC voltage flicker evaluation standard,the reasonable design of PDM power regulating period makes the power supply meet the voltage flicker evaluation standard.Again for the soft switching characteristics of dual mode inverter are analyzed theoretically,the influence of parameter variation on dead zone time of class D inverter in PFM power regulation is studied and the influence of the switch tube drive pulse width on DE inverter ZVS features is studied,as well as the DE class inverter can avoid the reverse parallel diode on-state loss and reduce the switching loss of IGBT;Finally,PSIM simulation model and hardware experiment platform are built to verify the theoretical analysis.