Class DE Research And Implementation Of High Power High Frequency Inverter

In this thesis,with induction heating power as object,a soft switching technique of full bridge inverter based on class DE power amplifier is studied.The power devices of class DE power amplifier operate in soft switching state,which can maintain high efficiency at very high operating frequency,and the voltage stress of class DE power amplifier is low.The power device of the conventional class DE power amplifier is MOSFET(field-effect tube).This is due to the high switching speed and small loss of the MOSFET,and the operating frequency can reach MHz.In this thesis,the induction heating technology is studied.The output power of the inverter is relatively large,so the IGBT with large capacity is selected as the power device of the inverter.Therefore,the class DE soft switching technology adopts IGBT as the high-frequency and high-power switching tube.The Class DE power amplifier is based on half-bridge inverter topology.However the Class DE full-bridge inverter is based on full-bridge inverter topology.At the same operating frequency,the output power of this kind of topology is 2 times larger than that of the class DE power amplifier.It improves the output power and provides a broad prospect for the research of high-frequency and high-power inverter power supply.In the heating process of induction heating power,the equivalent load in the resonant network changes with the heating environment,and the equivalent load is not constant.When the inverter resonant frequency and the parallel capacitance are fixed,the ZVS and ZDS conditions of the Class DE full-bridge inverter are implemented by controlling the dead time of the drive signal.According to the characteristics of Class DE full-bridge inverter,the DC power regulation mode is selected as the power regulation mode of this inverter structure.Comparing the advantages and disadvantages of the two DC power regulating modes,the DC chopper regulating mode is chosen in this thesis.And the DC chopper modulation is Buck constant current source instead of voltage source.The advantages anddisadvantages of the two DC power modes are compared.In order to verify the feasibility of Class DE full-bridge inverter soft-switching technology,an experimental prototype was fabricated.The experimental prototype includes the former Buck constant current source part and the posterior Class DE full bridge inverter part.The Buck constant current source adopts the output power of20 k W,the switching frequency of 30 k Hz,the output current adjustment range of 5 ~50A.Class DE full bridge inverter adopts output power of 20 k W,IGBT operating frequency of 60 k Hz,drive signal duty cycle adjustable range 0.25 to 0.5.By observing the sinusoidal current in the inverter circuit and the voltage waveform at both ends of the IGBT,and referring to the theoretical analysis of the Class DE full-bridge inverter,the experimental results show that the Class DE soft switch can improve the working frequency of the IGBT and control the switching loss in the proper range.