Research On "parasitic Intermediate Frequency" Dual Frequency Induction Heating Power Supply For Single Inverter Bridge

The induction heating technique utilizes Faraday's law of electromagnetic induction to generate eddy currents in a time-varying magnetic field to heat the workpiece.Currently widely used in industrial fields such as metallurgy,machining,national defense,etc.Compared with the traditional direct heating technology,it has the advantages of fast heating speed,high heating efficiency,more uniform heating,safety and reliability,and low pollution.The dual-frequency induction heating technology uses two different frequencies and the penetration depth of the induction current at different frequencies is different,which can evenly heat the tooth root and the tip of the gear,making the gear more rigid and wear-resistant.Synchronous dualfrequency induction heating technology has outstanding advantages for heat treatment of workpiece with complicated surface,such as gear.This paper studies a new type of synchronous dual-frequency induction heating technology,which is different from the dual-inverter bridge synchronous dualfrequency and SPWM-driven single-inverter bridge synchronous dual-frequency.This study uses the disturbance of the circuit and the zero-crossing feedback,so An intermediate frequency current is "parasitic" in the high frequency circuit,forming a synchronous dual frequency.In comparison,the power supply structure is simpler and smaller.The main research contents are as follows:1.Research on resonant circuits.Including the resonance frequency and Q value of series resonance and parallel resonance circuits;analysis of the inverter's resistive and weak inductive operating conditions;problems solved by secondary resonance technology;calculation and analysis of the resonance frequency of composite resonance circuits.2.Principle analysis of "parasitic intermediate frequency" dual frequency generation.This section introduces the overall design framework of the power supply,and uses graphics and theoretical calculation methods to introduce in detail how the parasitic intermediate frequency is generated and the conditions that need to be met to produce a stable dual frequency.3.Design of high-frequency transformer.The transformer plays the role of voltage reduction,blocking matching and electrical isolation in the circuit.Appropriate transformer parameters can improve the power and efficiency of the power supply.4.Design of power circuit.It mainly includes the rectifier and filter circuit of the main circuit,the drive circuit of the inverter circuit and the control circuit,the frequency tracking circuit,and the protection circuit.Among them,the frequency tracking circuit is the key to the design.It not only ensures that the high-frequency power supply works in the resonance state,but also generates "Parasitic intermediate frequency".The frequency tracking adopts the zero-crossing frequency tracking method.The signal is collected at the zero-crossing point of the high-frequency current to generate a driving pulse,which is fed back to the control chip to adjust the frequency of the driving signal.The simulation modeling of the circuit is performed by the Saber simulation software,and the dual-frequency current simulation waveforms are obtained.The comparative theoretical analysis has initially verified the correctness of the research.Finally,an experimental prototype with a high frequency of 100 k Hz and an intermediate frequency of 5k Hz was produced and built by the actual object.After the chip was debugged,the experimental verification was performed.Finally,a dualfrequency current waveform with the same design frequency was obtained.The feasibility of the bridge “parasitic intermediate frequency” dual-frequency induction heating technology lays the foundation for further research on new dual-frequency induction heating power supplies in the future.