Research On Power Regulation Of LLC Resonant Load Induction Heating Power Supply

Induction heating technology is a non-contact heating method.It has been widely used in industry.The traditional induction heating power supply uses a series or parallel LC resonant load structure,which requires a transformer to achieve load matching,resulting in large equipment size,high cost,low efficiency and complex transformer design.LLC resonant load realizes current conversion through series resonant inductor.It does not need transformer to achieve impedance conversion,so it has a great advantage over LC resonant load.Induction heating power supply needs to adjust the output power during the work according to the requirements of different heat treatment processes.The power regulation method for LLC resonant load has been a research focus in the industry.Asymmetrical Voltage-Cancellation control(AVC)is a classical method of power regulation,which has the advantages of constant frequency power regulation and high efficiency.The traditional asymmetrical voltage-cancellation control will cause the losses of the two bridge arms to be inconsistent,leading to a reduction in the safe operating range and reliability of the power supply.This paper presents an improved asymmetrical voltage-cancellation control and applies it to LLC resonant loads to solve the problem of unbalanced loss of traditional asymmetrical voltage-cancellation control.The asymmetrical voltage-cancellation control will cause the phase shift of the fundamental component of the output voltage,which will cause the phase-locked frequency and current phase to change.This paper deduces the mathematical expression of the phase shift,and proves the validity of using the phase of the drive signal and the phase of the capacitor voltage as the phase-locked control variables through mathematical methods.This article also researches the ZVS loss that may occur during the power-on and phase-lock processes,and designs a stable and reliable power-on startup scheme.Finally,the complete main circuit topology and LLC resonant load parameter design are given,and a control system with DSP chip TMS320F28335 as the control core is designed,and a 150 kW prototype experimental platform is completed.The feasibility of the control method proposed in this paper is verified from two aspects of software simulation and prototype experiment.