Research On Automatic Dead Time Tuning Control Of Inductive Heating Power Supply Based On LLC Resonant Load

The heat treatment industry is one of the four basic process industries in the equipment manufacturing industry and one of the key industries to improve the overall level of China's machinery.Inductive heating technology is a non-contact heating method.Since its birth,it has been widely used in various aspects of industrial heating due to its high efficiency,energy saving and environmental protection.With the continuous development of power electronics technology,induction heating technology with high reliability,high frequency and large capacity has become the focus of research.In this paper,the LLC inductive heating power supply is studied.In view of the problem that the IGBT has a large switch-off loss under the traditional PFM,the shunt capacitor is used to reduce the switch-off loss,and a calculation method for selecting parallel capacitance is proposed,which has great value for practical engineering applications.At the same time,with the parallel capacitor,the circuit under the PFM can not meet the ZVS in the wide frequency range under the fixed dead time,and then an improved PFM for dynamically adjusting the dead time is provided,which makes the range of ZVS expanded.The first chapter of this paper introduces the basic principle of inductive heating,the research status and development trend at home and abroad,and then introduces the research content and meaning of this topic.The second chapter first introduces the topology and working principle of two voltage-type inductive heating power supplies.By comparing the characteristics of them,the LLC has the advantage of not requiring an additional matching transformer and easy expansion.Then the power adjustment mode is introduced,and the PSPWM and PFM are mainly introduced.Finally the simple PFM is adopted.The third chapter first introduces the problem that the switch-loss is relatively large under the PFM.In this paper,the method of parallel capacitors at both ends of the IGBT is used to reduce the switch-off loss.By deriving the expression of the switch-off loss ratio,the value of the shunt capacitor is obtained according to the calculation formula instead of the test.With the parallel capacitors,the PFM with tuning dead time is adopted to achieve ZVS as wide as possible.That not only reduces the switch-off loss but also ensures ZVS,which improves the life of the IGBT and the reliability of the circuit.The fourth chapter introduces the main circuit and control circuit of the LLC inductive heating system,and chooses the parameters of the key components.Finally the LLC inductive heating power platform was built.The fifth chapter firstly performs Psim simulation based on the parameters of the circuit,and obtains the simulation waveform to further verify the method proposed in the third chapter.Then the experimental results are introduced to further verify the correctness of the proposed method.