Research On Phase-Locked Control Technique Of High Frequency Series-Resonant Induction Heating Power Supply

The induction heating power supply plays an important role and is widely applied in industry field because of the advantages of clean,energy saving and high efficiency.It is suitable for metal smelting,welding and metal heat treatment etc.The load equivalent parameters of induction heating power supply will change and affect the efficiency of induction heating power supply.In view of this problem,the phase locked control technology of high frequency induction heating power supply is analyzed and researched.1.The topology and operating characteristics of series resonant inverter and parallel resonant inverter are analyzed and compared particularly.The advantages and disadvantages of the two inverters are compared.And the series resonant inverter is selected as the inverter circuit of induction heating power supply.2.The basic principle of each part of PLL is analyzed.Based on the mathematical model of phase-locked loop,the influence of delay compensation on the performance of phase locked control is analyzed.A method for improving the dynamic response speed of phase locked control when the load frequency is increasing during induction heating is presented,and simulation results show that the control method can effectively improve the phase locked control performance.3.The three operating states of the series resonant inverter are analyzed,and the suitable operating state of the series resonant inverter is obtained.The commutation process of inverter in inductive state is analyzed in detail,and the optimal operating state of series resonant inverter is obtained.According to the DC voltage,working frequency and absorbing capacitance,the optimal phase locking angle is calculated.And the correctness of theoretical analysis is verified by experiments.4.A kind of voltage and current double feedback fixed angle phase locked control strategy of digital and analog hybrid is designed by combining analog circuit with programmable device FPGA.The design of phase-locked loop based on integrated PLL 74HC4046 and dynamic delay circuit is accomplished.The generation of dead time of trigger pulse and the comparison of voltage and current phases are completed by FPGA control chip.In order to build the experimental platform of induction heating power supply,the main circuit structure of induction heating power supply,the driving circuit of power switch device and the over-current protection circuit and the phase loss protection circuit are designed.Experimental results show that the design of voltage and current double feedback fixed angle phase lock control strategy is effective and feasible.