Research On Induction Heating Power Based On Fuzzy Power Regulation And Digital Phase-locked Loop

Induction heating power supply based on the principle of electromagnetic induction has many advantages, such as the high heating efficiency and speed, the good controllability, and easy to implement mechanization and automation etc. Being the advanced and basic technology of metal industrial heating, it has been extensively used in so many areas, such as melting casting, bend, hot forging, welding and surface heat treatment etc.This paper introduced the origin, principle, characteristics and application of induction heating power. It also summed up the developing state and trend at home and abroad. Besides, it analyzed the load and resonant characteristics of induction heating power, described the principles of series and parallel inverter, and both were compared to choose the series inverter for the study. By comparing all forms of power regulation, we chose uncontrolled rectifying circuit and Buck chopper power regulation method. By analyzing load parameters of induction power supply, state space model and small signal model of Buck converter, it concluded that induction heating power supply was a complex and multivariate object and couldn't be built model because parameters and structures changed with time. So it adopted fuzzy closed-loop to regulate power. It also introduced the principle and implementing methods of fuzzy control which were both modeled and simulated. The load equivalent electrical parameters change with temperature in heating process, which will result in the change of load inherent resonant frequency. In order to guarantee the inverter switching working in the soft-switching mode and remain higher efficiency and output power factor, there must be automatic frequency tracking and PLL function in inverter. The traditional analog phase-locked loop based on the CD4046 is mostly used in induction heating power supply frequency tracking channel, but the traditional simulation phase-locked loop has some shortcomings, such as the narrow frequency track scope, the slow dynamic response, the bad reliability, the need of using auxiliary circuit to realize dead time and so on. This paper analyzed the principle of the Digital Phase-locked Loop and established the mathematical model of it. In view of the shortcomings of traditional PLL, DPLL which is based on DSP was proposed and the simulation of DPLL verified the validation of the system.Basing on theoretical analysis above, an induction heating power supply was designed, the power of which is 10kW with the frequency 20 kHz for the chopper and 30 kHz for the inverter. The special DSP chip of TMS320LF2407A produced by TI Company is used as the main controller to simplify system structure and improve the performance of the system and anti-jamming capabilities. Finally, the experimental results were listed, which demonstrates the validity of the entire system design.