The Digital Control Research Of Induction Heating Power Supply

Considering induction heating having many advantages such as high heating temperature, high heating efficiency, fast heating speed, heating temperature being controlled easily, being prone to realize mechanization and automatization and having no air pollution, nowadays induction heating has been widely applied in many industry fields such as metal fusion, heat processing, welding and so on. However, most of the induction heating power supply adopts analog circuit to control which has low control accuracy, less flexibility and less reliability. Conversely, digital circuit has higher control precision, better flexibility and more reliable performance. Therefore, it makes sense to do some research on digital control of induction heating power supply.Based on the analysis of the main circuit topology about induction heating power supply, determine to study serial resonant converter. Then present some usual ways of power modulation about serial resonant converter, and ascertain the scheme: digital induction heating power supply of PFM (Pulse Frequency Modulation) and digital induction heating power supply of improved PWM (Pulse Width Modulation).To the digital induction heating power supply of PFM, we design the main circuit and choose the parameter of electronic components. Meanwhile advance the digital control algorithm of PFM, and form the double-closed-loop control system of current and phase based on FPGA and AVR single ship. The control circuit design is given including the current adjuster, the control circuit based on FPGA and the control circuit based on AVR single ship. At the same time the control circuit based on FPGA is simulated and validated depending on the QuartusII software, and the result proves that the PFM digital control system is more accurate, more reliable and regulable to the dead time. Then the digital control system of PFM is proved to be superior and feasible by experiment.A novel main circuit topology is put forward to the digital induction heating power supply of improved PWM. The novel topology has simple structure, low cost and simple control way. Then design the main circuit and choose the parameter of electronic components.Digital control algorithm of improved PWM is brought forward based on the detailed analysis about improved PWM way, and then form the double-closed-loop control system of current and frequency phase based on FPGA, DSP and AVR single ship. Because of the disadvantages of the analog PI algorithm about digital induction heating power supply of PFM, the paper selects DSP to realize digital PI algorithm making the system have more reliable performance and higher control precision. Given the change of the load parameter resulting to the change of the load resonant frequency when heating, in order to ensure the induction heating power supply to be the feeble inductance quasi resonance state, the paper chooses FPGA to finish digital PLL (Phase Locked Logic) realizing the frequency logic and phase logic of the voltage and current. The digital PLL has high control precision, flexible software design ability and adjustable time of the dead area. Meanwhile FPGA completes the control algorithm of improved PWM, and then simulates and validates the digital PLL and control algorithm of improved PWM based on FPGA depending on the QuartusII software. The digital control system of improved PWM is proved to be superior and feasible by experiment.In the end the paper gives the driving circuit of power device and the protecting circuit of the power supply, and also develops the fault handling circuit to take relevant measures.