Analysis and selection of 1T intermediate frequency furnace power adjustment scheme
The induction heating power supply should be able to adjust the power of the load due to changes in the load equivalent parameters as the temperature and the melting of the charge change as well as the heating process. Since the series resonant inverter has many different power adjustment modes, we need to make reasonable choices in the development process according to the actual application and performance requirements. The system's power adjustment mode can be divided into DC side power adjustment and inverter side power adjustment.
The DC side power adjustment means that the inverter output power is adjusted by adjusting the input voltage amplitude of the inverter link on the DC power supply side of the inverter, that is, the voltage regulation and power adjustment mode (PAM). In this way, the load can be operated at a resonant or near-resonant operating frequency by means of phase-locking measures. The way to adjust the output voltage of the 1T intermediate frequency furnace can be roughly divided into two types: phase-controlled rectification or uncontrolled rectification.
Inverter side regulation is to adjust the output state of the inverter by controlling the switching characteristics of the power component of the inverter link in the inverter measurement, thereby realizing the adjustment of the output power of the inverter. The inverter side power adjustment can be divided into three types: pulse frequency modulation (PFM), pulse density modulation (PDM), and pulse phase shift modulation. When the inverter side power adjustment scheme is adopted, uncontrolled rectification can be adopted on the DC side, the rectifier 1T intermediate frequency furnace is simplified, and the overall grid side power factor is improved, and the response speed of the inverter side power adjustment is faster than that of the DC side.
The phase-controlled rectifier power adjustment 1T intermediate frequency furnace is simple and mature, and the control is convenient; the power efficiency and reliability of the power supply in the high-power occasion will be reduced, which is not suitable for the normal operation of the power supply. Pulse frequency modulation will have a great influence on the heating of the workpiece due to the change of frequency during the power adjustment process; the pulse density modulation has poor stability in the case of power closed loop, and it has a step-level power adjustment mode; pulse phase shifting Increasing the power loss, such as the use of soft switching, increases the complexity of the 1T intermediate frequency furnace.
Combining the advantages and disadvantages of these five kinds of power-modulation methods, combined with the work of this subject in high-power occasions, choose to use thyristor phase-controlled rectifier power adjustment, and adjust the thyristor conduction angle to obtain the DC output voltage of the university to supply the inverter link. Thereby changing the output power of the inverter link. This kind of power adjustment mode 1T intermediate frequency furnace is simple and mature, and the control is convenient.
