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IGBT medium frequency induction heating equipment load impedance matching

The load impedance of IGBT intermediate frequency induction heating equipment is relative to the internal resistance of the power supply. The internal impedance of the power supply is determined once the input voltage and output current are determined. For the same power supply, when the input AC voltage changes, the internal impedance of the power supply will also change, and there will be changes in the impedance indicator set. When the indicator set reaches 100%, the impedance of load & the internal impedance of power supply are equal; The load impedance is lower than the left deviation of the source impedance; Load impedance is higher than the right deviation of the source impedance; As the impedance of the load varies greatly with the temperature of the workpiece, the constant impedance matching of the load cannot be realized when the hf machine heats a single piece of work. In this case, the impedance indication has a large range of variation, so a dynamic impedance matching method is needed.

1. Can eat to dry, how to eat, eat more

2. The load impedance should be as high as possible under the premise of ensuring the maximum resonant current

3. The host machine operates in a limited VA area, where the voltage is limited by the power supply, and the current is limited by IGBT. In this area, it is the flying point area where the host machine operates, and the maximum output power of the host machine is at the vertex of the rectangular area

4. Oscillating current and induction heating are two different physical phenomena. There is an oscillating current but induction heating may not occur.

5. The main idea of induction heating is to change electricity into heat.

6. The design purpose of the load coil is to convert the energy in the magnetic field into Joule heat. The typical characteristics of the load are impedance.

7. Excessive load will suppress the output current of the host. The load will suppress the output current, which cannot be recovered from the control, resulting in the double drop of the output current and the input current;

8. Too light load will lead to the host has the output current increase trend, the host will actively suppress the output current, showing constant current external characteristics, this feature is the internal impedance of the host when the impedance of the load is equal to the host’s impedance, the transfer of maximum power; Too light load will result in a single drop of input current.

9. The critical value of the best load is at the intersection of the host control suppression and load suppression of the oscillating output current, which is also the peak of the host operation area;

10. Load & relative impedance characteristics of the host. The load impedance of the left area is smaller than that of the host. The load impedance on the right side is greater than that of the host, and the load is suppressed. The best matching effect is achieved only when the load impedance is equal to that of the host. The impedance is indicated to 100%;

11. The purpose of impedance matching is the maximum power from the power supply to the load transfer, strictly distinguish, IGBT output after can be included in the load of the component, including resonant capacitance, cables, the main transformer, flexible water-cooled cable, induction coil, the workpiece is an important part of the best match can be relatively rapid heating, but the main goal of impedance matching has not fully included in technical measures to achieve the highest thermal efficiency, fast and the concept of energy saving is different;

12. Dynamic impedance matching When the HF machine is in the state of single heating, the dynamic impedance method should be used. The principle is that the load impedance indicator on the screen should be symmetrically distributed with 100% of the time on the left or right side as the centerline, and the load indicator on the left or right side for a long time is not matched;(For example, the heating starts from 75%, gradually reaches 100% when the temperature rises, and then begins to decay on the right side, reaching -40% at the far right end. Then, after the impedance approaches the peak, it begins to decline and develops towards the Curie point. At this time, the impedance indicates that it retracts from -40%, returns to the left after the peak of 100%, and even drops to 30%)

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