Induction heating technology currently has the highest heating efficiency, the fastest speed for metal materials, and low consumption and environmental protection.It has been widely used in the thermal processing, heat processing, thermal assembly, welding and smelting of metal materials.It can not only heat the workparts, but also heat the workparts; deep heat transmission of workparts, but also only the surface and surface; not only directly heat metal materials, but also indirect heating of non-metallic materials, etc.Therefore, the induction heating technology will be more and more widely used.Basic principle: put the workpiece into the sensor (coil), when the sensor into a certain frequency of alternating current, the alternating magnetic field is generated around.The electromagnetic induction of the alternating magnetic field causes a closed induction current ── vortex in the workpiece.The distribution of the induction current on the work piece cross section is not uniform, and the work piece surface current density is very high, which gradually decreases inward. This phenomenon is called the skin collecting effect.The electric energy of the high-density current on the surface layer of the workpiece is converted into heat energy, raising the temperature on the surface layer, that is, realizing the surface heating.The higher the current frequency, the greater the difference in current density between the surface and the workpiece, and the thinner the heating layer.Surface quenching can be achieved by rapid cooling after the temperature of the heating layer exceeds the critical point temperature of the steel.The recent development of induction heating technology: the industrial application of induction heating in China started in the 1950s, with the earliest application in machine tools, machine manufacturing and textile machine manufacturing, automobile, tractor industry and other departments. At that time, most of the induction heating technology at that time came from the former Soviet Union, and a few part came from the Czech Republic, Belgium and other countries.At the end of the 1950s, China has made homemade electronic tube-type high-frequency power supply and mechanical medium-frequency generator, and various equipment and processes, such as induction smelting, induction heat transmission, quenching and medium heating, have been applied in industry.After the 1960s, encouraged by the spirit of self-reliance, various departments and enterprises developed the thyristor medium-frequency power supply, improved the electronic tube type high-frequency power supply, and designed and manufactured various types of quenching machine tools. Its typical structure has been compiled into the quenching machine tool atlas of the Sixth Design Institute of the original Department of Machinery, with a total of 55 kinds.Since the opening up to the outside world, through various channels such as investigation abroad, equipment imported and technology introduced, modern induction heating technology in industrial developed countries has gradually entered various departments of industry in China, so that induction heating, an energy-saving, efficient, automatic, high reproducibility and environmental protection technology, has been made more effectively utilized.
At present, the induction heating power supply mainly adopts thyristor in the medium frequency section, and the super audio frequency band mainly adopts IGBT, while in the high frequency band, due to the high conduction loss such as SIT thermal deficiency power supply, there are many special requirements for power devices, passive devices, cables, wiring, grounding and shielding.Therefore, the development of induction heating power supply high frequency local heating power supply.Considering the large capacity of the induction heating power supply from the perspective of the circuit, the large capacity technology can be divided into two categories: one is the device series and parallel; the other is the string and parallel of multiple bridges or multiple power sources.In the serial and parallel mode of devices, the mean pressure problem of series devices and parallel devices must be dealt with seriously. Due to the discretization of the device manufacturing process and parameters, the number of serial and parallel devices is limited, and the more the number of string and parallel, the worse the reliability of the device.The serial and parallel technologies of multiple power sources are an effective means to further recapacitate on the basis of device serial and parallel technology. With the help of reliable power supply serial and parallel technology, when the single machine capacity is appropriate, the large capacity device can be simply obtained through the mode of serial and parallel operation. Each single machine is only one unit of the device.Inductive heating power supply inverter mainly has parallel inverter and series inverter, The series inverter output can be equivalent to a voltage source with a low impedance, When the two voltage sources are connected in parallel, Mutual amplitude, phase, and frequency when different or fluctuating will cause a large circulation, So that the current of the inverter parts is seriously uneven, therefore, It is difficult to expand the series inverter; shunt chopper, The DC large reactor at the input of the inverter can act as a current buffer between the parallel inverters, Give the AG / DG or DG / DG / D G link at the input sufficient time to correct the DC current deviation, To achieve multi-machine parallel capacity expansion, Transistor ultra-audio, high-frequency current mostly adopts the parallel inverter structure, Parallel inverter is easily modular and has large capacity.Induction heating power load objects, and power inverter and load is an organic whole, generally use matching transformer connection power supply and load sensor, high frequency, super audio power supply matching transformer from the magnetic material to the winding structure is being further optimized and improved, at the same time, from the circuit topology can use three passive elements instead of two passive elements, to cancel the transformer, to achieve efficient and low cost matching.
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