Application and Development Prospect of High Frequency Induction Heating Equipment

Induction heating power supply technology currently has the highest heating efficiency and fastest speed for metal materials, and is low-consumption and environmentally friendly. It has been widely used in thermal processing, heat treatment, thermal assembly, welding and smelting of metal materials in various industries. It can not only heat the workpiece as a whole, but also heat the parts of the workpiece in a targeted manner; it can realize the deep heat penetration of the workpiece, and it can also only heat the surface and surface layer; it can not only directly heat metal materials, but also non-metallic materials. Materials are heated indirectly, etc. Therefore, induction heating technology will be more and more widely used.
Basic principle: Put the workpiece into the inductor (coil), and when an alternating current of a certain frequency is passed into the inductor, an alternating magnetic field will be generated around it. The electromagnetic induction of the alternating magnetic field causes a closed induced current in the workpiece—eddy current. The distribution of induced current on the cross-section of the workpiece is very uneven, and the current density on the surface of the workpiece is very high and gradually decreases inward. This phenomenon is called the skin effect. The electrical energy of the high-density current on the surface of the workpiece is converted into heat energy, which increases the temperature of the surface, that is, realizes surface heating. The higher the current frequency, the greater the current density difference between the surface and the interior of the workpiece, and the thinner the heating layer. Surface quenching can be realized by cooling rapidly after the heating layer temperature exceeds the critical point temperature of the steel.

The recent development of induction heating technology: the industrial application of induction heating in my country started in the 1950s, and it was the earliest application in machine tool manufacturing, textile machine manufacturing, automobile, tractor industry and other departments. At that time, most of the induction heating technology came from The former Soviet Union, a small part from the Czech Republic, Belgium and other countries. At the end of the 1950s, my country had self-made tube-type high-frequency power supply and mechanical medium-frequency generator, and various equipment and processes such as induction melting, induction diathermy, quenching, and medium heating were successively applied in industry. After the 1960s, inspired by the spirit of self-reliance, various departments and enterprises developed thyristor intermediate frequency power supplies, improved electronic tube high frequency power supplies, and designed and manufactured various types of quenching machine tools. The typical structures have been compiled into the original machinery department. Atlas of quenching machine tools of the Sixth Design Institute, a total of 55 types. Since the opening to the outside world, through various channels such as overseas inspections, imported equipment, and introduced technologies, modern induction heating technology in industrially developed countries has gradually entered various sectors of my country's industry, making induction heating an energy-saving, efficient, automated, and highly reproducible technology. , Environmentally friendly technologies are more effectively utilized. At present, induction heating power supplies mainly use thyristors in the intermediate frequency band, and IGBTs in the super-audio frequency band. In the high-frequency band, due to the high conduction loss of the SIT, the heat-deficiency power supply usually has a large flying power hot air rate, which is harmful to power devices and wireless devices. Source components, cables, wiring, grounding and shielding all have many special requirements. Therefore, the development of high-frequency local heating power supply for induction heating power supply is realized.

Considering the large-capacity induction heating power supply from the circuit point of view, the large-capacity technology can be divided into two categories: one is the series and parallel connection of devices; the other is the series and parallel connection of multiple bridges or multiple power supplies. In the series and parallel connection of devices, the voltage sharing problem of series devices and the current sharing problem of parallel devices must be carefully dealt with. Due to the discreteness of device manufacturing process and parameters, the number of series and parallel connections of devices is limited, and the number of series and parallel connections The more, the worse the reliability of the device.
The series and parallel connection technology of multiple power supplies is an effective means to further recapacity on the basis of the device series and parallel connection technology. With the help of reliable power supply series and parallel The operation mode obtains a large-capacity device, and each single machine is only a unit of the device.
Induction heating power inverters mainly include parallel inverters and series inverters. The output of series inverters can be equivalent to a low-impedance voltage source. When two voltage sources are connected in parallel, the mutual amplitude, phase and frequency When different or fluctuating, it will lead to a large circulating current, so that the current of the inverter device is seriously uneven. Therefore, it is difficult to expand the capacity of the series inverter in parallel; parallel inverters, the DC reactor at the input end of the inverter can act as The current buffer link between the parallel inverters allows the AG/DG or DG/DG link at the input end to have enough time to correct the deviation of the DC current, to achieve multi-machine parallel expansion, transistorized super audio frequency, and high-frequency current. One of the main reasons for the parallel inverter structure is that the parallel inverter is easy to be modularized and has a large capacity.
The load objects of the induction heating power supply are various, and the power inverter and the load are an organic whole. Generally, matching transformers are used to connect the power supply and load sensors. The matching transformers for high frequency and super audio power supplies are from magnetic materials to windings. The structure is being further optimized and improved. At the same time, from the circuit topology, three passive components can be used instead of two passive components to cancel the transformer and achieve high-efficiency and low-cost matching.