| The traditional heating method uses fuel combustion or electric resistance heat as a heat source, and heats the conductor by thermal conduction. It has many disadvantages such as high energy consumption, low energy utilization ratio, serious environmental pollution, and difficulty of the control processes and results, which becomes the bottleneck of the development of China's machinery industry. As a non-contact heating method, induction heating method is based on the principle of electromagnetic induction, using the thermal heating effect of induced eddy current on the conductor, which is widely used in industry nowadays. Its main advantages are: environmental protection, and almost no dust and noise; using non-contact heating, no incorporation of impurities and no oxidization during the heating process; with a great precision the depth and region of heating; can be quickly and frequently start, suspend or stop.With the growing proportion of mechanical products in China, which need surface heat treatment, brazing and other processes, the requirement of heating equipments with high heating efficiency, fast speed, simple control, and implement automated and mechanized will increase. Because of the low level of design, manufacturing process backward and poor reliability reasons, our induction heating power supply developed slowly and Induction heating technology was limited. Since the beginning of reform and opening up, Chinese scientists have imported and developed a number of advanced induction heating equipment and technology. Not only the equipment design and manufacturing standards have been improved, but also the variety of equipment, and the specs been enriched and developed. Since the 90's of the last century, the modern heating technology develops dramatically. Especially, the progress of high-frequency induction heating technology is the most prominent. Induction heating equipment becomes the key equipment in the mechanization and automation. China's high-frequency induction heating technologies at modern heating technology, heating equipment and heating power supply have achieved notable success. However, the induction heating power supply in China compared with the industrialized countries, who reached a large capacity of high frequency technology, intelligent control of the level of induction heating power supply, is still a gap. Therefore, in order to speed up technological progress of China machinery industry and the development of the national economy, the development of energy efficiency high-frequency induction heating power supply should be highly focused on. while the use of mechanization, automation, high efficiency induction heating technology should be vigorously promoted. We Chinese scientific and technological workers must learn and master the design of advanced induction heating power supply and control technology, developed cheap and good domestic induction heating power supply for China's national conditions.The theme of this thesis is the three-phase inverter high-frequency induction heating power supply. The principle of inverter power supply is that let the industrial frequency alternating current pass through the input rectifier for rectification and filtering, and export DC. Then the high power electronic switch components, such as SCR, GTR, MOSFET, IGBT, translate DC into AC with high-frequency of several thousands Hz. The inverter induction heating power supply in this thesis adjustable output frequency range of 20kHz ~ 100kHz, adjustable output current RMS 100A ~ 400A.According to the parameters of induction heating power supply requirements, this design chooses the full-bridge inverter as the main circuit; in the choice of power switching components, this paper on the basis of the power supply voltage, current capacity and design of manufacturing costs, decides to use MOSFET as the switching devices; according to the capacity, this paper designs high-frequency output transformer. Because of the skin effect, the secondary side of high frequency transformer is made of multi-strand hollow copper pipe in parallel, aim to separate the current, to saving material and to cool the high frequency induction heating coil with the water inside the pipe. The main circuit consists of rectification and filtering circuit, and full-bridge inverter circuit, which achieves the changes that from the frequency AC to DC, then to high frequency alternating current. The switch of the main circuit is MOSFET K2611. So the dead zone time must be considered, which is longer than the turn-off delay time and current fall time, to avoid the four groups of switches turning on at the same time, which may damage the components due to excessive current. The Switches are in parallel with resistors and capacitors which play the role of RC protection against excessive transient current. Each bridge arm is in the parallel of three MOSFET because of its small rated current to separate the current.The design of the control circuit is the focus of this thesis, which contains power supply circuit, driver circuit, feedback circuit, pulse width and frequency adjustment circuit and protection circuit. Power supply circuit outputs regulated DC power supply required for the control circuit. Drive circuit includes pulse circuit, power amplifier, and trigger circuit. the pulse signal is produced from pulse circuit, and then pass through the power amplification and pulse transformer, finally output to the gate of the MOSFET of the main circuit. The pulse width and frequency of pulse signal can also be manually adjusted to control the opening and closing time of the switches. The negative feedback signal sampling point from the main circuit compared with the given potential may directly control the current size of the main circuit over the feedback circuit. In addition, the thermal protection circuit and over-current protection circuit are also designed. Once the overheating signal of the main circuit was detected, immediately the drive pulse output stop; Once the over-current signal was detected, immediately the induction heating power supply start self-lock protection, need to be repaired after power shut-off. Control circuit is designed to suit design target of the induction heating power supply for the decline external characteristics to ensure a constant current output. The core of this control circuit is SG3525 PWM controller, high and low electric potentials was inputted to the pins to control the trigger pulse signal, thereby ensuring the stabilization and security of the induction heating power supply.Finally, the design of the main circuit was simulated by software. Under the different pulse frequencies and pulses widths of the driver voltage, the voltage and current conditions of the high-frequency transformer primary side can be observed directly with no-load condition by simulation. The results confirm that the design principles of the control circuit completely conform to expectations, and provide a theoretical support for a stabile work of this induction heating equipment. In addition, the current of the main circuit is decreased as the width decrease and the frequency increase of the pulse driver voltage.This induction heating power supply could meet the demands of all kinds of different technology of heating, which can be easily controlled and manufactured in batch, have stable output, low cost, satisfying usability.
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