Development Of Mid-frequency Pulsed Power Supply For Plasma Carburizing

On the base of reading many literatures and investigation, the development of plasma carburizing in China and abroad was introduced in this paper. As the future development direction of carburizing,plasma carburizing have a series of advantages comparing with other traditional methods of carburizing, while also having some disadvantages, such as costly equipment and batch productivity not high. In this paper, the parameters of mid-frequency plasma carburizing pulse power supply were proposed according to investigation and literature. The detail parameters are that the output power is 20kW, the output pulse voltage can be varied between 0V and 1000V,the frequency of output pulse is 50kHz,the Duty Ratio of output pulse can be varied between 25% and 80%.According to the parameters of power electronic component and the characteristic of plasma carburizing, the overall solution of the power supply was proposed. And according to the overall solution, this article gives the detailed analysis and discussion of choosing topology for main circuit, design of high frequency power transformer, power electronic component's selection, design of control circuit and design of driving circuit. Through comparing the advantage and the disadvantage of all kinds of topologies, the three phase half-controlled rectifier was chosen as the voltage regulating circuit of the power supply. The full bridge inverter circuit based on IGBT was chosen. Two secondary side winging of the high frequency power transformer serial output .A PIC16F73 Microcontroller was chosen as controlling chip for the three phase half-controlled rectifier, and a UC3825B as the PWM controlling chip for the full bridge inverter. The inverter control circuit can eliminate transformer magnetic bias and regulate Duty Ratio in certain extent. And a new protecting circuit for arc extinguishing was designed. The protecting circuit can extinguish arc quickly and reliably; and extinguishing time is about 1.5μs.This paper also in detail described the questions which appears in debugging the power supply and the methods of solving these questions. The key point waveforms were tested by oscilloscope and described in detailed. Finally, the primary applied effects of the power supply obtained by applying it to the stove body. The design goals of mid-frequency plasma carburizing pulse power supply were achieved functionally.