High-power Electron Beam Melting Furnace Developed High Voltage Power Supply

Electron Beam Furnace is a device which can smelt and purify high-activity refractory metal in the low vacuum condition. This device is made up of high-voltage DC power supply, control system, electron gun, furnace stack, etc.The high-voltage DC power supply for electron beam furnace belongs to Special Power Supplies. It has the characteristics of high voltage (>30kV) and high power (>30kW). At present, the high voltage DC power supplies for electron beam furnace are mostly power frequency boost power supply controlled by thyristors. The transformers and the filters have a very large volume. The power supply doesn’t have the characteristics of anti-short circuit capacity, rapid protection and restart which have serious influences for the service life of electron gun and the quality of the smelting. To solve the above problems, a high frequency resonant converter has been used in the high voltage power supply, which can reduce the volume of the transformers and filters, cut down the switching loss, achieve rapid protection and restart. Simulation and experimental research show that the power supply can satisfy the requirement of smelting.This paper researches the operating principle of the Electron Beam Furnace and determines a solution of power supply system aimed at the characteristics of electron gun load and the requirements of smelting technology. The power supply is three-phase power frequency AC power supply, made of thyristor rectifier and the high frequency inverter. The output voltage is30kV and the power rating is450kW.The topology of the full bridge converter is determined among high frequency boost converters by Comparative study. The LC series resonance operating mode which is fit for Electron Beam Furnace is finally selected by studying the characteristics of PWM operating mode and resonant mode (including series resonance and parallel resonance).A Frequency modulation control mode is selected to reduce the switching loss.When the inverter works at the resonance point by natural frequency, the high output voltage can be measured by adjusting the dc bus voltage of thyristor rectifier’s output voltage. This method benefits the design of filters and achieving soft switching. A series of simulation experiments of the main circuit and the control method are accomplished by using Matlab.The design of the control system consists of the control panel based on TMS320F28335chip, flyback auxiliary power supply panel, drive panel, voltage sampling and Pre conditioning panel. A high-frequency and high-voltage power supply is designed and made. The design technique, the calculation of parameters and the methods of simulation and experiment are expounded.