The high efficiency and miniaturization of high voltage power supplies for electron beam welding machines are a necessity for the development of electron beam welding machines [1]. Since the electron beam welding machine was first applied in the laboratory and then applied in the industrial field, its high voltage power supply has also undergone nearly 50 years of development. From the development stage of high voltage power supply, the initial high voltage power supply was manually controlled and regulated by a voltage regulator in open loop, and the rectifier device was a thyristor. This primitive control and regulation was only satisfied with experimental research and applications with low requirements. Large size, low efficiency, complicated operation and poor reliability are the main disadvantages of this type of power supply. With the rapid development of modern electronic technology and power electronics technology, some advanced components such as thyristors have been successfully applied to the design and manufacturing of high voltage power supplies. Since the power supply adopts closed loop control, the high voltage is automatically controlled and regulated, which significantly improves the technical indicators such as the stability, ripple voltage and reliability of the power supply. The improvement of the high voltage power supply performance has also improved the welding quality of electron beam welding machines and promoted the development of electron beam welding machines. Since the 1990s, the rapid development and widespread application of new power electronic devices (such as IGBT), digital control technology and automatic control technology have further promoted the development of electron beam welding machine power supplies. Western countries have begun to use modern new technologies and new materials to develop electron beam welding machines. For example, relatively large electron beam welding machines and electron beam technology application production lines are all computer controlled to realize artificial intelligence operation and management. Small machines are generally controlled by PLC. Due to the strong anti-interference ability and strong control function of PLC, it is easy to realize reliable control of electron beam welding machines. 2 Main circuit system and parameters of high voltage power supply The system block diagram of high voltage power supply is shown in Figure 1, and its main circuit is shown in Figure 2. It is mainly composed of the following circuits. 2.1 EMC filter circuit When the switching power supply is working, it will generate conducted noise that returns to the mains network, affecting the normal operation of the power control circuit and interfering with other electrical equipment. Therefore, it must be overcome [2]. This power supply adopts an EMC filter circuit, which is mainly composed of L and C power line filters, including differential mode suppression and common mode suppression circuits, which can effectively suppress differential mode and common mode noise. 2.2 Controllable Rectifier Circuit The controllable rectifier circuit consists of an integrated intelligent voltage regulation module. Inductor L1 and capacitor C3 form a filter circuit to obtain a relatively stable DC voltage. Rc and Rd form a precise feedback sampling circuit to ensure that the output voltage remains stable under the action of the control circuit. 2.3 IGBT Inverter Circuit The inverter circuit consists of a half-bridge capacitor C, IGBT, high-voltage transformer, protection components, etc. IGBT is a fast series module from Fuji Electric, model 1MBH600-100. T is a high-voltage transformer. The square wave voltage after IGBT inversion is stepped up to a high-frequency AC voltage of about 40kV by the high-voltage transformer. Since the high-voltage coil has a large number of turns, at high frequencies, parasitic capacitance and self-inductance will affect the output characteristics of the power supply [3]. Therefore, electrostatic shielding must be taken for the coil. In addition, due to the effect of ground capacitance, a high-frequency AC signal will be superimposed on the beam sampling resistor [4]. Compensation measures must be taken to eliminate it. This power supply employs double shielding to eliminate beam interference signals. Specifically, a double-layer shield is installed between the high and low voltage coils; the first layer is grounded, and the second layer is connected to the beam sampling resistor. VL11, R9, C9, VL21, R19, and C19 form the IGBT's spike voltage absorption circuit, ensuring the safe operation of the IGBT. 2.4 High-Voltage Rectifier Circuit The high-voltage rectifier circuit consists of a high-frequency high-voltage silicon stack, high-voltage filter capacitors, protective resistors, and a sampling circuit. Since the voltage after being stepped up by the high-voltage transformer has a high frequency, a high-frequency high-voltage fast rectifier silicon stack is selected to meet the requirements of high-frequency high-voltage rectification. High-voltage polystyrene capacitors are selected for the filter capacitors. These capacitors have a small tanδ and high-frequency performance, minimizing their impact on the power supply's output characteristics. Current-limiting resistors and protective resistors, used to effectively limit short-circuit current and internal overvoltage, are all solid resistors with stable thermal performance, low self-inductance, large current capacity, and strong withstand capability against overvoltage and current surges. The high-voltage sampling signal in the sampling circuit is obtained by a precision resistor divider, which is made of a precision wire-wound non-inductive resistor with a shielded electrode on top to ensure the stability of the sampling voltage. Electron beam sampling is also made using a precision non-inductive wire-wound resistor. Both sampling resistors are placed in an electromagnetic shielding box to prevent interference signals from entering the control circuit. 3. Control Circuit The control circuit consists of a PI setpoint adjustment circuit, a PWM and its drive circuit, etc. The rectifier control circuit ensures the stability of the output voltage after mains rectification. The PI setpoint adjustment circuit and the PWM and its drive circuit achieve the stability and automatic adjustment of the DC high voltage. The working principle of each circuit is as follows. 3.1 Rectifier Phase-Shift Control Circuit The rectifier control circuit is a thick-film integrated circuit integrated into the voltage regulation module. The rectified DC voltage is sampled by the resistor divider and sent to the feedback terminal of the PI regulator through a power isolation circuit. Under the combined action of the setpoint and feedback, the PI regulator outputs a DC signal after amplification to the control terminal of the intelligent voltage regulation module to control the firing angle of the thyristor, thereby achieving stable adjustment of the DC output voltage. The auxiliary power supply adopts an integrated high-precision linear power supply, and each power supply ground is independent to reduce the influence of ground current interference signal on the control circuit. 3.2 PI setpoint adjustment circuit The PI setpoint adjustment circuit consists of PLC and D/A module, PI regulator, feedback signal sampling and isolation circuit, etc. The setpoint signal is set by PLC program, which includes rising ramp function and falling ramp function. The digital quantity after calculation is output to the setpoint potentiometer through D/A module. Adjusting the potentiometer can adjust the magnitude of the setpoint signal of PI regulation. The feedback signal is taken from the low voltage arm of high precision resistor voltage divider and input to the feedback terminal of PI regulator through electrical isolation circuit. The PI regulator consists of TL494[6] internal amplifier and external resistor and capacitor. The specific principle circuit is shown in Figure 3. 3.3 PWM and its driving circuit The circuit diagram of PWM and its driving circuit is shown in Figure 3. The PWM signal is modulated by TL494. Another amplifier inside TL494 is connected to an external current signal for overcurrent protection. The current sensor uses a current sensing isolation device manufactured by LEM, ensuring reliable isolation between the control circuit and the main circuit. It features fast dynamic response and good linearity between the sampled current signal and the output current, effectively overcoming the influence of interference signals from the high-voltage circuit on the sampling circuit. The feedback signal and the setpoint signal, after being regulated by the PI controller, are modulated into two complementary PWM pulses by a TL494. The pulses output by the TL494 are fed into the input terminal of the IGBT's dedicated driver module, EXB840. The IGBT driver circuit uses Fujifilm's EXB840 dedicated driver module (1200V, 70A), internally employing a 2500V opto-isolation circuit. Its input voltage is +20V, of which +15V serves as the IGBT's forward drive voltage, and -5V is the reverse voltage applied between the IGBT's gate and emitter when the IGBT is turned off, ensuring reliable turn-off. Pin 14 connects to the PWM signal output from the TL494 to drive the IGBT. Pin 6, connected to the IGBT via a diode, detects the IGBT's overcurrent signal. Pin 4 connects to the external control circuit, inputting the overcurrent signal to the PLC. The PLC processes and calculates the signal before issuing an overcurrent signal. The control circuit works as follows: the signal after passing through the PI regulator is input to the TL494. The TL494 outputs PWM pulses, the duty cycle of which is determined by the magnitude of the PI regulator's output signal. These PWM pulses with a specific duty cycle drive the IGBT after passing through the EXB840, thus achieving stable regulation of the transformer's output voltage. 4. Protection Circuit During operation, the high-voltage power supply may experience overvoltage or overcurrent, potentially damaging the power supply or the IGBT. Therefore, a protection circuit is necessary to ensure power supply safety. The power supply includes overvoltage protection, gradient rise and fall circuits, and overcurrent protection circuits. The overcurrent protection employs a three-level protection system: The first level utilizes the overcurrent detection function of the EXB840 circuit itself. When an IGBT experiences overcurrent, pin 6 of the IGBT driver module detects the overcurrent signal and directly blocks the output pulse, turning off the IGBT. Simultaneously, pin 4 of the EXB840 outputs a signal to the PLC via an external circuit. After program processing, the PLC issues an overcurrent signal indication and provides a blocking pulse signal to the thyristor phase-shift control circuit, turning off the thyristor main circuit. The second level of protection utilizes an external current isolation sensor connected to pins 15 and 16 of the TL494's internal amplifier. When the detected current signal exceeds a set value, the TL494 blocks the output pulse, thereby turning off the IGBT. The third level of protection is the high-voltage side electron beam overcurrent protection. When an overcurrent occurs, the beam sampling signal is fed back to the control circuit, which sends an overcurrent signal to the PLC. The PLC then issues a main circuit shutdown signal and an overcurrent display signal, thus achieving overcurrent protection. The power supply also features an overvoltage protection circuit, effectively protecting against overvoltage. Internally, the high-voltage power supply incorporates current-limiting and protective resistors to effectively limit overcurrent and overvoltage. To overcome the impact of mains power on the power supply during startup, a soft-start ramp function is set within the PLC program. This function, calculated by the D/A module, serves as the input to the PI regulator, enabling soft-start of the power supply. 5. Power Supply System Technical Specifications The power supply's technical specifications are as follows: Input voltage 220V, 50Hz; Output voltage 0～60kV, ripple coefficient <1%, stability 10⁻⁴; Electron beam current 0～167mA, ripple coefficient <1%; Inverter frequency 20kHz; Output power 0～10kW; Efficiency >80%. 6. Conclusion Through testing, all technical specifications of the power supply have met the expected design goals. The high-voltage power supply for electron beam welding machines adopts an inverter-type high-voltage power supply, which is beneficial for the miniaturization of the entire equipment, especially suitable for portable electron beam welding machines. This improves the efficiency of the equipment and makes it easier to achieve automated interlocking protection for high voltage, simplifying operation. Further research is needed on the use of inverter-type high-voltage power supplies for high-power electron beam welding machines. For high-power welding machine power supplies (above 30kW), size and energy consumption are relatively less prominent. However, protection technologies during high-voltage discharge, high-frequency transformer manufacturing technologies, and inverter control technologies require further research and development. Due to improved reliability and power efficiency, the high-voltage power supply (3-15kW) designed in this paper is worth promoting and applying to medium-power welding machines. Effective measures have been taken regarding the impact of the power supply on low-voltage circuits during high-voltage arcing, IGBT overcurrent and overvoltage protection, and EMC, ensuring the operational needs of the electron beam welding machine. The high-voltage power supply (150kV) for high-voltage welding machines using an inverter-type high-voltage power supply has significant advantages in high-voltage interlocking protection, especially in improving electron beam spot quality and welding processes. Research on high-voltage power supplies for high-voltage welding machines is a new topic in my country's electron beam welding machine manufacturing industry. The experience and design data of this power supply have reference value for the research on high-voltage power supplies for high-voltage welding machines.