The traditional electron beam welding machine power system adopts the power frequency or intermediate frequency technology, and has the disadvantages of large volume, low efficiency and poor beam stability. Analyze the shortcomings of the current power supply of electron beam welding machine and combine with modern power electronics technology. This paper proposes a full-digital control filament power supply scheme based on Arm, and introduces the hardware and software implementation methods in detail. Experiments show that the filament power supply can accurately stabilize the cathode filament current, and the filament emission electron density stability is good, achieving good performance requirements. 1 Introduction The working principle of the electron beam welder is shown in Figure 1. When the cathode filament in the high-pressure electron gun is heated to a certain temperature, electrons will escape, and the scattered electrons will be accelerated to the speed of light or near the speed of light in the high-voltage electric field. After focusing by the electromagnetic lens, an electron beam with an extremely high energy density is formed. When the electron beam bombards the surface of the weldment, the powerful kinetic energy of the electron is instantaneously converted into heat energy, which melts the metal and naturally solidifies after cooling to achieve the purpose of welding. The electron beam welding cathode filament power supply is mainly used for heating the cathode filament to emit electrons after being heated, and controlling the output voltage or current of the filament heating power source can achieve the purpose of controlling the overflow electrons, thereby indirectly controlling the beam current size. In the actual welding process, the cathode filament is required to stably emit electrons and maintain the electron density in the electron gun to be almost constant, so the requirement for the filament heating power source is high. 2. System structure and main circuit design 2 is a circuit block diagram of a digitally controlled electron beam welding machine cathode filament heating power supply. The filament power supply is mainly composed of a filter rectifier circuit, a Buck regulator circuit, an inverter circuit, a signal processing circuit, an Arm control board, a filament transformer, and a high frequency rectifier circuit. The single-phase 200V mains is smoothed by a full-bridge uncontrolled rectification filter, and a smooth DC voltage of about 310V is obtained. The Buck circuit composed of IGBTs adjusts the DC voltage amplitude, and the inverter circuit completes the DC/AC conversion. The signal acquisition circuit will After the feedback of the primary current and voltage of the filament transformer is processed, it is sent to the A/D input terminal of the controller STM32, and after the controller converts and completes the digital PI adjustment, the corresponding PWM wave is output, and then amplified by the driving circuit to drive The IGBT completes the closed loop control of the entire filament power supply. Changing the duty cycle of the PWM wave changes the amplitude and current of the output voltage. 2.1 CPU controller The CPU is the core part of the entire filament power supply. It is mainly responsible for the acquisition of feedback signals, digital PI closed-loop calculation, PWM wave output, parameter setting and external communication. The CPU adopts ST's latest STM32F107 series ARM chip. This series of chips uses ARM's 32-bit Cortex M3 as the core, and the highest frequency is 72MHz. The Cortex core has a single-cycle hardware multiplication and division unit, so it is suitable for high-speed data processing. The chip features three independent conversion cycles, a low-speed 1μs high-speed analog-to-digital converter, and three independent digital-to-analog converters with separate sample-and-hold circuits, making them ideal for three-phase motor control, digital power, and networking applications. The chip also has a rich communication unit, including an Ethernet interface, five asynchronous serial interfaces, a USB slave device, a CAN device, I2C and SPI modules. 2.2 display circuit and other circuits For the independent application of the electron beam welding machine cathode filament heating power supply, it is necessary to be able to set various parameters of the power supply, including setting the output current, PID parameters, etc., and display the current current and voltage values ​​in real time, and also need to display the fault type when a fault occurs. The display unit of the filament power supply uses a four-digit digital tube for dynamic display, which has the advantages of intuitive display and long life. The filament power supply also includes a driving circuit, a signal conditioning circuit, a protection circuit, a communication circuit, and the like.
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