Research And Design Of Full Digital Pulsed MIG Welding Control System

With the development of welding technology and industrial automation, the demand of welding quality is becoming higher and higher. Since the ability of flexible control, powerful system stability and high welding quality, pulsed MIG welding system is widely used. However, most pulsed MIG welding systems are still using analog control circuits. Compared with poor adaptability and lower product consistency of traditional welding system, the advantages of digital welding system are more significant. However, domestic research and development of digital pulsed MIG welding system are still at a primary level. There are less mature products. Therefore, the research and design of full digital pulsed welding power source have very important significance and practical value.Through researching on the current status of welding power supply, the paper analyzes the existing problems and control requirements of full digital pulsed MIG welding power resource, then designs the high-speed digital inverter drive circuit based on FPGA, welding current control scheme, welding arc control scheme and human-machine interface.Through analyzing the control requirements of welding current, welding arc and melting droplet transfer of pulsed MIG, the paper designs a double feedback control loop based on welding current and welding arc voltage. Pulsed MIG requires welding current can follow a given current waveform quickly and accurately in order to achieve stable melting droplet transfer. The paper, through analysis and research on digital PWM generation principle, designs high-speed PWM controller based on FPGA. Variable PI controller is also analyzed and realized in FPGA in order to achieve better time response of pulse current control. Magnetic bias is harmful to main circuit and digital current PWM couldn't suppress it. So the paper designs a novel magnetic bias detection circuit to solve the problem. It ensures the FPGA-based PWM can drive main circuit safely and reliably. Welding arc model is very complex and traditional control methods don't perform well to stabilize the welding arc dynamically. The paper adopts fuzzy control algorithm to control welding arc through changing base time of pulse current waveform to ensure stability of welding process.With the development of welding technology, the requirement for the human-computer interface has becoming increasingly much higher. Through analyzing the requirements, the paper designs a human-machine interface display panel based on USB interface and LCD, making the parameter input and display more clear. The paper uses USB host interface to operate on U disk to complete technology parameter setting through reading the parameter files. It can also complete the storage of welder working conditions to realize the off-line analysis.Finally, the paper concludes the full digital pulsed MIG welding system design, points out the deficiencies of the system and makes improvement plans for the next step.