Design Of Control System Of Full Digital SAW Power Source Based On Mixed-signal FPGA

With the rapid development of country modern industries, welding technology is presenting a brand new look which is part of important industry technologies. With high efficiency, good working conditions and automation, the submerged arc welding (SAW) is one of the most widely used welding techniques, which has broad development prospects. Domestic SAW power sources products are mostly analog. Some digital power sources haven’t realized full digital which can’t get good wielding quality, while the high-grade market is basically occupied by foreign sources. At present the domestic welding theoretical study isn’t far away from world advanced level which needs good power sources to implement. As the study on full digital SAW power sources have important research value and application significances.Firstly, the present research situation of domestic and abroad on SAW power sources and brief introduction of the SAW power sources is illustrated. Then the paper analyze the process of SAW, built a control model on the characters of SAW arc, the transition of droplet and welding technique process, extract the arc voltage, welding current as the main control objects of the controller and carry out the state analysis of the welding process. Based on the requirement analysis of the control model, taking the mixed-signal FPGA as core controller, a single chip solution with is established combine with the more flexible variable wire speed mode, drawing on the existing domestic and foreign solutions. The single chip control solution adopts three closed-loop strategy of welding voltage, welding current and carrier armature voltage, with taking Fuzzy PID algorithms as the core of the controller of welding current.Based on analysis of the chosen control solution hardware requirements, the paper brings in the control box in corporate with main control board structure with considering the practical operate environment. The main control board established the mixed signal FPGA as the kernel core with peripheral module such as dive modules for IGBT, carrier motor and feeding wire motor, several signal sample circuits to realize teal-time detection, man-machine circuits in control box and communication circuits. Aiming at the harsh EMI environment, some hardware anti-interference circuits is designed to reduce the electromagnetic interference.Then, the software design based on the hardware system is introduced. The welding process state machine, communication with ACE module to sample the analog signal and data transition to FPGA function module are realized in the ARM-Cortex M3core of FPGA while the FPGA fabric module contains three-closed-loop strategy controller, high speed PWM generator. Meantime, human-machine and communication between control box and main control board software are also designed in the control box.After the primary design, non-load, static load and practical welding tests are carried out in sequence on the full digital SAW inverter power sources. Through the results analysis, the power source has good performances with high efficiency and welding seam quality, fast response and friendly user interfaces.At last, the paper summary the work and point out the disadvantage in the designed system. Besides, prospects on the designed full digital SAW power source are mentioned.