Design Of Pulsed MIG Welding Power Controller Based On Mixed-Signal FPGA

Welding process is the basic technology of manufacturing. It has made important contributions to the development of industrial economy in the 20th century. With the deepening research of welding process, many complex algorithms of welding process have been constantly raised. It puts forward higher requirements to the welding method and control of the welding machine. Pulsed MIG welding process has the characteristics of reliable and stable quality of welding, wide adjustment of welding parameters and better achievement of all-position welding, so it is widely used in the welding field. Currently, pulsed MIG welding process makes a combination of artificial intelligence technology, digital information processing technology and computer technology. It is moving in the direction of high efficient, all-digital and intelligence.By analyzing the circuit structure and working principle of the IGBT arc welding invert, combining the technology characteristics of pulsed MIG and the effect of every technology parameter, the paper designs welding arc length control strategy based on sync pulse method and welding current control strategy based on fuzzy-adaptive PID controller. In order to keep the arc length stable, welding arc length control adjusts the base-value current time to make sure the average voltage of the arc output following a given average voltage input. The current control strategy meets the different input current needs of different PID control parameters and achieves the required pulsed MIG welding metal transfer form:a pulse, a drop. And this two-closed loop control strategy can effectively suppress disturbance. It has obvious advantages compared with the traditional open-loop control.According to the switching characteristics of the driving IGBT power device and combining the advantage of current-mode PWM, the paper designs digital PWM drive circuit. It uses the given signal, the feedback signal and the sawtooth wave together to generate the drive pulse. The designed PWM drive circuit has a small current fluctuation and a high control precision. Meanwhile, the paper designs a protect circuit based on the current feedback of the transformer primary side to suppress over-current phenomenon caused by transformer bias.The paper combines the current development of the FPGA technology. And the paper selects a mixed-signal FPGA of Actel company based on flash architecture which has analog functions as the master chip. The selection of the FPGA effectively solutes the problem that the CPU has a heavy burden of computing using DSP as the master chip. Meanwhile, compared with FPGA based on SRAM architecture, the chip has a characteristics of low system cost, high security, live at Power-up, high reliability and low power consumption. The program is designed modularly in FPGA by verilog hardware description language. Every module runs in parallel. The program achieves the functions as bellow, two-closed loop control of welding current and voltage, control of AD sample, control of reading and writing dual port RAM and control of welding timing process. Because the program is designed modularly, every module can be used for debugging independently. It improves the speed and facilitates debugging.Finally, the designed system is tested, including the control of arc test, the current loop test, welding process test and the whole welding test. It indicates that the welding process of the designed system is smooth and achieves the control requirement.