Research On Intelligent Control System For CO₂Welding Power Source

CO₂gas shielded arc welding is a molten electrode arc welding method usingCO₂as shielded gas，which has characteristics of high efficiency，low cost，resistance to rust and low hydrogen.CO₂gas shielded arc welding is focused onpromotion technology of gas shielded welding in our country.CO₂gas shielded arcwelding is limited by factors such as the welding power source and controltechnology，and has the problems of large quantity of metal spatter，poor appearanceof welding and arc length fluctuation and so on. The key to solve these problems is tocontrol the welding current and arc voltage.CO₂welding load has characteristics ofnonlinearity， coupling， time-varying， and it is difficult to establish accuratemathematical model of the load.Thus，fuzzy neural network which has characteristicsof good robustness，strong adaptability is used in this paper.The intelligent controltechnology is applied to CO₂welding inverter power source control system. Accordingto the characteristics of CO₂welding short-circuit transfer process in every stage，theDSP as the core of the control system，several aspects such as the modeling of load，the composition of control system，control algorithm and control strategy are studiedfor CO₂welding inverter power supply control system in this paper.The change process of the welding wire，molten droplet，liquid bridge duringthe burning arc and short circuit stage is analysed detailedly，and mathematical modelof load in short circuit transition period by dynamic modeling is established in thispaper.Matlab/Simulink simulation model of load-power source system by simplifyingthe pulse width modulation in welding power source main circuit is established.PIcontroller which can automatically adjust the parameters is designed，and the fuzzycontrol algorithm is introduced to adjust automatically the proportion coefficient K ofneuron PI controller，consisting a hybrid fuzzy neuron PI controller.Uninterruptedswitching control strategy of STT （surface tension transition） current waveformcontrol and arc voltage control is adopted in this paper.STT current waveform control during short circuit stage and earlier stage of burning arc stage is adopted to improvethe appearance of welding and realize surface tension without splash transition.Arcvoltage control is adopted at the end of burning arc stage to make the arc goodadaptive characteristics.Under arc length without suffering external disturbance，CO₂welding inverter power source system simulation platform is established in thispaper.Selected rational arc voltage control given value and adopted strategy of big andsmall loop inductance continuously switching，the simulation results show that thearc voltage control stage， current waveform can well match the ideal currentwaveform，and the fuzzy neuron PI control algorithm has better adaptability thandigital PI control algorithm.To guarantee the stability of arc and realize the surfacetension transition without splash，based on current，arc voltage and big，smallinductance switch control system，on the basis of loop big resistance used constantlyswitching strategy， the simulation results show that system can improve theappearance of welding，realization surface tension without splash transition.Addedpositive or negative disturbance，arc length self-adjusting character during burningarc stage is discussed.Based on the above discussion of CO₂welding inverter powersource control system structure chart，CO₂welding power source circuit diagram isdesigned based on DSP as the core of control system.Based on the arc voltagesimulation waveform，short circuit-burning arc detection circuit，the liquid bridgeshrinking detection circuit and inductance switch circuit is designed.CO₂weldinginverter power source control system software module is designed.Module includeswhole control module，short circuit stage subprogram module，burning arc stagesubprogram module， fuzzy neuron PI control program module， digital PWMprogram module.The intelligent control technology is applied to CO₂welding inverter powersource control system in this paper.According to the characteristics of CO₂weldingshort circuit transfer process in every stage，CO₂welding inverter power sourceintelligent control system is researched and designed in this paper.The simulationresults show that the control output of the welding current and welding voltage canimprove the appearance of welding，realizes the surface tension without splashtransition， make arc good adaptive characteristic.This paper has good value tocontinue to study.