Study On Variable Polarity Square-wave AC TIG Welding Power Supply

There are many good qualities about inverter welding power supply, suchas smart volume, lightness, high efficiency and dynamic response, and it willbecome the development trend that welds power supply. Variable polaritysquare-wave AC TIG welding power supply is a kind of specialsquare-waveAC inverter power, the output's current frequency, direct current value ofelectrode positive anddirect current value of electrode negativeof the powercan be adjusted respective. Therefore become the square-wave AC TIGwelding under the premise 'cathode pulverization', can reduce the DCEPtimewithmaximumlimit,and maketheweldingcharacteristicclosetotowardthe DCEN, so that this method keeping the welding electricity stability anextending Tungsten-Pole service life. The depth of the welding pool and theshape double sidesof weldingpass can be controlled through the method ofcontrolling the shape and strength of the welding arc and the quantity ofwelding arc heat by adjust parameter of the welding electricity. Variablepolarity square-wave AC TIG welding is a kind of pushed TIG welding, andthe pushed TIG weld have very strong agitation function to the welding poor,as aresultcanreduceandrepresstheairgap.Traditional PWM (Pulse Width Modulation) switch weld power supplydeveloped for more than 20 years, which change the electric voltage pulsewidth to adjust to output electric voltage with stabilitypassing to breakoff thepower supply with regulate to duty ratio for instance method, makes theIGBT working in hard-switch mode, namely forcing the working IGBT tobreak (welding current is not zero) and forcing IGBT switch to work (weldingvoltage is not zero), make the power switch exist the high voltage and bigcurrent to cross in the meantime for period, so the switch exhaust greatly,and electronic magnetic interference heavily. The high electric voltage peakthat the transformer leakage inductance arises with the big electric currentvariety rate, not only damage the power switch easily, but also produceobvious electromagnetism radiation, lower the credibility and power supplyefficiency.This paper analyzes the structure and principle of the Variable polaritysquare-wave AC TIG power supply, and divides the power supply into twounits --(first inverting unit) and output waveform controlling unit (secondinvertingunit), and designstowunitssynthetically. Energysupplyunitadoptsa soft-switching inverting technique, this technique synthesizesadvantage ofhard-switch mode and syntony technique: efficient power delivery andexcellent parameter control of thehard-switch mode, and low exhaust of thesyntony technique. Therefore the soft-switching inverting technique reducesexhaust. By excellent controlling with energy supply unit, it makes outputwaveform controllingunit getthe good characterthatbetter controlofelectricvoltage peak, and gets the purpose that good completed control of outputwaveform. With emergence of computer simulation, it simplifies the designprocess and economizes on cost of experiment. This paper makes use ofPspice's powerful function to carry on no-paper design through the wholeprogram design. The waveforms between the actual experiment and thePspiceresultarealmostsame.A great deal of mature Integrated circuit is used in the experiment. Withthe application of the these components, makes it possible to reduce theelement quantity of the controlling and drivingcircuit, and makes the work ofthe circuitmorecredibilityand stability,atthe sametime ofsimplifyingcircuit.According to the diode flow principle ,get a simple waveform judgment toestimate whetherornot IGBTworksinsoft-switchingcondition.