Research On Variable Polarity TIG AC Welding Power Source Based On Sotf-switching

Traditional ways of welding aluminum and its alloys can hardly provide a satisfiedwelding result, because they do not have the ability of both cathode cleaning and reduction oftungsten burning. Recently, variable polarity inverter welding power, with the features of fastsurpassing current zero and adjustable cathode cleaning ability, can achieve a stable weldingprocess and good welding quality. It can reduce or even suppress the generation of poresduring its welding process because of its similar features with pulse power. Most traditionalwelding power adopts hard switch circuit. As is known, variable polarity TIG inverter weldingpower uses dual inverter circuit, the circuit’s power tube may have relatively larger switchlosses in the hard switch way, its circuit efficiency is very low, it also may cause serioussecurity problems, such as over current, overvoltage, overheat, thus cause damage to thecircuit.The paper combines soft-switch technology with inverter technology. Variable polaritypower increases one inverter circuit on the basis of the DC submerged arc welding inverter.This paper introduces a variable polarity TIG melding power based on soft-switch technology.The main work includes design of main circuit topology, choice of computation parameterand digital control circuit’s design. After carefully analyze the topology structure of the firstand the second inverter circuit, new modified inverter circuits are proposed. First invertercircuit series reverse diode in lagging arm of a full-bridge inverter circuit, while achievingsoft switching, blocking reverse current, and reducing the circuit losses. Secondary invertcircuit adopts half-bridge inverter circuit with coupled inductor, so it can provide re-burn arcvoltage by freewheeling coupled inductor and achieve the current commutation by conductingupper and lower switch in turns. TMS320F2407DSP chip is used as the core digital controlsystem in control circuit, with extra sampling, protecting and anti-interference circuit. In thedesign of system software program, the paper designs the main control process according tothe main working principle of circuit. The paper also designs PI conditioner according to PIalgorithm through module methods, thus achieve an accurate control over melding parameter.Because the variable polarity power’s constraint of first and second level inverter’scoordinated control, two universal timers’ synchronization of DSP are used to solve thesynchronization of its first and second inverter by means of software programming.Pspice is used to simulate each circuit and analyze all the relative waveform on the basisof theoretical analysis. The experiment result is good. The current frequency, duty ratio,positive and negative half-wave amplitude of the waveform is both independent andadjustable, and its control system has an accurate control over current’s outer characteristic.At last, a12kW experiment platform is built to verify the correctness and feasibility of thetheory. The system’s correctness and feasibility are validated.