| Firstly, development condition and research progress of arc welding inverter technique are introduced in this paper. Limitation of conventional hard switching inverter and merits of the novel soft-switching arc inverter source are expounded. Circuit topology and operating principle of soft-switching arc welding inverter are studied systematically. A novel soft-switching circuit topology which is the full bridge phase shifting zero voltage zero current switching (FB-ZVZCS-PWM) is adopted.Computer simulation study of soft-switching inverter source is carry through, mathematical model of system and SIMULINK model is set up, and transition phase figure of FB-ZVZCS-PWM and simulation waveform such as phase shifting control signal, circuit load state of soft-switching, generator characteristic, dynamic performance duty cycle loss, and so on, are obtained. So it is verified that FB-ZVZCS-PWM is in the nature of minimal circulating current loss and maximal energy transfer efficiency, and it provides theoretical laws for power design.Main circuit sign, control circuit sign and system software of soft-switching inverter source are introduced systematically and debugging and analysis of system is completed in this paper.The structure of full bridge second inverter is adopted, while IGBT (insulated gate bipolar transistor) is chosen as switch component to perform energy transfer and power conversion. The parameter design of high-frequency transformer, input and output circuit, IGBT circuit and resonant loop is introduced in detail.High performance 16-bit micro-processor 80C196KC is chosen as the core of control system who adopts closed-loop and minus-feedback control. The welding current and voltage are sampled in real time, and control of power output is realized through adjusting pulse duty cycle. Phase shifting control circuit, first stage and second stage driver and synchronous driver circuit, wire feed circuit preset parameter & display circuit, serial communication circuit and protect circuit are introduced emphatically. First stage inverter is controlled by the major phase shifting chip -UC3879, and two pulses from high speed output (HSO) of 80C196KC are gained by software programming. The signal from HSO synchronizes with first stage driver signal to control second stage inverter, and alternating current (AC) square wave, which is adjusted in plus-minus half-wave, is obtained.Modular programming technology is adopted in control system software. Due to sententiousness and hardware oriented, the software is based on assembly languageprogramming. The constant current generator characteristic of source is realized by proportional integral (PI) algorithm. The interrupt service routine realizes real-time response and disposal of over current, over heat, over voltage and low voltage trouble in welding process.Besides, a variety of anti-interference designs about both hardware and software are accomplished, so reliability of system is increased prominently.Experimental data and related waveforms of model machine are achieved through debugging on-line and analysis. It is indicated that the AC PMIG power source attains asymmetrical square-wave whose current frequency, amplitude, DCEN/DCEP ratio can be adjusted separately in experiment. And the system of power source runs response rapidly and stably. |
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