| Firstly, the history, actuality and future of inverter technique in welding field are introduced in this paper. Secondly, the characteristics of VPPAW (variable polarity plasma arc welding) and its research actuality, as well as the far-reaching effect of micro-chip technique combined with inverter technique on the development of welding machine are set forth. Then the VPPAW power source is introduced according to the technological demands of welding aluminum alloy and the trend of inverter power source. Its design scheme includes main circuit, control system and control software.The build-up configuration and control principle of the VPPAW source are introduced in this paper. Main circuit, control circuit, safeguard circuit, wire feeding circuit and control software are expounded respectively. At the same time, test results are analyzed in detail.Full-bridge dual inverter configuration is adopted by main circuit which is supplied by single power source. IGBT (insulated gate bipolar transistor) is comparatively chosen as switch component to perform energy transfer and power conversion. The main circuit is made up of input rectifier & filter circuit, first inverter circuit, high-frequency transformer, second inverter circuit, rectifier & filter circuit and output reactor. The design kernel and parameters are discussed at length in this paper where the realization and control of second inverter are given emphasis to.High performance 16-bit micro-processor 80cl96KC is chosen as the core of control system who adopts closed-loop and minus-feedback control. The control variable is output by micro-processor system after real-time sampling current parameters are converted into digital signal. Adopting PI algorithm, constant current output characteristics is obtained after the variable is used to control the pulse width of PWM (pulse width modulation) chip SG3525 in order to adjust output current.The inverter circuit is composed of first and second inverter circuit. The PWM mode is accepted by first inverter circuit to control output current. The digital signal out of micro-processor is firstly converted into analog signal through MAX530, and then is modulated by SG3525 into two pulses not overlapped each other. At last, the pulses are used to trigger former IGBTs after they are magnified by M57959L, which can achieve pulsed DC output. Software programming is utilized by second inverter circuit to attain PWM pulse signal. Similarly, two pulses from HSO of 80cl96KC are used to trigger latter IGBTs after they are magnified by M57959L, which can achieve AC square waveto meet requirements of welding technics. Made up of HD7279 and LED, the display and keystroke circuit is designed to facilitate welding operation. In addition, the safeguard circuit is consisted of over-current, over-heat, over- voltage and low-voltage circuit.Reliability and anti-jamming design are also involved in both main circuit and control circuit of the welding machine. Various noises probably appearing in the whole system, as well as their mechanism, are analyzed systematically. Subsequently, in order to reduce their bad infections to great extent, some hardware and software measures are adopted while designing schematic chart, PCB board and compiling program code.Through online debugging, test data and results are attained and analyzed. Moreover, some unexpected problems are probed into and made corresponding improvement during test. The experiment results show that the VPPAW power source gains asymmetrical square-wave whose current frequency, amplitude, DCEN/DCEP ratio can be adjusted separately and VPPAW power source runs stably and reliably.
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