The Development Of The Microcomputer Control Variable Polarity Plasma Arc Welding Power

A new scheme of realizing variable polarity current waveform is introduced by comparing all the variable polarity plasma arc welding power sources and their control methods at home and abroad. The main circuit is supplied by two power sources and the current amplitude in every half-wave can be adjusted separately.With the control circuit in which a monolithic computer 80C552 is the core, the current frequency and the DCEN/DCEP ratio are regulated and controlled. This scheme not only eliminates the interference between main arc and pilot arc, but also reduces the deterioration of the tungsten electrode and improves the stability of welding process. Furthermore, parameter regulation is agile and convenient with real time displaying and fault alarming.Energy transfer and power conversion is performed by main circuit.The welding current and voltage wave forms are obtained by controlling IGBTS' on/off in main circuit to meet the need of welding process. Adopting two IGBT-inverting power sources, the main circuit is modularied, fast, and reliable.As an important part of the VPPAW equipment, the control circuit in which a timer 8253 is used as the pulse generator and a SG3525 produces the necessary clock signal can slowly turn off the drive signal in safety zone when overcurrent in IGBT happens and reduce the on/off switching loss.Adopting advanced language KeilC51 to design software is much better than assembly language in according with human's thinking ways without thinking about what the inside constructure of the monolithic computer is and how to calculate.To meet the control circuit's requirement, the function of sampling, calculating, displaying and interrupting is written separately and is called in main programme.As a dynamic load, variable polarity plasma arc requires HF to ignite.When polarity changes, the power switches work in higher frequency.All of these will be the interference source and make the system unstable.The cause of interference and the measurement of hardware and software are analyzed in detail in this paper.Tests show that the main circuit, control system and software are reasonable in design, reliable in operation.