To ensure stable arc combustion and adaptability to various welding process requirements, arc welding power sources have the following specific requirements: Static characteristics (or external characteristics) of the arc welding power source-that is, the relationship between steady-state output current and output voltage, exhibiting either a decreasing characteristic (constant current characteristic) or a flat characteristic (constant voltage characteristic). The external characteristic of CO2/MAG/MIG arc welding power sources is a flat characteristic (constant voltage characteristic); Dynamic characteristics of the arc welding power source-the relationship between the output current and output voltage and time when the load condition changes instantaneously (e.g., short-circuit transfer, particle transfer, jet transfer, etc.), used to characterize the responsiveness to load transients (i.e., dynamic responsiveness), abbreviated as "dynamic characteristics"; Open-circuit voltage-the voltage displayed by the power source before arc ignition; Adjustment characteristics-changing the external characteristics of the power source to adapt to the requirements of the welding specifications.
In a constant speed wire feeding system, changes in arc length cause changes in current and melting rate. The arc length recovery function becomes the self-regulating effect of the power source arc system. The finer the diameter of the welding wire used, the stronger the self-regulating effect of the arc, the more stable the arc, and the less spatter. CO2 welding power supplies are classified according to their external characteristics into steep-drop characteristic rectifier power supplies, flat characteristic rectifier power supplies, and multi-characteristic rectifier power supplies. They can also be classified according to the method of adjusting the external characteristics into transformer primary and secondary side tapped type, magnetic amplifier type, thyristor type, and transistor type.
Tapped silicon rectifier power supplies mainly consist of three parts: a main transformer, a rectifier, and a DC output reactor. The main transformer is a common three-phase step-down transformer. The primary winding of the transformer has several taps, or both the primary and secondary windings have taps, used for step-by-step adjustment of the output voltage. The three-phase rectifier is connected in a three-phase full-wave bridge rectifier circuit, its function being to convert AC to DC. The DC output reactor is a coil with an iron core at the output of the rectifier. This reactor is used to adjust the inductance of the DC output circuit. Its function is to regulate the dynamic characteristics of the power supply, mainly by limiting the rate of increase of short-circuit current and limiting the peak short-circuit current to meet the requirements of short-circuit transition CO2 welding. It also has a filtering function.
Arc welding inverters operate in harsh environments, and their load causes drastic changes in operating current. Overcurrent is the most complex, frequent, and damaging event for IGBTs. During welding, the harsh environment results in large currents flowing through the IGBTs, and the high switching frequency leads to significant device losses. If heat cannot be dissipated in time, it can damage the IGBTs. Therefore, limiting overcurrent and overvoltage, improving device operating characteristics, and reducing power consumption are all crucial aspects of arc welding inverter design.
Digital welding machines replace traditional analog control circuits with digital technology. This change gives them advantages in system flexibility, stability, control precision, and interface compatibility.
