Study On Three-phase Inverter CO₂ Welding Power

For a long time, the welding power machine made in China has been far away behind the others in the world, no matter in designing, making and producing. Because of the lower designed level, backward technological level and lower stability and reliability, China lists in the inferior in international competition. Since China has been gotten the accession to the WTO and carried one the Opening Up, some of the advanced technology and recommend a plenty of welding power machine were draw on. From then on China begins to develop welding power machine of China own. It first riches the Specification and variety of welding power machine, second reverses the situation that the ability to manufacture welding power machine is low. But this progression is not enough, compared with advanced country, there are still many shortcomings in producing welding power machine. In order to lower the distance with the developed country, reach the advanced level in the world, learned how to design and produce welding power machine, developed many welding power machine of its own with higher performance, lower price, easier to produce and easier to operate is neccesary. In one hand satisfied the domestic demand, in the other hand increases the export. Through the research of the welding power machine market, this research has practical significance. Inverter welding power source which was brought in 20th century 70s is a kind of new power. In structure and principle it is different from traditional welding power. Because it has many advantaged such as smaller volume, higher efficiency, smaller weight, lower consume and so on, since it is available, it have been highly valued and named"changed welding power".Inverter welding power source is that first put three-phase AC voltage frequency into rectifier which can conduct rectifier and filter, and translate AC into DC. Second by the on or off of high power electronic switch components such as SCR, GTR, MOSFET, IGBT, translate DC into AC with middle frequency .Then reduce the voltage of the transformer, in order to fit the requirements of welding technology. Finally export smooth and required DC used in welding. Why the process above through rectifier and filter by twice? If put the AC after inverter into welding power machine to make welding, because of the high frequency, it's easy to produce inductive, so reduce the power of the welding circuit.By the survey of the welding power machine market, Developing Three-phase Inverter CO2 Welding Power has feasibility.This design accord to the parameter requirements of the welding power machine chooses full bridge inverter main circuit in order to fit the requirements of high power of the welding power machine. Considering of the voltage, current and the design cost, I choose the MOSFET as the switch components. The frequency of the NBC-250 is 100kHz, the rated welding current is 250A, chooses EER-42×15 as core.Then this passage design input rectifier filter circuit, full-bridge inverter main circuit and output rectification filter circuit, which realize the AC→DC→AC→DC. The model of the MOSFET is K2611, of which there are resistance and capacitance in parallel in both sides. The RC protect the MOSFET against burnt if there were high voltage. Because the current capacity of MOSFET is small, each bridge of the main circuit uses MOSFET in parallel, in order to protect MOSFET.The control circuit includes welder start circuit, power circuit, voltage regulator circuit, current setting circuit, drive circuit and pulse width conditioning circuit. This design chooses PWM as control method. Because the external characteristics of the welding power machine is contented voltage characteristics, this paper designs voltage regulator circuit and current setting circuit, one hand they can revaluate voltage, the other hand they can limit the maximum current. The control circuit uses KA3525A as its main ford, controlled the trigger pulse signal by control the voltage of its pin.Wire control circuit includes regulator procedures power circuit, program control circuit, wire feed speed control circuit and move trigger circuit. This circuit use armature voltage feedback as its control method, which makes wire smooth and reliable.Finally, this paper designs an experiment, which put the made welding power machine into waveform analysis. This design get the waveforms of different output voltage without load, the second out put of transformers and output voltage of welding power machine. The experiment use 11 different test points to draw external characteristic curves. The experiment proves that the welding power machine designed reach the original design requirements.