| There are various resistance welding machines. They have unique technical characteristics and play an important role in many industrial fields such as automobile, family appliance, electron, spaceflight and navigation etc. Among them sub-grade rectifying welding machine has advantageous traits such as high proficiency, relatively high working frequency, stable current output and concentrative calefaction etc. However, this kind of welding machine has many shortcomings such as high price, strict applying conditions of components, excessive hidden safety dangers and tendency to introduce high-grade harmonious waves into power network etc. In addition, the working process of inverting power is complicated; performance will be greatly influenced by circuit parameters, the working process is difficult to grasp, the traditional designing method will cause bad consequences such as onerous designing task, low precision and long period etc. Therefore, methods with actual effects should be used to mitigate designers' working intension and improve designing precision. Computer simulation is a kind of simulation research on the base of math model construction of researched objects. When simulating, the simulation model of applied system should be firstly set up, and then be solved by employing computer. Therefore, it has some merits such as shortcut, convenience, safety etc, which other researching methods such as practicality experiment don't own. At present, computer simulation technique has been widely applied in the system design of power electron and has brought forth good practical effects. To apply this technique to spot welding inverting power not only has great advantages, but also can certainly improve the designing methods of spot welding power.Generally speaking, sub-grade circuit of spot welding inverter has great affect on its performance, which cannot be neglected. The sub-grade equivalent circuit structure of the inverting spot welding power mainly consists of alternatively changing power; high-power diode, loop resistance and loop inductance, and various parameters have great influence over virtual value of sub-grade current. The analysis shows that the virtual value of sub-grade current has something to do with sub-grade output voltage, diode's positive conducting voltage reduction, occupying ratio and loop resistance; whereas the sensitive degree of sub-grade current to occupying ratio alteration is in direct ratio with sub-grade output voltage and inverse ratio with loop resistance. The selection of inverting circuit forms is the important content of inverting spot welding power design. Phase-shifting soft-switching full-bridge circuit is widely used by arc welding inverter is not suitable for spot welding inverter because it has strict requirements for some component parameters and its pulse generating chip UC3875 doesn't support the working frequency of spot welding power.In a low-frequency hard-switching mode, switch tubes are always used for its calefaction is not so high. Cushion circuit is introduced in inverting circuit to decrease the switching stress of switch tube and improve working process. The hard-switching inverting mode, which employs RCD cushion bypasses, can meet the working requirements of spot welding inverter. The analysis shows that different cushion capacitance will lead to different shut-down states; in the turn-on process, there is a comparatively large current along the switch tube which results in a high pinnacle. In order to decrease delay of cushion circuit, speedy soft resuming diode, non-inductance capacitance and non-inductance resistance should be chosen to build RCD bypass. The non-equivalent of driving signal width of two IGBT circuits will cause DC bias and, even more seriously, the magnetism saturation of transformer. By serial connecting non-polar capacitance to the primary circuit, lopsided DC bias will be filtrated. The model of various components in the inverting circuit is the basis to construct inverting circuit model. However, some components... |
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