Research On EMC Design And PFC Device Manufacture For Inverter Resistance Spot Welding

As the high-power electronic devices, the electromagnetic environment of the inverterresistance spot welding machine is relatively poor. The secondary side circuit current canreach tens of thousands ampere or even higher. The high current can form strong magneticfield in the spot welding working environment. The complex current of the resistance spotwelding can produce a time-varying electromagnetic fields; not only can theelectromagnetic interference generated from the welding disturb equipment under the sameenvironment, but the EMI can reduce the quality of the electric system. Due to variouslimitations, domestic researchers usually rarely consider the problems of EMC when they doresearch about resistance spot welding machines. So the EMC during the production ofresistance spot welding machine have gradually been put on the agenda. In China, the studyof the EMC on the welding machine was carried out comparatively later by scientists andthe engineers. Especially after China joined the WTO, due to the faultiness of the standardsand slack of the policy, mass of the welding equipments especially the inverter arc weldingpower supply abroad have swarmed into the Chinese market, which have enormous impacton the manufacturers of the domestic market. While local welding machines often subjectthe foreign technical barriers when exported aboard. Therefore, in2009, in accordance withIEC60974-10, the national standards of EMC on welding machines is gradually introducedby the government, which can further regulate the arc welding power supply market, andimprove the competitiveness of domestic production of arc welding power source.In this paper, the characteristics of EMC and the commonly used methods to improvethe power factor of welding machines are studied on the basis of inverter resistance spotwelding, and we pay more attentions to the aspects of active power factor correction. Sincethe APFC circuit generally is a double close loops control circuit. In general, the outer loopis a voltage control loop, which can track a step signal; as inputting a constant referencevoltage, you can get a stable output voltage constant. It allows the output to maintain astable voltage which is higher than the input voltage peak, and it is critical for PFC circuits.The inner loop is a current control loop, which can track the ramp signals, as the sine wavesignal changes slower than the ramp signal, so it can also track the sine wave correctly aswell. The inner loop allows the input current to track the input voltage waveform precisely,so that the input current and the voltage both have the same sine waveform in phase, in order to achieve the purpose of improving the power factor. In this paper, the chip UC3854is chosen as the core, after ensuring the main circuit topology and the circuit working mode,the circuit parameters is determined and a PFC device of inverter resistance spot welding isdesigned. Recently experiment shows that the device enables to play a certain role inharmonic suppression, however, further investigations remains to be done latterly.