The automobile industry has become an important pillar industry of our country because of its long chain, high correlation and high consumption pull. The automobile body shell is a complex structural member, which is made up of more than one hundred or even hundreds of sheet stamping parts by welding, riveting, mechanical bonding and bonding. Because most of the materials of car body stamping parts are low carbon steel with good weldability, welding is the most widely used connection method in modern car body manufacturing.
The safety of automobile body structure and the application of new materials pose new challenges to the welding process of automobile body. For the welding of coated steel plate, glue-coated steel plate, multi-layer plate and different material plate, the traditional power frequency welding machine is difficult to meet the welding requirements, and the medium frequency welding machine has been used in more and more automobile production enterprises. Compared with the traditional power frequency welding machine, the energy cost of the medium frequency welding machine is nearly 1% less than that of the power frequency welding machine, which is suitable for automatic line application, high intelligent control, wide range of materials, especially stable and reliable solder joint quality. Intermediate frequency welding machine has also been more and more widely used in major automobile factories, such as FAW-Volkswagen, Chery Automobile, Beijing Hyundai, Dongfeng Nissan and other manufacturers have used intermediate frequency welding machine in automatic line welding or manual spot welding.
Power quality issues:
Because of the medium frequency spot welding of the welding machine, the welding parameters are about 400ms preloading time, 200ms welding time, 450ms welding time, welding current up to 510kA, welding pulse number of 1mm and 20 times, and holding time 100ms~300ms. The medium frequency welding machine works frequently, the working cycle is short, and the current conversion frequency is high, which is mainly manifested as instantaneous sudden current, low power factor, large fluctuation of reactive power and voltage, large harmonic current and voltage, serious three-phase voltage imbalance and so on. seriously affect the power quality of the workshop and plant, affect the normal operation of welding machines and other equipment.
Voltage fluctuation and flicker: the voltage fluctuation and flicker of the power supply system are mostly caused by the fluctuating load of the user. The electric welding machine belongs to the typical fluctuating load, and the voltage change caused by it not only affects the welding quality and efficiency, but also affects and harms other electrical equipment on the common connection point.
Power factor: a large amount of reactive power consumption caused by the electric welding machine, and the operation cycle is short, the operation process changes rapidly, and the sudden change is fast. The reactive current affects the output of the transformer, increases the loss of the transformer and the line, and increases the temperature rise of the transformer.
The harm of harmonics: after the AC signal passes through the inverter welding machine, it will produce high-order harmonics, increase harmonic loss, and cause a waste of energy.
Three-phase voltage imbalance: if the power supply connected to the welding machine is a single-phase power source, due to the generation of large current, the imbalance of three-phase voltage will be seriously affected, resulting in negative sequence current and zero sequence current.
Power quality control.
According to the load characteristics of the medium frequency spot welding machine, the operation cycle is short, the power changes quickly, and harmonics are generated, which seriously affect the power quality of the power grid and the safe operation of the power grid and electrical equipment. Traditional capacitance compensation devices such as TSC or TCR SVC can not quickly track and compensate the rapidly changing reactive power produced in the working process of the welding machine, which is very easy to cause over-compensation or undercompensation, and will magnify the system harmonics, cause system vibration, cause harm to the system, and can not solve the power quality problems caused by the welding machine. XT-SVG is the latest application product of reactive power compensation technology. XT-SVG can flexibly control the output reactive current in real time and quickly track the reactive power needed to compensate the load.