Aiming at the causes, characteristics and harms of harmonic generation of arc welding inverter power, the countermeasures such as passive filter, active filter and soft switching technology are introduced, as well as the characteristics of three harmonic suppression measures. Through analysis, it is pointed out that the traditional passive filtering method is insufficient, and active filtering can make up for its shortcomings. In addition, the application of soft switching technology can achieve good filtering effect to a certain extent.
0 PrefaceSince the 1970s, with the continuous development of power electronics technology, inverter technology has gradually been introduced into the field of welding. In the 1980s, high-performance electronic components such as power transistors, FETs, and IGBTs with excellent performance have emerged, which has promoted the further development of arc welding power supplies. The inverter power supply is developed by using these advanced power electronic components and inverter technology. It is 80% to 90% more than the traditional power frequency rectification power supply, energy saving 20% ​​to 30%, and dynamic response speed is improved 2~ 3 orders of magnitude. Due to the numerous advantages, the inverter power supply has become one of the main development directions of arc welding power supply. However, there are still many problems in the development of inverter power, such as reliability and market management. Among them, the electromagnetic compatibility (EMC) problem of harmonic interference is especially important. Harmonic suppression technology is a new research direction. Many experts and scholars at home and abroad have studied and explored the theory and suppression scheme of harmonics. Due to various conditions, the domestic welder developers often seldom consider the electromagnetic compatibility of the product. Since 1996, the European Community market has put forward stricter requirements on the electromagnetic compatibility of electronic products, and it is even more urgent to solve the harmonic problem. Although China started late, it also issued corresponding standards and imposed enforcement from August 2003.
1 Harmonic analysis of arc welding inverter power supply1.1 causes of harmonics
Since the development of the first 300A thyristor arc welding inverter power supply in the United States in 1972, the arc welding inverter power supply has developed greatly, and has experienced thyristor inverter, high power transistor inverter, field effect inverter and IGBT inverter. Its capacity and performance have been greatly improved. At present, arc welding inverter power has become the mainstream product of welding equipment in industrialized countries [1]. As a typical power electronic device, the arc welding inverter power supply has the advantages of small size, light weight, good control performance, etc., but there are rectification and inverter links in the circuit, resulting in distortion of the current waveform and a large number of high-orders. harmonic. There is a severe phase shift between the high voltage and current harmonics, resulting in a very low power factor of the welder. There are two main reasons for the generation of harmonics:
(1) Inverter power supply internal interference source The inverter power supply is a combination of strong power and weak current. During the welding process, the welding current can reach several hundred or even thousands of amps. Because the current will generate a large electromagnetic field, especially in the welding power system with high inverter frequency of the inverter main circuit, rectifier rectifier, high-frequency transformer leakage, control system oscillation, high-frequency arc ignition, power tube switch, etc. Will produce strong harmonic interference.
Secondly, if the tungsten argon arc welding machine adopts high frequency arc striking, because the welding machine uses a frequency of several hundred thousand Hz, the high frequency and high voltage of several thousand volts penetrates the air gap to form an arc, so the high frequency arc striking is also a Very strong source of harmonic interference. For the computer-controlled intelligent arc welding inverter power supply, the control panel itself has become a harmonic interference source due to the higher running speed of the computer control system, and the wiring of the control board is also raised. Requirements.
(2) Inverter power supply External interference source The pollution on the power grid is a serious interference to the power system. Due to the ever-increasing load on the power grid, these loads generate harmonic interference to the power grid more or less, such as high-power equipment. The use of the grid voltage waveform distortion, accidental factors cause instantaneous power outages, high-frequency equipment to open the grid voltage waveform has high-frequency pulse, spike components. In addition, in the welding workshop, the grounding wires may be connected to each other due to different welding power sources. Therefore, if the corresponding measures are not taken, the harmonic signals of the high-frequency components can easily enter the control system, so that the power supply cannot work normally or even be damaged.
1.2 Characteristics and hazards of harmonics
The arc welding inverter power supply is known for its high-efficiency power conversion. With the development of power control devices in the direction of practicality and large capacity, the arc welding inverter power supply will also enter the era of high frequency and large capacity. The arc welding inverter power supply is essentially a large rectified power supply for the power grid. As the power electronic components generate very steep pulses in the commutation process, serious harmonic interference is caused. The input current of the inverter is a sharp angle wave, which makes the grid contain a lot of higher harmonics. There is a severe phase shift between the high voltage and current harmonics, resulting in a very low power factor of the welder. The low frequency distortion problem is a common problem of current power electronic equipment. At present, it has attracted considerable attention in the communication industry and the home appliance industry. In addition, at present, the inverter welding machine adopts a hard switching mode, which inevitably generates harmonic interference to the space during the switching process of the power component. These interferences form conductive interference through the coupling of the near field and the far field, which seriously pollutes the surrounding electromagnetic environment and the power supply environment, which not only reduces the reliability of the inverter circuit itself, but also seriously affects the operation quality of the power grid and adjacent equipment.
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