Since the 1970s, with the continuous development of power electronics technology, inverter technology gradually be introduced to the field of welding. 1980s, the performance of high-power electronic components such as power transistors, FET, IGBT, etc. have emerged to promote the further development of arc welding power. Inverter power is the use of these advanced power electronic components and inverter technology developed, than traditional work-frequency rectifier power supply and materials from 80% to 90%, saving 20% ​​to 30%, the dynamic response speed is increased by 2 to three orders of magnitude. Many advantages, the power inverter has become one of the main development direction of the arc welding power source. Power inverter development, there are still many problems, such as reliability and market management, which is particularly important harmonic interference of electromagnetic compatibility (EMC). Harmonic suppression technique is a new direction of research, many experts and scholars at home and abroad of the harmonic theory and suppression programs of research and exploration. Limited by a variety of conditions, often with little regard to domestic welder developer of the electromagnetic compatibility of the product. Beginning in 1996, the European Community market electromagnetic compatibility of electronic products proposed more stringent requirements, that much more urgent to solve the harmonic problems. Although China started late, but also issued a corresponding standards and regulations enforced since August 2003.

　　1 arc welding inverter harmonic analysis

　　1.1 Harmonic causes

　　Since 1972, the United States developed the first the 300A arc welding inverter power since the arc welding inverter has made significant progress, experienced thyristor inverter high power transistor inverter, FET inverter IGBT inverter its capacity and performance is greatly improved welding inverter power source has become mainstream products of industrial welding equipment in developed countries [1]. Welding inverter power source as a typical power electronic devices, small size, light weight, and good control performance advantages, but its circuit, rectifier and inverter and other sectors, leading to the current waveform distortion, resulting in a large number of high-order harmonics. Serious phase shift between the high voltage and current harmonics resulting in a low power factor of the welder. Harmonic generation, mainly due to the following two factors:

　　(1) power inverter internal interference source power inverter is an electric and electronic portfolio system. In the welding process, the welding current can be up to hundreds or even thousands of amperes. High inverter frequency welding power system current produces a large electromagnetic field, particularly in the main circuit of the inverter, rectifier tube rectifier, high frequency transformer magnetic flux leakage control system oscillation frequency arc power tube switch are will produce strong harmonic interference.

　　Second, TIG welding machine with high frequency arc due to the welder use of frequencies up to hundreds of kilohertz, voltage up to several thousand volts of high frequency high voltage breakdown of the air gap is formed arc frequency arc is a strong harmonic interference source. Increasing the running speed of the computer control system for the the intelligent welding inverter power source for the computer-controlled, the control panel itself has become a harmonic interference source, the wiring of the control panel also proposed more high demand.

　　(2) power inverter external power line interference source pollution is more serious interference to the power system, due to the added electrical load ever-changing online, these loads are more or less on the grid harmonic interference, such as high-power the use of the device so that the grid voltage waveform distortion caused by accidental factors momentary power outage, the opening of the high-frequency equipment caused grid voltage waveform has a high frequency pulse spikes ingredients. In addition, in a welding shop, in the use of different welding power ground wire may be connected to each other, if not take the appropriate measures, the high frequency components of harmonic signals easily fleeing into the control system, the power is not working properly, or even damaged.

　　1.2 harmonic characteristics and hazards

　　Arc welding inverter is known for its high efficiency power conversion arc welding inverter will also be entering the era of high-frequency, high-capacity power control devices to the development of practical and large capacity direction. Arc welding inverter power on the grid, it is essentially a big rectifier power supply, power electronic devices along a very steep pulse before and after the commutation process, causing serious harmonic interference. The input current of the inverter power supply is a cusp wave contains a large number of high-order harmonics in the grid. Serious phase shift between the high voltage and current harmonics resulting in a low power factor of the welder. The low-frequency distortion problem is a common problem of the current power electronic devices in the communications industry, the appliance industry have aroused considerable attention. In addition, the inverter welding machine to use more hard switch, switch power components inevitably produce harmonic interference of space. By the near-field and far-field coupling of these interfere with the formation of conducted interference, serious pollution to the surrounding electromagnetic environment and the power of the environment, which will not only reduce the reliability of the inverter circuit, and will make the grid and close to the quality of equipment operation have been seriously affected.

　　2 arc welding inverter harmonic suppression measures

　　Harmonic interference is an important issue to affect the normal operation of arc welding inverter power should be given adequate attention. Harmonic suppression level, to ensure the normal work of the welding inverter power source, can usually be filtering method. Depending on the device used in its filtering principle, can be divided into passive filters and active filters.

　　2.1 passive filter (PassiveFilter, referred to as PF)

　　The traditional harmonic suppression and reactive power compensation method is power passive filtering technology, also known as indirect filtering method using power capacitors and other passive components constitute a passive filter, with the need to compensate for nonlinear load in parallel, provide a low impedance path for harmonic, while providing the reactive power required by the load. Specifically, the distortion of the 50Hz sine wave decomposes into a fundamental and of relevance to the main harmonic component, and then a series resonant principle, by L, C (Or there R) of each filter branch tuning (or partial tuning) form a low-impedance path to the main harmonic frequency of the filter [2-3]. It is in the case of the generated harmonics, passive defense, mitigate the hazards of harmonics to the electrical equipment.

　　Passive filtering programs, low cost, mature technology, but there are also the following deficiencies: (1) the filtering effect of the system impedance; (2) fixed resonant frequency, the frequency offset effect is not good; (3) The system impedance may occur in series or parallel resonance, causing the overload.

　　Medium power applications, being active filter replaced.

　　2.2 active filter (ActiveFi1ter, referred to as AF) as early as in the early 1970s, scholars have asked the basic principles of active power filter, but due to the lack of high-power switching elements and control technology, can only use the line linear amplifiers and other methods to produce the compensation current, there is a low efficiency, high cost, is difficult to a large capacity, etc. fatal weakness failed practical. Harmonic current generator with the improved performance of the power semiconductor switching elements, as well as the corresponding PWM technology development, making the development of large-capacity low loss as possible, so that the active filter technology to practical use, when the system harmonic generation source, a harmonic currents of equal size, the opposite phase of the compensation current, and become a harmonic The harmonics generating source circuit connected in parallel to offset the harmonic generating source, so that the DC side of the current is only produced by some method The fundamental component, does not contain harmonic components. When the harmonics generating source generates harmonics can not be expected from which the higher harmonic current, and are subject to change, must be detected from the load current il harmonic current ih signal, by detecting the harmonic currents ih signal, passes through the modulator is modulated in accordance with the methodology developed conversion control for the switch-mode current inverters work, so that the current generated by the inverter compensation current IFM and injected into the circuit in order to counteract the harmonic current IH inverter main circuits generally use a full-bridge DC / AC inverter circuit, wherein the switching element can be used such as GTO, GTR, SIT or IGBT large power control type power semiconductor element, with the switching element is off, the control of the output current waveform generated by The required compensation current. Active power filter as suppress harmonics and reactive power compensation to improve the quality of power supply of the most promising power device has the following advantages compared with passive power filter [5]: (1) to achieve a dynamic compensation of the harmonic frequency and size changes and a change of the reactive power to be compensated, a fast response for compensation object changes; (2) can compensate for the harmonics and reactive power, and the size of the compensation of reactive power can be achieved continuous adjustment; without energy storage element (3) to compensate reactive power compensation harmonic energy storage components required capacity is not large; (4) even if the compensation object too much current, power active filter does not happen overload, and can play a role in compensating normally; (5) the impact of the grid impedance is not easy and the grid impedance resonance; (6) can track changes in grid frequency, so the compensation performance not frequency change; (7) both a harmonic and reactive power compensation alone, also be focused on the number of harmonics and reactive power compensation.

　　3 soft switch technology

　　With the development of power electronics technology toward high frequency, high power density direction, work hard switching switching losses and harmonic interference problems have become increasingly prominent. To improve the conversion efficiency of the device utilization, enhanced electromagnetic compatibility and device reliability focus, soft-switching technology are useful for any switching power converter. Particularly necessary in certain special circumstances (if power density requirements or heat conditions occasions). In the two categories of passive and active soft-switch technology, do not use the additional switching elements, detection methods and control strategies of passive mode has additional low cost, high reliability, conversion efficiency and cost performance advantage in the industry single end converter manufacturing basically established mainstream. Topology, series inductance and capacitance method is the only means of passive soft switching, thus evolved from the so-called passive soft-switching technology, is actually no loss absorption technology. Bridge inverter circuit, the proposed from early energy absorber to later part of the feed can, without loss program, the load dependence, narrow operating frequency range, additional stress is high, the network is too complex problems, usefulness poor. Switching power devices modular trend at the same time, available to place absorbing element space is getting smaller and smaller, suitable for inverter module lossless absorption technology is also rarely seen in the literature. Overall, suitable for inverter modular passive absorption technology because of its special structure and the difficulty still further research and development [6-7]. Backward

　　4 Conclusion

　　There are a large number of harmonics in the arc welding inverter serious harm. In order to suppress the harmonics and improve the power factor, you must take the appropriate measures for the suppression. Traditional PF is obviously insufficient to restrict its application, the AF mode to make up for the lack of PF, effective inhibition of arc welding inverter harmonics, has been more widely used. Soft-switching techniques to a certain extent, but also can achieve a good filter effect.