Harmonic suppression analysis of the hottest arc w

Harmonic suppression analysis of arc welding inverter power supply

aiming at the causes, characteristics and harm of harmonic generation of arc welding inverter power supply, this paper introduces the suppression countermeasures such as passive filter, active filter and soft switching technology, as well as the characteristics of three harmonic suppression measures. Through analysis, it is pointed out that the traditional passive filtering method has shortcomings, and active filtering can make up for its shortcomings. In addition, the application of soft switching technology can also achieve good filtering effect to a certain extent

since the 1970s, with the continuous development of power electronics technology, inverter technology has been gradually introduced into the welding field. In the 1980s, high-power electronic components with excellent performance, such as power transistors, field effect tubes, IGBT, etc., have appeared one after another, which has promoted the further development of arc welding power sources. Inverter power supply is developed by using these advanced power electronic components and inverter technology. Compared with the traditional power frequency rectifier power supply, it saves 80% - 90% of materials, saves 20% - 30% of energy, and improves the dynamic response speed by 2-3 orders of magnitude. Because of its many advantages, 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 supply, such as reliability and market management, especially the electromagnetic compatibility (EMC) of harmonic interference. 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 harmonic. Limited by various conditions, domestic welding machine developers often seldom consider the electromagnetic compatibility of products. Since 1996, the European Community market has put forward stricter requirements for the electromagnetic compatibility performance of electronic products, and it is even more urgent to solve the harmonic problem. Although China started late, it has also promulgated the corresponding standards, which have been enforced since August 2003

1 harmonic analysis of arc welding inverter power supply

1.1 causes of harmonic generation

since the first 300A thyristor arc welding inverter power supply was developed in the United States in 1972, the arc welding inverter power supply has made great progress. It has experienced thyristor inverter, high-power transistor inverter, field effect inverter and IGBT inverter, and its capacity and performance have been greatly improved. At present, the arc welding inverter power supply has become the mainstream product of welding equipment in industrial developed countries [1]. As a typical power electronic device, arc welding inverter power supply has the advantages of small volume, light weight and good control performance, but there are rectification and inversion links in its circuit, resulting in current waveform distortion and a large number of high-order harmonics. There is a serious phase shift between high-order voltage and current harmonics, resulting in the low power factor of the welding machine. The causes of harmonic generation mainly include the following two factors:

(1) the internal interference source of the inverter power supply. The inverter power supply is a system of strong current and weak current. In the welding process, the welding current can reach hundreds or even thousands of amperes. Because the current will produce a large electromagnetic field, especially in the welding power supply system with high inverter frequency used in the inverter main circuit, rectifier rectification, high-frequency transformer leakage, control system oscillation, high-frequency arc striking, 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 high-frequency and high-voltage with a frequency of hundreds of thousands of Hertz and a voltage of thousands of volts to puncture the air gap to form an arc, high-frequency arc striking is also a strong harmonic interference source. For the intelligent arc welding inverter controlled by computer, the running speed of the computer control system is getting higher and higher, so the control board itself has become a harmonic interference source, and higher requirements are put forward for the wiring of the control board

(2) the electrical pollution of external interference sources of inverter power supply is a serious interference to the power system. Due to the ever-changing loads added to the electricity, these loads more or less produce harmonic interference to the electricity, such as the use of high-power equipment distorts the electrical voltage waveform, accidental factors cause instantaneous power failure, and the opening of high-frequency equipment causes the electrical voltage waveform to have high-frequency pulse and peak pulse components

in addition, in the welding workshop, because the grounding wires of different welding power supplies may be connected with each other when they are used, if no corresponding measures are taken, the harmonic signal of high-frequency components can easily escape into the control system, making the power supply unable to work normally, or even damaged

1.2 characteristics and harm of harmonics

arc welding inverter power supply is famous for its high-efficiency electric energy conversion. With the development of power controller towards practicality and large capacity, arc welding inverter power supply will also enter the era of high frequency and large capacity. Arc welding inverter power supply is essentially a large rectifier power supply for electricity. Because power electronic devices produce steep pulses in the process of commutation, it causes serious harmonic interference. The input current of the inverter is a kind of sharp angle wave, which makes the electricity contain a large number of high-order harmonics. There is a serious phase shift between high-order voltage and current harmonics, resulting in the low power factor of the welding machine. Low frequency distortion is a common problem of current power electronic equipment, which has attracted considerable attention in the communication industry and home appliance industry. In addition, at present, inverter welding machines mostly use hard switching mode, which inevitably produces harmonic interference to space in the switching process of power components. These interferences form conducted interference through near-field and far-field coupling, seriously polluting the surrounding electromagnetic environment and power environment, which will not only reduce the reliability of the inverter circuit itself, but also seriously affect the operation quality of electricity and adjacent equipment

2 common harmonic suppression measures for arc welding inverter power supply

harmonic interference is an important problem affecting the normal operation of arc welding inverter power supply, which should be paid enough attention. In order to suppress the harmonic level and ensure the normal operation of arc welding inverter power supply, filtering method can usually be used. According to the different devices used and their filtering principles, they can be divided into passive filters and active filters

2.1 passivefilter (PF)

the traditional method of harmonic suppression and reactive power compensation is power passive filtering technology, also known as indirect filtering method, that is, using passive components such as power capacitors to form a passive filter, which is connected in parallel with the nonlinear load that needs compensation, to provide a low resistance path for harmonics and provide the reactive power required by the load. Specifically, the distorted 50Hz sine wave is decomposed into fundamental wave and related primary harmonic components, and then the series resonance principle is adopted to tune (or partially tune) each filter branch composed of L, C (or also R) to each main harmonic frequency to form a low resistance channel and filter it []. It passively defends and reduces the harm of harmonics to electrical equipment when harmonics have been generated

the passive filtering scheme has low cost and mature technology, but it also has the following shortcomings: (1) the filtering effect is affected by the system impedance; (2) Because its resonant frequency is fixed, the effect of frequency offset is not good; (3) Series or parallel resonance may occur with the system impedance, resulting in overload

in medium and small power occasions, it is gradually replaced by active filter

2.2 activefi1ter (AF for short) as early as the early 1970s, some scholars proposed the basic principle of active power filter. However, due to the lack of high-power switching elements and corresponding control technology at that time, only linear amplifiers and other methods can be used to generate compensation current, which has fatal weaknesses such as low efficiency, high cost, and difficulty in large capacity, so it cannot be applied. With the improvement of the performance of power semiconductor switching elements and the development of the corresponding PWM technology, it is possible to develop a harmonic current generator with large capacity and low loss, so as to make the active filter technology practical. When a harmonic generation source appears in the system, a compensation current with the same size and opposite phase of the harmonic current is generated by some method, and it is connected in parallel with the circuit that becomes the harmonic generation source to offset the harmonic of the harmonic generation source, The current on the DC side is only the fundamental component and does not contain harmonic components. When the harmonic generated by the harmonic generation source cannot be predicted as what kind of high-order harmonic current, and changes at any time, the harmonic current IH signal must be detected from the load current IL. The detected harmonic current IH signal is modulated by the modulator and converted into the switching mode according to the established method to control the working mode of the current inverter, so that the current inverter generates the compensation current IFM and injects it into the circuit, In order to offset the harmonic current IH, the main inverter circuit generally adopts dc/ac full bridge inverter circuit, in which the switching elements can be high-power controllable power semiconductor elements such as GTO, GTR, sit or IGBT. With the help of the on-off of the switching elements, the output current waveform is controlled to generate the required compensation current

active power filter is the most promising power device to suppress electric harmonics, compensate reactive power and improve the quality of electric power supply. Compared with passive power filter, it has the following advantages [5]: (1) it realizes dynamic compensation, including specific processing recommendations from solvent to cooling, which can compensate harmonics with varying frequency and magnitude and varying reactive power, and has a very fast response to the change of compensation object; (2) Harmonic and reactive power can be compensated at the same time, and the magnitude of compensated reactive power can be adjusted continuously; (3) No energy storage element is required for reactive power compensation, and the capacity of energy storage element required for harmonic compensation is not large; (4) Even if the current of the compensation object is too large, the active power filter will not be overloaded and can play a normal compensation role; (5) It is not easy to resonate with the impedance because of the little influence of the electrical impedance; (6) It can track the change of electrical frequency, so the compensation performance is not affected by the change of frequency; (7) One harmonic and reactive power can be compensated separately, and multiple harmonic and reactive power can be compensated collectively

3 soft switching technology

with the development of power electronic technology towards high frequency and high power density, the switching loss and harmonic interference of hard switching mode are becoming increasingly prominent. From the perspective of improving the conversion efficiency, device utilization, enhancing electromagnetic compatibility and device reliability, soft switching technology is beneficial to any switching power converter. It is especially necessary in some special cases (such as occasions with power density requirements or heat dissipation conditions). Among the passive and active soft switching technologies, the passive mode without using additional switching elements, detection means and control strategies has many advantages, such as low additional cost, high reliability, conversion efficiency and high performance price ratio. It has basically established a mainstream position in the manufacturing field of single ended converters in the industrial world. In terms of topology, the method of series inductance and parallel capacitance is the only passive soft switching means. The so-called passive soft switching technology evolved from this is actually a loss free absorption technology. As for the bridge inverter circuit, from the early energy consumption absorption to the later partial energy feeding and loss free scheme, there are many problems, such as strong load dependence, narrow operating frequency range, high additional stress, too complex network and so on, which are not practical. At the same time, under the trend of modularization of switching power devices, the space for placing absorption components is becoming smaller and smaller, and the lossless absorption technology suitable for inverter modules is also rare in the literature. In general, the passive absorption technology suitable for inverter modularization is still in further research and development due to its special structure and difficulty []

4 conclusion

there are a large number of harmonics in arc welding inverter power supply, which are seriously harmful. In order to suppress harmonics and improve power factor, corresponding suppression measures must be taken. The traditional pf mode has obvious shortcomings, which limits its application, while AF mode can make up for the shortcomings of PF and effectively suppress the harmonics of arc welding inverter power supply, which has been more and more widely used. Soft switching technology in a certain