Research On Key Technique Of Special Digital Arc-welding Power Source

Great advancements have been made in the area of the arc-welding inverter power source in recent years. However, there are still some problems, and one of them is the harmonic interference of the arc-welding inverter power source. The harmonic interference includes two sides. One is the high frequency harmonics interference, which can be eliminated by using soft switching mode. Meanwhile, the efficiency and reliability of the arc-welding inverter power source could be improved by using soft switching mode. The other is low frequency harmonics interference. The arc-welding inverter power source is in essence a power rectifier to the electric network, so the input current distorts seriously, and the power factor correction and the harmonic distortion factor reduction are necessary. From the internal and international developments' standpoint, the intelligent green welding power source with high reliability, efficiency and electromagnetic compatibility is the developing direction of the welding power source.This dissertation focuses on the research of the multiple pulses rectifying technology based on the axial splitting autotransformer, used in the special arc-welding power source, with special voltage level, low harmonic distortion and high power factor. The characteristics of each magnetic element in the rectifier are analyzed in detail, as well as the relation between the input current distortion, the output voltage ripple and the system parameters. In addition, the system performance when the input voltage distorts is also analyzed. In the three-phase no controlled rectifier system, the unbalanced input voltage will influence the switching point. To the influence, the exact relation between the imbalance of the input voltage and the switching function is deduced for the first time. The deviation angle of the switching function has the sine curve relation with the initial phase angle between the negative sequence and the positive sequence, and the three curves of the three switching functions deviation angles are three phase symmetry. Meanwhile, the amplitude of the sine curve has the linear relation with the proportion that the negative sequence relatives to the positive sequence. Therefore, the exact relation between the unbalanced input voltage and the noncharacteristic harmonics of the output voltage in the 12-pulse rectifier system is obtained. In addition, the relation between the input current and the imbalance of the input voltage is obtained, which could help to choose the filter elements and exactly analyze the characteristics of the no controlled rectifier circuit. The theoretic analysis is verified by the simulation and experiment results.The topological structure of the Phase-Shift Full-Bridge ZVS (PS-FB-ZVS) is widely used in high power arc welding power source. A uniform equivalent circuit model is built, which offers a new method to analyze different circuit organizations based on PS-FB-ZVS circuit and a universal equivalent model for the tapped transformer. Based on the equivalent circuit model, there are some researches are engaged in this dissertation: the necessary and sufficient condition, which resonance inductors and parallel capacitors should meet to realize the ZVS of lag bridges, is exactly defined in this dissertation; the transient process under the nonideal switching work is analyzed, as well as the different influences to the working process which are produced by the leakage inductance of the transformer, and the influences which are produced by the interturn capacitance of the transformer, the parasite capacitance of output rectifiers and output buffer capacitors. The theoretic analysis is verified by the simulation and provides the reference meaning to future researchers.With the rapid development of the microprocessor, digital control is increasingly used due to its strategic flexibility and strong decision ability, and complex and intelligent arithmetic is realized. However, digital control also brings some problems. This dissertation is focused on the research of the causes which decrease the performance of the digital controlled PS-FB-ZVS induced by the process of zero hold and sample. There're two main causes. One is the change of the property arising from the process of the zero hold. The influence of the process of the zero hold is analyzes, also its influence on open loop frequency property and the system close loop stability of PS-FB-ZVS. Another one is the effect of the delay arising from the sample and calculation. To resolve this problem, one-step-delay control is always adopted. The influence of this control method on the system close loop stability is also analyzed.These analysis show there're three key causes effecting the digital controlled PS-FB-ZVS's performance: (1) The process of the zero hold changes the open-loop frequency property of the PS-FB-ZVS that is for under damp systems, the property varies periodically with sample time changing and for over damp systems, varies monotonously; (2) The process of the zero hold changes the system's stability and the stable zone lessens greatly; (3) The one-step-delay control method changes the system's stability too. Simulations and experiments verify the lightness of the analysis and the feasibility of the proposed control strategy.Based on the requirements of the special arc welding power source, the soft switching arc welding power source with high power factor and low harmonic distortion is researched and developed in this dissertation. The digital control system is designed, and the theoretic analysis is verified by the experiments.