| The application of plasma technology in metal processing or surface processing can not only exceed the effect of traditional technology,but also has the advantages of high efficiency,environmental protection as well as simple process.Which make it become the focus of current research.And the key technical issues such as power control,pulse circuit and plasma processing are studied in this thesis for the requirements of gas-liquid load.First,there are strong nonlinear and time-varying characteristics in the plasma discharge process,and the process is also susceptible to many external factors,which challenge the dynamic response capability of the power supply.In order to solve the problem of film defects and power failure which caused by the area crossing from the glow discharge to the arc discharge during the processing of magnetron sputtering gas plasma load,a constant current close-loop with the output voltage feedforward control strategy is designed and implemented.Simulation and experimental results verify that the proposed strategy can effectively improve the dynamic response performance of the system,and the defects of magnetron sputtering film is effectively reduced.In addition,for the problems of the abnormally arc interrupting and cutting torch over-burning,a current predictive control method is presented,which is used to perform a fast response to current reference under non-high frequency conditions.Combining with traditional buck and boost circuits,the methods is modeled and verified by simulation and experiment.Secondly,asymmetric bipolar pulse circuit can effectively improve the effect of plasma processing,but it has the problems of low switching frequency and high power lost,which restricts its further development.An asymmetric bipolar pulse converter with auxiliary LC network to achieve zero voltage and zero current soft switching is presented,and its working mode is provided and analyzed as well.Furthermore,an asymmetric bipolar pulse converter based on coupled inductor is proposed to improve the traditional asymmetric bipolar pulse circuit,which only needs one DC source,the positive and negative two pole asymmetrical pulsed outputs are realized by using the energy storage and voltage conversion function of the coupled inductor.The soft switching performance and the proposed asymmetric bipolar pulse converter are also verified by the simulation and experiment.Finally,the sophisticated study for the asymmetric bipolar pulse mechanism and energy consumption management technology are carried out,which provides the basic ideas for the improving of plasma processing effect and guidelines for the power designing.The limitation of unipolar positive pulse waveform is analyzed from the analysis of the micro-arc oxidation load model.Meanwhile,the reverse polarity negative pulse can improve micro arc oxidation film performance,and its mechanism is revealed as well.The pulse parameters are also optimized by experimental study,which provides the guidelines for the growth control of ceramic layer and the design of the power supply.Based on the experimental analysis,the discipline of the micro-arc oxidation reaction process is summarized,and a cross-stage-mode based on anode gradually immersed of micro arc oxidation is thereby proposed for improving the problem of excessive energy consumption in micro arc oxidation.The experimental results indicate that the energy consumption before arcing,the critical current density and the time required for the arc initiation process are effectively reduced,and the performance of the ceramic layer is not changed.In addition,the technology has been successfully applied to the mass production of magnesium alloy wheels. |
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