The High-frequency High-voltage Low Temperature Plasmas Discharge Technology For Material Surface Treatment

Atmospheric pressure plasmas are subdivided into the non-thermal and thermal ones. The non-thermal plasmas are so-called the low temperature plasmas. The conditions of low temperature plasmas are mainly characterized by a relatively low temperature of the neutral gas in contrast to a significantly higher temperature of the electrons. The low temperature plasmas technologies have been paid much attention in recent years, due to their prospective applications in industry, especially in the material surface modifications. The low temperature plasmas not only etches the surface, making it rough, but also incorporates hydrophilic functionalities such as -OH, -C=O, -NH₂, etc. It can increase the surface energy of the materials. The modified surface shows good wettability and bondability.Presently, the power electronics technology has been widely used in the low temperature plasma discharge surface treatment. However, the low efficiency and high cost of existing low temperature plasma discharge power sources have prevented it from application. Accordingly, the research and development of efficient low temperatures plasma discharge surface treatment system suitable for various kinds of material loads becomes inevitable. The research field in this paper is interdiscipline, including the low temperature plasma science, power electronics, and material science. So, the research contents of this paper include the three subjects.1 , This paper analyses the related factors of dielectric barrier discharge(DBD).a) The effect of the rotating grounding electrode on dielectric barrier discharge is determined. The experiment results indicate that the dielectric barrier discharge will show different discharge forms and current waveforms by still or rotating grounding electrode. The reason is discussed in this paper.b) The characteristics of the different electrode geometries and the different discharge modes of dielectric barrier discharge are discussed. A method to generate an atmospheric pressure uniform discharge with the electrode geometric of the DBD is presented.c) The influences of the dielectric barrier in different place on the discharge current and the influences of the dielectric barrier on the discharge starting voltage are analyzed in detail. The influences of the dielectric barrier on the characteristics of DBD are analyzed and summarized.2 -, Based on a lot of simulations and experimentations, this paper comprehensively analyzes the characteristics of dielectric barrier discharge loads thoroughly. The dynamic curves of variable voltage variable frequency, constant frequency variable voltage and constant voltage variable frequency are given respectively. Experiments are carried out to verify the validity of analysis. A series of different rated power low temperature plasma power systems by different control methods are designed for using in different situationsa) A dielectric barrier discharge surface treatment based on a pulse density modulation (PDM) and pulse frequency modulation (PFM) hybrid control scheme is presented. The PDM scheme is used to regulate the output power of the inverter and the PFM scheme is used to compensate for temperature and other environmental influences on the discharge. The experimental results show that the PDM and PFM hybrid control series-resonant inverter (SRI) makes the DBD treatment simple and compact, thus leading to higher efficiency. The hybrid control SRI is able to realize the constant frequency control and linear power adjustment, and is thus becoming an ideal choice for dielectric barrier discharge treatment.b) A high frequency and high voltage power supply is essential for material surface treatment. In general, the dielectric barrier discharge processes require specifically designed ac power supplies of 10-20kV, 10-30kHz, and l-50kW to maintain a stable discharge at the atmospheric pressure. In order to ensure the capability of adjusting the affinity adaptability according to various kinds of materials with different thickness requires an ac power supply capable of controlling the discharge power in a wide range. To meet domestic needs, the l⁵0kW, 20kV, 20kHz dielectric barrier discharge inverter based on PAM control is developed. It can realize the soft switching conditions for the IGBTs, and also be adapted to the variety of discharge loads.c) The dielectric barrier load is represented as a varied nonlinear capacitance load, and its equivalent capacitance becomes higher as the applied voltage increased. A phase-shifted pulse width modulated (PS-PWM) series resonant inverter is developed for plastic film surface treatment, with such the characteristic of the load, and the tracing of the load resonant frequency is realized with a close-loop control.d) The characteristics of atmosphere pressure glow discharge loads areanalyzed, and the load resonant frequency of atmosphere glow discharge changes with the applied voltage nonlinearly. Based on the analysis and comparison of the control methods in experience, a PDM controlled atmosphere glow discharge high frequency and high voltage power source is presented. The PDM control series resonant inverter can meet the requirement of atmosphere glow regulation in the whole output power range.3> The high-frequency, high-voltage discharge power source developed in this paper is practically used in the surface treatment.a) Surface modifications of the organic material and inorganic material are achieved by the DBD. The experimental results are given.b) The related factors of the polymeric materials surface modification are analyzed in detail.c) The flammable wool fibers are surface treatment by the dielectric barrier discharge and atmospheric pressure glow discharge respectively. The analysis and experimental results show that the filamentary discharge is not suitable for the surface treatment of the flammable wool fibers, but the atmospheric pressure glow discharge can accomplish the task very well.