Study On Key Technologies Of Dielectric Barrier Discharge Power Supply Applied To Material Surface Modification

Discharge power source is the core equipment of the plasma surface modification system based on dielectric barrier discharge(DBD),and it is the key to improve the reliability and treatment effect.With the rapid development of plasma surface modification technology in aeronautics and astronautics,semiconductor manufacturing,biomedicine,packaging printing and dyeing and other important fields,high-quality discharge power source has become one of the research hotspots both in academia and industry.Unfortunately,there is still a predicament of repeated trials and high cost,which is caused by the difficulty of obtaining load parameters in advance and the imperfect parasitic parameter design methods of magnetic components.Besides,there is hardly any optimization research conducted on the correlation between operation mode of power source and treatment effect.Therefore,how to solve the above problems,so as to really promote the development of high-quality power source,has become an important research topic.For this reason,starting from load model improvement,the dissertation has done in-depth research on three aspects of the discharge power source,including prediction of load model parameters,parasitic parameters design of magnetic components,and optimization control of operation mode.To begin with,aiming at the problem that it is difficult to obtain the DBD load model parameters in advance,a load model parameter prediction method based on equivalent discharge region is proposed.In this method,the spatially dispersed filament discharge regions are concentrated and equivalent,and the equivalent discharge region is assumed to gradually expand as the applied voltage increases.Considering the particularity of the DBD load,the nonlinear piecewise load model is used to analyze the circuit,and the influence on the load voltage and transfer charge is found,which is brought by the sudden change of the dielectric equivalent capacitance at the beginning of the discharge state.To reflect the influence,based on the piecewise model,the gas discharge maintenance voltage and charge conservation voltage are defined respectively,by analyzing the critical conditions between the discharge state and the nondischarge state.The introduction of these two parameters provides a model basis for accurately grasping the effective discharge time in a wide power range,and it is revealed that the difference between them is inseparable from the load equivalent capacitances.Using this improved model,the equivalent capacitances and electric field distribution are simulated by finite element method(FEM)under electrostatic field,with the gradual expansion of the equivalent discharge region as the changing condition.Combined with the derived theoretical calculation formula,the one-toone correspondence among the parameters such as load equivalent capacitance,applied voltage peak value,discharge sustaining voltage,discharge power and the equivalent discharge area is established,and the load model parameter prediction under various working conditions is realized.Taking parallel ceramic rods as the DBD load,the experiment verifies the validity of the proposed prediction method,which provides a new idea for obtaining the load model parameters without experimental conditions.Then,for the parasitic parameters design of magnetic components in a power source,a design method for leakage inductance of high-frequency(HF)high-voltage(HV)transformers based on the concept of segmented low-voltage windings and a method for estimating the parasitic capacitance of windings based on the analytical calculation of electrostatic energy stored in the energy domain are proposed.For one thing,by studying the law of leakage variation of the interleaved windings,it is found that the number of turns for segments has an important influence on the leakage inductance.By analogizing with the linear axiom in plane geometry that any two distinct points determine a straight line,the analytic formula of leakage circuit reluctance is derived with a few leakage inductances of special cases as fixed points.The special leakage inductances are obtained through finite element simulation.And then a numerical regulation model of leakage inductance is constructed with the turn numbers of segments as variables,which provides easy access to the number of turns for segments satisfying the desired leakage inductance.For another,by dividing the electrostatic storage area inside and outside the winding,analytical models for energy calculation based on ideal electric field distribution are established.Using the energy conservation law,the conversion from energy to parasitic capacitance is realized.In addition,the theoretical error caused by the relative displacement between layers of the U-winding is corrected by introducing a compensation factor.By applying this method to the HV transformer,and considering the electrostatic energy stored between the windings,and between the windings and the magnetic core/shield as appropriate,the accurate estimation of transformer parasitic capacitance can be achieved.Simulation analysis and experimental results substantiate the effectiveness of the proposed parasitic parameter design methods,which are suitable for industrial application.Especially,the proposed leakage inductance design method combines the advantages of traditional analytical calculation method and FEM,which is time-saving,simple and widely applicable.The proposed parasitic capacitance estimation scheme takes both the internal and external energy of the winding into account,which is more comprehensive in energy calculation,so the parasitic capacitance is more accurate.Furthermore,the relationship between the power source operation modes and the material surface modification effect is studied.Foremost,the correlation between the discharge current peak and the equivalent reactive species density is analyzed,and the analytical expressions of discharge current peak under two discontinuous current operation modes(mode 1 and mode 2)are deduced theoretically.It is pointed out that the small discharge current in the pre-discharge region in mode 1 has a negative effect on the increase of the equivalent reactive species density.And the equivalent reactive species density is very important for the effect of material surface modification.Based on this,the essential reason why the discharge power continues to increase,while the modification effect decreases after switching from mode 2 to mode 1 is clarified.Then,the outstanding advantages of critical mode for energy saving and efficient processing are revealed.By studying the switching conditions and influencing factors of operation mode,an optimal control strategy is proposed,which takes the air-gap as the controllable degree of freedom(DOF)and the critical operation mode as the target.The superiority of the critical mode and the effectiveness of adjusting the air-gap to control mode are confirmed through a 750 W prototype.Moreover,the concept of the main discharge pre-recovery region is introduced to account for the appearance of the pre-discharge region in mode 2 with large air gap.Last but not the least,an airgap selection principle is formulated.That is,on the premise of meeting the actual industrial application,selecting the minimum air gap that enables the power source to work in the critical mode.Finally,the importance of the three research aspects of the dissertation in the power source system is emphasized once more: the load model and its parameter prediction are the foundation of circuit analysis and design,the parasitic parameter design is critical for energy transfer and transformation,and the operation mode regulation has a direct impact on the sur face modification effect.By combining these three technologies,a new scheme is conceived for the design of the power source system.In the new scheme,the load model parameter prediction method is responsible for obtaining the critical mode power curves with different resonance parameters,and the design methods for parasitic parameters are responsible for the optimal design of magneti c components.Using the resonant parameters and air-gap as design variables,the goal of nominally operating in critical mode is accomplished with the aid of the critical mode power curves.This new scheme has an important guiding significance for customizing high-quality power source with high processing efficiency and energy-saving features for new DBD loads.