This paper is devoted to the task of back converter simulation and control in the application area of thermal evaporation. Unstable conditions and non-linear phenomena during vacuum evaporation requires special approaches in simplification and control system design.
The main results of the dissertation are as follows:
1. The mathematical model of the Buck topology converter, which, in contrast to the existing ones, takes into account more nonlinear effects, which allows to correctly describe the dynamics of converter when working on loads with low and unstable resistance, has been further developed.
2. The gradual simplification of the Buck topology converter model was first proposed and substantiated, which makes it possible to significantly reduce the amount of computational resources in the simulation and to determine the conditions under which this simplification is acceptable.
3. Improved method of control of the heater by thermal evaporation in vacuum on the basis of the developed model of the Buck topology converter, which allows to set a given profile of voltage, current and power (and indirectly and temperature) under conditions of low thermal inertia, small and substantially non-stationary resistance.
4. The method of adaptation of the parameters of the control system of the heater for thermal evaporation in vacuum was developed for the first time, which allows to reduce considerably the error of regulation at sharp changes of the parameters of the task and the system as a whole.
5. Further developed a numerical method for determining the fractal dimension of images of surfaces from a microscope, which avoids the errors associated with the uneven illumination of the working field, as well as automatically determine the level of binarization.
6. For the first time the dependence between the pressure at metal coatings to the coefficient of friction of these surfaces is established, as well as the dependence of the fractal dimension on the coefficient of friction, which allows, on the one hand, to set the parameters of the coating when creating it, on the other - to evaluate some mechanical properties of coatings for them microimage.
7. In the course of the work: a device for thermal evaporation in vacuum was constructed for vacuum post GDP - 4; a controlled Buck topology pulse controller for controlling the power of a thermal evaporator in a vacuum, as well as calculating all its components; created a hardware and software system responsible for collecting data from the vacuum post and measuring complex based on INA226; Based on the control methods proposed in the dissertation, a control system was developed that includes a controlled pulse controller of the buck topology, an INA226-based measuring complex, and a STM32F407WBT based control board. The developed control system allows to support not only stable power, but also output current or voltage.
Keywords: mathematical models of pulse converters, Buck topology, thermal sputtering in vacuum, thin film coatings, digital control, fractal.
