Vol 31, No 1 (2023)
Information Technology and Communications
Synthesis of a feedforward control system for object with distributed parameters
Abstract
This study is researching a synthesis of an automatic control system for maintaining the temperature of petroleum products during storage in tanks. A new approach for the system construction has been developed during this research. It helps to get rid of disadvantages of existing methods of heating tanks. Developed control system is built on the basis of the feedforward control principle. The object of control is the tank insulation layer, considered as an object with distributed parameters, which provides opportunity to take into account the high inertia of the object. The uneven distribution of temperature is taken into account only over the thickness of the thermal insulation layer, thus, when modeling the control object, a linear one-dimensional heat conduction equation was used, supplemented by initial and boundary conditions of the third kind.
To ensure invariance to a disturbing effect in the form of a negative ambient temperature, a compensation element is built using the method of periodic structures. The required heating power dynamics of the heating cable is calculated to compensate for heat losses by the compensation element, depending on the current ambient temperature. Result of this study is a high-performance system that allows maintaining the high precision temperature of the oil in the tank. The article also provides research of the periodic structure parameters impact on the quality of the control algorithm.
6-20
Numerical analytical model of metal temperature of steam boiler drum
Abstract
The problem of developing and identifying a temperature distribution model in the wall of the boiler drum was solved. The numerical model is based on the analytical solution of the one-dimensional heat conduction equation with heat exchange at the boundaries at constant heat transfer coefficients. The model is implemented in a dynamic systems simulation package. Using the bounded series of eigenfunctions of the analytic solution, a representation of the plant in the state space was obtained. A universal algorithm for calculating the eigennumbers of the analytic solution was proposed. The eigenvalues dependences of the analytical solution on the values of heat transfer coefficients and thermal conductivity was investigated. Based on the results of the study, data tables were obtained to approximate the dependences of eigennumbers on heat transfer coefficients in a limited range of variation. The methodology for implementing a dynamic temperature distribution model, which takes into account changes in heat transfer coefficients during simulation, was tested. The time of change of coefficients is perceived as the beginning of a new transient from the current state of the model. Presented structural diagrams of the implementation of the model in dynamic systems simulation packages. The proposed structures allow the introduction of parametric disturbances at the time of their occurrence in the simulation. According to the experimental data of steam boiler firing, identification of the dependence of the heat transfer coefficient on the temperature of the metal wall of the boiler drum was carried out. The results showed that the heat transfer coefficients are influenced not only by the metal temperature, but also by additional parameters of the steam boiler operation. As a result of experiments, it was found that the accuracy of the model can be improved by taking into account the dependence of the heat transfer coefficient on the internal surface of the drum on the flow rate of feed water into the boiler drum. The results of the numerical experiment are presented.
21-33
Analysis of the influence of the discrete period of the zero-order hold of the digital automatic control system on dynamic indicators of control quality
Abstract
The issue of increasing the accuracy of reproduction of the master signal in a digital system for automatic control of an electric drive in the presence of a zero-order extrapolator in the block diagram is considered. The formation of discreteness in a control system with a zero-order extrapolator is considered. The analysis of the influence of the extrapolator discreteness on the dynamic indicators of the system control quality is carried out. As indicators of the quality of control direct indicators: overshoot and time of the transition process. The necessary relationship between the zero-order extrapolator quantization frequency and the bandwidth frequency of the linear part of the system is shown, which ensures the approximation of the above indicators of the quality of control of a discrete system to those of an analog prototype. The bandwidth of the analog part of the system is determined from the logarithmic frequency response. The article provides a recommendation for choosing the quantization frequency of digital controllers with zero-order extrapolators for multi-loop control systems, for example, built on the principle of slave control systems.
34-46
Purpose and prospects for the development of cyberphysical systems for technoligical processes
Abstract
The article is devoted to a new way of organizing production that is actively developing in the conditions of the industry's information transformation associated with the introduction of cyber-physical systems. Market analysis shows a positive trend in the growth of capitalization of this industry, indicating the widespread use of digital transformation tools for production and increased investment in the development of information technologies, including the creation and implementation of cyber-physical systems. The article analyzes the existing definitions of "cyber-physical systems" and "cyber-physical complexes." It also reveals the concept of a cyber-physical control system for the technological processes" and describes its main structure. The cyber-physical control system is considered a number of interconnected subsystems that perform strictly defined functions. The article presents a description of each of these subsystems, a generalized scheme of their hierarchical connections, and interactions. The article also considers the role of cyber-physical control systems in the information transformation of the industry and discusses the prospects for their future development.
47-59
Energy and Electrical Engineering
Mathematical models and structures of the vehicle lateral stability stabilization system
Abstract
Currently, intensive research is being carried out to improve the operational characteristics of the car: vibration protection, smoothness, stability, controllability. These properties are largely determined by the characteristics of the vehicle suspension, which provides a connection between the carrier system and the wheels of the vehicle. Significant attention is paid to the development of active suspensions, in which additional actuators are used to form the necessary characteristics, in particular, linear DC motors. The use of active actuators allows you to control the position of the car body, including its lateral roll. In the article, relations are obtained that establish the dependence of additional elastic deformations in the suspension and the car's roll angle on the centrifugal force in a stationary mode. When developing a linearized mathematical model of the control object for the study of non-stationary modes, a two-mass design scheme was used and operator equations were obtained that take into account the elastic-dissipative properties of the sprung and unsprung parts of the car, as well as an additional control action created by the actuator. It is shown that the dynamic properties of the studied control object can be approximately described by the transfer functions of a second-order aperiodic link or an oscillatory link. For the first case, a single-loop system was developed, closed in terms of the angle of heel with a PID controller. In the second situation, it is advisable to use a two-loop system with an internal flexible feedback loop for suspension deformation and an external loop closed for the roll angle using a PID controller. The possibility of forming a feedback signal on the strain rate of the suspension in the wind circuit with the help of an EMF sensor of a linear DC motor is shown.
On the basis of the block diagram, a computer model of the system was developed, and for typical parameters of the control object, a study was made of transient processes of working off a disturbance in the form of a change in centrifugal force. Based on the simulation results, it was found that the use of the developed ACS provides high accuracy in stabilizing the vehicle roll angle.
60-75
Induction system for heating large rings before rolling
Abstract
The paper considers the issues of designing an induction system for heating large-sized hollow cylindrical billets before rolling. The specific features of the billets heating process at the installation built into the technological processing line are noted. It is shown that for increasing the efficiency of the process of heating large-sized steel billets it is expedient to carry out the system of inductors with the use of a heat shield. A study of the process of heating of workpieces taking into account the nonlinear dependence of the physical characteristics of the metal of heated workpieces on the temperature changing in the process of heating is performed. The parameters of the induction system are calculated on the basis of a two-dimensional model. The geometric parameters of the circular billet resulted in a significant nonuniformity of the current density distribution along the axial coordinate of the billet due to the strongly pronounced boundary effects. The results of numerical calculation of the electromagnetic and thermal fields at different variations of the induction system design are presented. In order to substantiate and select the design of induction system that provides heating of the ring for the time caused by the work rate of the deforming equipment. A series of calculations was made, including three options: heating by an external cylindrical inductor; heating by two inductors: heating by inductor system with a heat shield. Analysis of efficiency of the investigated variants is based on multiple refinement of the results in the process of iterative design. Results of calculation of temperature distribution in the billet during heating are presented. The results of the research can be used to develop design and operating parameters of induction ring heating system in the rolling line.
76-90
Analysis of the operation of electromagnetic bearings in the difference of the center of the magnetic system relative to the axis of rotation and variations of the supply voltage
Abstract
The article sets the task of reducing the consumption of electrical energy by electromagnetic bearings. To achieve this goal, it is proposed to shift the center of the magnetic system of bearings that compensate for the weight of the rotor relative to the axis of rotation. The displacement value is assumed to be equal to half the clearance value in the safety bearings of the unit under consideration. A mathematical model of a radial electromagnetic bearing, its design scheme, taking into account the displacement of the center of the magnetic system relative to the axis of rotation, a block diagram of a three-loop control system and formulas for calculating the parameters of regulators are presented. Regulator settings for a specific type of electromagnetic bearings are determined. A calculation model has been developed that makes it possible to study the operation of an electromagnetic bearing when the center of the magnetic system is displaced relative to the axis of rotation and the supply voltage is varied. The results of simulation in the Matlab Simulink software environment of the process of rotor ascent from safety bearings and rotor levitation in a displaced state at different values of the supply voltage are given. It is shown that the voltage reduction by 16.7% ensures stable operation of the electromagnetic suspension of the rotor in all possible modes. Therefore, shifting the center of the magnetic system can reduce the power consumption of electromagnetic bearings by 30%.
103-113
Methods and installations for utilization of fine screenings of ferroalloys
Abstract
To date, the production of such ferroalloys as ferrosilicon, ferromanganese, ferosilicomanganese, high-carbon ferrochrome amounts to thousands of tons per year. Preparation of the ferroalloy for sale involves crushing the ferroalloy ingot to the commercial fraction, as a result of which there are dust-like screenings, which are further stored in warehouses and harm the environment. The existing sieving is a finished product, which in composition is close to the final fraction, the size of which is 10-250 mm. To apply sieving in steel production technology, it must be re-melted and cast into an ingot. The resulting ingot is repeatedly crushed until a commercial fraction is obtained. The main problem is the remelting of the dropout, since various difficulties arise due to its size and electrophysical properties. This article presents methods and installations for remelting sieving ferroalloys of various brands, as well as their comparison, disadvantages and advantages. The article describes plasma, induction crucible, as well as dual DC and AC installations designed for remelting sieving of various ferroalloys with a fraction less than 10 mm. The disadvantages and advantages of each method and remelting installation are described. Various experimental data obtained during the melting of ferroalloys sieving in the described installations are presented. Based on the data described in the article, as well as relying on other conclusions, in conclusion, a method of remelting with the removal of ferroalloys was proposed, including the advantages of existing ones, as well as excluding their disadvantages.
91-102