Stable Mode Operation Research Articles

СТІЙКІСТЬ РОБОЧИХ РЕЖИМІВ АВТОНОМНИХ АСИНХРОННИХ ГЕНЕРАТОРІВ ІЗ САМОЗБУДЖЕННЯМ

The paper presents the results of investigation the stability conditions of self-excited induction generators. A mathematical model of the generating system with an analytical description of the dependence of the magnetization inductance on the current is used. It allows to avoid the iterative procedure and to scale the dependence to determine the magnetization inductance for induction machines of different types and power. The influence of the load inductance on the stability of the generating system at different rotational speeds is investigated. It is shown that an increase in the inductance value increases the system stability margins in the self-excitation zone. Also this article deals with the issues of system stability within the self-excitation zone of an induction generator at different rotational speeds depending on the value of the capacitance of self-excitation capacitors. It is depicted that at low rotational speeds there may not exist a stable operation mode in the self-excitation zone regardless of the value of the capacitance in the motor stator circuit. This method of determination the stability of the operation modes of the generation system will be useful both for the design of new systems and for the modification and adjustment of existing ones. References 9, figures 4.

Specific Removal and Recovery of Bromide Ions: The Search for Stable Electrodes and Operation Modes

In previous work, we introduced an elegant approach for bromide recovery from water by the introduction of a hybrid physical adsorption and capacitive deionization processes for selective removal and recovery of boron from water. In this paper, we show that the harsh environment of water contaminated with bromine-moieties adversely affects the longevity of relevant electrodes, with close to 100 consecutive work hours of bromides removal without noticeable degradation. To extend the lifespan of electrodes, we used an asymmetric CDI cell with a 1:5 positive/negative electrodes ratio in which a polarity switch between electrodes is applied every six adsorption-desorption cycles in a way that in each adsorption-desorption cycle, a different electrode of the six electrodes, functions as the positive electrode. We deduce that the polarity switch reduces oxidation and subsequent degradation of the positive electrodes, resulting in an extended lifecycle. After examining nine different carbonaceous materials, carbon cloth was chosen to be incorporated in the bromide- recovery cells because of its favorable kinetics and its physical and mechanical properties. We show that with a combination between endurance of the electrodes and asymmetric mode of operation, it is possible to overcome the main barrier that holds the technology from being practical.

Self-powered powerline monitor with strong anti-interference based on Maxwell’s displacement current-driven LED

A smart grid is a new generation power system, which realizes the interconnection of information in intelligent, efficient, and stable operation modes. Thus, high-voltage monitoring is an important part of ensuring efficient power transmission in a smart grid. However, traditional voltage monitors that rely on wired connections have limitations in meeting the adaptability requirement for smart grids. In this work, inspired by the double-TENG structure, we propose a self-powered high-voltage monitoring device with strong anti-interference, namely, the Maxwell’s displacement current-driven lighting emitting diode (MDC-LED), and proved that the MDC-LED with four electrodes can reorganize the electric field near the powerline, leading to an approximately uniform electric field. Therefore, the light output from the MDC-LED is highly sensitive to the electrical signal of the powerline and has a strong anti-device vibration. Because of the MDC-LED’s high sensitivity to alternating electric fields, it can detect the electric pollution in the powerline, as well as the powerline’s vibration frequency and amplitude. We believe the MDC-LED can provide a novel technical approach for the development of detection systems for use in smart grids.

ЦИФРОВИЙ МЕНЕДЖМЕНТ ЯК ПЛАТФОРМА СТІЙКОГО РОЗВИТКУ ПІДПРИЄМСТВА В УМОВАХ СУЧАСНИХ КРИЗ

Digital management transformation is becoming increasingly relevant for enterprises worldwide, including in Ukraine, as it creates a platform facilitating the transition of management systems into a continuous, stable operating mode. It ensures increased economic efficiency of the enterprise while simultaneously raising accountability levels towards partners, clients, and society. Moreover, during the current crisis affecting our country's economy, it is particularly crucial to have digitized management. It helps enterprises to establish a flexible and informative system for preventing or addressing adverse business phenomena. Therefore, the article aims to explore the features of utilizing digital management as a platform for the sustainable development of enterprises amidst contemporary crises. The research confirms that digital management plays a pivotal role in ensuring the sustainable development of enterprises. Its implementation facilitates the automation, analysis, and optimization of managerial processes, enabling enterprises to respond more effectively to environmental changes and enhancing their competitiveness.

Формування динамічних моделей газотурбінних двигунів для використання в системах автоматичного керування та контролю

The subject of the study is the process of forming a mathematical model (MM) of an aviation gas turbine engine, which provides the calculation of parameters of the work process in stable and transient operating modes for use in the evaluation of dynamic characteristics, in the analysis and synthesis of automatic engine and aircraft control systems, as part of aviation simulators, and in on-board control and diagnostics algorithms. The goal is to substantiate the structure and methodology of MM formation, intended for use in real and accelerated time scale systems. Task: formulation of requirements for MM, substantiation of the interaction between static and dynamic submodels, substantiation of the composition of arguments and the way of considering the influence of external conditions, as well as the position of the elements of the mechanization of the gas flow duct. For this, the methods of the theory of airjet engines are used. The following results were obtained: the requirements for MM of aircraft gas turbine engines designed to solve the problems of engine and aircraft control were formulated, and the structural forms of MM were substantiated, which ensure high accuracy of modeling with minimal complexity and the possibility of real-time implementation. The scientific and practical novelty of the obtained results is as follows: the requirements for dynamic MM of aircraft engines have been summarized, the problems of structural implementation and combination of static and dynamic submodels, the rational selection of their input parameters and considering the influence of external conditions on static and dynamic characteristics have been analyzed, the software implementation of MM in in the Matlab Simulink environment of a two-shaft turbofan engine and compared the simulation results obtained using the developed simplified MM and the original nonlinear thermo-gas-dynamic model based on the solution of the joint operation equations of components. It is shown that in the working range of modes, the MM error does not exceed 5%, the dynamic errors of the rotor rotation frequencies are less than 4%, the compressor pressure and gas temperature are less than 7%, or the thrust is less than 10%. Errors in estimating the duration of acceleration and deceleration of the engine are within 0.2...0.6 s.

Numerical and experimental investigation of thermal regimes of thermionic cathodes of arc plasma torches

The modelling method based on decoupling the simulation of the cathodic part of the arc (the cathode and the near-cathode non-equilibrium plasma layer) from the simulation of the arc on the whole has been extended to cathodes of arc plasma torches, consisting of an insert with a conical tip, made of pure or doped tungsten, and a surrounding water-cooled copper holder. The method was validated by comparison with the experiment, performed on a 200 A DC arc in atmospheric-pressure argon. Standard work function of polycrystalline tungsten of 4.54 eV was used for modelling of pure-tungsten insert and a good agreement with the experiment was found with respect to both the insert tip shape and the temperature distribution in the tip, recorded in the stable operation mode. There are no unambiguous data on the work function for arc cathodes made of doped tungsten, although in situ measurements of the effective work function of cathodes of high-pressure arc discharges provide useful hints. On the other hand, the experiments reported in this work show that the tip temperatures of inserts made of tungsten doped with of thorium, or lanthanum, or yttrium, recorded during the stable-mode operation at the arc current of 200 A, vary in a rather narrow range 3100–3200 K. This suggests that the work functions of doped tungsten inserts, operated in the stable mode, are close to each other as well. Indeed, the results of modelling with the same value of the work function of 3 eV give a reasonably good agreement with the experiment in all three cases.

Study on the evolution of silicon integrated circuit technology: fromscaling to lower power consumption

Silicon-integrated circuit technology has a profound influence on people’s daily lives. Throughout history, the goal ofthe evolution of this integrated technology has changed from scaling to lower power consumption because of multipledifficulties scientists face. By measuring and estimating the trade-off between circuit size and power, scientists havealready developed multiple new technologies to upgrade the silicon-integrated circuit. Some new methods people aretrying to find out that could be better to solve the problem. We did the research through one of the methods called postscaling technology. We found out it is possible to control the heat and power consumption of the circuit, which, underthe circumstance of minor scaling and stable operation mode.

The Study of Forced Power Supply Modes of a Xenon Flash Tube with Reinforced Electrode Assemblies

An INP‑16/350 xenon flash tube based on reinforced electrode assemblies was developed. As compared to the similar serially produced lamp INP‑16/580, the new lamp has the same dimensions but reduced discharge gap and reduced filling gas pressure. A stable quasi-arc operating mode of the lamp was reached with duration of radiation pulses of up to ten seconds when forcing power supply. The amplitude on time dependences of the lamp’s radiant exitance are formed by means of computer control of the temporal shape of the thyristor rectifier current pulses. For studying of the thermal overloads of the lamps, the methodology and IR-range optical pyrometry means were designed both, for the quartz bulb and for the electrode. The dependence of the latter’s temperature on energy deposition was studied using two custom-made radiometers. The load and radiation characteristics of the new lamp and the said analogue were compared. The new lamp is capable to operate rather reliably with high-power supply and energy deposition overload of up to 100 times in the single second-long flash mode with natural air cooling.

A digital thread-driven distributed collaboration mechanism between digital twin manufacturing units

The trialing of new products in production typically suffers from quality and productivity problems because of immature manufacturing processes. As an efficient virtual-real interaction technology, digital twin technology can optimize the manufacturing process adaptively in a single station. However, existing digital twin systems lack an effective collaboration mechanism between manufacturing units, thus failing to optimize the overall manufacturing processes dynamically. This paper proposes a practical collaboration theory and methodology between digital twin manufacturing units. To overcome the above challenges, this digital thread-driven method models the manufacturing tasks by heterogeneous information network to analyze the product quality information during the manufacturing process, and adjusts the subsequent manufacturing tasks according to the analysis results. The collaboration between manufacturing units forms a stable and reliable operation mode for improving production efficiency during the whole manufacturing process. The graph-based manufacturing task model can help analyze the machining and assembly process based on the digital thread, distinguish the error sources of products, and dynamically reconstruct production tasks. Finally, the feasibility of the proposed method is verified by a case of a crank and connecting rod mechanism in a manufacturing workshop.

Controlling power of short circuited induction motor via modern sensors without speed change

Short-circuited rotor induction motors are the most common and largest power consumers in industry. Therefore, it is necessary to find ways to ensure optimal performance of this type of motors and reduce their energy consumption. By this work, we will have the opportunity to automatically control the power of motors used in processes that do not have a stable operating mode. To perform this experiment, we use modern sensors and make special changes to the stator coil. Through our work, we create a special induction motor that is efficient, energy-saving and has a long service life. However it should be kept in mind that our developed motor is distinguished by its slightly complicated construction.

MINIMIZATION OF THE ROOT ERROR OF THE SYNCHRONIZATION SYSTEM OF THE COHERENT DEMODULATOR OF SATELLITE TELECOMMUNICATIONS UNDER THE CONDITION OF LIMITING THE TRANSIENT COMPONENT PHASE ERROR

A successful solution to the task of further increasing the efficiency of satellite communication systems largely depends on the quality of functioning of the systems and devices included in them. One of the directions for improving the efficiency of satellite telecommunications can be the development and improvement of phase synchronization systems in the direction of minimizing the phase error while maintaining high dynamics in stable and transient modes of operation. Mathematical dependencies are developed and presented in the work, which allow for the synthesis of open communication in the combined synchronization system of satellite telecommunications, which ensure the minimization of the root mean square error of the synchronization system under the condition of limiting the transient component of the phase error. The open communication scheme proposed in the work includes a link with a transfer function, the parameters of which make it possible to minimize the rms phase error under the condition of increasing the dynamics of the system in transient modes. The results of evaluating the effectiveness of the proposed method of minimizing the rms error of the combined synchronization system under the condition of limiting the transient component of the phase error showed that the value of the rms error for the combined synchronization system depends on the gain parameter of the open link link. The gain parameter can be effective in minimizing the phase error in the case of its positive values. The optimal value of the gain parameter in the presented open-loop synthesis model has an unambiguous relationship with the conditions for limiting the transient component of the phase error, and its deviation from the optimal values reduces the effect of the open-loop link when operating in transient modes.

Modeling of the thermal regime of a platformless navigation system with thermal stabilization of accelerated warm-up

Currently, platformless inertial navigation systems (IBS) based on fiber optic gyroscopes (FOG) are widely used in modern aviation and space technology. In connection with the high sensitivity of VOG to the influence of temperature changes, ensuring stable thermal modes of operation is an urgent problem. The most important task of increasing the accuracy of system operation is the development of methods of thermal protection and thermostabilization of VOG. The work is devoted to the modeling of the temperature field of the platformless inertial unit (BIB), which is part of the BINS, in order to ensure a minimum temperature difference on the VOG platform with the use of thermal stabilization. The purpose of the work is to simulate the temperature field of the BIB measuring unit and determine the conditions that ensure a minimum of temperature differences on the VOG platform under thermal stabilization conditions. To achieve the goal, the following tasks were solved: creation of a calculation scheme and finite element model of the BIB device, modeling of the effect of changes in external temperatures on the temperature field of the BIB device, numerical determination of temperature gradients at given points of the device. According to the results of numerical modeling, the parameters of the temperature field of the device and the characteristics of the thermal stabilization system were studied. The thermal mode of the device with a thermostabilization system for accelerated heating and reduction of temperature change gradients on VOG sensors with a governing law corresponding to base temperature changes is considered. The temperature gradients at the given points of the device are numerically determined. It was established that the law of thermostabilization should ensure the stability of the temperature field (the smallness of the temperature gradient). The value of the VOG temperature itself does not have a significant effect on the amount of drift. It is advisable to use the thermal stabilization system only to bring the system to the working temperature mode for no more than 30 minutes, and not to use it in the working mode.

RESEARCH OF A MICROCONTROLLER CHARGER FOR LITHIUM BATTERIES

Lithium battery chargers work on the principle of limiting the charge voltage. Among the features of such a charge, the following parameters are distinguished, such as a 3—4 times increase in the voltage of the lithium battery cell, smaller allowable deviations of the charge voltage (linearity of the current-voltage characteristic) and the absence of the need for a compensatory charge (jet recharging) after the battery reaches a state of full charge . Let's consider the specifics of the charge on the example of portable lithium batteries with an output voltage of 4.2 V, the specifics of the charge of which (and with a higher output voltage) consists in the use of the CC-CV method.
 To simulate the operation of the charger and debug the MK program, an electrical schematic diagram was compiled in the ISIS Proteus environment. To test this circuit, the model includes an STM32F103 MC, which is used to generate a PWM signal whose frequency is 62 kHz. Next, the output current is measured, with a setting of the PWM signal strength within 50 %. According to the indicators at the output of the operational amplifier in the current measurement mode, it is possible to determine the current in the ammeter battery circuit.
 Based on the simulation results of the developed scheme and algorithm, it can be concluded that this scheme ensures the fulfillment of the necessary modes of operation of the investigated charging device and is suitable for further implementation. A 32-bit MC of the STM32F103C8 series, located on the BluePill platform — a development board for the ARM Cortex M3 microcontroller, was selected as the control element of the control unit. The stable operating mode of the MK is ensured by two crystal oscillators of 8 MHz and 32768 Hz, and using the built-in frequency multiplier, the MK provides support for the operating frequency equal to 72 MHz.
 As a result, the functionality of the charger circuit and the SS-СV algorithm for fast charging of lithium batteries was developed and confirmed. The use of the CC-CV charge method made it possible to increase the output current of the charge, as well as reduce the time required to restore the energy properties of the battery, while current fluctuations are reduced by 96 %, compared to schemes that use only constant voltage methods.

SEMI-EMPIRICAL MATHEMATICAL MODEL OF NITROGEN OXIDES EMISSION FROM LOW-EMISSION COMBUSTION CHAMBER AS A PART OF AUTOMATIC CONTROL SYSTEM OF AN AERO ENGINE

The article is devoted to the problem of automatic control of nitrogen oxide emissions from a low-emission combustion chamber (LECC) of a gas turbine engines' (GTE) new generation. Since the measurement technologies have not reached the required level of availability today, and the reliability of the automatic control system (ACS) depends on the validity of input information about the engine state, it is proposed to use the built - in predictive mathematical model of the LECC. The model equations are functions of the measured parameters. The compact design requirements and significant nonlinearity of combustion determine the stochastic nature of the LECC. Taking into account the strict ICAO standards for the emission of harmful substances, all this leads to a narrow range of stable operating modes, limited, on the one hand, by the normalized level of nitrogen oxide emissions, and, on the other hand, by unacceptable modes of flame blowout or vibration combustion (thermoacoustic vibrations). It is proposed to build into the ACS a hybrid model of the processes of generating harmful emissions in the MEKS GTE, consisting two parts. The first semi-empirical submodel combines the physical equation of Zeldovich and the generalized empirical coefficient calculating as a function of several critical variables. This submodel allows generating training samples for the second submodel in case of insufficient experimental data. The second submodel is based on a neural network. The article discusses the development and testing of the first submodel, which identification algorithm is based on the accepted hypothesis of the possibility of applying the principle of superposition in describing the interaction of diffusion and homogeneous flames. The algorithm is based on the Zeldovich equation, which makes it possible to determine the dependence of the generation of nitrogen oxides on the composition of the air-fuel mixture using the distribution function of the probability density of its pulsations depending on the value of the integral equivalent ratio φ, which characterizes the concentration of fuel in the mixture. A feature of the LECC is the presence in the flame tube of longitudinal acoustic waves, excited by the release of heat during combustion, having a frequency equal to natural frequency of the gas-air column. These acoustic waves are leading to fluctuations of φ and causing the harmonic fluctuations in the mathematical expectation of the mixture composition. In this work the numerical modeling of the distribution of the inhomogeneity and pulsation of the fuel-air mixture concentration over the area of the flames in the CFX package allowed to obtain the characteristics of the mathematical expectations and dispersion, as well as the natural frequencies of the object. The distribution functions of the probability density of pulsations of the mixture concentration for diffusion and homogeneous circuits are calculated analytically, taking into account the acoustics of the combustion chamber. The analysis of the effect of dispersion of acoustic waves on the form of the resulting probability density curves in diffusion and homogeneous plumes is carried out.

Fault monitoring-oriented transition process identification of complex industrial processes with neighbor inconsistent pair-based attribute reduction

Complex industrial processes (CIPs) tend to run in multiple operating modes due to a variety of factors, such as the changes in load or raw material quality, random interferences from external environments, and the changing of set-points due to diverse personalized demands on product qualities. Successive stable operation modes will inevitably go through a transition stage that is extremely similar to abnormal conditions (faults). Traditional fault detection methods struggle to distinguish transition processes from faults, usually leading to high false alarm rates and resulting in frequent system fluctuations with low product quality or high production consumption. Therefore, this article proposes a well-performing CIP fault monitoring scheme with intelligent identification of transition processes. Firstly, a neighbor inconsistent pairs-based incremental attribute (or process variable) reduction approach is proposed. It extracts key process variables, which can effectively reflect the intrinsic dynamical characteristics of CIPs, from process data with high dimension, complexity, inconsistency and redundancy. Successively, an adaptive optimal sliding-window-based transition process identification approach is proposed, and the corresponding sub-phase-based fault monitoring criteria are established to realize the online fault identification of CIPs. Extensive confirmatory and comparative experiments on a numerical simulation system and the benchmark Tennessee Eastman process show that the proposed method can accurately identify the transition process, which effectively improves the fault monitoring performance of CIPs.

РОЗВ'ЯЗАННЯ ЗАДАЧІ АНАЛІЗУ ДИНАМІЧНИХ ПРОЦЕСІВ У ВЕНТИЛЬНІЙ ЕЛЕКТРИЧНІЙ МАШИНІ

The work solves an actual problem related to the development of a mathematical description and creation of models of valve machines, which are of important scientific and practical importance for the study of operating characteristics and the design of new control algorithms. We proposed a solution to the problem of analysis of dynamic processes in a valve electric machine using the Simulink application of the MATLAB environment. We proposed a solution to the problem of analysis of dynamic processes in a valve electric machine using the Simulink application of the MATLAB environment. The created models make it possible to obtain the main characteristics by which the working properties of engines are evaluated: electromechanical, mechanical. The results show that the operation of the valve machine is practically similar to the direct current machine. When building a model of a valve electric machine, control with current feedback and maintaining id = 0 should be carried out. This reduces the deterioration of mechanical, control and energy characteristics in a stable mode of operation. In general, if we compare a valve machine with a direct current machine, then its features are mainly manifested in the stable mode in the form of deterioration of mechanical, control and energy characteristics. As for the dynamics, the simulation results show that the valve machine is practically analogous to the DC machine. Analyzing the model as a whole and using the measuring tools provided by Simulink, it is possible to determine the losses in the motor, calculate the equivalent currents, torques and powers and check the correctness of the motor selection. The results obtained from such a generalized analysis can be extended to different engine operating modes. The proposed model for solving the problem of analysis of dynamic processes in a valve electric machine using the Simulink application of the MATLAB environment is characterized by functionality and the possibility of using the obtained results and the model itself in the design of modern electrical equipment.

Random Laser Based on Ytterbium-Doped Fiber with a Bragg Grating Array as the Source of Continuous-Wave 976 nm Wavelength Radiation

A random narrow-linewidth lasing at a wavelength of 976 nm was obtained in an ytterbium-doped germanophosphosilicate fiber with an array of weakly reflecting fiber Bragg gratings (FBGs). A random laser cavity was formed by implementing the standard phase mask method of FBG inscription directly during the fiber drawing process. The UV radiation pulses of a KrF excimer laser (248 nm wavelength) synchronized with the fiber drawing speed were used to fabricate the in-fiber array of hundreds of similar FBGs. The developed laser’s slope efficiency in the backward-pumping scheme was measured as high as 33%. The stable continuous-wave operation mode of the laser was detected. The magnitude of the laser power fluctuations depends linearly on the cavity length. The random laser cavity modified with a single highlyreflected (90%) FBG demonstrates significantly better power stability and higher slope efficiency than the same one without an FBG.

Modelling of the cyclic chemisorption-catalytic process for production of elemental sulfur and hydrogen from hydrogen sulfide

The research is devoted to simulation of cyclic chemisorption-catalytic process for H2S decomposition on the base of bulk FeS catalyst-chemisorbent. The performed simulation of the process has confirmed the possibility to create the stable cyclic non-stationary operation mode with a technologically acceptable duration of chemisorption/regeneration cycles (10-15 minutes and more). Though the maximum calculated per pass conversion of H2S was not higher than 30%, it is possible to achieve practically complete decomposition of H2S to hydrogen and sulfur by recirculation of unreacted H2S. The process may be performed at rather moderate temperatures (not higher 600-650°), it makes possible to use the conventional construction materials for process equipment with reasonable capital costs. The preliminary evaluation has demonstrated that the proposed process, being compared to conventional Claus process, will be characterized with better economic parameters due to the manufacturing of hydrogen which will have ∼5 times higher cost than that of produced sulfur. From the other side, the process may potentially provide the self-cost of the produced hydrogen quite competitive to that of conventional technologies such as conversion of hydrocarbons or water electrolysis. The technology may be applied at oil refineries and natural gas processing plants.

Optimization as one of the forms of changes in the system of central executive authorities

Introduction. Optimization of the system of central executive authorities, the implementation dates of which are set for 2018-2021, was provided by the order of the Cabinet of Ministers of Ukraine «On approval of the Concept of optimizing the system of central executive authorities» of December 27, 2017 № 1013-r. Previous processes of optimizing the system of central executive authorities took place in 2010 and 2014. Optimization is one of the forms of changes in the organization and operation of the system of central executive authorities. It has a corresponding purpose, content and features and diff ers from other forms of change («reform», «optimization», «improvement», «modernization», etc.). These terms should not be equated. However, such identifi cation is not uncommon both in the scientifi c literature and in legal acts and practice of public administration. The aim of the article. The aim of the article is to deepen the theoretical foundations of the processes of optimizing the system of central executive authorities that took place in 2010, 2014 and optimizing the system of central executive authorities, which has been going on since 2017 and until now. Results. Optimizing the system of central executive authorities is bringing it to a certain positive level of its functioning. Optimization is the achievement of the maximum allowable value of effi ciency under a stable and high-quality mode of operation of the system. Optimization is a set of measures to increase the effi ciency and eff ectiveness of activities. The terms «optimization» and «reform» are used interchangeably, as part and whole, or even identifi ed. Although each of them contains its own content. The key results of the 2010 optimization were the change of the components of the system of central executive authorities and the consolidation of relevant functions for specifi c types of central executive authorities. The optimization of the system of central executive authorities in 2014 was actually reduced to the formation, liquidation and reorganization of a number of central executive authorities, as well as the assignment of additional functions to certain ministries. Unfortunately, the optimization of the central executive system, which has been going on since 2017, is lagging behind the planned deadlines, in many ministries it is being carried out formally, or it does not meet the goal to be changed. As a result, there is a threat to increase the effi ciency and eff ectiveness of the organization and operation of the system of central executive authorities. Existing terminological inconsistencies and arbitrary choice of form for changes required by the central executive system may be among the reasons for not achieving the expected result of such changes. As well as the processes of optimization, reform of the system of central executive authorities should be preceded by the preparation of a conceptual document that defi nes their purpose, criteria, content, stages and deadlines. Conclusions. The changes required by the system of central executive authorities in the relevant periods of its development must correspond to a certain form of change with its own characteristics (optimization, reform, improvement, modernization, etc.). Changes in the organization and operation of the central executive system in 2010 and current changes are more in line with the form of «reform» of the central executive system than «optimization». The purpose of these processes in diff erent years coincided and was to achieve positive changes in the organization and operation of the system of central executive authorities. The content of the changes and its scope were diff erent – comprehensive changes in 2010 in the organization of the system of central executive authorities and the functions performed by central executive authorities; smaller-scale changes in 2014; strengthening the role of ministries in shaping public policy and depriving them of their inappropriate powers from 2017 to the present. The results of changes in the organization and operation of the central executive system in 2010 in terms of the new species classifi cation of central executive authorities and their functions justify themselves in practice and can be used as basic data to improve the central executive system in modern times. Key words: system of central executive authorities, optimization, reforming, improvement, effi ciency, eff ectiveness.

Investigation of the Impact of Large-Scale Wind Power and Solar Power Plants on a Vietnamese Transmission Network

Integrating wind power and solar power plants into a power system has significantly grown over the past decade and is expected to grow to unprecedented levels in the coming years. In Vietnam, much large-scale wind power and solar power plants have been built and connected to the power system in recent years. To investigate and evaluate the impact of these power plants on system power operation, the 110kV power transmission network of Binh Dinh province in Vietnam is used in this paper. In the system, the Phuong Mai 3 wind power plant with a capacity of 21MW, the Fujiwara solar power plant with a peak capacity of 50MWp, and the Cat Hiep solar power plant with a peak capacity of 49.5MWp are modeled by using the PSS/E software to simulate and analyze their impacts on power system stability of the 110kV transmission network in Binh Dinh province, Vietnam. Besides, the control strategies of these power plants are also established to investigate their impacts on the network. In addition, this paper proposes three typical scenarios for the wind power and solar power plants in the system. For each scenario, the grid's operating parameters such as voltage variations and frequency variations are acquired for analyzing and evaluating their impacts on the frequency and voltage variations of the network. The simulation results show that the 110kV power transmission network remains in a stable operation mode after the fault scenarios for the wind and solar power plants. Furthermore, these simulation results provide some guidance for the actual operation