Stability Of Such Systems Research Articles

Functional stability of technological processes based on nonlinear dynamics with the application of neural networks

The processes of transformation of global information infrastructure and large-scale automation of production lead to the actual merger of automated production, data exchange and production technologies into a single self-regulatory system with minimal or no human intervention in the production process. Currently, there is a mass introduction of cyberphysical systems into production with the simultaneous application of the results obtained in the fields of artificial intelligence, robotics, the Internet of Things and so on. Implementing the goal of developing methods for organizing production processes of metal processing at machine-building enterprises using neural networks, the processes of global transformation of IT infrastructure were studied against the background of mass introduction of cyberphysical systems and breakthroughs in artificial intelligence and technological processes. The characteristics of the behavior of complex technical systems that implement the property of functional stability of such systems are studied. The processes of metal processing by cutting are characterized taking into account the peculiarities of the influence of deformation hardening, plastic deformations, self-oscillations and chaotic dynamics that occur in machining centers. Methods of application of neural networks in modeling of processes of mechanical processing of metals by cutting are described. A universal technique for constructing neural network models of the machining process on the basis of an artificial counter-propagation neural network is given. Based on the analysis, an intelligent system of analysis and forecasting of the dynamic stability of the technological process of cutting using parallel calculations, which guarantees the fulfillment of the necessary conditions to ensure the functional stability of the production process.

Study of Dynamic Modes of Current Stabilization Systems of Powerful Electromagnets with Pulse-Width Modulation

This study is devoted to the consideration of a method for assessing the stability of systems with pulse-width modulation, based on the linearization of its equivalent system with pulse-width modulation. An approximate study of the dynamic modes of operation of systems with pulse-width modulation, taking into account the stability for the system of automatic control of the supply current of electromagnets under the conditions of external and internal interference, is carried out. Variants of execution of schemes of pulse-width regulators for the power supply of an electromagnet based on a unipolar and bipolar element with pulse-width modulation are presented. The possibility of linearization of systems with pulse-width modulation for the subsequent detailed assessment of the stability of such systems is shown. The prospects of using functional differential equations for stability analysis of automatic systems with pulse-width modulation are shown. The frequency characteristics of an equivalent pulse system are analyzed using the example of a current stabilization system of high-power electromagnets with a pulse-width regulator, taking into account the replacement of the latitude modulation by the amplitude one. Based on the analysis of the resulting transfer function, which is a stable linearized equivalent open system, the ways of evaluating the stability of the original system with pulse-width modulation using the Nyquist stability criterion are proposed. The conclusion is made about the advantage of a system with PWM, in relation to a system with AIM, in terms of stability, and recommendations are given for the use of the obtained data in the analysis oftransients in such systems.

Power Hardware-in-the-Loop-Based Performance Analysis of Different Converter Controllers for Fast Active Power Regulation in Low-Inertia Power Systems

Future electrical power systems will be dominated by power electronic converters, which are deployed for the integration of renewable power plants, responsive demand, and different types of storage systems. The stability of such systems will strongly depend on the control strategies attached to the converters. In this context, laboratory-scale setups are becoming the key tools for prototyping and evaluating the performance and robustness of different converter technologies and control strategies. The performance evaluation of control strategies for dynamic frequency support using fast active power regulation (FAPR) requires the urgent development of a suitable power hardware-in-the-loop (PHIL) setup. In this paper, the most prominent emerging types of FAPR are selected and studied: droop-based FAPR, droop derivative-based FAPR, and virtual synchronous power (VSP)-based FAPR. A novel setup for PHIL-based performance evaluation of these strategies is proposed. The setup combines the advanced modeling and simulation functions of a real-time digital simulation platform (RTDS), an external programmable unit to implement the studied FAPR control strategies as digital controllers, and actual hardware. The hardware setup consists of a grid emulator to recreate the dynamic response as seen from the interface bus of the grid side converter of a power electronic-interfaced device (e.g., type-IV wind turbines), and a mockup voltage source converter (VSC, i.e., a device under test (DUT)). The DUT is virtually interfaced to one high-voltage bus of the electromagnetic transient (EMT) representation of a variant of the IEEE 9 bus test system, which has been modified to consider an operating condition with 52% of the total supply provided by wind power generation. The selected and programmed FAPR strategies are applied to the DUT, with the ultimate goal of ascertaining its feasibility and effectiveness with respect to the pure software-based EMT representation performed in real time. Particularly, the time-varying response of the active power injection by each FAPR control strategy and the impact on the instantaneous frequency excursions occurring in the frequency containment periods are analyzed. The performed tests show the degree of improvements on both the rate-of-change-of-frequency (RoCoF) and the maximum frequency excursion (e.g., nadir).

Coulomb-actuated microbeams revisited: experimental and numerical modal decomposition of the saddle-node bifurcation

Electrostatic micromechanical actuators have numerous applications in science and technology. In many applications, they are operated in a narrow frequency range close to resonance and at a drive voltage of low variation. Recently, new applications, such as microelectromechanical systems (MEMS) microspeakers (µSpeakers), have emerged that require operation over a wide frequency and dynamic range. Simulating the dynamic performance under such circumstances is still highly cumbersome. State-of-the-art finite element analysis struggles with pull-in instability and does not deliver the necessary information about unstable equilibrium states accordingly. Convincing lumped-parameter models amenable to direct physical interpretation are missing. This inhibits the indispensable in-depth analysis of the dynamic stability of such systems. In this paper, we take a major step towards mending the situation. By combining the finite element method (FEM) with an arc-length solver, we obtain the full bifurcation diagram for electrostatic actuators based on prismatic Euler-Bernoulli beams. A subsequent modal analysis then shows that within very narrow error margins, it is exclusively the lowest Euler-Bernoulli eigenmode that dominates the beam physics over the entire relevant drive voltage range. An experiment directly recording the deflection profile of a MEMS microbeam is performed and confirms the numerical findings with astonishing precision. This enables modeling the system using a single spatial degree of freedom.

Stability analysis of fractional-order systems with randomly time-varying parameters

This paper is concerned with the stability of fractional-order systems with randomly timevarying parameters. Two approaches are provided to check the stability of such systems in mean sense. The first approach is based on suitable Lyapunov functionals to assess the stability, which is of vital importance in the theory of stability. By an example one finds that the stability conditions obtained by the first approach can be tabulated for some special cases. For some complicated linear and nonlinear systems, the stability conditions present computational difficulties. The second alternative approach is based on integral inequalities and ingenious mathematical method. Finally, we also give two examples to demonstrate the feasibility and advantage of the second approach. Compared with the stability conditions obtained by the first approach, the stability conditions obtained by the second one are easily verified by simple computation rather than complicated functional construction. The derived criteria improve the existing related results.

Cone-Copositive Lyapunov Functions for Complementarity Systems: Converse Result and Polynomial Approximation

This article establishes the existence of Lyapunov functions for analyzing the stability of a class of state-constrained systems, and it describes algorithms for their numerical computation. The system model consists of a differential equation coupled with a set-valued relation which introduces discontinuities in the vector field at the boundaries of the constraint set. In particular, the set-valued relation is described by the subdifferential of the indicator function of a closed convex cone, which results in a cone-complementarity system. The question of analyzing stability of such systems is addressed by constructing cone-copositive Lyapunov functions. As a first analytical result, we show that exponentially stable complementarity systems always admit a continuously differentiable cone-copositive Lyapunov function. Putting some more structure on the system vector field, such as homogeneity, we can show that the aforementioned functions can be approximated by a rational function of cone-copositive homogeneous polynomials. This later class of functions is seen to be particularly amenable for numerical computation as we provide two types of algorithms for precisely that purpose. These algorithms consist of a hierarchy of either linear or semidefinite optimization problems for computing the desired cone-copositive Lyapunov function. Some examples are given to illustrate our approach.

Event-triggered positive l1-gain non-fragile filter design for positive Markov jump systems

This paper is concerned with the event-triggered positive l 1 -gain non-fragile filter design of positive Markov jump systems. By using the upper and lower bounds of the error vector of system measurement outputs, the positive l 1 -gain filtering system to be designed is transformed into interval uncertain systems. Combining linear Lyapunov functions and linear programming, the positivity and stability of such systems can be obtained. Then, the proposed approach is developed to investigate positive l 1 -gain additive and multiplicative non-fragile filters, respectively. Furthermore, two classes of non-fragile positive filters are proposed for positive Markov jump systems with incomplete measurements and sensors saturation, respectively. Finally, two examples are provided to verify the effectiveness of the proposed design.

Dispersing insoluble yolk low-density lipoprotein (LDL) recovered by complexing with carboxymethylcellulose (CMC) for the nanoencapsulation of hemp cannabidiol (CBD) through emulsification at neutral pH

Insoluble yolk low-density lipoprotein (LDL) recovered by complexing with carboxymethylcellulose (CMC) was studied as an encapsulation agent for nanoencapsulation formulation at neutral pH. The effect of emulsifier and defatting on the dispersibility of the LDL-CMC complex was investigated. A novel dispersion containing partially defatted LDL, CMC, low quantity of Tween 80 and sodium lauryl sulfate (SLS) were successfully created and investigated for encapsulating lipophilic terpenes-cannabidiols mixture (TP-CBD) and crystalline CBD. The stability of such system under different environmental stresses was also evaluated. The defatting of LDL played an important role and the combination of Tween 80 and SLS synergistically improved the dispersibility of LDL-CMC complex. Non-defatted and fully defatted LDL did not fully disperse even with the assistance of Tween 80 and SLS (at 2,000 ppm each). Partially defatted LDL (average fat content of 42%) could be fully dispersed, while LDL with 25% fat had lower dispersibility. The 2% LDL (42% fat) dispersed with Tween 80 and SLS at 1,000 ppm each of the emulsifiers was identified as an excellent encapsulation system. TP-CBD and pure crystalline CBD nanoencapsulations were successfully formulated and found to be stable (no phase separation) under ambient condition and after freeze-thawing and heating (10 min at 90 °C), although instrumental measurement of their turbidity and particle size varied. Low viscosity of a carrier oil for pure CBD is preferred and medium chain triglyceride (MCT) resulted in better nanoencapsulations compared to vegetable oils such as high oleic soybean oil. Overall, a novel encapsulation system was developed, and crystalline CBD was successfully encapsulated within the LDL particles.

Asymptotic properties and stabilization of a neutral type system with constant delay

The problem of obtaining sufficient conditions for the asymptotic stability for a certain class of linear systems of a neutral type with constant delay is analyzed in the article. Some coefficients of these systems in the right side have an exponential factor. As a consequence, the study of the stability of such systems with the help of the Lyapunov—Krasovskii functionals is not possible; methods of receiving asymptotic appreciations lead to extremely rough results. By applying the apparatus of difference systems and the properties of simpler systems, which the author examined previous, sufficient conditions for the exponential stability of such systems are obtained. As an example, a second-order system is considered. The graphs of the solutions of the corresponding system, both without neutral members and with the original system where the right-hand side contains neutral terms, are provided. On the basis of theory difference systems, the author proposes an algorithm of stabilization for some systems of a similar type.

Дослідження стійкості та збіжності децентралізованої координації локальних систем управління розподіленими кібер-фізичними системами

The use of decentralized coordination of state control of distributed cyber-physical systems with continuous objects, in which, in addition to the physical interaction of the elements of a continuous object, there is information interaction of local coordinators as part of agents of a multi-agent system, leads to the formation of multi-loop control systems. The features of decentralized coordination control of such systems (nonlinearity of coordinators, mutual physical impact of the elements of the object, the presence of production costs of the accumulated resource, which determines the state of the elements, etc.) necessitate additional studies of the stability of the system and the convergence of the coordination process. The aim of the work is to study the conditions of stability and convergence of decentralized coordination of a distributed cyber-physical control system with a wave coordination method. A condition for the stability of such systems is obtained. The model of a system of two connected controllable elements and local control systems has been developed. The transfer function of the system is obtained using the method of equivalent transformations. It is shown that in the absence of coordination, such system is stable under the condition of attenuation under the propagation of influences on the elements of a continuous object. The stability and convergence of decentralized coordination of local control systems with the wave coordination method based on a simulation model is investigated using the example of three-element systems. The simulation model was created in the Scilab/Xcos system. As a result of the studies, it was shown that although the system is stable, the state of the object's elements coincides with the specified one, however, the duration of the coordination process significantly exceeds the duration of the transient processes of individual elements. Further research is supposed to be directed at the proof the hipotesis that the stability of the system independent of the number of controlled elements of a continuous object and studying the conditions for the stability of active systems (with an increase in the influence in the process of propagation).

Structural Analysis of Large-Scale Socio-Technical Systems Based on the Concept of Influence

Abstract The paper is devoted to studying the stability of complex systems, which include diversified and heterogeneous elements. In order to analyze the stability of such systems, it is proposed to develop the process of dynamic determination of the main factors. For this purpose, this paper uses a variant of cognitive modeling based on the concept of “influence”. The proposed approach implies, in a sense, a broader view of the concept of the “fuzzy cognitive map” introduced by B. Kosko. “Influence” does not mean “causality”, allows a broader interpretation range, and is calculated in a special way that makes it possible to prove rigorous theorems. A complex system is represented as a digraph, and the selection of the main factors is proposed to be based on the concept of “influence”, which is introduced as follows. All nodes of the graph are assigned an abstract property “significance”, which allows you to compare heterogeneous factors, and a particular computational procedure is introduced that allows this “significance” to be calculated. The “influence” of factors on each other is defined as a mathematically formalized response in accordance with the introduced computational procedure of the “significance” of the studied factor to the variation in the “significance” of input factors. For example, the analysis of the sustainability of a large-scale model of the Russian economy in terms of the strength of the “influence” is provided.

Dynamic and Information Properties of Intelligent Control Systems

The paper considers the dynamic and informational properties of intelligent systems. The relationship is established between control quality and stability in such systems. The method was developed and a study was conducted of the dependence of the control quality and the time spent by the human operator on the evaluation of the test image. The influence of the clean delay time on the stability margin and the quality of the setting process is studied. The study shows that in intelligent systems that work in connection with a human-operator (a group of people) or independently, the time spent (a latent period) to implement thinking forms affects on the one hand the control quality, on the other the system stability. The desired value clean delay time is set. The research results are presented. The new parameter of information properties of intelligent systems has been introduced – the control quality.

Stability Evaluation of AC/DC Hybrid Microgrids Considering Bidirectional Power Flow Through the Interlinking Converters

The bidirectional power flow through the interlinking converter (IC), in ac/dc hybrid microgrids (HMGs) consisting of distributed generators (DGs) with droop controllers, plays an important role on the stability of such systems during islanding. This paper investigates the impact of the power flow direction on the small-signal stability of islanded droop-based HMGs. Firstly, a linearized state-space model of an HMG is developed. Secondly, eigenvalue analysis is carried out to realize the dominant modes, which are the rightmost eigenvalues. Thirdly, participation factor analysis is performed to identify the system and control parameters that effect stability the most. Lastly, sensitivity analysis is conducted to determine the critical droop gains and stability margin. It is observed from the eigenvalue and sensitivity analysis that the dominant modes of HMGs become more stable as more power flows from dc to ac subgrid. On the contrary, an increase in the power flow from ac to dc subgrid degrades the HMG stability. Additionally, the sensitivity of the dominant modes to changes in ac and dc droop gains is studied under bidirectional power flow through the IC to ascertain their impact on the stability margins. Finally, time-domain simulations, in MATLAB/Simulink, suggest that more generation on the dc subgrid would enhance the overall HMG stability margin during islanding.

Systematic stability analysis, evaluation and testing process, and platform for grid-connected power electronic equipment

The proportion of grid-connected power electronic equipment is already large enough to influence the dynamic characteristics of the modern power system. Ensuring the stability of grid-connected power electronic equipment in all relevant situations is one of the foundations for reliable power system operation. In contrast to conventional rotating machines, the stability of power electronic devices mostly depends on the applied control strategy, and a large diversity of different complex control strategies are in practical use. Also, the investigation of stability of such systems needs to take into account the non-linear behaviour of the power electronic equipment. These are the main reasons why the system behavior of grid-connected power electronic equipment cannot be reproduced satisfactorily when aplying a single method of stability analysis, evaluation and testing method. During the last years, faults which led to tripping of converters due to stability problems occurred frequently even though standardized fault compliance tests were performed on these converters. In this paper these stability issues are analyzed. Also, a three-dimensional stability analysis method is suggested in order to comprehensively cover system behavior. The three dimensions are the time/scale dimension, the equipment number dimension and the local or global range of the stability analysis dimension. Based on this three-dimensional framework, this paper proposes a stability evaluation as well as a test process applying a hardware-in-the-loop test concept. Through the verification and testing of the stability of the actual grid-connected power electronic equipment, the method proposed in this paper is verified for up-to-date equipment.

Robust stability of uncertain fractional order systems of neutral type with distributed delays and control input saturation

Time delay occurs naturally due to the limited bandwidth of any real-world system. However, this problem can deteriorate the system performance and can even result in system instability. Input saturation is also an essential issue due to the energy constraint in real actuators that makes the control design procedure more difficult. This article concerns with the stability of uncertain fractional order (FO) delay systems of neutral type including structured uncertainties, distributed delays and actuator saturation. A Lyapunov–Krasovskii functional allows the formulation of the conditions to insure the asymptotic robust stability of such systems via the linear matrix inequalities (LMI) and to compute the gain of a state feedback controller. In addition, by using the cone complementarity linearization method, we obtain the controller gains that extend the domain of attraction. Several simulations validate the theoretical analysis.

Stability of fluid flows coupled by a deformable solid layer

Abstract

On thermal stability of cryovacuum deposited CH4+H2O films

Whereas stable homogenous states of aqueous hydrocarbon solutions are typically observed at high temperatures and pressures far beyond the critical values corresponding to individual components, the stability of such system may be preserved upon transition into the region of metastable states at low temperatures and low pressures. This work is dedicated to the study of the thermal stability of a water-methane mixture formed by cryogenic vapor phase deposition. The obtained thin films were studied using vibrational spectroscopy in the temperature range of 16–180 K. During thermal annealing of the samples, characteristic vibrational C–H modes of methane were monitored alongside the chamber pressure to register both structural changes and desorption of the film material. The obtained results reveal that upon the co-deposition of methane and water, methane molecules appear both in non-bound and trapped states. The observed broadening of the characteristic C–H stretching mode at 3010 cm−1 upon an increase in temperature of the sample from 16 to 90 K, followed by narrowing of the peak as the temperature is reduced back to 16 K, indicates localization of methane molecules within the water matrix at lower temperatures.

Precise Exciton Management of Quaternary Emission Layers for Highly Stable Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence.

Simultaneous achievement of both high electroluminescence efficiency and high operational stability in organic light-emitting diodes (OLEDs) is required for their use in various practical applications. Although OLEDs based on thermally activated delayed fluorescence-assisted fluorescence (TAF) are considered to possess a promising device architecture to exploit the full potential of OLEDs, the operational stability of such systems still requires further improvement. In this study, a quaternary emission layer consisting of a combination of TAF and mixed-host systems is developed. OLEDs containing this emission layer show improved operational stability through the management of exciton generation processes while maintaining high electroluminescence efficiency. Furthermore, a gradient of the mixed ratio of the co-host matrix is used to optimize the recombination zone profile in the emission layer, leading to 17 times improvement of the operational lifetime compared with that of the corresponding single-host-based device. This research provides a simple and general method to develop highly stable TAF-OLEDs.

Consensus Tracking of Data-Sampled Nonlinear Multi-Agent Systems With Packet Loss and Communication Delay

This paper investigates the tracking consistency regulation of high-order multi-agent systems (MASs) subject to Lipschitz nonlinear perturbations. Rooting at the leader node, the interagent interaction is described by a directed graph that contains a directed spanning tree. On designing the tracking protocol, an aperiodic data sampling scheme is introduced such that in-neighbors' information can be aperiodically sampled and transmitted via broadcast channels, where packet loss and communication delay are unavoidably existent. Thanks to algebraic graph theory and Lyapunov-Krasovskii functional technique, the concerned consensus tracking issue is cast into asymptotically stabilizing a class of switched nonlinear systems which consist of delayed and non-delayed components. It is proved that, moreover, the asymptotic stabilization of such systems essentially depends on packet loss characteristics. By explicitly characterizing the interplay among sampling interval, communication delay and network structure, consensualization criteria are formulated within the linear matrix inequality (LMI) framework. The design method is validated by numerical simulations.

Non-linear dynamics of single phase rectangular natural circulation loop

The future nuclear reactors are being engineered to function completely on the phenomena of thermosiphoning. These reactors are equipped with various natural circulation-based systems which offer several benefits. The linear stability analysis examines the stability for such systems for small perturbations. If perturbations are slightly large, linear stability fails to fathom the stability of the system. In such cases, it becomes imperative to perform non-linear stability analysis. In the present work, a rectangular natural circulation loop has been simulated for small as well as large perturbations to underscore the importance of non-linear stability analysis. The key objectives of the present work include identification of the subcritical Hopf bifurcation and unravelling the repercussions of larger perturbation on the system in each region of the parametric space. The unfolding of dynamics from unstable limit cycles to chaos and then back to stable fixed points have been investigated through numerical simulations.