Stability Of Such Systems Research Articles

A Systematic Stability Enhancement Method for Microgrids With Unknown-Parameter Inverters

With massive electronic inverters, microgrids are threatened by the instability problems caused by the impedance interactions among inverters and the network. For the microgrids with black-box inverters (whose parameters are unknown due to industry secrets), it is hard to assess, much less enhance, the stability of such systems. This article proposes a systematic impedance-based stability assessment and enhancement method for the microgrids with black-box inverters. First, the return-ratio matrix <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">net</sub> of the system with both current-controlled and voltage-controlled inverters is formulated based on the nodal admittance matrix. And then, the sensitivities of the critical eigenvalues of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">net</sub> are calculated with respect to individual admittances/impedances of inverters, which can identify the “trouble maker(s).” Moreover, the low voltage active damper (LVAD) is proposed for the stability enhancement of the system. An eigenvalue perturbation sensitivity analysis method is presented to calculate the sensitivities of the critical eigenvalues with respect to nodal parallel admittances, which identifies the optimal installation position for LVAD, and accordingly provides the guidance for the design of LVAD. The effectiveness of the proposed method is verified using a modified IEEE 6-bus system in PSACD/EMTDC and RT-Lab platforms.

Global fractional Halanay inequalities approach to finite-time stability of nonlinear fractional order delay systems

In this paper, we investigate the robust finite time stability of fractional order systems with time varying delay and nonlinear perturbation. We improve the sufficient condition for general fractional delay systems by utilizing the special structure of a singular Gronwall inequality. For stable fractional delay systems, our approach bases on a global Halanay type inequality in differential and integral forms. A sharper delay dependent sufficient condition for robust finite time stability of such systems is formulated in terms of the Mittag-Leffler functions and the delayed size. The connection between the new sufficient condition and the previous results is compared and discussed thoroughly.

Dynamic stabilization for a cascaded beam PDE–ODE system with boundary disturbance

We are concerned with the dynamic stabilization for a cascaded Euler–Bernoulli beam (EBB) partial differential equation (PDE)–ordinary differential equation (ODE) system subject to boundary control and matched internal uncertainty and external disturbance. State feedback stabilization of such system without disturbance has been recently discussed by X.H. Wu, H. Feng (Sci China Inf Sci, 2022, 65(5): 159202). An infinite‐dimensional disturbance estimator is constructed in order to estimate the total disturbance. By compensating the total disturbance, we design a state observer to trace the state and then an estimated state and estimated total disturbance‐based output feedback control law. It is proved that the original system is exponentially stable, and other states of the closed‐loop are bounded. Some numerical simulations are presented.

Combining π-Conjugation and Cation-π Interaction for Water-Stable and Photoconductive One-Dimensional Hybrid Lead Bromide.

Hybrid lead halide perovskites and their derivatives are important optoelectronic materials but suffer from water instability. Combining both the optoelectronics and the water stability of such systems is a major challenge in material design today. To address this issue, we employ the well-known π-conjugation and cation-π interaction concepts in designing a hybrid lead halide perovskite derivative system. (4,4'-VDP)Pb2Br6 (VDP = vinylenedipyridinium) single crystals are prepared. They have a one-dimensional (1D) arrangement of inorganic Pb-Br sublattices connected via the 4,4'-VDP organic sublattice. The π-conjugation in the 4,4'-VDP sublattice allows electronic communication between the 1D Pb-Br units, reducing the band gap and improving the photoconductivity. Importantly, N+ of one 4,4'-VDP molecular ion interacts with the π-electron cloud of the adjacent one. This intermolecular cation-π interaction extends throughout the organic sublattice, making the hybrid crystal stable when stored under water for more than a year without requiring any encapsulations.

A novel approach to stability analysis of a wide class of irrational linear systems

This paper presents a general methodology for finding stability equivalence regions, of a wide class of linear time-invariant systems with irrational transfer functions, inside a parametric space. The proposed methodology can be applied to distributed-parameter, time-delay and fractional systems. Unlike rational transfer functions which have only a finite number of poles, irrational transfer functions may generally possess an infinite number of poles, branch points and even essential singularities. Due to this, stability of such systems is more difficult to analyze. Two variants of the new methodology are presented. The first one analyzes stability equivalence along a curve in the parametric space, starting from a given parametric point. The second one finds the maximal stability equivalence region in the parametric space around a given parametric point. Both methodologies are based on iterative application of Rouché’s theorem. They are illustrated on several examples, including heat diffusion equation and generalized time-fractional telegrapher’s equation, which exhibit special functions such as \(\sinh \) and \(\cosh \) of \(\sqrt{s}\), the Laplace variable of order 0.5.

Safety-Critical Control for Systems With Impulsive Actuators and Dwell Time Constraints

This paper presents extensions of control barrier function (CBF) and control Lyapunov function (CLF) theory to systems wherein all actuators cause impulsive changes to the state trajectory, and can only be used again after a minimum dwell time has elapsed. These rules define a hybrid system, wherein the controller must at each control cycle choose whether to remain on the current state flow or to jump to a new trajectory. We first derive a sufficient condition to render a specified set forward invariant using extensions of CBF theory. We then derive related conditions to ensure asymptotic stability in such systems, and apply both conditions online in an optimization-based control law with aperiodic impulses. We simulate both results on a spacecraft docking problem with multiple obstacles.

The Electrochemical Stabilization of Silicon Anodes via a Locally Concentrated LiNO3 Complex

The solid electrolyte interphase (SEI) plays an integral role in regulating the stability of lithium-ion batteries, particularly those employing next-generation anode materials like lithium (Li)-metal or silicon (Si). Herein, a locally concentrated additive framework is designed to incorporate a LiNO3 sacrificial additive into conventional carbonate-containing electrolytes to heighten electrochemical stability in such systems. Though LiNO3 is effectively insoluble in carbonate solvents, it is introduced in moderate amounts to the electrolyte in the form of a highly concentrated diglyme complex, which is then dispersed and diluted throughout the bulk carbonate electrolyte in a homogenous, liquid, phase-stable solution. The addition of this additive complex considerably enhances the electrochemical stability of 4 V systems containing Li-metal or Si anodes over the course of cycling as well as during potentiostatic holds. It is shown that the sacrificial reduction of LiNO3 leads to the formation of favorable nitrogen-containing species on the surface of Si, like what is known to occur with Li-metal. However, the initial deposition of these products is found to transform the SEI towards having greater inorganic character overall, with significantly more embedded LiF throughout. These insights expand our understanding of electrolyte and SEI design for electrochemically resilient next-generation anode systems.

Investigating the participation of battery energy storage systems in the Nordic ancillary services markets from a business perspective

Battery energy storage systems (BESSs) are gaining potential recognition in renewable-based power systems. To maintain the stability of such systems, BESSs units are being deployed for the provision of ancillary services (ASs). For BESS owners, it is vital to assess the business value of providing ASs to engage in a profitable trade. However, studies so far have mainly focused on the operational control of BESS units in ancillary services markets (ASMs) while ignoring investigations from a business viewpoint. Therefore, in this paper, we analyse the BESS-based provision of Nordic ASs from a BESS-business perspective. To this aim, we identify the profitable bidding hours for the BESS units by investigating hourly patterns in the market prices of the past six years. We also analyse the monthly and yearly trends in historic price datasets of ASs to help BESS owners develop long-term business plans. Moreover, for the BESS owners to choose between different markets, we investigate the revenue streams associated with each ASs and determine the yearly income from their availability and capacity payments. Our findings imply that BESS business viability in the Nordic ASMs can be increased by stacking ASs based on their availability payments, energy content, and activation requirements.

A direct analysis method to globalh‐stability of delayed time‐varying nonlinear positive systems

SummaryThis paper focuses on the global ‐stability of the nonlinear positive system with multiple time‐varying delays. Through differentiated expressions of the function , the global ‐stability could be referred to as several known stabilities, including Lagrange stability, asymptotic stability, global exponential stability, global practical stability, and so forth. By proposing a direct analysis method that differs from the so‐called Lyapunov‐Krasovskii functional method, we presented a sufficient condition for the global ‐stability of such system. The obtained stability condition appeared in the form of a number of simple inequalities, which could be easily handled by the toolbox YALMIP loaded in MATLAB. The applicability of our results have been illustrated by three numerical examples.

Stable secure key distribution scheme via orthogonal polarizations and a joint source-channel model.

Optical secure key distribution (SKD) based on reciprocity has been the subject of increasing discussion, for its inherent information-theoretic safety and because there is less occupation of fiber channels. The combination of reciprocal polarization and broadband entropy sources has proven effective in increasing the rate of SKD. However, the stabilization of such systems suffers from the limited span of polarization states and inconsistent polarization detection. The specific causes are analyzed in principle. To solve this issue, we propose a strategy for extracting secure keys from orthogonal polarizations. Optical carriers with orthogonal polarizations at interactive parties are modulated by external random signals using polarization division multiplexing dual-parallel Mach-Zehnder modulators. After bidirectional transmission through a 10-km fiber channel, error-free SKD with a rate of 2.07 Gbit/s is experimentally realized. The high correlation coefficient of the extracted analog vectors can be maintained for over 30 min. The proposed method is a step toward the development of secure communication with high speed and feasibility.

Differential scanning calorimetry investigation of crystallization kinetics and glass-forming ability of sulfonamides

Robust determination of the parameters governing the stability of the amorphous drugs is one of the key tasks of modern pharmaceutics. The kinetic stability of such systems is of crucial importance, as it affects their practical applications. In the present work we have determined the critical cooling rates, and the kinetic parameters of the cold crystallization of four slowly crystallizing sulfonamides, i.e. sulfaguanidine, sulfapyridine, sulfalene, and sulfadimidine. The Nakamura crystallization model was shown to have a good prognostic ability, as it allows determination of the stability time profile of the drug systems prone to crystallization from the non-isothermal thermokinetic data.

Threshold for Blowup and Stability for Nonlinear Schrödinger Equation with Rotation

We consider the focusing NLS with an angular momentum and a harmonic potential, which models Bose–Einstein condensate under a rotating magnetic trap. We give a sharp condition on the global existence and blowup in the mass-critical case. We further consider the stability of such systems via variational method. We determine that at the critical exponent $$p=1+4/n$$ , the mass of Q, the ground state for the NLS with zero potential, is the threshold for both finite time blowup and orbital instability. Moreover, we prove a sharp threshold theorem for the rotational NLS with an inhomogeneous nonlinearity. The analysis relies on the existence of ground state as well as a virial identity for the associated kinetic-magnetic operator.

Robustification of stabilizing controllers for ODE-PDE-ODE systems: A filtering approach

In this paper, we present a filtering technique that robustifies stabilizing controllers for systems composed of heterodirectional linear first-order hyperbolic Partial Differential Equations (PDEs) interconnected with Ordinary Differential Equations (ODEs) through their boundaries. The actuation is either available through one of the ODE or at the boundary of the PDE. The proposed framework covers a broad general class of interconnected systems. Assuming that a stabilizing controller is available, we derive simple sufficient conditions under which appropriate low-pass filters can be combined with the control law to robustify the closed-loop system. Our approach is based on a rewriting of the distributed dynamics as a delay-differential algebraic equation and an analysis in the Laplace domain. The proposed technique will simplify the design of stabilizing controllers for the class of systems under consideration (which can now be done only on a case-by-case basis due to the complexity and generality of the underlying interconnections) since it dissociates the stabilization problem from the robustness aspects. Indeed, it becomes possible to use convenient (but non-robust) techniques for the stabilization of such systems (as the cancellation of the boundary coupling terms or the inversion of the ODE dynamics), knowing that the resulting control law can be made robust (to delays and uncertainties) using the proposed filtering methodology.

Solid state fiber-dye sensitized solar cells (SS-FDSSC): A mini review

Fiber-shaped dye-sensitized solar cells (FDSSC) can fulfill the energy demand of portable electronic devices, specifically in remote applications; however, the stability of such systems is a bottleneck, due to the use of liquid electrolytes. Liquid electrolytes pose evaporation problem, leakage issue, and possibility of short circuit, hence solid electrolytes are the ultimate solution for long-lasting FDSSCs. Considering this, recent advances in solid electrolytes, photoanode materials, and counter electrode materials are summarized for all solid-FDSSCs. A special focus has been given to the types of solid electrolytes, their synthesis, and associated photovoltaic performance. The performance parameters of solid electrolytes, such as ionic conductivity, light transmittance, and photovoltaic performance are summarized in this review. Furthermore, the works related to novel photoanode and counter electrode materials employing solid electrolytes are also included in the review. A comparison table of power conversion efficiencies and lifetime of solid-state-FDSSCs is provided, which shows that the highest efficiency is possible for Li-TFSI (bis(trifluoromethane)sulfonimide lithium salt) soaked Iodide electrolytes. Better transparency and conductivity of such electrolytes are key parameters in imparting high efficiency of such electrolytes, i.e. 6.5%.

Sedimentation of Microparticles in Highly Concentrated Non-Newtonian Emulsions

From the perspective of many industrial products, it is important that no phase separation occurs over time, as this affects their quality. Therefore, every effort is made to maintain the stability of the systems by the addition of various stabilizers, but additional artificial ingredients often discourage consumers. However, there is another alternative possibility to maintain the stability of such systems by consciously controlling the parameters of liquids and solids, based on the knowledge of the mechanisms occurring between the components. This is of immeasurable importance also in cases where multicomponent systems need to be separated, which is particularly important in chemical engineering and environmental engineering. The paper presents an experimental study of the solids-sedimentation process in highly concentrated, stable emulsions that exhibit the properties of non-Newtonian liquids. A study based on turbidimetric techniques is presented in which the influence of both solids (average grain diameters 150–700 μm and concentration 0.2–0.4 g/mL) and emulsion parameters (concentration 60–70% and average droplet diameters of 8.24–15.72 μm) were taken into account. The occurring phenomena have been also explained. As a result, the dependence of system parameters on the intensity of the sedimentation process was determined. This can be of great practical importance in product design in the chemical, food, pharmaceutical, or even cosmetic industry.

Multi‐Responsive Jammed Micro‐Gels Ink: Toward Control over the Resolution and the Stability of 3D Printed Scaffolds

Abstract3D printing of hydrogels usually relies on a combination of fine‐tuned material chemistry and polymer chain architecture to obtain an ink with adequate yield‐stress flow, shear‐thinning, and self‐healing behavior. Recent approaches in hydrogel ink design include introduction of reversible covalent or supramolecular bonds or jamming of microparticles into a granular hydrogel. However, the dimensional stability of such systems is typically afforded by a post‐printing covalent cross‐linking step that impedes further on‐demand degradation of the scaffolds. Here, a jammed micro‐gels ink made of thermosensitive poly(N‐isopropylacrylamide) micro‐gels incorporating terpyridine ligand linkers are proposed as a 3D printable ink that is cured post‐printing by iron (II) cations for long‐term stabilization. The uncross‐linked micro‐gels ink exhibits the rheological characteristics of granular materials, meaning yield‐stress, shear‐thinning and fast recovery. Upon curing, iron (II)‐bis‐terpyridine coordination complexes between neighboring micro‐gels are formed. The supramolecular bonds are sufficiently strong and long‐lived to maintain scaffold integrity during manual handling or immersion in liquid medium for over two months. The thermosensitivity of the micro‐gels endows the printed construct with reversible and cyclable temperature‐induced resolution enhancement, while the supramolecular cross‐linking provides an asset of disintegration on‐demand. The proposed micro‐gel scaffolds are biocompatible, revealing the potential for biomedical applications and 4D bioprinting.

A formula for the Bohl exponent of discrete time-varying systems

In this note, a formula for the Bohl exponent of a discrete system with slowly varying coefficients was proved. This formula expresses the Bohl exponent through the eigenvalues of the coefficients. Based on these formulae a necessary and sufficient condition for uniform exponential stability of such systems are also presented.

Zeta potential and particle size in dispersions of alumina in 50–50 w/w ethylene glycol-water mixture

HypothesisDispersions of solid particles in glycols and in their mixtures in water have been proposed as promising heat transfer fluids, and the zeta potentials in such systems are often reported. We challenge a popular approach in which high absolute value of zeta potential implies excellent stability in such systems. ExperimentsNanoparticles of alumina were dispersed in 50–50 ethylene glycol-water mixture, and zeta potential and particle size were studied as a function of concentration of various solutes. FindingsAddition of HCl and CTMABr induced positive zeta potentials. A maximum value of about 120 mV was obtained at CTMABr concentration of about 10−5 M, and further increase in the concentration of the surfactant had moderate effect on the zeta potential. A maximum value of about 120 mV was obtained at HCl concentrations of 10−5 - 10−4 M, and further increase in the HCl concentration led to depression of the zeta potential. Addition of NaOH and KOH, and of anionic surfactants induced negative zeta potentials. With NaOH and KOH the maximum negative zeta potential of − 60 mV was obtained at base concentration of about 10−3 M, and increase in the base concentration to 10−2 M had moderate effect on the zeta potential. Negatively charged particles showed substantial aggregation in spite of high negative zeta potentials.

Inherent stability analysis for multibody systems with semi-active inerters

Inherent stability reflects the reliability performance of a semi-active control system, where for “active” semi-active inerter-based systems, the inherent stability problem has not been studied. The motivation of this paper is to present sufficient conditions that ensure inherent stability for such systems. The absolute stability theory is adopted, and the general multibody system with semi-active inerters is formulated in a Lurè form. Sufficient conditions are derived based on the circle criterion for three different cases including the case with only one semi-active inerter, the case with several semi-active inerters without common connection points, and the case with several semi-active inerters where the ground is the common connection point. Extensive numerical examples based on low-degree-of-freedom systems are provided to show the effectiveness of the derived conditions.

Advances, Challenges and Future Trends of Cell-Free Transcription-Translation Biosensors.

In recent years, the application of cell-free protein synthesis systems in biosensing has been developing rapidly. Cell-free synthetic biology, with its advantages of high biosafety, fast material transport, and high sensitivity, has overcome many defects of cell-based biosensors and provided an abiotic substitute for biosensors. In addition, the application of freeze-drying technology has improved the stability of such systems, making it possible to realize point-of-care application of field detection and broadening the application prospects of cell-free biosensors. However, despite these advancements, challenges such as the risk of sample interference due to the lack of physical barriers, maintenance of activity during storage, and poor robustness still need to be addressed before the full potential of cell-free biosensors can be realized on a larger scale. In this review, current strategies and research results for improving the performance of cell-free biosensors are summarized, including a comprehensive discussion of the existing challenges, future trends, and potential investments needed for improvement.