Terms Of System Stability Research Articles

Gas Sensing by Metal and Nonmetal Co-Doped Graphene on a Ni Substrate

Gas sensors based on graphene are gaining more and more attention. The unique properties of the single-atom-thick, flexible, robust, and quanta-sensitive graphene make it an excellent candidate for sensors. However, its characteristics can be modified to suit specific applications by means of metal and nonmetal doping. In this systematic and detailed study, with the aid of density functional theory (DFT)-based simulations, we investigate the gas sensing capabilities of trapped transition-metal (TM) atoms at the graphene double vacancy (2VG). Eight different gas molecules, ranging from electron acceptors (Lewis acids) to donor species (Lewis bases), are investigated, namely, O2, NO2, NO, CO2, SO2, H2O, NH3, and CO. Four TM atoms Fe, Co, Ni, and Cu are considered as active sites for gas sensing. The effects of N-doping and the Ni(111) substrate are also examined. The performance of these systems in terms of stability, sensitivity, selectivity, and reusability is discussed for practical applications.

SAR performance-based fault diagnosis for electro-hydraulic control system: A novel FDI framework for closed-loop system

Model-based fault diagnosis serves as an efficient and powerful technique in addressing fault detection and isolation (FDI) issues for control systems. However, the standard methods and their modifications still encounter some difficulties in algorithm design and application for complex higher-order systems. To avoid these difficulties, a novel fault diagnosis framework based on multiple performance indicators of closed-loop control system is proposed. Under this framework, a so-called performance residual vector is constructed to measure the differences between the real system and the nominal model in terms of system stability, accuracy, and rapidity (SAR) respectively. The criteria for quantification, normalization of the SAR residuals and the explicit mappings between the thresholds and the required performance are given. FDI can be easily achieved simultaneously by monitoring the normalized residual vector length and direction in the SAR performance residual space. A case study on electro-hydraulic servo control system of turbofan engine is adopted to demonstrate the effectiveness of the proposed method.

Local synchronization of nonlinear dynamical networks with hybrid impulsive saturation control inputs

Under the hybrid impulsive control with actuator saturations, this paper studies the local synchronization problem of a class of nonlinear dynamical networks. However, the discontinuity caused by the impulsive effect and the saturation nonlinearity caused by the actuator saturation have brought great challenge to the theoretical analysis of such problems. Firstly, this paper uses mathematical induction to estimate the admissible set of the system state at the impulse instant, which is used to ensure that the saturation nonlinear problem can be dealt with by the sector nonlinear model method and the polyhedral representation method. Secondly, by constructing a suitable time-dependent Lyapunov-Krasovsknii functional (LKF), using Jensen’s inequality, Wirtinger-based inequality and the sector nonlinearity model approach, a sufficient condition has been derived, which guarantee the exponential stability of the synchronization error system in terms of linear matrix inequalities (LMIs). Thirdly, some synchronization criteria are obtained by using polytopic representation approach to deal with the saturation nonlinearity. Based on these criteria, the saturated impulsive and sampled-data controller is designed, and the region of attraction of the drive response error system is estimated. As a corollary, exponentially synchronization conditions and controller design are also presented for the nonlinear dynamical networks without actuator saturation. Finally, two numerical examples shows the effectiveness of the obtained results.

Управління фінансовою стійкістю банківської системи в контексті волатильності фінансового ринку

ms of a systematic approach and analysis of the financial stability of the banking system of Ukraine during 2018-2020, which allowed to draw conclusions about the impact of taking into account new factors of influence. A conceptual approach to improving the mechanism for managing the financial stability of the banking system in the context of financial market volatility, which is designed to ensure a sufficient level of financial stability of the banking system. Purpose. The aim of the article is to improve the conceptual approach to the mechanism of managing the financial stability of the banking system in the context of financial market volatility, which will prevent the development of long-term banking crises. Results. The article analyzes the state of financial stability of the banking system in terms of economic standards governing banks, indicators of financial stability and the index of financial stress. A conceptual approach to improving the mechanism of managing the financial stability of the banking system in the context of financial market volatility is proposed. Management will be improved in such areas as: creation of legislative and other conditions that would allow banking institutions to realize their economic interests; establishing economic standards and supervising their observance in order to ensure the liquidity of banking activities; use of more indicators of financial stability of the banking system. Conclusions. The application of this conceptual approach will allow on the basis of coordinated use of instruments to comprehensively affect financial stability avoiding, minimizing or compensating for possible threats in a dynamic financial environment. As the banking system will be able to respond quickly to financial threats and prevent negative phenomena that may lead to its financial failure stability.

Review on load frequency control for power system stability

Power system stability is the capability of power systems to maintain load magnitude within specified limits under steady state conditions in electrical power transmission. In modern days, the electrical power systems have grown in terms of complexity due to increasing interconnected power line exchange. For that, an inherent of controllers were essential to correct the deviation in the presence of external disturbances. This paper hence aims to review the basic concepts of power system stability in load frequency control. Various control techniques were analyzed and presented. Power system stability can be classified in terms of method to improve power system stability, which are rotor angle stability, frequency stability and voltage stability. It is found that each method has different purpose and focus on solving different types of problem occurred. It is hoped that this study can contribute to clarify the different types of power system stability in terms of where it occurs, and which is the best method based on different situation.

Dead-Zone ESO Based Sensorless Force/Position Control for Dynamic Contact Systems

In this paper, the sensorless force/position control problem is investigated for a general class of dynamic contact systems with both motion sensor noise and unknown kinetic friction by designing a force observer-based controller. Firstly, in order to suppress the effect of motion sensor noise, a dead-zone extended state observer (ESO) is introduced, and the contact force is estimated. Then, based on the force estimate, a controller is designed to realize force/position tracking control, where the parameters of the observer and controller are obtained by a linear matrix inequality (LMI) method. The sufficient conditions are provided to ensure the stability of the closed-loop system in terms of LMIs. Finally, a numerical simulation is carried out to illustrate the applicability and effectiveness of the proposed method.

A novel approach of order diminution using time moment concept with Routh array and salp swarm algorithm

In control engineering, there may be two systems that have the same input-output characteristic with differentdegrees of complexity. This concept leads to order diminution(OD) of a large scale system. In this article, the authorspropose a new hybrid order diminution technique based on the time moment matching method with the Routh arrayconcept and a recently developed fast and accurate salp swarm optimization (SSO) technique. The proposed methodcombines the advantages of both the classical method of OD and the optimization technique. The unknown coe?icient ofthe divisor of the reduced system is obtained by exploring the time moment matching methodology with the Routh arrayconcept, whereas the unknown coe?icients of dividend polynomial are obtained by the SSO technique. The time momentmatching with the Routh array ensures the nature of the system in terms of stability, and better search capability of theSSO technique reduces the error between the original and the diminished system. The proposed technique is tested ondifferent benchmark problems, including a time-delay system. An intensive comparative study in terms of different errors,time, and frequency domain provides better performance of the proposed method compared to the existing techniques. Agood match to the parameters of transient specifications indicates the success of this proposed technique. Comparatively,the matching of rise time, settling time, and maximum overshoots are 99.6076%,99.1611%, and 100%, respectively.

Stability Analysis upon High-Pressure Common Rail Fuel Injection System under Multiple Injection Modes

Fuel injection stability of high-pressure common rail fuel injection system (HPCRFIS) under multiple injection modes is a recognized technical problem. To explain it essentially, a numerical model based on bond graph method, which provides a standardized series of symbol system to describe various components in different physical fields as well as interactive effect analysis tool for different energy categories, was used to investigate the problem. As HPCRFIS is a typical nonlinear system with multi-physical coupling, it is very difficult to analyze system stability directly. Therefore, the system was linearized at typical moments. The system matrix for each typical moment was obtained thereby. To investigate the influential mechanism of system stability deeply, the variations of rank and eigenvalues distributions of state matrices were analyzed. The results show that the rank of state matrices changes abruptly when the needle or control valve moves. In terms of system stability, the oscillation characteristics are subject to the movement of needle or control valve. The ending of the former injection causes the system to show damping oscillation characteristics before the latter injection starts. The motion of control valve makes more contribution to system stability than that of needle, which could be concluded by Lyapunov stability criterion.

Design and Characterization of a Textile Electrode System for the Detection of High-Density sEMG.

Muscle activity monitoring in dynamic conditions is a crucial need in different scenarios, ranging from sport to rehabilitation science and applied physiology. The acquisition of surface electromyographic (sEMG) signals by means of grids of electrodes (High-Density sEMG, HD-sEMG) allows obtaining relevant information on muscle function and recruitment strategies. During dynamic conditions, this possibility demands both a wearable and miniaturized acquisition system and a system of electrodes easy to wear, assuring a stable electrode-skin interface. While recent advancements have been made on the former issue, detection systems specifically designed for dynamic conditions are at best incipient. The aim of this work is to design, characterize, and test a wearable, HD-sEMG detection system based on textile technology. A 32-electrodes, 15 mm inter-electrode distance textile grid was designed and prototyped. The electrical properties of the material constituting the detection system and of the electrode-skin interface were characterized. The quality of sEMG signals was assessed in both static and dynamic contractions. The performance of the textile detection system was comparable to that of conventional systems in terms of stability of the traces, properties of the electrode-skin interface and quality of the collected sEMG signals during quasi-isometric and highly dynamic tasks.

Gaped Two-Loop Antenna-Based Magnetic Transceiver With an Empirical Model for Wireless Underground Communication

This paper presents a practical low-power, low-frequency magnetic induction (MI) transceiver based on symmetrical gaped two-loop antennas with an empirical circuit model for wireless underground communication. Because of the quasi-two-dimensional loop antennas for the transmitter (Tx) and the receiver (Rx), the tailored hardware platform is not only simple, but can be readily extended to a mutually orthogonal 3-D scheme. Through a mixed model of actual measurement data and theoretical parameters, we developed the two-loop antenna with the space of the antenna radius optimized for energy efficiency. The Tx power almost doubles that of the single Tx one, which provides channel expansion as well as system stability in terms of the Tx current level. Accordingly, the Rx signal is considerably increased by 9.5 dB in contrast with a typical single-Tx single-Rx configuration. Moreover, we used empirical-based modeling for a reliable electrical model. The empirical mutual inductance, which was modeled in a 25 m corridor, resulted in a channel correction factor of 0.86, showing that the signal intensity was reduced by 14% in the underground corridor compared to the free space. A maximum range of 68 m under a SNR of 9.5 dB and a path loss of 100.7 dB on a load of $50~\Omega $ at 34.5 dBm were predicted from the model. In addition, this study confirmed the system feasibility by a SNR of 8.7 dB in a practical lossy environment between two floors, where its value was converted into a MI channel at a distance of 70 m in the underground corridor.

Robust Recursive Regulator for Systems Subject to Polytopic Uncertainties

We present a robust recursive framework for the regulation of discrete-time linear systems subject to polytopic uncertainties. Based on regularized least-squares with a penalty parameter, we formulate a convex optimization problem and weight the polytope vertices altogether. In this sense, the main contribution of this paper consists of a robust recursive framework for the computation of stabilizing feedback gains. The solution does not require numerical optimization packages and relies ultimately on a single penalty parameter which is easily tuned. Moreover, the gains are obtained recursively through algebraic expressions, as opposed to related works which employ linear matrix inequalities. Under observability and controllability conditions, we demonstrate convergence and stability of the closed-loop system in terms of an algebraic Riccati equation. We provide numerical and real-world examples to validate the proposed approach and for comparison with a robust $H_{\infty }$ controller.

Stability of neural-network based train cruise advisory control with aperiodical measurements

Abstract In this paper, a neural-network based driver advisory train cruise control system is considered. The controller assists the train driver with advisory signals by considering train and driver’s actual state information (attention and fatigue) measured by dedicated sensors. Considering delays in sensor measurements, this paper aims to assess closed-loop stability of driver-in-the-loop advisory train cruise control. For this purpose, the driver model is considered as a time-varying system, the train model includes rolling and aerodynamic resistance forces and the advisory control is considered to be a sampled-data based three layer multi-layer perceptron. Further, the aperiodic measurement problem is approached as stability analysis of time-varying delayed system. Based on recent developments on the design of augemented Lyapunov Krasovskii Functional (LKF) using Bessel-Legendre inequality for time-varying delays, sufficiency conditions for the existence of L2 stability of the driver-train system in terms of solvable Linear Matrix Inequalities are provided. Further a case study is presented to illustrate the effectiveness of the proposed method.

LCL resonant current depression control strategy against pulse width modulated harmonic voltage under low switching frequency

The LCL filter is widely used in grid connected converters for good harmonic mitigation performance. With pulse width modulation strategy, converter terminal voltage contains various sideband harmonic components together with expected components corresponding to the modulation wave, especially under a low switching frequency. Considerable resonant current can be generated if the undesired sideband harmonic voltage is located around the LCL resonant frequency. With the background of a medium voltage three-level wind power converter, where the switching frequency is as low as 1.5 kHz, a resonant current depression strategy is proposed against undesired sideband harmonic voltage under low switching frequency. Additional compensators are adopted in the converter current loop. Depending on the system mathematical model, two solutions, a Butterworth low pass filter and a notch filter, based on phase compensation and amplitude compensation, are proposed in this paper. It is shown that the Butterworth low pass filter exhibits better resonant current depression performance, while the notch filter performance is better in terms of system stability. Simulation and experimental results validated the proposed control method.

Why do people switch mobile payment service platforms? An empirical study in Taiwan

Although an increasing number of studies have recently investigated mobile payment service (MPS) platform user behaviours, the majority of these studies have focused on user adoption. However, user switching behaviour has been paid limited attention as yet. The current study investigates critical antecedents of user switching intention of MPS platform drawing on the perspective of the push-pull-mooring framework. The proposed model was empirically tested with 612 valid responses collected using on-line questionnaire survey in Taiwan. The results of this study revealed that user regret, alternative attractiveness, perceived complementarity of the alternative, and perceived network size of the alternative positively relate to user intention to switch. The most critical push effect driving MPS platform users to switch is user regret caused by dissatisfaction with system quality and information quality, especially in terms of system stability and visual attractiveness. In terms of pull effects, the improvement of alternative attractiveness and perceived network size of the alternative should be paid more attention, so thereby expanding their provision of complementary resources can be considered as an effective tactic. Furthermore, inertia is also negatively associated with user switching intention. Of all of the sources of inertia, uncertainty costs are a major crucial mooring effect. The performance of sunk costs still leaves much to be increased because of the insufficient user use and investment in the incumbent MPS platform. The findings will be helpful for MPS platform practitioners when fully comprehending users’ switching behaviour and formulating appropriate strategies to retain existing users while still attracting potential new users.

Effect of liquid digestate recirculation on the ethanol-type two-phase semi-continuous anaerobic digestion system of food waste

This study set up four groups for semi-continuous 150-days experiment to explore the effect of liquid digestate recirculation on the food waste ethanol-type anaerobic digestion system. Results showed that this operation improved the maximum organic load rates to 6.0 g-VS·L−1·d−1, and increased the average alkalinity of methanogenic phase under high load condition by 1.3 times. Total volatile fatty acids/total alkalinity (threshold value was approximately 0.5) could be used as an early warning indicator of methanogenic phase instability. Besides, approximately 64.5% of bacterial species in the hydrolysed acidified phase of ethanol-type liquid digestate recirculation group originated from the recirculated liquid digestate, which enriched the diversity of microbial community, thereby improving the hydrolysis acidification efficiency. Therefore, liquid digestate recirculation improved the stability of system in terms of alkalinity and microecology and then increased the maximum organic load rates.

Intelligent environment for advanced brain imaging: multi-agent system for an automated Alzheimer diagnosis

Over decades Alzheimer’s disease (AD) researches presented increasing challenges. However, various methods were proposed to detect AD including image processing. This paper presents a concrete solution to diagnose AD based on a multi-agent system (MAS). This approach highlights the importance of the cooperation paradigm within a robust system, in which all agents cooperate to accomplish the segmentation tasks. The exchanges between agents remain an essential part of the segmentation process. The original contribution of this paper is twofold: (1) To present an agent-based segmentation methodology by highlighting the main characteristics, advantages, and disadvantages of MAS. (2) To provide a usable solution by facilitating the detection of AD while taking into account both the expertise and the requirements of specialists in the application domain. Ensuring a cooperative segmentation using the multi-agent system offers a strong point in terms of system stability as well as clarity of the process for physicians. For this, several tests have been carried out to prove the effectiveness of our work. The results ensure that the performance indices in our proposed method were higher.

Distributed Secondary Voltage Control in Islanded Microgrids With Consideration of Communication Network and Time Delays

The extensive usage of open communication mechanisms in distributed secondary control of islanded microgrids (MGs) suggests that the effects of the communication network and time delays on system performance cannot be negligible. Based on the relationship between convergence and algebraic connectivity, this paper proposes an optimal design for a directed communication topology and pinning location through the mirror operation and global propagation rates, respectively. Alternatively, a small-signal dynamic model of an MG equipped with time-delayed distributed secondary voltage control is derived, to investigate the delay-dependent stability of MG system in terms of the controller, network and pinning conditions. An analytical formula is then developed to determine the individual delay margins with respect to different sets of controller gains and pinning. Through a series of trials, the qualitative effects of controller parameters and pinning conditions on delay margins can be used to guide the design of both controllers and pinning for the improved system performance. The effectiveness of proposed methodology is verified via the real-time hardware-in-the-loop (HIL) simulations.

Particle swarm optimization and spiral dynamic algorithm-based interval type-2 fuzzy logic control of triple-link inverted pendulum system: A comparative assessment

This paper presents investigations into the development of an interval type-2 fuzzy logic control (IT2FLC) mechanism integrated with particle swarm optimization and spiral dynamic algorithm. The particle swarm optimization and spiral dynamic algorithm are used for enhanced performance of the IT2FLC by finding optimised values for input and output controller gains and parameter values of IT2FLC membership function as comparison purpose in order to identify better solution for the system. A new model of triple-link inverted pendulum on two-wheels system, developed within SimWise 4D software environment and integrated with Matlab/Simulink for control purpose. Several tests comprising system stabilization, disturbance rejection and convergence accuracy of the algorithms are carried out to demonstrate the robustness of the control approach. It is shown that the particle swarm optimization-based control mechanism performs better than the spiral dynamic algorithm-based control in terms of system stability, disturbance rejection and reduce noise. Moreover, the particle swarm optimization-based IT2FLC shows better performance in comparison to previous research. It is envisaged that this system and control algorithm can be very useful for the development of a mobile robot with extended functionality.

Controlled Brushless De-Excitation Structure for Synchronous Generators

The main weakness of the brushless excitation system in a synchronous generator (SG) is the slow de-excitation response obtained during a load rejection. That is why voltage overshoots may be observed on the generator terminals. This behavior is mainly due to the exciter machine response time and the rotating diode bridge which is not able to quickly de-excite the generator by negative excitation voltages. This paper presents a new brushless de-excitation structure able to perform a quick de-excitation of the generator by providing controlled negative excitation voltage to the generator main field winding. The proposed structure is based on a new brushless de-excitation machine, called a control machine, and mounted on the same shaft of the generator and the brushless exciter. The brushless control machine is a low power one and used to transfer the orders from the voltage regulator to the discharge system located on the rotor side of the main generator. The dynamic performance of the proposed de-excitation system is evaluated in terms of system stability, voltage regulation response times and voltage overshoots during different load rejection tests. The proposed system is compared to the conventional brushless excitation system without the proposed de-excitation structure. In addition, a comparison is done with the static excitation system. The simulation tests are realized on an experimentally validated model of 11kVA synchronous generator developed in Matlab/Simulink.

Impact of renewable energy balancing power in tertiary balancing market on Japanese power system based on automatic generation control standard model

Due to the environmental burden, natural hazard and energy dilemma in Japan, renewable energy integration has become a key technology in the development of power systems and there has been significant increase in the use of wind and solar power generation. With the development of technologies and free fuel source offering, renewable energy power has been widely used in power system all over the world. On the other hand, because of diversification of generation operating in power system, it becomes more and more important to ensure the security and stability of power system in terms of supply–demand balance with a proper frequency range, to this end, balancing market has been developed in some European countries and regions in order to purchase the balancing power capacity and energy efficiently. In Japan, with the feed-in tariff policy spreading from 2012, it becomes a possibility that renewable energy balancing power participating in balancing market which will be newly established in 2020.