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This paper proposes a fault-tolerant control allocation (FTCA) scheme for a flexible satellite. A novel control strategy is implemented, which fulfills the satellite mission and also decreases vibrations, saturation time of the actuators, and required energy. Avoiding spillover instability, an infinite-dimensional model of the flexible satellite is considered, which is one of the important benefits of the proposed control scheme over the previously presented FTCA methods. External disturbances, the uncertainty of moment of inertia, actuator fault and failure, imprecision in fault estimation, and control constraints are considered. The designed control system is comprised of two modules: the virtual control module that designs the virtual control law to stabilize the satellite and control vibrations without any in-domain actuators on panels, and a distribution control module that distributes the virtual control law among actuators based on their fault information and distance of bound of the control limit. The proposed virtual control law consists of an observer-based PD-like nominal control and adaptive control parts, and the internal reaction torque is estimated using a nonlinear observer. The closed-loop uniformly ultimately bounded (UUB) stability is achieved using Lyapunov criteria. A numerical example illustrates the effectiveness of the proposed approach regarding attitude stabilization and vibration control objectives. [ABSTRACT FROM AUTHOR]

This study investigates finite-time attitude synchronization and tracking control of multiple rigid bodies under event-triggered control strategy in presence of actuator faults and an external disturbance. The event-triggered implementation technique aims to reduce resource utilization in regard to control effort and communication burden. To achieve this aim, the adaptive sliding mode structure is used, and a novel triggering condition is proposed. In presence of unknown actuator faults and external disturbance, it is shown that the multiple rigid bodies track a time-varying attitude of a virtual leader synchronously in finite time under limited data communication. Moreover, a lower bound on the inter-event times has been derived to ensure that the Zeno behavior is avoided. The effectiveness of the proposed method is validated by numerical simulation along with comparison with another relevant research. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper, is to solve the problem of finite-time fault-tolerant attitude synchronization and tracking control of multiple rigid bodies in presence of model uncertainty, external disturbances, actuator faults and saturation. It is assumed that the rigid bodies in the formation may encounter loss of effectiveness and/or bias actuator faults. Design/methodology/approach: For the purpose, adaptive terminal sliding mode control and neural network structure are used, and a new sliding surface is proposed to guarantee known finite-time convergence not only at the reaching phase but also on the sliding surface. The sliding surface is then modified using a proposed auxiliary system to maintain stability under actuator saturation. Findings: Assuming that the communication topology between the rigid bodies is governed by an undirected connected graph and the upper bounds on the actuators' faults, estimation error of model uncertainty and external disturbance are unknown, not only the attitudes of the rigid bodies in the formation are synchronized but also they track the time-varying attitude of a virtual leader. Using Lyapunov stability approach, finite-time stability of the proposed control algorithms demonstrated on the sliding phase as well as the reaching phase. The effectiveness of the proposed algorithm is also validated by simulation. Originality/value: The proposed controller has the advantage that the need for any fault detection and diagnosis mechanism and the upper bounds information on estimation error and external disturbance is eliminated. [ABSTRACT FROM AUTHOR]

Fault-tolerant control (FTC) strategy based on adaptive integral sliding mode (AISM) is proposed to stabilize a flexible satellite, subject to inertia uncertainties, external disturbances, and actuator faults. Using Hamilton's principle, the satellite dynamics is presented as a coupled Ordinary Differential Equation (ODE) and Partial Differential Equation (PDE). The control scheme is based on the infinite-dimensional model of the flexible satellite with no discretization, so the spillover instability phenomenon is eliminated. This is the most important advantage of the proposed control scheme over the previous FTC schemes that have been used for the flexible satellite. Stabilization and vibration suppression are performed using control torque that is applied to the rigid center, and there is no need to implement in-domain actuators on panels to stabilize their vibration. First, a novel nominal controller based on the infinite-dimensional model of the satellite is designed for a healthy system. Then, an integral sliding surface, including angular velocities, internal reaction torques, and nominal control, is proposed. Finally, an AISM controller with an adaptive estimator is designed to accommodate actuator faults and other uncertainties. System stability is guaranteed for small changes in a neighborhood around the sliding surface with simultaneous vibration damping. Numerical simulations illustrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Fault-tolerant control (FTC) strategy based on adaptive integral sliding mode (AISM) is proposed to stabilize a flexible satellite, subject to inertia uncertainties, external disturbances, and actuator faults. Using Hamilton's principle, the satellite dynamics is presented as a coupled Ordinary Differential Equation (ODE) and Partial Differential Equation (PDE). The control scheme is based on the infinite-dimensional model of the flexible satellite with no discretization, so the spillover instability phenomenon is eliminated. This is the most important advantage of the proposed control scheme over the previous FTC schemes that have been used for the flexible satellite. Stabilization and vibration suppression are performed using control torque that is applied to the rigid center, and there is no need to implement in-domain actuators on panels to stabilize their vibration. First, a novel nominal controller based on the infinite-dimensional model of the satellite is designed for a healthy system. Then, an integral sliding surface, including angular velocities, internal reaction torques, and nominal control, is proposed. Finally, an AISM controller with an adaptive estimator is designed to accommodate actuator faults and other uncertainties. System stability is guaranteed for small changes in a neighborhood around the sliding surface with simultaneous vibration damping. Numerical simulations illustrate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Cyber-physical systems have posed new challenges, affecting their users. The information security of these systems against cyber-attacks is considered one of the most complex issues in a wide range of defences. The present study proposes a new approach for detecting deception attacks based on moving target defence (MTD). The existing MTD algorithms can only recognize few attacks, including integrity attacks on the cyber-physical system, by limiting the adversary's knowledge of the original system. However, the proposed approach detects replay attacks as well. Moreover, a robust defence system is developed to mislead the adversary and make the attack identifiable from the defender's perspective by introducing a chaotic, hybrid, and extended MTD. Thus, three primary deception attacks, including False Data Injection (FDI), covert, and replay attacks, are detectable based on the proposed approach. The effectiveness of the proposed approach is validated by comparing it with continuous watermarking defence in a cyber-physical testbed. [ABSTRACT FROM AUTHOR]

Wireless network sensing and control systems are becoming increasingly important in many application domains due to advent of nanotechnology. The size of a wireless sensor network can easily reach hundreds or even thousands of sensor nodes. Since these types of networks usually have limited battery resources, power consumption optimization for prolonging system lifetime of such networks have received a great attention by the researchers in this field in recent years. In this paper, a centralized approach for clustering and data transmission mechanism is proposed that optimizes the power consumption and hence lifetime of the network. The mechanism is comprised of two phases. In the first phase, a mechanism based on a centralized cluster head selection that utilizes information such as nodes residual energies and their locations in the network is proposed in order to select the most appropriate candidates as cluster heads. In the second phase, the concept of a 'window size' is introduced where minimization of the number of cluster head changes of a node and consequently maximization of the network lifetime is considered. Simulation results validate that the proposed mechanism does effectively reduce data traffic and therefore increases network lifetime. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a logistic based approach is used to forecast the natural gas consumption for residential as well as commercial sectors in Iran. This approach is relatively simple compared with other forecasting approaches. To make this approach even simpler, two different methods are proposed to estimate the logistic parameters. The first method is based on the concept of the nonlinear programming (NLP) and the second one is based on genetic algorithm (GA). The forecast implemented in this paper is based on yearly and seasonal consumptions. In some unusual situations, such as abnormal temperature changes, the forecasting error is as high as 8.76%. Although this error might seem high, one does not need to be deeply concerned about the overall results since these unusual situations could be filtered out to yield more reliable predictions. In general, the overall results obtained using NLP and GA approaches are as well as or even in some cases better than the results obtained using some older approaches such as Cavallini’s. These two approaches along with the gas consumption data in Iran for the previous 10 years are used to predict the consumption for the 11th, 12th, and 13th years. It is shown that the logistic approach with the use of NLP and GA yields very promising results. [Copyright &y& Elsevier]

This paper develops a robust adaptive model reference impedance controller for an ${n}$ -link robotic manipulator with parameter uncertainties, actuator saturation, and imprecise force sensor measurement. In order to handle the system uncertainties, the adaptive technique and prediction error are used. To reduce calculation complexity, the adaptation law for robot parameters estimation is designed in the joint space. Actuator saturation is also overcome by an auxiliary system, and imprecise force sensor measurement is compensated with utilization of adaptive bounding technique. Moreover, the joint acceleration vector problem, which is nonmeasurable, is covered by the filtered regressor matrix. Using Lyapunov’s direct method, as long as two conditions are satisfied the proposed controller ensures the exponential stability of all the signals of the closed loop system; otherwise, the closed loop system is globally stable. Finally, simulations are performed on prototyped robots to analyze and evaluate the established controller as well as to demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Once blackouts occur the system operators should re‐energise the affected system in the shortest time. To attain this, restoration plans should be developed beforehand. A deliberate restoration plan considers the supply duration of the cranking power to non‐black‐start units (NBSUs), besides the static and dynamic constraints of the power system. Hence, there should be a method to estimate the restoration duration of NBSUs considering the failure in breakers operating mechanism and the stochastic nature of restoration actions. Accordingly, in this study, generally distributed transition stochastic Petri net is employed to calculate the supply duration of NBSUs, critical loads and the execution time of restoration actions. This is significant because the planners can validate their restoration plans from the NBSUs critical times' point of view or determine energisation time of critical loads. The proposed method has been applied in three test cases, two of these are used for benchmarking, and the other one is a part of Iran bulk power system, which includes a real black‐start test. The results show the effectiveness of the method in estimating the restoration duration. [ABSTRACT FROM AUTHOR]

Summary: Blackouts rarely occur in power systems; nevertheless, in case of occurrence, its impact on the economy, industry, and social life can be noticeable. To minimize the negative financial and social impacts of blackouts, power systems should be restored in the shortest possible time. Therefore, system operators should access a formulated method to estimate the restoration duration. In this paper, a method based on the Petri Net is used to calculate the restoration duration. Therefore, a restoration plan is resolved into its constituent steps, and for each step, a stochastic duration is considered. Applying the Petri Net model of the restoration plan and the duration of each restoration step, the total restoration time can be calculated. The proposed method is applied in two system tests, and the results show consistency with those of the critical path method. [ABSTRACT FROM AUTHOR]

Arresters are widely used in power systems to protect other equipment against overvoltages. However, in some conditions, they can't operate successfully. One of the disturbances leading to the failure of the riser pole arresters is the ferroresonance overvoltages. In this paper, at first the influence of different transformer simulation models of ATP software on the occurrence of ferroresonance is studied and then the effect of ferroresonance on the riser pole arrester has been scrutinized through the thermal and electrical performance of the arrester in an underground distribution system. The results show that the arrester temperature rises due to energy dissipation in a ferroresonance circumstance, which indeed may result into the explosion of the arrester. Also, applying different models of the transformer in the ATP software and comparing the results, it is shown that the available models do not show the same effect on the arrester. [ABSTRACT FROM AUTHOR]

This paper proposes a robust adaptive observer for a class of singular nonlinear non-autonomous uncertain systems with unstructured unknown system and derivative matrices, and unknown bounded nonlinearities. Unlike many existing observers, no strong assumption such as Lipschitz condition is imposed on the recommended system. An augmented system is constructed, and the unknown bounds are calculated online using adaptive bounding technique. Considering the continuous nonlinear gain removes the chattering which may appear in practical applications such as analysis of electrical circuits and estimation of interaction force in beating heart robotic-assisted surgery. Moreover, a simple yet precise structure is attained which is easy to implement in many systems with significant uncertainties. The existence conditions of the standard form observer are obtained in terms of linear matrix inequality and the constrained generalised Sylvester's equations, and global stability is ensured. Finally, simulation results are obtained to evaluate the performance of the proposed estimator and demonstrate the effectiveness of the developed scheme. [ABSTRACT FROM PUBLISHER]

Summary: Despite power system operators' efforts, blackouts occur; therefore, power systems should be restored. To attain this, power system restoration is done applying different strategies after a complete blackout. The most famous one is the bottom‐up strategy. Determining the islands is of extreme importance in this strategy. Hence, this paper proposes a new version of multi‐objective populated simulated annealing considering the cohesiveness and the quality of islands as objective functions. The proposed method takes into account miscellaneous constraints such as black‐start availability in each island, load‐generation balance, power flow establishment equations, and the availability of synchronization devices. Simulation results for the IEEE 39 and 118‐bus test systems confirm the effectiveness of the proposed method in determining the islands. [ABSTRACT FROM AUTHOR]