910 publications from this institution
This study is concerned with the stability of a linear system with an interval time‐varying delay. First, a new augmented Lyapunov–Krasovskii functional (LKF) is constructed, which includes three integral terms in the form of ∫ t−h t ( h − t )+) s ) j ẋ T R j ẋ (s) d s ( j )=) 1, 2, 3). Second, three novel integral inequalities are established to estimate the upper bounds of the integrals ∫ t−h t ( h − t )+) s ) j ẋ T R j ẋ (s) d s ( j )=) 0, 1, 2) appearing in the derivative of the LKF. Third, a matrix‐based quadratic convex approach is introduced to prove not only the negative definiteness of the derivative of the LKF along with the trajectory of the system, but also the positive definiteness of the LKF. Finally, a novel delay‐derivative‐dependent stability criterion is formulated. The effectiveness of the stability criterion is shown through two numerical examples.
In this article, a novel proactive attack defense strategy is proposed to deal with the secure remote estimation issue in cyber-physical systems with unknown-but-bounded noises in the presence of man-in-the-middle attacks. It is assumed that the residue calculated by the smart sensor is sent to the remote estimator and the abnormal intrusion detector via a wireless network, and the watermark is assumed to belong to a zonotope. In order to guarantee the detection rate, the data processes and the watermark are time-varying and secret to an adversary. Moreover, the effect on system performance caused by the watermark can be removed when the system is attack free. Furthermore, four different attack scenarios are discussed to analyze the detection ability of the proposed defense approach, and the designed strategy can be applied to detect replay attacks. Finally, an unmanned aircraft system subject to malicious attacks is leveraged to illustrate the effectiveness of the proposed proactive defense strategy.
The full information estimation (FIE) problem is addressed for discrete time-varying systems (TVSs) subject to the effects of a round-Robin (RR) protocol. A shared communication network is adopted for data transmissions between sensor nodes and the state estimator. In order to avoid data collisions in signal transmission, only one sensor node could have access to the network and communicate with the state estimator per time instant. The so-called RR protocol, which is also known as the token ring protocol, is employed to orchestrate the access sequence of sensor nodes, under which the chosen sensor node communicating with the state estimator could be modeled by a periodic function. A novel recursive FIE scheme is developed by defining a modified cost function and using a so-called "backward-propagation-constraints." The modified cost function represents a special global estimation performance. The solution of the proposed FIE scheme is achieved by solving a minimization problem. Then, the recursive manner of such a solution is studied for the purpose of online applications. For the purpose of ensuring the estimation performance, sufficient conditions are obtained to derive the upper bound of the norm of the state estimation error (SEE). Finally, two illustrative examples are proposed to demonstrate the effectiveness of the developed estimation algorithm.
Kirigami is the art of cutting paper to make it articulated and deployable, allowing for it to be shaped into complex two and three-dimensional geometries. The mechanical response of a kirigami sheet when it is pulled at its ends is enabled and limited by the presence of cuts that serve to guide the possible non-planar deformations. Inspired by the geometry of this art form, we ask two questions: (i) What is the shortest path between points at which forces are applied? (ii) What is the nature of the ultimate shape of the sheet when it is strongly stretched? Mathematically, these questions are related to the nature and form of geodesics in the Euclidean plane with linear obstructions (cuts), and the nature and form of isometric immersions of the sheet with cuts when it can be folded on itself. We provide a constructive proof that the geodesic connecting any two points in the plane is piecewise polygonal. We then prove that the family of polygonal geodesics can be simultaneously rectified into a straight line by flat-folding the sheet so that its configuration is a (non-unique) piecewise affine planar isometric immersion.
This is the second in a series of two papers to establish the conjectured mass-angular momentum inequality for multiple black holes, modulo the extreme black hole 'no hair theorem'. More precisely it is shown that either there is a counterexample to black hole uniqueness, in the form of a regular axisymmetric stationary vacuum spacetime with an asymptotically flat end and multiple degenerate horizons which is 'ADM minimizing', or the following statement holds. Complete, simply connected, maximal initial data sets for the Einstein equations with multiple ends that are either asymptotically flat or asymptotically cylindrical, admit an ADM mass lower bound given by the square root of total angular momentum, under the assumption of nonnegative energy density and axisymmetry. Moreover, equality is achieved in the mass lower bound only for a constant time slice of an extreme Kerr spacetime. The proof is based on a novel flow of singular harmonic maps with hyperbolic plane target, under which the renormalized harmonic map energy is monotonically nonincreasing. Relevant properties of the flow are achieved through a refined asymptotic analysis of solutions to the harmonic map equations and their linearization.
This paper is concerned with sliding mode control of offshore steel jacket platforms subject to nonlinear wave-induced forces. Two sliding mode control schemes are proposed to reduce the oscillation amplitudes of the platforms. One scheme is that a conventional sliding mode controller (SMC) is designed, under the SMC the oscillation amplitudes of the platform are effectively reduced; however, a very large control force is required. The other scheme is that by intentionally introducing a time-delay into the control channel, a delayed sliding mode controller (DSMC) is designed. Compared with the SMC, the DSMC improves the control performances in two aspects: (i) the oscillation amplitudes of the first, second and third floors under the control of the DSMC are less than those under the control of the SMC; (ii) the control force required by the DSMC is much less than that by the SMC, which are confirmed by simulation results.
treatment, and measurement of industrial processes.
This chapter is concerned with a delayed non-fragile H ∞ control scheme for an offshore steel jacket platform subject to self-excited nonlinear hydrodynamic force and external disturbance. By intentionally introducing a time-delay into the control channel, a...
This paper deals with the observer-based dynamic optimal recoil controller design of a deepwater drilling riser system subject to friction force of fluid discharge and platform heave motion. First, by using exponential and polynomial functions conjunctively, a novel nonlinear computational model of the friction force is presented. Then, a linear system model is developed to describe dynamic characteristics of the friction force. Third, by using feedforward mechanisms and internal model principle jointly, a dynamic optimal recoil control scheme is proposed for the riser, where the feedforward mechanism is designed to compensate the friction force of fluid discharge, and the internal model principle is introduced to reject platform heave motion. The conditions of existence and uniqueness of a dynamic optimal recoil controller of the riser are developed. Fourth, a friction force observer is designed to solve the physically realizable problem of the recoil controller. Simulation results show that under the observer-based dynamic optimal recoil controller, the recoil of the riser can be attenuated significantly, and zero steady state errors of the riser can be guaranteed. In addition, from the perspective of achieving steady performance of the riser, the designed dynamic optimal recoil control scheme outperforms existing linear quadratic optimal control schemes.
This paper is concerned with the distributed H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> filtering problem for a class of discrete time-varying stochastic parameter systems with error variance constraints over a sensor network where the sensor outputs are subject to successive missing measurements. The phenomenon of the successive missing measurements for each sensor is modeled via a sequence of mutually independent random variables obeying the Bernoulli binary distribution law. To reduce the frequency of unnecessary data transmission and alleviate the communication burden, an event-triggered mechanism is introduced for the sensor node such that only some vitally important data is transmitted to its neighboring sensors when specific events occur. The objective of the problem addressed is to design a time-varying filter such that both the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> requirements and the variance constraints are guaranteed over a given finite-horizon against the random parameter matrices, successive missing measurements, and stochastic noises. By recurring to stochastic analysis techniques, sufficient conditions are established to ensure the existence of the time-varying filters whose gain matrices are then explicitly characterized in term of the solutions to a series of recursive matrix inequalities. A numerical simulation example is provided to illustrate the effectiveness of the developed event-triggered distributed filter design strategy.
This article is concerned with set-membership global estimation for a networked system under unknown-but-bounded process and measurement noises. First, a group of local set-membership estimators is deployed to obtain the local ellipsoidal estimate of the true system state. Each estimator is capable of communicating with its neighbors within its communication range. Second, a global estimation approach is proposed which generates a trace-maximal ellipsoid within the intersection of all the local estimation sets with an aim to improve the difference of the local estimate at each time instant. Sufficient conditions for providing a global estimate under both complete and incomplete measurement transmissions are derived. Third, as an application, a modified distributed photovoltaic grid-connected generation system is provided to verify the effectiveness of the developed set-membership global estimation approach. Furthermore, an islanding fault detection scheme is derived based on the calculated global ellipsoidal estimate. Finally, simulation verification of the obtained theoretical results on the distributed generation system is presented.
This paper is concerned with the distributed secondary control problem of multiple battery energy storage systems (BESSs) in an islanded microgrid, where the dynamics of each battery is heterogeneous. It is assumed that each battery can communicate with its neighbors via communication networks whose communication topologies are switching over time. A distributed finite-time secondary control scheme is proposed to ensure frequency regulation, active power sharing and energy level balancing of BESSs in a finite time, while operational constraints can be satisfied at any control transient time. Finally, validity and effectiveness of the proposed control scheme are demonstrated by case studies on a modified IEEE 57-bus testing system.
This paper is concerned with cyber attack detection in a networked control system. A novel cyber attack detection method, which consists of two steps: 1) a prediction step and 2) a measurement update step, is developed. An estimation ellipsoid set is calculated through updating the prediction ellipsoid set with the current sensor measurement data. Based on the intersection between these two ellipsoid sets, two criteria are provided to detect cyber attacks injecting malicious signals into physical components (i.e., sensors and actuators) or into a communication network through which information among physical components is transmitted. There exists a cyber attack on sensors or a network exchanging data between sensors and controllers if there is no intersection between the prediction set and the estimation set updated at the current time instant. Actuators or network transmitting data between controllers and actuators are under a cyber attack if the prediction set has no intersection with the estimation set updated at the previous time instant. Recursive algorithms for the calculation of the two ellipsoid sets and for the attack detection on physical components and the communication network are proposed. Simulation results for two types of cyber attacks, namely a replay attack and a bias injection attack, are provided to demonstrate the effectiveness of the proposed method.
Some mathematical models in engineering and physics, such as rotating pendulums, governors and phase locked loops in circuits, can be described as nonautonomous systems in which there exist chaotic attractors. This paper investigates master-slave synchronization for two nonautonomous chaotic systems by using time-delayed feedback control. Firstly, three delay-dependent synchronization criteria, which are formulated in the form of linear matrix inequalities (LMIs), are established for complete synchronization, lag synchronization and anticipating synchronization, respectively. Secondly, sufficient conditions on the existence of a time-delayed feedback controller are derived by employing these newly-obtained synchronization criteria. The controller gain can be obtained by solving a set of LMIs. Finally, the synchronization criteria and the design method are applied to master-slave synchronization for rotating pendulum systems.
