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In this paper, we address the state/fault estimation and observer-based control issues for switched systems with sensor faults. The main objective is to estimate sensor faults and compensate for their effects on the system state estimation, and then stabilize the switched system by the estimated state feedback. Applying the mode-dependent average dwell time (MDADT) concept and the Lyapunov stability theory, a new separation principle is developed, which allows formalizing the observer-based controller design in the form of linear matrix inequalities (LMI) instead of bilinear ones. Finally, a highly manoeuvrable aircraft technology (HiMAT) example, a DC–DC boost converter example, and a numerical example are investigated to show the practicability and efficiency of the obtained results. • Simultaneously estimate sensor faults and system states. • Stabilize continuous-time switched systems even in the presence of sensor faults. • Develop a new separation principle to formalize the observer-based controller design in the form of LMIs instead of BMIs. [ABSTRACT FROM AUTHOR]

In this paper, the network-based observation and stabilization problems for Lipschitz nonlinear systems under scheduling communication are investigated. It is assumed that the signal transmission between the sensors and the controller or between the controller and the plant is implemented through a wireless network. Moreover, the scheduling of the sensed signal towards the controller is ruled by the Round-Robin (RR) protocol or the i.i.d. stochastic protocol. A general framework for observer-based feedback stabilization is proposed in which the control input is generated by a zero-order device which stores the sampled output of the sample-and-hold Luenberger observer-based controller. The resulting closed-loop system is modeled as a cascaded hybrid system with partial state subject to impulsive perturbation. Sufficient conditions for the existence of sample-and-hold Luenberger observer-based sampled-data controllers are derived by applying separation principle and time-dependent Lyapunov functionals. These conditions allow to design observers and controllers separately. A numerical example is presented to illustrate the effectiveness of the developed methodology. [ABSTRACT FROM AUTHOR]

Abstract Automatic machines have recently advanced into diverse environments. A periodic state and an aperiodic state of the system usually have different physical meanings and require different control objectives in the diverse environments. To enable a new control approach based on the periodic and aperiodic states for the different control objectives, a periodic/aperiodic separation filter (PASF) that separates a state into a periodic state and an aperiodic state is proposed in this paper. Furthermore, using the PASF, the periodic/aperiodic state feedback control and the separation principle are established. [ABSTRACT FROM AUTHOR]

In this paper, we establish a separation principle in the practical sense for a class of time varying delay uncertain perturbed systems with a delay perturbation and an independent delay perturbation. Furthermore, based on Lyapunov-Krasovskii functionals, we study the possibility to stabilize globally in practical sense by an estimated state controller. Finally, an illustrative example is given to prove the applicability of the main result. [ABSTRACT FROM AUTHOR]

The current understanding and developments of phase separation technology based on ultrasonic standing waves (USWs) are reviewed. Most previous reviews have focused on microscale applications of this technology in the fields of biological materials and food processing. This review covers different applications of ultrasonic separation technology, especially in petrochemical industry. The kinetic mechanism of ultrasonic, design of reactors, separation principles, and related applications are discussed in detail. We lay special stress on the motion characteristics of particles in USWs. According to the particle numbers, particle properties, and frequency characteristics, the separation principles are reasonably categorized as: (1) Bands effect; (2) Acoustophoretic coefficient; (3) Particle density; (4) Sweep frequency. Diverse separation principles improve the universality of ultrasonic separation technology. However, acoustic streaming and acoustic cavitation are two of the main challenges in the application of ultrasonic separation. Based on the current research, the future research can focus on the following aspects: (1) Explore the mechanism of ultrasonic demulsification; (2) Establish unified evaluation criteria for acoustic separation systems; (3) Develop the basis for determination of acoustic cavitation and non-cavitation. [ABSTRACT FROM AUTHOR]

An optimal control design approach is applied to a novel HIV/AIDS model to reduce the infection diffusion. Two classes of susceptible subjects, the wise one and the incautious ones, and three classes of infectious subjects, the ones not aware of their condition and the subjects in the pre-aids or in the aids status, are considered. The control input, represented by information campaigns and the medication action, is designed by means of a linear quadratic approach on the linearized model. Moreover, a preliminary state observer for the unmeasurable number of the unconscious infectious subjects is introduced. Numerical results show the effectiveness of the solution, and its robustness with respect to the approximations introduced by the linearization. [ABSTRACT FROM AUTHOR]

This article focuses on the class of linear systems coupled with a nonlinearity satisfying a sector bound or a monotonic condition. First, we present a set of sufficient conditions based on Linear Matrix Inequalities (LMIs) to establish if such a system defines a contraction. Then, we propose a contractive state-feedback control law designed via the use of LMIs which may include nonlinear terms. Furthermore, the design is extended to the case in which an integral action is included in order to achieve constant output regulation. Following a similar approach, the design of contractive observers for the aforementioned class of systems is also considered. Finally, based on previous conditions, we establish a new nonlinear separation principle in which the feedback and the observer gains may be designed independently. Throughout the paper, we illustrate our results by means of practical examples. [ABSTRACT FROM AUTHOR]

This paper presents a rolling horizon stochastic optimal control strategy for both Adaptive Cruise Control and Cooperative Adaptive Cruise Control under uncertainty based on the constant time gap policy. Specifically, uncertainties that can arise in vehicle control systems and vehicle sensor measurements are represented as normally-distributed disturbances to state and measurement equations in a state-space formulation. Then, acceleration sequence of a controlled vehicle is determined by optimizing an objective function that captures control efficiency and driving comfort over a predictive horizon, constrained by bounded acceleration/deceleration and collision protection. The optimization problem is formulated as a linearly constrained linear quadratic Gaussian problem and solved using a separation principle, Lagrangian relaxation, and Kalman filter. A sensitivity analysis and a scenario-based analysis via simulations demonstrate that the proposed control strategy can generate smoother vehicle control and perform better than a deterministic feedback controller, particularly under small system disturbances and large measurement disturbances. [ABSTRACT FROM AUTHOR]

This paper studies the stabilization of linear systems with both state and input delays where the input delay can be arbitrarily large yet exactly known. Observer–predictor based controllers are designed to predict the future states so that the input delay can be properly compensated. Necessary and sufficient conditions guaranteeing the stability of the closed-loop system are provided in terms of the stability of some simple linear time-delay systems refereed to as observer-error systems, by which the separation principle is discovered. Moreover, approaches in terms of linear matrix inequalities are also provided to design both the state feedback gains and observer gains. Finally, a numerical example illustrates that the proposed approaches are more effective and safe to implement than the existing methods. [ABSTRACT FROM AUTHOR]

In the classical theory of finite-dimensional linear time-invariant systems in state space form the term deterministic separation principle refers to the observation that a stabilizing output feedback controller can be constructed by first constructing an asymptotic state observer that is then coupled to a stabilizing state feedback controller. In this paper we discuss the following converse problem: Can every stabilizing output feedback controller be realized as interconnection of an asymptotic state observer and a stabilizing state feedback controller? We will provide an affirmative answer to this question (modulo a number of technicalities) in a behavioral setting and with the help of rational representations. [ABSTRACT FROM AUTHOR]

In this article, a parametric method of observer-based partial eigenstrunt in second-order linear time-invariant (LTI) systems is explored. First, an observer is constructed to approximate the full sate vector when the entire state vector is not available for measurement. Meanwhile, the separation principle of the first-order linear systems is extended to second-order linear systems. Second, by partitioning the system matrix of the open-loop system into two parts, the satisfactory and unsatisfactory eigenstructures are selected. On the premise of retaining the satisfactory part in the open-loop system, the unsatisfactory eigenstructure assignment problem can be converted into the solutions of a type of generalized Sylvester equations (GSE). Third, by introducing a group of arbitrary parameters, complete parametric expressions of the proportional plus derivative (PD) state feedback controller can be obtained. The main advantage of the proposed method is that it provides all the design degrees of freedom and reduces the design complexity of the controller. Finally, the correctness of the proposed method is verified by two examples and simulation results. Using the degrees of freedom of the parameters, the gain matrices are optimized through the optimization index provided by the optimization function, and better performance is obtained. [ABSTRACT FROM AUTHOR]

In this paper we focus on networked control systems subject to data dropouts. We consider that the controller communicates with the plant through multiple independent erasure channels, and that each actuator sends acknowledgement packages to the controller. We restrict our attention to the optimal design of a class of controllers that embeds a data dropout compensator and where, besides this compensation mechanism, all processing is an affine function of the available data. Our first result shows that the optimal design consists in solving, separately, an estimation problem and a control problem. The optimal controller is a linear function of the estimated state, which is obtained exploiting the information given by the acknowledgement packages and the data dropout compensator. Since we focus on a specific class of controllers, our proposal is suboptimal, however, unlike the optimal LQG controller found in the literature, our proposal is easier to implement, and its steady state behaviour can be simply determined. We also show that, under standard conditions, the affine part of the optimal controller converges to an LTI filter, which can be used as a simple alternative to the time varying controller. [ABSTRACT FROM AUTHOR]

This paper considers fault estimation (FE) and fault-tolerant control (FTC) for linear parameter varying systems with actuator and sensor faults, uncertainties, and disturbances. The inevitable coupling between the FE and FTC functions needs to be taken into account in the design to ensure the overall FE-based FTC closed-loop system performance and robustness. This paper proposes an iterative strategy to achieve the robust integration of FE and FTC by leveraging the concepts of Separation Principle and Small Gain Theorem. The iterative algorithm involves solving multi-objective linear matrix inequality optimisation problems at each iteration and has finite-step convergence guarantee. Efficacy of the proposed algorithm and its advantages over the existing works are illustrated through numerical simulations. [ABSTRACT FROM AUTHOR]

In this work we address the problem of feedback control design for scalar systems in the presence of a non-ideal communication channel, which gives rise to tightly coupled limitations in terms of quantization errors, decoding/computational delays and packet loss affecting the closed loop control performance. We restrict our analysis to the context of LQG-like control, where the estimator and controller gains are forced to be constant, subject to SNR limitations, packet loss, and constant delay, and we derive their impact on the optimal design of the controller parameters. In particular, we show that the stability of the closed loop system depends on a tradeoff among SNR, packet loss probability and delay. Through this analysis we are also able to recover, as special cases, several results already available in the literature that have treated packet loss, quantization error and delay separately. We also show that the estimator and controller cannot be designed independently even if the controller has full knowledge of the packet loss sequence and the control inputs to the plant. In fact the optimal control gain, when accounting for the communication constraints is, in general, different from the optimal gain derived under the classical LQG scenario, which is recaptured when the SNR over the channel goes to infinity. [ABSTRACT FROM AUTHOR]

In this paper, we deal with the problem of the stabilization and the estimation of the state for a class of linear impulsive systems. We show that, under the classical Kalman׳s conditions of controllability and observability it is possible to design an observer based controller for the linear impulsive system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a scheme of designing finite-time high-order sliding mode (HOSM) observer which provides some essential requirements to be used in a sensorless control. The observer design technique is proposed to estimate some key states in a Multi-Input Multi-Output (MIMO) proton exchange membrane fuel cell (PEMFC) in a finite-time. Since variation of the load current deeply affects the life time of the cell, estimation and control of oxygen excess ratio ( ) is suggested to detect and prevent the damage. As a practical application, the observer reconstructs oxygen excess ratio using measurable variables, such as the compressor angular speed, the supply, the return manifold pressures and the load current. The estimation is performed to keep stability without need of any transformation to a canonical form in a finite time. The designed finite-time observer is shown with some increases in the response time indices, improves the accuracy whilst guarantees a fast convergence with respect to using flow sensors. Simulation results verify the achievements whilst signify the fast response as well as robust against uncertainties and disturbances. [Copyright &y& Elsevier]

Abstract: In this work, we investigate the observer-driven switching stabilization problem for a class of switched linear systems. By incorporating the switched observer presented in Sun, Wang, Xie, and Yu (2006) into the control loop, we construct an observer-driven path-wise switching law for the switched linear system. We prove that any stabilizable switched linear system is exponentially stable under the switching law, and establish a weak version of the separation principle for switching and observer design. [Copyright &y& Elsevier]

Abstract: This paper is concerned with observer based output feedback control of linear systems with both (multiple) input and output delays. Our recently developed truncated predictor feedback (TPF) approach for state feedback stabilization of time-delay systems is generalized to the design of observers. By imposing some restrictions on the open-loop system, two classes of observer based output feedback controllers, one being finite dimensional and the other infinite dimensional, are constructed. It is further shown that, the infinite dimensional observer based output feedback controllers can be generalized to linear systems with both time-varying input and output delays. It is also shown that the separation principle holds for the infinite dimensional observer based output feedback controllers, but does not hold for the finite dimensional ones. Numerical examples are worked out to illustrate the effectiveness of the proposed approaches. [Copyright &y& Elsevier]

Abstract: DMFC (direct methanol fuel cell) systems usually employ two pumps for supplying the methanol solution. The conventional system configuration, however, may bring about free flow from the methanol reservoir and malfunctions in the self-priming of the pumps. When instruments such as check valves and pressure regulators are applied, they result in excessive weight and control system malfunctions. In this paper, a light and robust DMFC system is proposed. By using the time sharing approach to supply fuel with a 3-way valve, free flow does not occur because only one inlet is opened at one time which means that both the circulation flow from gas liquid separator and the fuel flow from the methanol cartridge are not allowed to be opened at same time. As a result, back flow and self-priming problems do not occur. This makes the system stable and robust due to the removal of both the check valves and the fluctuation from unstable back pressure. Stabilized system doesn''t need excessive battery buffering and recycling water any more, which are responsible for the heavy system. The proposed system performs the same level of power and efficiency with the conventional system. Adaptability is also carried out in various environmental temperature conditions. [Copyright &y& Elsevier]

Abstract: The general feedback controller for a class of control variable delayed systems has recently been shown to be the general linear functional of an extended state of the system. Using only plant input/output data, this work formulates a memoryless observer for the reconstruction of this extended state. It is also shown that the observer and the feedback controller can be independently designed in conformity with the separation principle. [ABSTRACT FROM AUTHOR]

Abstract: As the important issue in fuzzy control system, some studies on separation principle for total fuzzy system have been done up to now. However, these existing results are far from enough. In order to supplement such theoretical study, this paper proves that separation principle for T–S fuzzy system with switching fuzzy controller and switching fuzzy observer does hold both in the continuous- and discrete-time case, which can guarantee the stability of total fuzzy system when designing corresponding controller and observer independently. At last, a numerical simulation, some conclusions and discussions about the future work are also presented. [ABSTRACT FROM AUTHOR]

Abstract: We examine two special cases of the problem of optimal linear quadratic Gaussian control of a system whose state is being measured by sensors that communicate with the controller over packet-dropping links. We pose the problem as an information transmission problem. Using a separation principle, we decompose the problem into a standard LQR state-feedback controller design, along with an optimal encoder–decoder design for propagating and using the information across the unreliable links. Our design is optimal among all causal algorithms for any arbitrary packet-drop pattern. Further, the solution is appealing from a practical point of view because it can be implemented as a small modification of an existing LQG control design. [Copyright &y& Elsevier]

Abstract: A class of approximate nonlinear observers is presented and, when used to implement stabilizing state feedback control laws, shown to yield asymptotically stable output feedback regulation. [Copyright &y& Elsevier]

Abstract: In the control systems literature, it is well known that a separation principle holds locally for nonlinear control systems, when exponential feedback stabilizers and exponential observers are used. In this paper, we present a counterexample to show that the global separation principle need not hold for nonlinear control systems. Our example demonstrates that global stability might be lost when an exponential observer is introduced into the nonlinear feedback loop associated with an exponentially stabilizing feedback control law. [Copyright &y& Elsevier]

Abstract: In this paper, we present an output feedback receding horizon control for a class of SISO nonlinear systems. A globally stabilizing state feedback receding horizon control scheme is combined with a discretized high gain observer. This is motivated by the fact that measurable system’s outputs are only available at specific sampling intervals. Our result follows from the application of a separation principle applicable to a class of sampled-data nonlinear systems. It is shown that the output-feedback scheme recovers the performance (rate of convergence) achieved under state feedback receding horizon control for a sufficiently large observer gain and sampling frequency. [Copyright &y& Elsevier]

Abstract: In this paper, we present necessary and sufficient conditions for both observer design and stabilization of the dominant state of discrete-time linear systems. Our method essentially uses the model reduction of the original linear control system. We also establish a separation principle so that when the reduced-order plant is stabilizable, the state of the reduced order observer may be used in lieu of the state of the reduced order plant for implementing the stabilizing state feedback control law. The model reduction and the observer design detailed in this paper are discrete-time analogs of the results of Aldeen and Trinh (1994) for continuous-time linear systems. [Copyright &y& Elsevier]

In this paper we consider the problem of output feedback stabilization of a general nonlinear jump system. We shall show that the combination of a locally asymptotically stabilizing state feedback law and a local asymptotic observer yields a locally asymptotically stabilizing output feedback controller. Hence, the local separation principle holds for the nonlinear jump system. This result can be applied to nonlinear sampled-data systems. [Copyright &y& Elsevier]

In this paper, we derive a result for stabilizability and a separation principle for periodic orbits. First, using degree theory, we derive a necessary condition for local asymptotic stabilizability of periodic orbits. This condition is similar to the famous Brockett''s necessary condition (1983) for local asymptotic stabilizability for equilibria. Next, we derive a separation principle for periodic orbits. Our separation principle states that if a state feedback system defined in the neighborhood of a periodic orbit is asymptotically stabilizable and if an exponentially good state estimator is known, then the composite state feedback-state estimator scheme is locally orbitally asymptotically stable. [Copyright &y& Elsevier]

In this paper, we study finite-time control of multiagent networks as systems , where they involve floating agents that exchange local information and driver agents that not only exchange local information but also take input and output roles. For this class of multiagent networks, control algorithms are applied to the driver agents based on the measurements collected from them for the purpose of influencing the overall behavior of the resulting system. Specifically, we consider time-critical applications in the control of multiagent networks as systems and propose a finite-time control approach predicated on a recent time transformation method. The proposed method guarantees execution of control algorithms over a prescribed time interval [ 0 , T) with T being a user-defined convergence time based on analysis performed over a stretched, infinite-time interval [ 0 , ∞). We analytically show that the resulting system achieves user-defined finite-time convergence regardless of the initial conditions of agents, where we also discuss the separation principle obtained with the proposed method. The presented theoretical contributions are not only illustrated by numerical examples but also experimentally validated using ground mobile robots. [ABSTRACT FROM AUTHOR]

This paper investigates the linear quadratic Gaussian Stackelberg game under asymmetric information. Two decision makers implement control strategies using different information patterns: The follower uses its observation information to design its strategy, whereas the leader implements its strategy using global information. For this problem, the separation principle becomes invalid. Instead, we apply the classical variation method to derive conditions to be satisfied by both decision makers. We show that the solution attributes to solving a two-point boundary value problem of stochastic version whose drift terms contain some conditional mean terms. We then propose a layered calculation method to solve this problem. In the inner layer calculation, the adjoint state variable's estimate is expressed as a linear functional of the state estimate. In the outer layer calculation, the adjoint state variable is expressed as a linear functional of the state and its estimate. We also verify that the Kalman–Bucy filter works for computing the state estimate. The result is also applied to dynamic duopoly with sticky prices and pursuit–evasion problem. [ABSTRACT FROM AUTHOR]

We consider a multidimensional closed-loop control problem where a stochastic linear time-invariant plant is connected via a communication system that includes an encoder, vector additive Gaussian noise (AGN) channel, decoder to a controller. For this setup, we first examine the impact of the communication link when causal side information (CSI) that is correlated to the plant is (possibly) allowed at the decoder and the performance criterion is the classical linear quadratic (LQ) cost. The CSI is modeled as a time-invariant vector-valued Gaussian process and when available at the decoder, it happens concurrently to the signal obtained from the vector AGN channel. Under the assumption that our encoder is linear, we leverage the separation principle of control and estimation, to obtain the following new results. (i) For multivariate Gaussian processes, we completely characterize a lower bound on the communication cost term of the optimal LQ Gaussian (LQG) cost in the form of a convex optimization problem and identify the best linear policies that achieve this bound. (ii) For scalar-valued Gaussian processes, we derive an analytical solution to the lower bound of the optimal communication cost term and show that for linear policies, CSI at the encoder does not improve the specific bound. (iii) For scalar-valued Gaussian processes, we also derive a linear time-invariant low delay joint source-channel coding (JSCC) scheme without bandwidth constraints, when CSI is available at the encoder, which demonstrates the case at which the specific lower bound communication cost expression is achievable. Further, we give a suboptimal linear time-invariant JSCC scheme when CSI is available only at the decoder. We supplement our results with various simulation studies. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the global practical uniform stability analysis problem of a class of time-varying multiple delayed perturbed systems where the associated nominal system is linear and the multiple delayed perturbation term satisfies some conditions. Furthermore, based on Lyapunov-Krasovskii functionals, we study the possibility to stabilize globally and uniformly in practical sense by an estimated state controller. Finally an illustrative example is given to demonstrate the applicability of main result. [ABSTRACT FROM AUTHOR]

• A discrete-time luenberger reduced-order SM capacitor voltage observer is designed. • The MMC closed-loop controller using the observed capacitor voltages is designed. • The stability and robustness of the above-mentioned systems are analyzed. • The importance of the PSE condition of the switching functions is pointed out. At present, the capacitor voltage balancing control and the closed-loop control algorithms are two important issues in a modular multilevel converter (MMC) control system. In the published papers, the majority of the proposed balancing and closed-loop control methods require the measurement of the sub-module (SM) capacitor voltages. To reduce the cost and control complexity, firstly, this paper presents a discrete-time luenberger capacitor-voltage observer to estimate the SM capacitor voltages. Concerning the difficulty of the observation system's stability analysis caused by the time-varying input and output switching function matrices, this paper manages to obtain the observer gain matrix design method from the point of stability analysis by the passive theory. In this process, the persistently and sufficiently exciting (PSE) condition about the switching functions to ensure the uniformly asymptotic convergence of the observation errors is obtained. This condition is also necessary for the feedback control system based on the observed state variables. Secondly, this paper presents a discrete-time state-error feedback controller using the observed capacitor voltages. According to the passive theory and separation principle, the stability of the MMC closed-loop system is analyzed. Finally, the correctness of the results obtained in this paper under different conditions, including the convergence and robustness of the observer and the state-error feedback controller using the observed capacitor voltages, are verified through the simulation. [ABSTRACT FROM AUTHOR]