Exogenous System Research Articles

Real-time modelling of wavepackets in turbulent jets

Three methods are considered for estimating the downstream evolution of wavepackets in turbulent jets based on upstream measurements. The parabolised stability equations are used to compute a transfer function between axially and radially separated points in the flow, and the performance of this theoretical model is compared with that of two empirical approaches, direct transfer function calculation and autoregressive moving-average exogenous system identification, both of which require unsteady experimental data. The three approaches, which perform equally well, prove suitable for estimation of the downstream evolution of wavepackets using pressure data measured in the near-nozzle region. Over distances of the order of a couple of jet diameters, correlations of up to 80 % are observed between estimation and measurement. The performance deteriorates as axial separation between input and output is increased. While the two empirical approaches are limited in terms of both the number of input–output pairs and the number of flow variables that can be reasonably considered, the parabolised stability equations-based approach has no such limitation and can be used to perform full-field estimates comprising all of the dependent variables; in this it constitutes a potentially formidable means by which to perform single-input–multiple-output estimation. It has the further advantage of not requiring unsteady data for its construction, the only necessary ingredients being the mean flow and the linearised equations of motion.

Output regulation by error dynamic feedback in hybrid systems with periodic state jumps

This work deals with output regulation in multivariable hybrid systems featuring a continuous-time linear dynamics periodically affected by instantaneous changes of the state. More precisely, given a hybrid linear plant and a hybrid linear exogenous system, with periodic state jumps, the problem consists in finding a hybrid feedback regulator, with the same characteristics, achieving global asymptotic stability of the closed-loop dynamics and asymptotic tracking of the reference generated by the exogenous system for all the initial states. Starting from a general, necessary and sufficient condition for the existence of a solution, the discussion leads to a more specific, sufficient condition which outlines the computational framework for a straightforward synthesis of the compensator. The internal model principle is shown to hold in a more general formulation than the original one, adapted to the hybrid systems considered. A numerical example is worked out with the aim of illustrating how to implement the devised technique. The geometric approach is the key methodology in attaining these results.

Disturbance Observer‐Based Elegant Anti‐Disturbance Control for Stochastic Systems with Multiple Disturbances

AbstractDisturbance observer‐based elegant anti‐disturbance control (DOBEADC) scheme is proposed for a class of stochastic systems with nonlinear dynamics and multiple disturbances. The stochastic disturbance observer based on pole placement is constructed to estimate disturbance which is generated by an exogenous system. Then, composite DOBC and controller is designed to guarantee the composite system is mean‐square stable and its performance satisfies a prescribed level. Finally, simulations on an A4D aircraft model show the effectiveness of the proposed approaches.

Interventional bipartite consensus on coopetition networks with unknown dynamics

In this paper, an interventional bipartite consensus problem is considered for a high-order multi-agent system with unknown disturbance dynamics. The interactions among the agents are cooperative and competitive simultaneously and thus the interaction network (just called coopetition network in sequel for simplicity) is conveniently modeled by a signed graph. When the coopetition network is structurally balanced, all the agents are split into two competitive subgroups. An exogenous system (called leader for simplicity) is introduced to intervene the two competitive subgroups such that they can reach a bipartite consensus. The unknown disturbance dynamics are assumed to have linear parametric models. With the help of the notation of a disagreement state variable, decentralized adaptive laws are proposed to estimate the unknown disturbances and a dynamic output-feedback consensus control is designed for each agent in a fully distributed fashion, respectively. The controller design guarantees that the state matrix of the closed-loop system can be an arbitrary predefined Hurwitz matrix. Under the assumption that the coopetition network is structurally balanced and the leader is a root of the spanning tree in an augmented graph, the bipartite consensus and the parameter estimation are analyzed by invoking a common Lyapunov function method when the coopetition network is time-varying according to a piecewise constant switching signal. Finally, simulation results are given to demonstrate the effectiveness of the proposed control strategy.

Discrete approximate optimal vibration control for nonlinear vehicle active suspension

This paper presents the approximate optimal vibration control methodology for discrete nonlinear vehicle active suspension subject to persistent road disturbances. Based on a dynamic model of nonlinear vehicle active suspension and a linear exogenous system model of the persistent road disturbances, a nonlinear two-point boundary value (TPBV) problem is introduced. By introducing a sensitive parameter, the original TPBV problem is reformed as a series of TPBV problems without nonlinear items. A discrete approximate optimal vibration controller (DAOVC) can be obtained by solving a Riccati equation, Stein equation, and nonlinear compensation item, respectively. An iteration algorithm is designed to realize the computational realizability of DAOVC based on the control performance. It is demonstrated that the control performance of ride comfort, road holding ability, and suspension deflection under the DAOVC are much smaller than the ones under the classical feedforward and feedback optimal vibration controller (FFOVC) and open-loop vehicle suspension system.

Disturbance rejection for nonlinear systems with mismatched disturbances based on disturbance observer

A disturbance rejection approach based on disturbance observer is proposed for a class of nonlinear systems subject to mismatched disturbances. The mismatched disturbances are described by exogenous systems and satisfy partially-known information, which enter the system in the different channels with the control input. The disturbance observer is designed to estimate the mismatched disturbances, which can be introduced separately from the controller design. By integrating disturbance observer with back-stepping method, the disturbance observer plus back-stepping (DOPBS) controller can be constructed to reject the mismatched disturbances. And the asymptotically stability for the closed-loop system can be achieved. Finally, simulation examples are given to demonstrate the feasibility and effectiveness of the proposed scheme compared with existing methods.

Sensor Fault and Delay Tolerant Control for Networked Control Systems Subject to External Disturbances.

In this paper, the problem of sensor fault and delay tolerant control problem for a class of networked control systems under external disturbances is investigated. More precisely, the dynamic characteristics of the external disturbance and sensor fault are described as the output of exogenous systems first. The original sensor fault and delay tolerant control problem is reformulated as an equivalence problem with designed available system output and reformed performance index. The feedforward and feedback sensor fault tolerant controller (FFSFTC) can be obtained by utilizing the solutions of Riccati matrix equation and Stein matrix equation. Based on the designed fault diagnoser, the proposed FFSFTC is further reconstructed to compensate for the sensor fault and delayed measurement effects. Finally, numerical examples are provided to illustrate the effectiveness of our proposed FFSFTC with different cases with various types of sensor faults, measurement delays and external disturbances.

Adaptive output feedback disturbance attenuation control for nonlinear systems with non-harmonic multisource disturbances

This paper focuses on the output feedback regulation for a class nonlinear systems with dynamic non-harmonic multisource disturbances. The key point of this paper is that a kind of non-harmonic disturbances, which have complex nonlinear features, are investigated by using a nonlinear exogenous system. By introducing a nonlinear damping term, a novel adaptive augmented state observer is constructed to estimate the system states, the harmonic disturbances and the non-harmonic disturbances. By integrating the output of the observer with an anti-disturbance controller, an output feedback disturbance attenuation control structure is synthesized such that the closed-loop stability can be guaranteed. Moreover, the results are extended to the disturbances which have intense non-harmonic characteristics. Several illustrative examples are employed to demonstrate the effectiveness of the proposed control structure.

Discrete optimal actuator-fault-tolerant control for vehicle active suspension

This paper studies the discrete actuator-fault-tolerant control problem for a vehicle active suspension system under persistent road disturbances. The discrete model of vehicle active suspension with actuator faults is formulated firstly, in which the actuator faults are described as the output of an exogenous system with unknown initial values. By designed a fault diagnoser, the optimal actuator-fault-tolerant controller is derived from the discrete Riccati equation and Stein equations, respectively. Simulation results illustrate that the ride comfort, road holding ability, and suspension deflection can be reduced significantly and the reliability of the vehicle active suspension can be improved.

The evolution of regulators of G protein signalling proteins as drug targets - 20 years in the making: IUPHAR Review 21.

Regulators of G protein signalling (RGS) proteins are celebrating the 20th anniversary of their discovery. The unveiling of this new family of negative regulators of G protein signalling in the mid-1990s solved a persistent conundrum in the G protein signalling field, in which the rate of deactivation of signalling cascades in vivo could not be replicated in exogenous systems. Since then, there has been tremendous advancement in the knowledge of RGS protein structure, function, regulation and their role as novel drug targets. RGS proteins play an important modulatory role through their GTPase-activating protein (GAP) activity at active, GTP-bound Gα subunits of heterotrimeric G proteins. They also possess many non-canonical functions not related to G protein signalling. Here, an update on the status of RGS proteins as drug targets is provided, highlighting advances that have led to the inclusion of RGS proteins in the IUPHAR/BPS Guide to PHARMACOLOGY database of drug targets.

Disturbance Observer-Based Input-Output Finite-Time Control of a Class of Nonlinear Systems

This paper is concerned with disturbance observer-based input-output finite-time control of a class of nonlinear systems with one-sided Lipschitz condition, as well as multiple disturbances. Firstly, a disturbance observer is constructed to estimate the disturbance generated by an exogenous system. Secondly, by integrating the estimation of disturbance with a classical state feedback control law, a composite control law is designed and sufficient conditions for input-output finite-time stability (IO-FTS) of the closed-loop system are attained. Such conditions can be converted into linear matrix inequalities (LMIs). Finally, two examples are given to show the effectiveness of the proposed method.

Insights of breast cancer epigenetics: An intersection between the endogenous and exogenous systems

Insights of breast cancer epigenetics: An intersection between the endogenous and exogenous systems

Finite-Time Stabilization for a Class of Nonlinear Differential-Algebraic Systems Subject to Disturbance

In this paper, finite-time stabilization problem for a class of nonlinear differential-algebraic systems (NDASs) subject to external disturbance is investigated via a composite control manner. A composite finite-time controller (CFTC) is proposed with a three-stage design procedure. Firstly, based on the adding a power integrator technique, a finite-time control (FTC) law is explicitly designed for the nominal NDAS by only using differential variables. Then, by using homogeneous system theory, a continuous finite-time disturbance observer (CFTDO) is constructed to estimate the disturbance generated by an exogenous system. Finally, a composite controller which consists of a feedforward compensation part based on CFTDO and the obtained FTC law is proposed. Rigorous analysis demonstrates that not only the proposed composite controller can stabilize the NDAS in finite time, but also the proposed control scheme exhibits nominal performance recovery property. Simulation examples are provided to illustrate the effectiveness of the proposed control approach.

Identification of the Response of a Controlled Building Structure Subjected to Seismic Load by Using Nonlinear System Models

The present study investigates the prediction efficiency of nonlinear system-identification models, in assessing the behavior of a coupled structure-passive vibration controller. Two system-identification models, including Nonlinear AutoRegresive with eXogenous inputs (NARX) and adaptive neuro-fuzzy inference system (ANFIS), are used to model the behavior of an experimentally scaled three-story building incorporated with a tuned mass damper (TMD) subjected to seismic loads. The experimental study is performed to generate the input and output data sets for training and testing the designed models. The parameters of root-mean-squared error, mean absolute error and determination coefficient statistics are used to compare the performance of the aforementioned models. A TMD controller system works efficiently to mitigate the structural vibration. The results revealed that the NARX and ANFIS models could be used to identify the response of a controlled structure. The parameters of both two time-delays of the structure response and the seismic load were proven to be effective tools in identifying the performance of the models. A comparison based on the parametric evaluation of the two methods showed that the NARX model outperforms the ANFIS model in identifying structures response.

Composite anti‐disturbance resilient control for Markovian jump nonlinear systems with partly unknown transition probabilities and multiple disturbances

SummaryIn this paper, the problem of composite anti‐disturbance resilient control is studied for Markovian jump nonlinear systems with partly unknown transition probabilities and multiple disturbances. The multiple disturbances include two types: one is in the input channel generated by an exogenous system with perturbations, and the other is belong to L2[0,∞). The first class of disturbances is estimated by designing a disturbance observer. Combining the disturbance estimation with conventional L2 − L∞ resilient control law, a composite anti‐disturbance control scheme is constructed such that the closed‐loop system is stochastically stable, and different types of disturbances can be attenuated and rejected. By using Lyapunov function method and linear matrix inequalities technique, some sufficient conditions for the desired controller and observer gains are developed. Finally, an application example is provided to demonstrate the effectiveness of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.

Composite anti‐disturbance control for switched systems via mixed state‐dependent and time‐driven switching

This study is concerned with the problem of composite anti-disturbance control for switched linear systems with multiple disturbances. The authors' aim is to construct a disturbance observer to estimate the disturbance generated by an exogenous system, then design a composite controller based on the disturbance observer and a mixed state-dependent and time-driven switching law, such that the closed-loop system is internally stable, and different types of disturbances are attenuated and rejected. First, a mixed switching law is designed, which guarantees a dwell time even when all subsystems are unstable. Then, a sufficient condition ensuring the solvability of the composite anti-disturbance control problem is presented via multiple Lyapunov functions. Finally, the effectiveness of the proposed control design scheme is illustrated by its application to an aero-engine, which cannot be handled by the existing approaches.

Anti‐disturbance control for nonlinear system via adaptive disturbance observer

SummaryThis paper addresses the problems of disturbance estimation and anti‐disturbance control for nonlinear system with exogenous disturbance, which is generated from an unknown exogenous system. The state observer and the adaptive disturbance observer are designed, simultaneously. Compared with the existing methods, which assumed that the exogenous system parameter matrix was known, our disturbance observer is more applicable in practice. Utilizing the estimation information, an observer‐based dynamic output feedback controller is designed, which avoids the influence of output disturbance on the closed‐loop system, and contains a disturbance compensation term to compensate the input disturbance. Finally, simulations are provided to demonstrate the effectiveness of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd.

Savings Adequacy Assessment: The Case of Malaysian Employees Provident Fund Members

This study examines the potential consequences of early withdrawals from the Malaysian Employees Provident Fund in patterns of savings adequacy by studying the impact of house purchase on household lifecycle consumption. The authors develop an overlapping generations model of a small open economy where investment is available to capital, housing, and financial instruments. Housing is modelled as an asset subject of transaction costs. In equilibrium setting, the empirical estimation of exogenous system parameters sets the optimal levels of consumption and savings. The authors perform empirical analysis by taking into consideration four different scenarios: different employment periods (18-55 vs. 25-55), different retirement periods (55-65 vs. 55-75 vs. 55-85), housing vs. non-housing consumption, and theoretical vs actual contribution rates. Actuarial evaluation shows that low-income employees can have sufficient income to meet their retirement needs in the absence of housing consumption. Policy directions are also discussed.

Interventional consensus for high-order multi-agent systems with unknown disturbances on coopetition networks

In this paper, an interventional consensus problem is formulated mathematically with signed graph theory and dynamical system theory. The interaction network associated with a multi-agent system is modeled by a signed graph (called coopetition network in sequel) and the dynamics of each agent is described by a high order differential equation with a nonlinear unknown time-varying disturbance. Then a distributed interaction law is designed for each agent to drive all agents belonging to two competitive subgroups to reach a bipartite consensus on a reference signal, which is generated by an exogenous system (called leader in sequel). Simultaneously, some neural network (NN) based adaptive estimators are proposed to estimate the nonlinear disturbances in the agent dynamics. The convergence of the bipartite consensus is analyzed by using a Lyapunov function method. Finally, some simulation results are presented to demonstrate the formation of the bipartite consensus.

PDE-based tracking control for multi-agent deployment

Abstract: A two-degree-of-freedom control concept is developed for the deployment of multi-agent systems into desired formation profiles by exploiting a continuum model in terms of a modified viscous Burger’s equation. For this, flatness-based motion planning and feedforward control is combined with a backstepping-based boundary controller to stabilise the distributed parameter tracking error system. An exogenous system is introduced, which is shown to enable translational movement of the complete formation as well as its separation and reunion. The transfer of the control strategy to a finite-dimensional discrete multi-agent system is obtained by proper discretization of the continuum model PDEs, which in addition imposes the required communication topology. The results are evaluated in different simulation scenarios for a leader-follower configuration.