Methods for constructing observers for linear dynamical systems under uncertainty

We consider various methods for constructing asymptotic observers for linear stationary MIMO systems under an unknown external perturbation. Square systems (in which the number of measured outputs coincides with that of unknown inputs) are considered separately. For such systems we propose a method for constructing observers that yields either an asymptotic observer (for systems of maximal relative order) or an arbitrarily accurate observer. Hyperoutput systems (in which the number of measured outputs exceeds that of unknown inputs) are considered separately as well. For such systems we propose a method for synthesizing asymptotic observers of the phase vector.     

Observer design for bilinear systems of a special form

We consider the problem of uniform (input-irrespective) observation of a scalar bilinear system. For state estimation, we use a linear observer with observation error feedback whose feedback coefficients form a hierarchy in powers of the feedback parameter. For a sufficiently large value of the parameter, the observer provides an asymptotic estimate of the unknown system state vector.     

Modelling and control of a shell structure based on a finite dimensional variational formulation

A mathematical model of a controlled shell structure based on Hamilton’s principle and the generalized Ritz–Galerkin method is proposed in this paper. The problem of minimizing the stress energy is solved explicitly for a static version of this model. For the dynamical system under consideration, a procedure for estimating external disturbances and the state vector is derived. We also propose an observer design scheme and solve the stabilization problem for an arbitrary dimension of the linearized model. This approach allows us to perform control design for double-curved shells of complex geometry by combining analytical computation of the controller parameters with numerical data that represent the reference configuration and modal displacements of the shell. As an example, the parameters of our model are validated by results of a finite element analysis for the Stuttgart SmartShell structure.     

Finite-time converging jump observer for switched linear systems with unknown inputs

This work addresses the state observation problem for a class of switched linear systems with unknown inputs. The proposed high-order sliding-mode observer provides a finite-time converging estimate of the continuous system’s state vector in spite of the presence of unknown inputs. The design procedure, which assumes knowledge of the discrete state of the switched system, is based on the principles of disturbance decoupling and hierarchical observer output injection. In order to cope with the switching nature of the plant under observation, jumps in the observer state space are enforced intentionally. The implementation of an additional observer allows for the reconstruction of the unknown inputs, which may be important in the framework of fault detection. Numerical examples illustrate the effectiveness of the suggested technique.     

Iterative learning control for MIMO nonlinear systems with arbitrary relative degree and no states measurement

This article presents a state observer based iterative learning control to solve the trajectory tracking problem of a class of time‐varying Multi‐Input‐Multi‐Output nonlinear systems with arbitrary relative degree. For this purpose, an asymptotically stable observer is derived for the system under consideration. There after, this observer is integrated with the iterative learning controller by replacing the state in the control law with its estimation yielded by the state observer. Hence, the stability of the whole control (nonlinear system plus controller plus observer) is guaranteed. Simulation result on nonlinear system shows that the trajectory tracking error decreases through the iterations. © 2013 Wiley Periodicals, Inc. Complexity 19: 37–45, 2013     

Minimum-order functional observers

The article considers the construction of a minimum-order observer for a linear state functional of a linear dynamical system. For a one-output system we derive a necessary and sufficient condition that allows reconstruction of the functional by a k th order observer. This result is generalized to a system with vector output. An algorithm for the construction of a minimal observer is proposed. The problem is solved by the method of decomposition into scalar observers.     

Variable structure control systems: synthesis of scalar and vector systems by state and output feedback

Modern views are applied to examine synthesis of variable structure systems (VSS) for SISO and MIMO systems of general position in the presence of information on the full phase vector or only on the output vector. In the latter case we consider separately the cases of organizing a sliding mode in plant output coordinates and in arbitrary coordinates. The latter case requires the construction of asymptotic observers for linear systems with uncertainty in the parameters or in inputs, and the corresponding observation theory is sketched. Special attention is given to the case of so-called hyperoutput systems, i.e., multiply connected systems in which the number of outputs exceeds the number of inputs. For hyperoutput systems under fairly general conditions we can arbitrarily choose the observer dynamics, which is important for improving the performance of the control system as a whole. We show that the observer dynamics does not change the VSS stability.     

Minimum dimension of a functional observer with specifiable dynamical properties

The article considers the construction of a functional observer with a given rate of convergence for the most general case: a vector state functional of a linear dynamical system with a vector output. An upper bound is derived on the minimum dimension of such an observer, which holds for almost all functionals. An algorithm is proposed for constructing an observer that achieves this bound. The algorithm can be used to construct a functional observer for almost all specified spectra (i.e., with the exception of a set of measure zero). The scalar observer method previously developed by the authors and proposed in the present article is based on canonical form Luenberger observability for systems with vector output.     

Lyapunov reducibility and stabilization of nonstationary systems with an observer

For a linear nonstationary control system with an observer, we assume that the coefficients are locally Lebesgue integrable and integrally bounded on ℝ and construct a linear feedback such that the closed-loop plant-controller system is Lyapunov reducible to the special triangular form corresponding to an independent shift of the diagonal coefficients in the original system and in the system of asymptotic estimation of the state by an arbitrary pregiven quantity. For a periodic system, we prove that the constructed controls and Lyapunov transformation are periodic. We obtain corollaries on the uniform stabilization and global controllability of the central and singular exponents of the system.     

An asymptotic theory of higher-order operator differential equations with nonsmooth nonlinearities

We develop an asymptotic theory of nonlinear operator differential equations of an arbitrary order in Banach spaces. The nonlinear part of the equation is written in a divergent form. It is shown that the main term in an asymptotic representation of solutions at infinity satisfies a finite-dimensional dynamical system perturbed by a small nonlocal operator.     

A Technique for Multiple Signal Differentiation

The state-space method is applied for noise-tolerant multiple differentiation of signals from a certain class. The construction of differentiators is reduced to the design of a state observer for a dynamical system with an unknown bounded input. Any prespecified differentiation accuracy of signals from the given class can be achieved by increasing the observer dimension, i.e., the order of the differentiator transfer function. The proposed differentiators are tolerant to high-frequency additive noise.     

The singular perturbation of boundary value problem for third-order nonlinear vector integro-differential equation and its application

In this paper, the singular perturbation of boundary value problem to a class of third-order nonlinear vector integro-differential equation is studied. Using the method of differential inequalities, under certain conditions, the existence of perturbed solution is proved, the uniformly valid asymptotic expansion for arbitrary order and the estimation of remainder term are given. Finally, the results are applied to study singularly perturbed boundary value problem to a nonlinear vector fourth-order differential equation. The existence of solution and its asymptotic estimation can be obtained conveniently.     

Asymptotic analysis of the interaction of a finite number of holes in an elastic plane or half-plane

The problem of the interaction of a finite number of holes in an elastic plane or half-plane is considered. The analysis is based on the complex potential method of Muskhelishvili as well as on the theory of compound asymptotic expansions by Maz'ya. An asymptotic expansion of the complex potentials in terms of relative hole radii is constructed. This expansion is uniformly valid in the whole domain. The method leads to a simple procedure which does not involve any coupled system of linear equations. The successive closed-form approximations can be obtained in an iterative manner to an arbitrary order without any need for numerical approximation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Singular observer approach for chaotic synchronization and private communication

Based on the singular system observer, this paper proposes an effective approach for chaotic synchronization and private communication. When the useful information is modulated in a chaotic system and its dynamic equation is not available, we can consider the transmitted signal as an external system state. Then we can design a singular observer which has higher dimension. The advantage of such a design is that we can avoid using the derivation information of the transmitted signal. By adopting the singular system observer approach, the transmitted signal can be recovered successfully by the observer. Numerical simulations show the effectiveness of the proposed method.     

Problems of the partial stability and detectability of dynamical systems

The conditions under which uniform stability (uniform asymptotic stability) with respect to a part of the variables of the zero equilibrium position of a non-linear non-stationary system of ordinary differential equations signifies uniform stability (uniform asymptotic stability) of this equilibrium position with respect the other, larger part of the variables, which include an additional group of coordinates of the phase vector, are established. These conditions include the condition for uniform asymptotic stability of the zero equilibrium position of the “reduced” subsystem of the original system with respect to the additional group of variables. Since within the conditions obtained the stability with respect to the remaining unmeasured coordinates of the phase vector remains undetermined or is investigated additionally, partial zero-detectability of the original system occurs in this case, and the conditions obtained supplement the series of known results from partial stability theory. The application of the results obtained to problems of the partial stabilization of non-linear controlled systems, particularly to the problem of stabilizing an asymmetric rigid body relative to an assigned direction in an inertial space, is considered. The partial detectability of linear systems with constant coefficients is also investigated.     

Introducing internal model to robust output synchronization of FitzHugh–Nagumo neurons in external electrical stimulation

A novel internal model control method is proposed for the robust output synchronization of FizHugh–Nagumo (FHN) neurons under external electrical stimulation. The output synchronization problem can be converted into a robust stabilization problem of an augmented system consisting of the original given plant and an internal model. Hence, the design procedures include the design of a satisfied internal model and a proper state-feedback stabilizer for this augmented system. The stability analysis of the resulting closed-loop system leads to semiglobal Lyapunov asymptotic stability of the robust output synchronization achieved for some appointed initial condition in the state space and for all possible values of the uncertain parameter vector. Finally, the simulation results demonstrate the validity of the proposed method.     

某类二阶非线性系统初值问题的奇摄动*

本文研究某类二阶非线性向量微分方程初值问题ε'x"=f(t,x,x',ε),x(0,ε)=a,x'(0,ε)=β的奇摄动,其中r>0为任意常数,ε>0为小参数,x,f,α,β∈Rn.在适当的假设下,利用多参数展开法和对角化技巧,证得摄动问题解的存在和导出解的高阶的一致有效渐近展开式.     

Stabilization of a one‐dimensional wave equation with variable coefficient under non‐collocated control and delayed observation

In this paper, we consider stabilization of a 1‐dimensional wave equation with variable coefficient where non‐collocated boundary observation suffers from an arbitrary time delay. Since input and output are non‐collocated with each other, it is more complex to design the observer system. After showing well‐posedness of the open‐loop system, the observer and predictor systems are constructed to give the estimated state feedback controller. Different from the partial differential equation with constant coefficients, the variable coefficient causes mathematical difficulties of the stabilization problem. By the approach of Riesz basis property, it is shown that the closed‐loop system is stable exponentially. Numerical simulations demonstrate the effect of the stable controller. This paper is devoted to the wave equation with variable coefficients generalized of that with constant coefficients for delayed observation and non‐collocated control.     

Transfer of a Passive Vector Admixture by a Two-Dimensional Turbulent Flow

We consider a model of a passive vector field transfer by a random two-dimensional transverse velocity field that is uncorrelated in time and has Gaussian spatial statistics given by a powerlike correlator. We use the renormalization group and the operator product expansion techniques to show that the asymptotic approximation of the structure functions of a vector field in the inertial range is determined by the energy dissipation fluctuations. The dependence of the asymptotic approximation on the external scale of turbulence is essential and has a powerlike form (the case of an anomalous scaling). The corresponding exponents are calculated in the one-loop approximation for structure functions of an arbitrary order.