Finite-Time H∞ Filtering for Singular Stochastic Systems
Abstract
This paper addresses the problem of finite-time H∞ filtering for one family of singular stochastic systems with parametric uncertainties and time-varying norm-bounded disturbance. Initially, the definitions of singular stochastic finite-time boundedness and singular stochastic H∞ finite-time boundedness are presented. Then, the H∞ filtering is designed for the class of singular stochastic systems with or without uncertain parameters to ensure singular stochastic finite-time boundedness of the filtering error system and satisfy a prescribed H∞ performance level in some given finite-time interval. Furthermore, sufficient criteria are presented for the solvability of the filtering problems by employing the linear matrix inequality technique. Finally, numerical examples are given to illustrate the validity of the proposed methodology.
1. Introduction
Singular systems also referred to as descriptor systems or generalized state-space systems represent one family of dynamical systems since it generalizes the linear system model and has extensive applications in economics systems, power systems, mechanics systems, chemical processes, and so on; see for more practical examples [1, 2] and the references therein. Many control results in state-space systems have been extended to singular systems, such as stability, stabilization, H∞ control, and the filtering problems, for instance, see [3–6] and the references therein. Meanwhile, Markovian jump systems are referred to as one special family of hybrid systems and stochastic systems, which are very appropriate to model plants whose structure is subject to random abrupt changes, see the reference [7]. Thus, many attracting results have been studied, such as stochastic stability and stabilization [8, 9], robust control [10–12], guaranteed cost control [13], and other issues. For more details, the readers may be refered to [7, 14] and the references therein. Recently, the problem of state estimation for singular Markovian jump systems has also attracted considerable attention. As far as we know, the traditional Kalman filtering requires the exact knowledge of statistics of the noise signals. To overcome the limitations regarding the system uncertainties and the statistical properties, the H∞ filtering problem has been proposed and tackled for both the continuous-time case and the discrete-time one including without or with time-delay and full-order or reduced-order [15–20]. For more details, we refer the readers to [7, 21] and the references therein.
On the other hand, in many practical processes, many concerned problems are the practical ones which described that system state does not exceed some bound during some time interval. Compared with classical Lyapunov asymptotical stability, in order to deal with the transient performance of control systems, finite-time stability or short-time stability was introduced in [22]. Employing linear matrix inequality (LMI) theory and Lyapunov function approach, some appealing results were obtained to ensure finite-time stability, finite-time boundedness, and finite-time stabilization of various systems including linear systems, nonlinear systems, and stochastic systems. For instance, Amato et al. [23] investigated the output feedback finite-time stabilization for continuous linear system. Zhang and An [24] considered finite-time control problems for linear stochastic system. For more details of the literature related to finite-time stability, the reader is referred to [25–34] and the references therein. However, to date and to the best of our knowledge, the H∞ filtering problem for singular stochastic systems has not investigated in finite-time interval. The problem is important and challenging in many practice applications, which motivates us for this study.
This paper deals with the problem of finite-time H∞ filtering for one family of singular stochastic systems with parametric uncertainties and time-varying norm-bounded disturbance. Our results are totally different from those previous results, although some studies on H∞ filtering and finite-time stability for singular stochastic systems have been addressed, see [19–21, 31, 32, 35]. The main aim of this paper is to design an H∞ filtering which guarantees the filtering error system singular stochastic finite-time boundedness and satisfies a prescribed H∞ performance level in the given finite-time interval. Sufficient criteria are presented for the solvability of the filtering problems by applying the LMI technique. Finally, simulation examples are presented to demonstrate the validity of the developed theoretical results.
Notations. Throughout the paper, ℝn and ℝn×m denote the sets of n component real vectors and n × m real matrices, respectively. The superscript T stands for matrix transposition or vector. 𝔼{·} denotes the expectation operator with respective to some probability measure ℙ. In addition, the symbol * denotes the term that is induced by symmetry and diag {⋯} stands for a block-diagonal matrix. λmin (P) and λmax (P) denote the smallest and the largest eigenvalue of matrix P, respectively. Notations sup . and inf . denote the supremum and infimum, respectively. Matrices, if their dimensions are not explicitly stated, are assumed to be compatible for algebraic operations.
2. Problem Formulation
Throughout the paper, we need the following definitions and lemmas.
Definition 2.1 (regular and impulse free, see [21]). (i) The singular system with Markovian jumps (2.1) is said to be regular in time interval [0, T] if the characteristic polynomial det (sE − Ai − ΔAi) is not identically zero for all t ∈ [0, T].
(ii) The singular systems with Markovian jumps (2.1) is said to be impulse free in time interval [0, T], if deg (det (sE − Ai − ΔAi)) = rank (E) for all t ∈ [0, T].
Definition 2.2 (singular stochastic finite-time boundedness (SSFTB)). The singular system with Markovian jumps (2.6) which satisfies (2.4) is said to be SSFTB with respect to , with c1 < c2, , if the stochastic system (2.6) is regular and impulse free in time interval [0, T] and satisfies
Remark 2.3. SSFTB implies that not only is dynamical mode of the filtering error system finite-time bounded but also whole mode of the one is finite-time bounded since the static mode is regular and impulse free.
Definition 2.4 (singular stochastic H∞ finite-time boundedness (SSH∞FTB)). The singular system with Markovian jumps (2.6) is said to be SSH∞FTB with respect to , if the singular system with Markovian jumps (2.6) is SSFTB with respect to and under the zero-initial condition, the output error e(t) satisfies the cost constrained function
Definition 2.5 (see [9].)Let V(x(t), rt = i, t > 0) be the stochastic function, define its weak infinitesimal operator L of stochastic process {(x(t), rt = i), t ≥ 0} by
Lemma 2.6 (see [36].)For matrices Y, M, and N of appropriate dimensions, where Y is a symmetric matrix, then
Lemma 2.7 (see [36].)The linear matrix inequality is equivalent to , where and .
Lemma 2.8. The following items are true.
(i) Assume that rank (E) = r, there exist two orthogonal matrices U and V such that E has the decomposition as
(ii) If P satisfies
(iii) If P is a nonsingular matrix, R and Λ are two symmetric positive definite matrices, P and E satisfy (2.14), X is a diagonal matrix from (2.16), and the following equality holds:
Proof. One only requires to prove that (ii) and (iii) hold. Let
By (i) and (ii), noticing and P = UXUTE + U2Y𝒱T, we have
In the paper, our main objective is to concentrate on designing the filter of system (2.1) which guarantees the resulting filtering error dynamic system (2.6) SSH∞FTB.
3. Main Results
In this section, firstly we give SSH∞FTB analysis results of the filtering problem for nominal system (2.1). Then these results will be extended to the uncertain systems. Linear matrix inequality conditions are established to show the nominal system or the uncertain system (2.6) is finite-time boundedness, and the output error e(t) and disturbance w(t) satisfy the constrain condition (2.9).
Lemma 3.1. The filtering error system (2.6) is SSFTB with respect to , if there exists a scalar α ≥ 0, a set of nonsingular matrices with , two sets of symmetric positive definite matrices with , with , and for all i ∈ 𝕄 such that the following inequalities hold:
Proof. Firstly, one proves the filtering error system (2.6) is regular and impulse free in time interval [0, T]. By Lemma 2.7 and noting that condition (3.1b), one has
Let us consider the quadratic Lyapunov function candidate for system (2.6). Computing LV, the derivative of along the solution of system (2.6), we obtain
Lemma 3.2. The filtering error system (2.6) is SSH∞FTB with respect to , if there exists a scalar α ≥ 0, a set of nonsingular matrices with , a set of symmetric positive definite matrices with , and for all i ∈ 𝕄 such that (3.1a), (3.1c) and the following inequalities hold:
Proof. Noting that
Denote , and Ef = E. Using Lemmas 2.7 and 3.2, we obtain the following theorem.
Theorem 3.3. The nominal filtering error system (2.6) is SSH∞FTB with respect to with , if there exists a scalar α ≥ 0, a set of nonsingular matrices {Pi, i ∈ 𝕄} with Pi ∈ ℝn×n, a set of positive definite matrices {Q1i, i ∈ 𝕄} with Q1i ∈ ℝn×n, three sets of matrices {Mi, i ∈ 𝕄} with Mi ∈ ℝn×n, {Ni, i ∈ 𝕄} with , {Cfi, i ∈ 𝕄} with , for all i ∈ 𝕄 such that
In addition, the desired filter parameters can be chosen by
Noting that Pi is nonsingular matrix, by Lemma 2.8, there exist two orthogonal matrices U and V, such that E has the decomposition as
From the above discussion, we have the following theorem.
Theorem 3.4. The nominal filtering error system (2.6) is SSH∞FTB with respect to with , if there exists a scalar α ≥ 0, a set of positive definite matrices {Xi, i ∈ 𝕄} with Xi ∈ ℝn×n, four sets of matrices {Yi, i ∈ 𝕄} with Yi ∈ ℝ(n−r)×n, {Mi, i ∈ 𝕄} with Mi ∈ ℝn×n, {Ni, i ∈ 𝕄} with , and {Cfi, i ∈ 𝕄} with , for all i ∈ 𝕄 such that (3.16d) and the following linear matrix inequality
By Theorems 3.3 and 3.4 and applying Lemmas 2.6–2.8, one can obtain the results stated as follows.
Theorem 3.5. The uncertain filtering error system (2.6) is SSH∞FTB with respect to with , if there exists a scalar α ≥ 0, a set of positive definite matrices {Xi, i ∈ 𝕄} with Xi ∈ ℝn×n, four sets of matrices {Yi, i ∈ 𝕄} with Yi ∈ ℝ(n−r)×n, {Mi, i ∈ 𝕄} with Mi ∈ ℝn×n, {Ni, i ∈ 𝕄} with , {Cfi, i ∈ 𝕄} with , and a set of positive scalars {ϵi, i ∈ 𝕄}, for all i ∈ 𝕄 such that (3.16d) and the following linear matrix inequality
Remark 3.6. Theorems 3.4 and 3.5 extend the H∞ filtering problem of singular stochastic systems to the finite-time H∞ filtering problem of singular stochastic systems. In fact, if we fix α = 0 without condition (3.16d), we can obtain sufficient conditions of the H∞ filtering of singular stochastic systems.
Let I < Q1i < ηI, then one can check that condition (3.16d) can be guaranteed by imposing the conditions
4. Simulation Examples
In this section, numerical results are given to illustrate the effectiveness of the suggested method.
Example 4.1. Consider a two-mode singular stochastic system (2.1) with uncertain parameters as follows:
(i) Mode #1,
(ii) Mode #2,
Then, we choose R1 = R2 = I3, T = 2, by Theorem 3.5, the optimal bound with minimum value of relies on the parameter α. We can find feasible solution when 0.34 ≤ α ≤ 11.02. Figures 1 and 2 show the optimal values with different value of α. Noting that when α = 2, it yields the optimal values γ = 9.4643 and c2 = 5.6786. Then, by using the program fminsearch in the optimization toolbox of Matlab starting at α = 2, the locally convergent solution can be derived as


Remark 4.2. From the above example and Remark 3.7, condition (3.22) in Theorem 3.5 is not strict in LMI form, however, one can find the parameter α by an unconstrained nonlinear optimization approach, which a locally convergent solution can be obtained by using the program fminsearch in the optimization toolbox of Matlab.
Example 4.3. Consider a two-mode singular stochastic system (2.1) with uncertain parameters as follows:
Let R1 = R2 = I3, then the feasible solution of the above filtering error system can be found when α = 0, Theorem 3.5 yields the optimal values γ = 3.7770, c2 = 2.2663, and
5. Conclusion
In this paper, we deal with the problem of finite-time H∞ filtering for a class of singular stochastic systems with parametric uncertainties and time-varying norm-bounded disturbance. Designed algorithms are provided to guarantee the filtering error system SSFTB and satisfy a prescribed H∞ performance level in a given finite-time interval, which can be reduced to feasibility problems involving restricted linear matrix equalities with a fixed parameter. Numerical examples are given to demonstrate the validity of the proposed methodology.
Acknowledgments
The authors would like to thank the reviewers and the editors for their very helpful comments and suggestions to improve the presentation of the paper. The paper was supported by the National Natural Science Foundation of P.R. China under Grant 60874006, by the Doctoral Foundation of Henan University of Technology under Grant 2009BS048, by the Natural Science Foundation of Henan Province of China under Grant 102300410118, by the Foundation of Henan Educational Committee under Grant 2011A120003 and 2011B110009, and by the Foundation of Henan University of Technology under Grant 09XJC011.