Siying Zhang

Adaptive backstepping controller design using stochastic small-gain theorem

A more general class of stochastic nonlinear systems with unmodeled dynamics and uncertain nonlinear functions are considered in this paper. With the concept of input-to-state practical stability (ISpS) and nonlinear small-gain theorem being extended to stochastic case, by combining stochastic small-gain theorem with backstepping design technique, an adaptive output-feedback controller is proposed. It is shown that the closed-loop system is practically stable in probability. A simulation example demonstrates the control scheme.

Reliable control using redundant controllers

This paper presents a methodology for the design of reliable control systems by using multiple identical controllers to a given plant. The resulting closed-loop control system is reliable in the sense that it provides guaranteed internal stability and H/sub /spl infin// performance (in terms of disturbance attenuation), not only when all controllers are operational but also when some controller outages (sensor and/or actuator) occur. A numerical example is given to illustrate the proposed design procedures.

Output-Feedback Stabilization of Stochastic High-Order Nonlinear Systems under Weaker Conditions

Under the weaker conditions on the power order and the nonlinear functions, this paper investigates the output-feedback stabilization problem for a class of stochastic high-order nonlinear systems. Based on the backstepping design method and homogeneous domination technique, the closed-loop system can be proved to be globally asymptotically stable in probability.

Decentralized output feedback robust stabilization for a class of nonlinear interconnected systems with similarity

In this paper, the problem of decentralized output feedback stabilization for a class of nonlinear uncertain interconnected systems with similar subsystems is considered, and a type of controller with holographic structure is developed. It is shown that both the analyses of systems and the design of controllers are simplified by a similar structure. Finally, an example is presented to illustrate the results given in this paper and an estimation of the associated stabilized domain. Simulation shows that our method is very effective.

Adaptive fuzzy tracking control of nonlinear time-delay systems with unknown virtual control coefficients

In this paper, a novel adaptive fuzzy control scheme is proposed for a class of uncertain single-input and single-output (SISO) nonlinear time-delay systems with the lower triangular form. Fuzzy logic systems are used to approximate unknown nonlinear functions, then the adaptive fuzzy tracking controller is constructed by combining Lyapunov-Krasovskii functionals and the backstepping approach. The proposed controller guarantees uniform ultimate boundedness of all the signals in the closed-loop system, while the tracking error converges to a small neighborhood of the origin. An advantage of the proposed control scheme lies in that the number of adaptive parameters is not more than the order of the systems under consideration. Finally, simulation studies are given to demonstrate the effectiveness of the proposed design scheme.

Brief paper: Output-feedback stabilization for stochastic nonlinear systems whose linearizations are not stabilizable

This brief paper investigates the problem of output-feedback stabilization for a class of high-order stochastic nonlinear systems which are neither necessarily feedback linearizable nor affine in the control input. Based on the ideas of the homogeneous systems theory and the adding a power integrator technique, an output-feedback controller is constructed to ensure that the equilibrium at the origin of the closed-loop system is globally asymptotically stable (GAS) in probability. The efficiency of the output-feedback controller is demonstrated by a simulation example.

Congestion Control for DiffServ Network Using Second-Order Sliding Mode Control

In this paper, a nonlinear fluid flow model is used to analyze and control DiffServ Network. The controller design is based on the integrated dynamic congestion control strategy and a leader-follower control scheme. With respect to standard sliding mode control (SMC), the second-order sliding mode technique shows the same properties of robustness to uncertainties of model and considerable simplification of model used in the design. Apart from the robustness feature, the proposed second-order SMC laws have the advantage of being continuous, thus eliminating the chattering effect and being more acceptable in application. The performance of the control scheme is verified by the simulation results.

Further results on adaptive state-feedback stabilization for stochastic high-order nonlinear systems

This paper aims to relax the results in Xie and Tian (2009) from the following two aspects: completely removing the power order restriction and largely relaxing the growth conditions of nonlinear functions. By using the backstepping design method and homogeneous domination technique, this paper investigates the problem of adaptive state-feedback stabilization for a class of stochastic high-order nonlinear systems with nonlinear parameterization. The closed-loop system can be proved to be globally stable in probability and the states can be regulated to the origin almost surely. The efficiency of the adaptive state-feedback controller is demonstrated by a simulation example.

Brief paper: Adaptive state-feedback stabilization for a large class of high-order stochastic nonlinear systems

Under the more general conditions on the power order and the nonlinear functions, this paper investigates the problem of adaptive state-feedback stabilization for a class of high-order stochastic nonlinear systems with time-varying control coefficients. Based on the backstepping design method and homogeneous domination technique, the closed-loop system can be proved to be globally stable in probability and the states can be regulated to the origin almost surely. The efficiency of the state-feedback controller is demonstrated by a simulation example.

Fault tolerant decentralized H/sub /spl infin// control for symmetric composite systems

Discusses a class of large-scale systems composed of symmetrically interconnected identical subsystems. We consider the decentralized H/sub /spl infin// control design problem and study the fault tolerance of the resulting system. By exploiting the special structure of the systems, a sufficient condition for the existence of a decentralized H/sub /spl infin// controller is derived. Moreover, for the nominal case as well as for contingent situations characterized by control channel failures, the poles and the H/sub /spl infin//-norm of the closed-loop system can be calculated easily based on certain systems of reduced dimensions. Consequently, the tolerance to actuator failure can, be easily tested.