Yang Guang-Hong

Robust adaptive synchronization of uncertain and delayed dynamical complex networks with faulty network

This paper presents a new robust adaptive synchronization method for a class of uncertain dynamical complex networks with network failures and coupling time-varying delays. Adaptive schemes are proposed to adjust controller parameters for the faulty network compensations, as well as to estimate the upper and lower bounds of delayed state errors and perturbations to compensate the effects of delay and perturbation on-line without assuming symmetry or irreducibility of networks. It is shown that, through Lyapunov stability theory, distributed adaptive controllers constructed by the adaptive schemes are successful in ensuring the achievement of asymptotic synchronization of networks in the present of faulty and delayed networks, and perturbation inputs. A Chuas circuit network example is finally given to show the effectiveness of the proposed synchronization criteria.

Fault-Tolerant H Control of Linear Systems: An Indirect Adaptive Approach

More and more advanced technological systems rely on sophisticated control systems to increase their safety and performances. In the event of system component failures, the conventional feedback control designs may result in unsatisfactory performances or even instability, especially for complex safety critical systems such as aircrafts, space crafts, nuclear power plants, etc. This has ignited enormous research activities in search for new design methodologies for accommodating the component failures and maintaining the acceptable system stability and performances, so that abrupt degradation and total system failures can be averted. This type of control is often known as fault-tolerant control (FTC). Faut-tolerant control design approaches can be broadly classified into two types: Passive approach such as robust fault accommodation approach, and active approach such as linear quadratic regulator(LQR); eigenstructure assignment(EA); multiple model (MM); adaptive approach; pseudoinverse; and neural networks. In the passive approach, the same controller is used throughout normal and faulty cases, and such that this passive fault-tolerant controller is easily implemented. Moreover, several performance indexes such as H1, H2 and cost functions mainly based on algebraic Riccati equation (ARE) or linear matrix inequality (LMI) methods can be used to describe the performances of closed-loop systems with fixed controller gains. However, as the number of possible failures and the degree of system redundancy increase, a controller designed based on the passive approach becomes more conservative and attainable control performances may not be satisfactory. On the other hand, a fault-tolerant control system based on active approach can compensate for faults either by selecting a pre-computed control law or by synthesizing a new control strategy on-line. Adaptive approach is very important in active FTC, which relies on the potential of the adjustments of parameters to assure reliability of closed-loop systems in the presence of a wide range of unknown faults. Most of the results in adaptive fault-tolerant control are based on model reference adaptive control (MRAC), where the outputs of closed-loop systems can track the prescribed referent outputs. But the disturbance attenuation performances of systems have not been addressed yet within the MRAC framework. Another typical approach for fault compensations is based on fault detection and isolation (FDI) subsystems. However, it should be noted that the fault detection diagnosis (FDI) mechanism might not always give the exact fault information. In this paper, the fault-tolerant H1 control problem for linear time-invariant systems against actuator faults is studied. A general actuator fault model is considered, which covers the outage cases and the possibility of partial faults. A notion of adaptive H1 performance index is proposed to describe the disturbance attenuation performances of systems, and the adaptive approach and LMI approach to robust control are combined successfully to give adaptive fault-tolerant H1 controller design methods for both state feedback case and dynamic output feedback case. Furthermore, the proposed design methods can deal with different fault modes. With the on-line estimations of fault values using adaptive laws instead of an FDI mechanism, a re-configurable control law can be designed to maintain satisfactory adaptive H1 performances. Sufficient conditions for the existence of the above-mentioned adaptive fault-tolerant H1 controllers are given, and it is shown that these conditions are more relaxed than those for the passive fault-tolerant controller designs with fixed controller gains. Comparing with the FTC approach with the need for an FDI mechanism to provide the exact fault information, the new proposed design methods rely on the on-line estimations of fault values using adaptive laws, where it is not necessary for the estimations to give the exact fault information.

Quantized Dynamic Output Feedback H ∞ Controller Design

This paper studies the quantized dynamic output feedback Hinfin control problem for discrete-time linear time-invariant (LTI) systems with the consideration of quantizer ranges. The quantizers considered here are dynamic and time-varying. An iterative LMI-based optimization algorithm is proposed to optimize the quantizer ranges, and with which a concrete dynamic output feedback control strategy dependent on not only the controller states but also the measurement outputs is proposed with updating quantizers parameters, such that the quantized closed-loop system is asymptotically stable and with a prescribed Hinfin performance bound. An example is presented to illustrate the effectiveness of the control strategy.

Stabilization of Power Systems by Switched Controllers

An interesting application of switched control is provided in the field of power systems with either temporary fault or permanent fault. Such a power system is modelled by a switched linear system. A switched controller is design to stabilize the overall system and to improve the transient performance of the closed-loop system.