Jianglin Lan

A new strategy for integration of fault estimation within fault-tolerant control

The problem of active fault tolerant control (FTC) of dynamical systems involves the process of fault detection and isolation/fault estimation (FDI/FE) used to either make a decision as to when and how to change the control, based on FDI or to compensate the fault in the control system via FE. The combination of the decision-making/estimation and control gives rise to a bi-directional uncertainty in which the modelling and fault uncertainties and disturbances all affect the quality and robustness of the FTC system. This leads to the FTC requirement for an integrated design of the FDI/FE and control system reconfiguration. This paper focuses on the FTC approach using FE and fault compensation within the control system in which the design is achieved by integrating together the FE and FTC controller modules. The FE is based on a modified reduced-/full-order unknown input observer and the FTC system is constructed by sliding mode control using state/output feedback. The integrated design is converted into an observer-based robust control problem solved via H ∞ optimization with a single-step LMI formulation. The performance effectiveness of the proposed integrated design approach is illustrated through studying the control of an uncertain model of a DC motor.

Integrated Design of Fault-Tolerant Control for Nonlinear Systems Based on Fault Estimation and T–S Fuzzy Modeling

This paper proposes an integrated design of fault-tolerant control (FTC) for nonlinear systems using Takagi–Sugeno (T–S) fuzzy models in the presence of modeling uncertainty along with actuator/sensor faults and external disturbance. An augmented state unknown input observer is proposed to estimate the faults and system states simultaneously, and using the estimates, an FTC controller is developed to ensure robust stability of the closed-loop system. The main challenge arises from the bidirectional robustness interactions, since the fault estimation (FE) and FTC functions have an uncertain effect on each other. The proposed strategy uses a single-step linear matrix inequality formulation to integrate together the designs of FE and FTC functions to satisfy the required robustness. The integrated strategy is demonstrated to be effective through a tutorial example of an inverted pendulum system (based on robust T–S fuzzy designs).

Integrated design of robust fault estimation and fault-tolerant control for linear systems

In the fault tolerant control (FTC) problem based on fault compensation a bi-directional uncertainty coupling exists between the controller and the joint state/fault estimation. This coupling arises from (a) the model mismatch between the system dynamics and the observer model as well as (b) the uncertainty arising from imperfect fault estimation. Hence, this paper deals with an approach to integrate together the designs of the observer and controller for a linear system subject to bounded actuator and sensor faults as well as disturbance. The fault estimation is achieved by using an augmented state form of an unknown input observer (UIO) which relaxes the well-known UIO rank restriction in terms the system coefficient matrices. The integrated design problem with fault compensation is an observer-based robust control system solved via H∞ optimization using single-step LMI formulation. The closed-loop system time response is improved using LMI regional pole placement. The FTC performance is illustrated using an example with both sensor and actuator faults as well as disturbance and uncertainty.

A continuous control approach to point absorber wave energy conversion

In recent years the control of Wave Energy Conversion (WEC) systems has been a challenging research topic. A 1/50th scale buoy system has been constructed at the University of Hull for modelling, verification and control. This study focuses on the time-varying state space model development of this direct-drive WEC with a tubular permanent magnet linear generator (TPMLG). A new form of control is developed, with (i) an adaptive impedance tuning system based on a mechanical-electrical analogue, and (ii) position and current tracking for power maximisation, physical constraint realisation and generator dynamic linearisation. Simulation results of regular and irregular waves indicate this control strategy can achieve an acceptable energy conversion efficiency.

Estimation of wave excitation force for wave energy converters

This paper presents a novel technique to estimate the wave excitation force which is an essential signal in the control of a Point Absorber Wave Energy Converter (PAWEC). The work uses a nonlinear PAWEC simulation together with a modified form of the well-known fast adaptive actuator fault estimation (FAFE) technique for nonlinear Lipschitz system, the fast adaptive unknown input estimation (FAUIE). The estimated wave excitation force is an important reference input for optimum power control and is considered as an unknown input. The results show accurate wave excitation force estimation based on irregular wave generation as well as the performance of the power tuning controller.

Integrated fault estimation and fault-tolerant control design for large-scale interconnected systems

An integrated fault estimation and fault-tolerant control (FTC) design is proposed in this paper for interconnected linear systems with uncertain nonlinear interactions subject to unknown bounded sensor faults. A decentralized FTC strategy, using the state/fault estimates obtained simultaneously by a decentralized unknown input observer, is employed to maintain the robust stability of the overall interconnected system and compensate the sensor fault effects. The observer and controller gains are solved together using a single-step linear matrix inequality (LMI) formulation. The performance effectiveness of the presented design is illustrated through an example of a 3-machine power system.

Decentralized fault estimation and fault-tolerant control for large-scale interconnected systems: An integrated design approach

A large-scale interconnected system consists of large numbers of coupled subsystems. This coupling gives rise an important problem of integrating the designs of fault estimation (FE) and fault-tolerant control (FTC) in the presence of unexpected faults. This paper proposes an integrated FE/FTC design for large-scale interconnected systems with uncertain nonlinear interactions and unknown bounded actuator faults. A decentralized FTC controller is developed to guarantee the robust stability of the overall interconnected system, using the state/fault estimates obtained simultaneously by a decentralized unknown input observer. The observer and controller gains are solved simultaneously using a single-step linear matrix inequality (LMI) formulation. The performance effectiveness of the proposed design is demonstrated by applying it to the stabilization of a 3-machine power system.

Sliding Mode State and Fault Estimation for Decentralized Systems

The interconnection of dynamical systems gives rise to interesting challenges for control in terms of stability, robustness and the overall performance of the global interconnected systems as well as the fault tolerance of the individual subsystems. Interconnected systems can be developed either from a standpoint of centrality of control based on the construction and design of a global system that satisfies the above requirements. Alternatively, the interconnected system can be decentralized which means that the stability, performance, etc., requirements are achieved at the local (subsystem) levels. To develop a good “fault-tolerant control” strategy for decentralized systems it is necessary to take account of various faults or uncertainties that may occur throughout all local levels of the system. A powerful way to achieve this is to use robust state and fault estimation methods accounting for the model–reality mismatch that is inevitable when (a) systems are linearized and (b) when faults occur in subsystem components such as actuators, sensors, etc. The chapter develops a strategy for decentralized state and fault estimation based on the Walcott–Żak form of sliding mode observer (SMO) with linear matrix inequality (LMI) formulation. This strategy is shown to be advantageous when considering the estimation problem for a large number of interconnected subsystems. After developing the design procedure a tutorial example of two interconnected linear systems with nonlinear interconnection functions shows that the states as well as actuator and sensor faults can be robustly estimated. Finally, an application-oriented example of a three-machine power system is given which has actuator faults as well as nonlinear machine interconnections.