Stabilizing controllers for systems with sensor or actuator failures

This thesis is concerned with the dissipative control and filtering problems of singular systems. Four classes of singular systems are considered: delay-free singular systems, singular systems with constant time-delay, uncertain singular systems with time-varying delay and sensor failures, and singular Markovian jump systems with actuator failures.
\nFor delay-free singular systems, the system augmentation approach is employed to study the dissipative control and filtering problems. First, the approach is used to solve the dissipative control problem by static output-feedback for standard state-space systems which are the special cases of singular systems. For a continuous-time standard state-space system, the closed-loop system is represented in an augmented system form. Based on the augmented system, a necessary and sufficient dissipativity condition is proposed, which decouples the Lyapunov matrix and controller matrix. To further separate the Lyapunov matrix and the system matrices, an equivalent condition is obtained by introducing some slack matrices. Then, a necessary and sufficient condition for the existence of a static output-feedback controller is proposed, and an iterative algorithm is given to solve the condition. For discrete-time singular systems, by giving an equivalent representation of the solution set, a necessary and sufficient dissipativity condition is proposed in terms of strict linear matrix inequality (LMI) which can be easily solved by standard commercial software. Then a state-feedback controller design method is given based on the augmentation system approach. The method is extended to the static output-feedback control problem and the reduced-order dissipative filtering problem.
\nFor continuous-time singular time-delay systems, the problem of state-feedback dissipative control is considered. An improved delay-dependent dissipativity condition in terms of LMIs is established by employing the delay-partitioning technique, which guarantees a singular system to be admissible and dissipative. Based on this, a delay-dependent sufficient condition for the existence of a state-feedback controller is proposed to guarantee the admissibility and dissipativity of the closed-loop system. In addition to delay-dependence, the obtained results are also dependent on the level of dissipativity. Moreover, the results obtained unify existing results on H∞ performance analysis and passivity analysis for singular systems.
\nFor discrete-time singular systems with polytopic uncertainties, time-varying delay and sensor failures, the problem of robust reliable dissipative filtering is considered. The filter is designed by the reciprocally convex approach such that the filtering error singular system is admissible and strictly (Q, S, R)-dissipative. For singular systems with time-varying delay and sensor failures, a sufficient condition of reliable dissipative analysis is obtained in terms of LMIs. Then the result is extended to the uncertain case by introducing some variables to decouple the Lyapunov matrices and the filtering error system matrices. Moreover, a desired filter for uncertain singular systems with time-varying delay and sensor failures is obtained by solving a set of LMIs.
\nFor continuous-time singular Markovian jump systems with actuator failures, the problem of reliable dissipative control is addressed. Attention is focused on the state-feedback controller design method such that the closed-loop system is admissible and strictly (Q, S, R)-dissipative. A sufficient condition is obtained in terms of strict LMIs. Moreover, the results obtained unify existing results on H∞control and passive control on singular Markovian jump systems.

Finite-horizon reliable control with randomly occurring uncertainties and nonlinearities subject to output quantization

The decentralized robust servomechanism problem (DRSP) for large flexible space structures (LFSS) under sensor and actuator failures is considered. Failure conditions are modelled by failure matrices. This permits a unified treatment of sensor and actuator failures. For colocated LFSS, stabilization, tracking of constant set points, and regulating constant disturbances can be simultaneously handled using a decentralized tuning PID output-feedback controller. Necessary and sufficient conditions for solvability of the DRSP for colocated LFSS under sensor and actuator failures are derived. Two detailed examples demonstrate the effectiveness of the controller.

This paper is concerned with the synthesis of constant output feedback law which possesses integrity against failures of actuator and sensor. For a linear time-invariant system, the redundancy of actuators and sensors is analyzed firstly. In the situation where actuators and sensors are redundant, the modes of open loop system which are outside a desired region of Complex plane (e.g. the open left complex plane) may remain controllable and observable after the failures of some actuator and sensor. For every such situation of permissible actuator or sensor failures, if a constant output feedback law can make the poles of close loop system in the desired region, then the feedback law is said to possess high integrity against actuator and sensor failures, A proper objective function is proposed in this paper. By using the parameter optimization method, the output feedback law possessing high integrity can be generated. A computer program is developed on the IBM PC. For a linear time invariant model of double effect evaporator and a model of a plane, the output feedback laws which possess integrity are obtained by the program. These examples illustrate the effectiveness of the method proposed in this paper. The method does not require that the open loop system is asymptotically stable, this is one of the main advantages of the method.

The issue of fault-tolerant decentralized control is investigated for large-scale civil engineering structures. Considering the correlation of the sub-control system, the sensor failures and the actuator failures, a sufficient condition for decentralized stabilizability is proposed for the class system of discrete-time systems with delay interconnections by using the Lyapunov stability theory and the linear matrix inequality (LMI) approach. It is shown that this condition is equivalent to the feasibility problem of the linear matrix inequality. Furthermore, a decentralized state feedback control law is derived as a convex optimization problem, and the latter can be solved by using existing efficient convex optimization techniques. The obtained controller enables the closed-loop systems to be stable. Considering sensor failures and the actuator failures, the ASCE 9-story benchmark building is selected as a numerical example to evaluate the control performance of the partially independent decentralized control and overlapping decentralized control. Numerical simulation results indicate that the proposed small gain decentralized stabilization control (LMI-SGDSC) algorithm performs as well as the traditional centralized control, and the overlapping decentralized control has a greater level of reliability. The fault tolerant decentralized control (LMI-SGFTDSC) achieves satisfactory control effects.

The unmanned aerial vehicle (UAV) has been developing rapidly recently, and the safety and the reliability of the UAV are significant to the mission execution and the life of UAV. Sensor and actuator failures of a UAV are one of the most common malfunctions, threating the safety and life of the UAV. Fault-tolerant control technology is an effective method to improve the reliability and safety of UAV, which also contributes to vehicle health management (VHM). This paper deals with the sliding mode fault-tolerant control of the UAV, considering the failures of sensor and actuator. Firstly, a terminal sliding surface is designed to ensure the state of the system on the sliding mode surface throughout the control process based on the simplified coupling dynamic model. Then, the sliding mode control (SMC) method combined with the RBF neural network algorithm is used to design the parameters of the sliding mode controller, and with this, the efficiency of the design process is improved and system chattering is minimized. Finally, the Simulink simulations are carried out using a fault tolerance controller under the conditions where accelerometer sensor, gyroscope sensor or actuator failures is assumed. The results show that the proposed control strategy is quite an effective method for the control of UAVs with accelerometer sensor, gyroscope sensor or actuator failures.

In passive redundancy, redundant control devices such as sensors, compensators, and actuators are used in industry to assure reliability against failures. Passive redundancy assures that even if some devices fail, the control system remains stable. Some results on the use of passive redundancy for reliability against compensator or actuator failures are already in existence. The objective of this paper is to explore the possibility of using passive redundancy to protect against sensor failures, which has never before been examined. First, the most fundamental failure mode of sensors is considered and reliability against sensor failures in passive redundancy is defined. Next, the possibility of using passive redundancy with the simplest and most thoroughly conventional studied control system configuration, i.e., the parallel configuration, is studied. Solving the essential problem of this configuration leads to an effective control system configuration. © 1997 Scripta Technica, Inc. 80(5): 96–104, 1997.

Our previous works have proposed a self-repairing PID (SRPID) control for plants with sensor failures. This method uses an I-controller (integrator) with a well-designed auxiliary signal to detect failures. However, the SRPID has not addressed actuator failures. This paper presents a two-step detection method for actuator and sensor failures based on the SRPID and confirms the effectiveness of the proposed detection method through experiments on a ball-and-beam system.

This paper is concerned with the reliable H∞ control design problem for linear state-delayed system using observed-based output feedback. It proposes a reliable control design scheme for the case of possibly a simultaneous presence of actuator failures and sensor failures. Modified algebraic Riccati inequalities are developed to solve the problem addressed. Based on this approach, observer-based feedback control laws are designed that guarantee closed-loop asymptotic stability and reduction of the effect of an augmented disturbance input on the controlled output of a prescribed level, not only when the system is operating properly, but also under actuator and sensor failures. A numerical example is presented to demonstrate the applicability and effectiveness of the proposed approach.

Two layer control systems are common in robot architectures. The lower level is designed to provide fast, fine grained control while the higher level plans longer term sequences of actions to achieve some goal. Our approach uses reinforcement learning (RL) for the low level and Partially Observable Markov Decision Process (POMDP) planning for the high level. Because both levels can adapt their behavior within the scope of their tasks, the combination is expected to be robust to degradations in sensor and actuator failures and so to enhance overall system reliability. We implemented our architecture for use in the Khepera robot simulator. In a set of experiments, we show that good performance can be difficult to achieve with hand coded low level control and that performance of our RL/POMDP system degrades slowly with increasing sensor and actuator failure.

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ABSTRACTThis paper investigates the static output feedback control problem for linear systems. The sensor and actuator may simultaneously suffer the total/partial loss of effectiveness. An adaptive fault-tolerant control scheme is developed by combination of linear matrix inequality method and adaptive mechanism. By estimating the inverses of failure factors online, the adverse effects of sensor and actuator failure can be compensated for. Finally, simulation results on the ‘Raptor-90’ helicopter verify the effectiveness of the proposed approaches.

Multiple model adaptive estimation (MMAE) is a method of estimating unknown system parameters by modeling different discrete parameter values in several filters that are run in parallel and compared. The parameters for this research are failure status conditions associated with flight control actuators and sensors on the LAMBDA unmanned research vehicle, an experimental aircraft. Six actuator failures and eight sensor failures are modeled, along with the fully functional aircraft, in fifteen elemental Kalman filters. These filters propagate and update their own aircraft state estimates in real time. A probability computation representing the likelihood of each elemental filter's match to the true condition of the aircraft is used to generate relative probabilities for each filter's hypothesis. The MMAE algorithm is extended for the identification of dual failures through the use of a hierarchical structure of filter banks. Aircraft state excitation is required for effective MMAE performance. Sinusoidal dither signals are applied to the command inputs of a flight control system which controls pitch rate, roll rate, and sideslip angle. >

Application of Multiple Model Adaptive Algorithms to Reconfigurable Flight Control

The purpose of this article is twofold The first goal is to present important issues in designing fault-tolerant systems for autonomous robots. The second is to present the fault-tolerance capabilities we implemented on our autonomous robot. Our approach is characterized by a distributed network of concurrently running processes. To tolerate hardware failures, a set of fault-tolerance processes is written for each component. These processes are responsible for detecting faults in their respective component and for minimizing the impact of the failure on the robot's performance. By exploiting concurrency and distributedness, the system monitors, detects, and compensates for component failures simultaneously. The capabilities of this system have been tested by physically disabling and enabling the robot's sensors and actuators. The system quickly recognizes and compensates for both minor and severe sensor and actuator failures. lt tolerates a variety of sensor failures such as decalibration, erroneous readings, and permanent failures. lt also tolerates various combinations of failures such as individual failures, concurrent failures, and accumulative failures.