Reconfigurable Fault-tolerant Control Research Articles

Partial State Feedback MRAC Based Reconfigurable Fault-Tolerant Control of Drag-Free Satellite With Bounded Estimation Error

Aiming at the ultra-precision and ultra-stable requirements of drag-free control in space detection missions, a multivariable model reference adaptive control (MRAC) scheme is proposed in this paper based on partial observation state, to provide adaptive suppression of uncertain disturbances and improve detection accuracy. The MRAC scheme utilizes model output matching with partial state containing uniform and bounded observation error, and estimates the unknown state parameters through the adaptive law and high-frequency gain decomposition. In response to the actuator bias fault of the drag-free satellite, a set of state error iterative convergence sequence in the actuator loop is established based on the sequence Lyapunov analysis, which is further introduced into the reconfiguration control input to achieve the fault-tolerant target without changing the nominal controller. Through the Lyapunov stability analysis, the convergence of the closed-loop system states in the presence of actuator faults and observation errors is obtained. Numerical simulation results for a 6-DOF drag-free control system demonstrate the effectiveness of the proposed MRAC-based reconfigurable fault-tolerant control scheme.

Reconfigurable Fault-Tolerant Control for Spacecraft Formation Flying Based on Iterative Learning Algorithms

This paper investigates the issues of iterative learning algorithm-based robust thruster fault reconstruction and reconfigurable fault-tolerant control for spacecraft formation flying systems subject to space perturbations. Motivated by sliding mode methodology, a novel iterative learning observer (ILO) was developed to robustly reconstruct the thruster faults. Based on the fault signals obtained from the ILO, a learning output–feedback fault-tolerant control (LOF2TC) approach was explored such that the closed-loop spacecraft formation configuration was accurately maintained in the presence of space perturbations and thruster faults. Numerical simulations were employed to demonstrate the effectiveness and superiority of the proposed ILO-based fault-reconstructing approach and LOF2TC-based configuration maintenance approach for spacecraft formation flying systems.

Prescribed performance incremental adaptive optimal fault-tolerant control for nonlinear systems with actuator faults

In this paper, a model-free incremental adaptive optimal fault-tolerant controller with prescribed performance is proposed for nonlinear systems subject to actuator faults. Considering the system actuator redundancy, an actuator grouping scheme is introduced according to the actuator functions. An incremental adaptive fault observer is designed to estimate the faults. The recursive least squares (RLS) identification is utilized to identify the incremental system parameters. Both dynamic process requirements and optimal performance index of the closed loop system are taken into consideration by combining prescribed performance bound (PPB) and incremental adaptive dynamic programming (IADP). Simulations are given to verify the effectiveness of the proposed IADP reconfigurable fault-tolerant control scheme.

Reconfigurable fault-tolerant control for supersonic missiles with actuator failures under actuation redundancy

Aircraft undergoing actuator failures into under-actuation have been seldom studied in literature. Aiming at addressing actuator failures of Total Loss of Effectiveness (TLOE) as well as Partial Loss of Effectiveness (PLOE) resulting in different system actuations, reconfigurable Fault-Tolerant Control (FTC) is proposed for supersonic wingless missiles under actuation redundancy. The under-actuated system of TLOE failure patterns is solved by transformation to cascade systems through a ‘shape variable’. Meanwhile, actuator TLOE faults of different unknown failure patterns from proper actuation to under-actuation are accommodated by a reconfigurable adaptive law on a multiple-model basis. The backstepping technique with the Extended State Observer (ESO) method adopted as a basic strategy is applied to an established symmetric coupled missile system with actuator PLOE faults, modeling errors, and external disturbances. Additionally, the nonlinear saturation characteristics of actuators are settled by an auxiliary system with the Nussbaum function technique. The stability of the control system is analyzed and proven through Lyapunov theory. Numerical simulations are implemented in the presences of aerodynamic uncertainties, gust disturbance, and actuator failures. Results demonstrate the effectiveness of the proposed method with satisfactory tracking performance and actuator fault tolerance capacity.

Reconfigurable Tolerant Control of Uncertain Mechanical Systems With Actuator Faults: A Sliding Mode Observer-Based Approach

This paper studies a key issue of developing reconfigurable fault-tolerant control to retain a nominal feedback controller and simultaneously handles actuator faults and system uncertainty, while the closed-loop system is stabilized with all control objectives achieved. A theoretical architecture of a reconfigurable control design is presented for a class of uncertain mechanical systems by using an observer technique. As a stepping stone, a nonlinear observer-based estimation mechanism is designed to reconstruct uncertain dynamics and actuator faults with the estimation error converging to zero within finite time. A reconfigurable control effort is then synthesized from the reconstructed knowledge. This control power operates as a compensation control part, and it is added to the nominal control part to accommodate system uncertainties and actuator faults. It is proved that the overall system resulted from the developed control framework has the same control performance of the nominal closed-loop system, including certain system dynamics and the nominal control effort. The effectiveness of the scheme is validated on a serial robotic manipulator.

Integrated multiple-model adaptive fault identification and reconfigurable fault-tolerant control for Lead-Wing close formation systems

ABSTRACTThis paper investigates the attitude and position tracking control problem for Lead-Wing close formation systems in the presence of loss of effectiveness and lock-in-place or hardover failure. In close formation flight, Wing unmanned aerial vehicle movements are influenced by vortex effects of the neighbouring Lead unmanned aerial vehicle. This situation allows modelling of aerodynamic coupling vortex-effects and linearisation based on optimal close formation geometry. Linearised Lead-Wing close formation model is transformed into nominal robust H-infinity models with respect to Mach hold, Heading hold, and Altitude hold autopilots; static feedback H-infinity controller is designed to guarantee effective tracking of attitude and position while manoeuvring Lead unmanned aerial vehicle. Based on H-infinity control design, an integrated multiple-model adaptive fault identification and reconfigurable fault-tolerant control scheme is developed to guarantee asymptotic stability of close-loop systems, error signal boundedness, and attitude and position tracking properties. Simulation results for Lead-Wing close formation systems validate the efficiency of the proposed integrated multiple-model adaptive control algorithm.

Coordinated and fault‐tolerant control of tandem 15‐phase induction motors in ship propulsion system

Electric propulsion is widely used in ship propulsion systems, and multiphase machines are gaining increasing popularity because of their fault-tolerant ability, high power density, and reduced torque ripple. This study concentrates on the tandem ship propulsion configuration with two 15-phase induction machines (IMs) fixed on the same shaft. Based on field-oriented control and reconfiguration fault-tolerant control for the single 15-phase IM, the master–slave coordinated control strategy is designed for the tandem motors, which can not only achieve power allocation between two motors during normal operation, but also minimise the total stator copper loss of the two motors and maximise the propulsion output power ability during fault-tolerant operation. Experiment results from a ship propulsion experimental platform verify the effectiveness of the proposed control strategies.

Smart Investment for Redundancies Selection Integrated to Reconfigurable Fault-Tolerant Control Design

This paper presents a methodology for the optimal hardware redundancies selection in the context of reconfigurable fault-tolerant control design. Assuming that a nominal controller of reduced dimension has been successfully designed, the objective is to accommodate a presumed set of failures, including partial, total, and simultaneous actuator faults, preserving the system stability and maintaining an acceptable dynamic performance. The methodology is based on a multiobjective optimization framework to obtain a suitable trade-off between conflicting design objectives such as controllability and performance. The selection of additional hardware devices (not included in the nominal controller) is penalized to determine the minimum number of redundancies that should be installed. In addition, the redundancies selection is performed without explicitly considering the type of control structure. The effectiveness of the proposed approach is tested using the well-known Tennessee Eastman benchmark.

Integrated design of fault reconstruction and fault-tolerant control against actuator faults using learning observers

ABSTRACTThis paper addresses the problem of integrated fault reconstruction and fault-tolerant control in linear systems subject to actuator faults via learning observers (LOs). A reconfigurable fault-tolerant controller is designed based on the constructed LO to compensate for the influence of actuator faults by stabilising the closed-loop system. An integrated design of the proposed LO and the fault-tolerant controller is explored such that their performance can be simultaneously considered and their coupling problem can be effectively solved. In addition, such an integrated design is formulated in terms of linear matrix inequalities (LMIs) that can be conveniently solved in a unified framework using LMI optimisation technique. At last, simulation studies on a micro-satellite attitude control system are provided to verify the effectiveness of the proposed approach.

INTEGRATION FAULT DETECTION AND TOLERANT CONTROL IN MICRO-SATELLITE ATTITUDE PROPULSION MODE APPLICATION

The paper refers to a tolerant control method which is reconfigurable to micro-satellites when they are out of order. The integrated approach to the design of thruster control reconfigurable fault-tolerant control system is proposed. The scheme includes a control effectiveness factor and a reconfigurable fault-tolerant controller. The fault detection, diagnosis and controller reconfiguration are carried out using the control effectiveness factor based on the information from a two-stage Kalman filter. By using the two-stage Kalman filter and digital controller, the nonlinear plant will be discretized. We present sufficient conditions under which a discrete-time controller that input-to-state stabilizes an approximate discrete-time model of a nonlinear plant with disturbances. The result shows the method enables us to solve the system faults and meet the requirement when there is a fault in the micro-satellites attitude control system.

Fault Reconstruction and Accommodation in Linear Parameter-Varying Systems via Learning Unknown-Input Observers

This paper addresses the problem of observer-based fault reconstruction and accommodation for polytopic linear parameter-varying (LPV) systems. A polytopic representation of an LPV system subject to actuator faults and external disturbances is first established; then, a novel polytopic learning unknown-input observer (LUIO) is constructed for simultaneous state estimation and robust fault reconstruction. The stability of the presented LUIO is proved using Lyapunov stability theory together with H∞ techniques. Further, using reconstructed fault information, a reconfigurable fault-tolerant controller is designed to compensate for the influence of actuator faults by stabilizing the closed-loop system. At last, an aircraft example is employed to illustrate the effectiveness and practicability of the proposed techniques.

Nominal Controller Design Based on Decentralized Integral Controllability in the Framework of Reconfigurable Fault-Tolerant Structures

A reconfigurable fault-tolerant control system typically includes a nominal controller (NC), a fault detection/diagnosis (FDD) and decision subsystem, a reconfiguration mechanism, and a reconfigurable controller (RC). Here, a systematic methodology for designing a fully decentralized NC of reduced dimension is presented, providing (i) fault-tolerant capability due to the structural flexibility and (ii) availability of redundancies for RC design. The fulfillment of a sufficient condition for decentralized integral controllability is searched to guarantee the stability while the FDD scheme is identifying the faults. A novel framework based on a genetic algorithm is developed for obtaining alternative NCs. They are screened considering quantitative measures derived from stability and performance considerations. The procedure features complexity reduction because (i) it only utilizes steady-state process information and (ii) it is independent from the controller design. The methodology is tested in the Tennes...

Flight Control: Challenges and Opportunities

摘要: 当前,飞行器控制的发展面临前所未有的机遇与挑战.基于对飞行器的发展趋势、新需求和新技术特征的分析,本文从飞行器新技术特征、信息化环境、无人系统自主性、高可靠可重构容错系统、飞控系统评估与确认五个方面研究和分析了飞行器控制面临的机遇与挑战.为了达到利用机遇和赢得挑战的目标,作者建议加强如下五个方面的研究: 加强面向飞行器新技术特征的飞行器控制概念、理论与方法研究; 加强面向信息化环境的控制、计算与通讯一体化,以及控制、决策与管理一体化的研究; 加强面向不确定性的无人系统高级别自主性的研究; 加强面向高可靠、高安全性的可重构容错飞控系统的研究; 加强面向高效、高可信度的飞控系统评估与确认方法的研究. 关键词: 飞行控制 / 飞行器新特征 / 信息化 / 容错系统 / 自主能力

Reconfigurable fault-tolerant controller synthesis for a steer-by-wire vehicle using independently driven wheels

In this paper, a synthesis method for a reconfigurable fault-tolerant control system for use in a steer-by-wire vehicle is proposed. The vehicle considered in this paper is also assumed to have independently driven wheels. The control objective in this work is to enable the vehicle yaw rate to track the reference signal even when the steering actuator breaks down. Since the vehicle yaw rate can be controlled with either the front wheel turn angle or the yaw moment generated by the independently driven wheels, this system has actuator redundancy. We attempt to design a control system that manages this actuator redundancy so that the performance degradation due to the actuator failure is minimised. We utilise a control allocator based on on-line optimisation for managing the actuator redundancy. The fault-tolerant control system with a control allocator has several excellent properties. For example, the method can handle various failure situations. Also, since the control allocation problem is reduced to a convex quadratic programming problem, the on-line computational effort is relatively little. However, so far, it has been unclear whether the stability of the control system with the control allocator is guaranteed when the actuator failure occurs. Therefore, we propose a design method of a fault-tolerant controller based on on-line optimisation that guarantees the stability of the overall system. The effectiveness of the method is established through numerical examples.

Detecting and Tolerating Faults in Switched Reluctance Motors

The switched reluctance motor (SRM) has inherently high level of fault tolerance. However despite of its high robustness and reliability it can face windings and bearings faults. The faults can cause costly downtimes in industrial environment, or they can bring about more severe consequences in safety critical applications. Therefore the detection of the faults in their incipient phase and the ability to tolerate them is a very important requirement for the electrical drive systems used in such applications. The paper deals with the most important faults of the SRMs, their effects on the machine performances and their detection. Also a reconfigurable fault tolerant control system for the SRMs is proposed, which is able to detect diverse winding faults and to mask these faults by imposing increased currents in the healthy remained coils of the machine. The fault detection capability and the correct reconfiguration of the proposed control system are proved by laboratory tests.

A mixed active and passive GLR test for a fault tolerant control system

A mixed active and passive GLR test for a fault tolerant control system This paper presents an adaptive Generalized Likelihood Ratio (GLR) test for multiple Faults Detection and Isolation (FDI) in stochastic linear dynamic systems. Based on the work of Willsky and Jones (1976), we propose a modified generalized likelihood ratio test, allowing detection, isolation and estimation of multiple sequential faults. Our contribution aims to maximise the good decision rate of fault detection using another updating strategy. This is based on a reference model updated on-line after each detection and isolation of one fault. To reduce the computational requirement, the passive GLR test will be derived from a state estimator designed on a fixed reference model directly sensitive to system changes. We will show that active and passive GLR tests will be mixed and give interesting results compared with the GLR of Willsky and Jones (1976), and that they can be easily integrated in a reconfigurable Fault-Tolerant Control System (FTCS) to asymptotically recover the nominal system performances of the jump-free system.

Decentralized Receding Horizon Control for Cooperative Multiple Vehicles Subject to Communication Delay

N this paper, a new approach is proposed for the decentralized receding horizon control (DRHC) of multiple cooperative vehicles with the possibility of communication failures leading to large intervehicle communication delay. Such large communication delays can lead to poor performance and even instability. The neighboring vehicles exchange their predicted trajectories at each sampletimetomaintainthecooperationobjectives.Itisassumedthat the communication failure is partial in nature, which in turn leads to large communication delays of the exchanged trajectories. The proposedfault-tolerantDRHCisbasedontwoextensionsofexisting work for the case of large communication delays. The first contributionisthedevelopment ofanewDRHC approachthat estimates thetrajectoryoftheneighboringvehiclesforthetailoftheprediction horizon, which would otherwise not be available due to the communication delay. In this approach, the tail of the cost function is estimated by adding extra decision variables in the cost function. A relatively small amount of existing work has investigated the implementation issues associated with exchange of trajectory information, but so far no work has proposed a tail estimation process to compensate for large delays. For instance, in [1–3], no prediction or estimation for the trajectory of neighboring vehicles is performed, and it is assumed that the neighboring vehicles remain at the last delayed states broadcasted by them. Such assumptions may yield poor performance for large communication delays because the constant state vector is not a good estimation of a trajectory of states in general. Similar issues are also investigated in [4,5]. The second contribution of this paper is an extension of the tubebased model predictive control (MPC) approach [6,7] for the case of thelargecommunicationdelaysinordertoguaranteethesafetyofthe fleet against possible collisions during formation control problems. The concept of the tube MPC [or tube receding horizon control (RHC)] in existing work [6,7] is normally used to calculate a robust bound on the states due to system uncertainty, whereas in this paper, the approach is used to calculate bounds that arise from large communication delays of the exchanged neighbor trajectories. The proposed algorithms in this paper are presented in the context of fault-tolerant control, as the communication delay/break may occur due to any failure and malfunction in the communication devices. Some examples of communication failures for the team of cooperative vehicles can be found in [8–10]. In [8], the wireless communicationpacketloss/delayisconsidered;oncethepacketloss/ delay occurs, the previous available trajectory of the faulty unmanned aerial vehicle (UAV) is extrapolated to predict the future reference trajectory. Also, in [9], the communication failure in formation flight of multiple UAVs leads to a break in the communicated messages that forces the fleet to redefine the communication graph. This paper is organized as follows. Section II deals with a general formulation of the decentralized receding horizon controller, and the corresponding algorithm for a fault-free (delay-free) condition. In Section III, a faulty condition is first defined, and a reconfigurable fault-tolerant controller is developed. A safety guarantee method forthefaultyconditionisalsodevelopedbasedontheconceptoftube RHC. In Section IV, the proposed algorithms are tested through simulation of a leaderless formation controller for a fleet of unmanned vehicles.

The design of a fault-tolerant vehicle control system

To improve the performance properties of heavy vehicles, i.e., to reduce the risk of rollovers, to improve passenger comfort and road holding, a reconfigurable fault-tolerant control design of the active suspensions and the active brake is performed. However, when a fault (loss in effectiveness) occurs at one of the suspension actuators a reconfiguration is needed in order to maintain the same performance level. The detection of the fault is based on a Fault Detection and Identification (FDI) filter, which is based on an observer design. The proposed reconfiguration scheme is based on an H∞ Linear Parameter Varying (LPV) method that uses the fault information as one of the scheduling variables. The LPV based control design and the operation of the control mechanism are demonstrated in a vehicle manoeuvre.

Actuator fault detection for suspension system

This paper focuses on the derivation of a Fault Detection and Identification (FDI) filter for the detection of the faults that might occur during the operation of the actuator built in the suspension system. The design of the proposed FDI filter is based on dynamic inversion and on a Linear Parameter Varying (LPV) observer design. To improve the performance properties of heavy vehicles, i.e. to reduce the risk of rollovers, improve passenger comfort and road holding, a reconfigurable fault-tolerant control design of the active suspensions and the active brake is performed. However when a fault (loss in effectiveness) occurs at one of the suspension actuators a further reconfiguration is needed in order to maintain the same performance level. The proposed reconfiguration scheme is based on an LPV method that uses the fault information as one of the scheduling variables. The LPV based control design and the operation of the control mechanism are demonstrated through a vehicle maneuver.

Bibliographical review on reconfigurable fault-tolerant control systems

In this paper, a bibliographical review on reconfigurable (active) fault-tolerant control systems (FTCS) is presented. The existing approaches to fault detection and diagnosis (FDD) and fault-tolerant control (FTC) in a general framework of active fault-tolerant control systems (AFTCS) are considered and classified according to different criteria such as design methodologies and applications. A comparison of different approaches is briefly carried out. Focuses in the field on the current research are also addressed with emphasis on the practical application of the techniques. In total, 376 references in the open literature, dating back to 1971, are compiled to provide an overall picture of historical, current, and future developments in this area.