A discussion on sensor recovery techniques for fault tolerant multisensor schemes

The present paper deals with the interplay between healthy and faulty sensor functioning in a multisensor scheme based on a switching control strategy. Fault tolerance guarantees have been recently obtained in this framework based upon the characterisation of invariant sets for state estimations in healthy and faulty functioning. A source of conservativeness of this approach is related to the issue of sensor recovery. A common working hypothesis has been to assume that once a sensor switches to faulty functioning it can no longer be used by the control mechanism even if at an ulterior moment it switches back to healthy functioning. In the current paper, we present necessary and sufficient conditions for the acknowledgement of sensor recovery and we propose and compare different techniques for the reintegration of sensors in the closed-loop decision-making mechanism.     

Multisensor switching control strategy with fault tolerance guarantees

In this paper we propose a novel fault tolerant multisensor switching strategy for feedback control. Each sensor of the proposed multisensor scheme has an associated state estimator which, together with a state feedback gain, is able to individually stabilise the closed-loop system. At each instant of time, the switching strategy selects the sensor-estimator pair that provides the best closed-loop performance, as measured by a control-performance criterion. We establish closed-loop stability of the resulting switching scheme under normal (fault-free) operating conditions. More importantly, we show that closed-loop stability is preserved in the presence of faulty sensors if a set of conditions on the system parameters (such as bounds on the sensor noises, maximum and minimum values of the reference signal, etc.) is satisfied. This result enhances and broadens the applicability of the proposed multisensor scheme since it provides guaranteed properties such as fault tolerance and robust closed-loop stability under sensor fault. The results are applied to the problem of automotive longitudinal control.     

Fault‐tolerant fusion‐based MPC with sensor recovery for constrained LPV systems

In this paper, we present a robust fault‐tolerant control scheme for constrained multisensor linear parameter‐varying systems, subject to bounded disturbances, that utilises multiple sensor fusion. The closed‐loop scheme consists of a tube model predictive control‐based feedback tracking controller and sensor‐estimate fusion strategy, which allows for the reintegration of previously faulty sensors. The active fault‐tolerant fusion‐based mechanism tracks the healthy‐faulty transitions of suitable residual variables by means of set separation and precomputed transition times. The sensor‐estimate pairings are then reconfigured based on available healthy sensors. Under the proposed scheme, robust preservation of closed‐loop system boundedness is guaranteed for a wide range of sensor fault situations. An example is presented to illustrate the performance of the fault‐tolerant control strategy.     

The development of a fault-tolerant control approach and its implementation on a flexible arm robot

This article presents a robust sensor fault-tolerant control (FTC) scheme and its implementation on a flexible arm robot. Sensor faults affect the system's performance in the closed loop when the faulty sensor readings are used to generate the control input. In this article, the non-faulty sensors are used to reconstruct the faults on the potentially faulty sensors. The reconstruction is subtracted from the faulty sensors to generate a 'virtual sensor' which (instead of the normally used faulty sensor output) is then used to generate the control input. A design method is also presented in which the virtual sensor is made insensitive to any system uncertainties (which could corrupt the fault reconstruction) that cannot fit into the framework of the model used. Two fault conditions are tested: total failure and incipient faults. Then the scheme robustness is tested and evaluated through its implementation on two flexible arm systems, one with a flexible joint and the other with a flexible link. Excellent results have been obtained for both cases (joint and link); the FTC scheme produced system performance almost identical to the fault-free scenario, whilst providing an indication that a fault is present, even for simultaneous faults.     

一类非线性系统的输出反馈容错控制

针对一类非线性系统,研究了故障情况下基于输出反馈的容错控制问题．首先基于Zhang的自适应观测器和Lin的输出反馈控制律设计了正常系统的标称控制律,分析了该控制律的性能,并得到了故障发生后仍然采用该控制律时闭环系统状态有界的充分条件．在此基础上,设计了故障系统的容错控制律,证明了若发生的故障满足前述的充分条件,则故障系统在该容错控制律下稳定．数值仿真表明了该方法的有效性．     

A fault tolerant control scheme based on sensor–actuation channel switching and dwell time

The present paper proposes a switching control scheme for a plant with multiple sensor–estimator/control–actuator pairs. The scheme is shown to handle the specific stability problems originated by the switching between the different feedback loops and accommodate to faults in the measurement (sensors) channels. The main contribution is a fault tolerant switching scheme with stability guarantees assured by a pre‐imposed dwell time. The detection and the fault tolerance capabilities are achieved through the separation of sets associated with suitable residual signals corresponding to healthy and faulty functioning. Another contribution of the paper resides in a recovery technique for the post‐fault reintegration of the biased estimations. This technique makes use of a virtual sensor whose associated estimation, based on an optimization procedure, minimizes the recovery time. Copyright © 2012 John Wiley & Sons, Ltd.     

Robust fault-tolerant self-recovering control of nonlinear uncertain systems

In this paper, the problem of devising a fault-tolerant robust control for a class of nonlinear uncertain systems is investigated. Possible failures of the sensor measuring the state variables are considered, and a robust measure is developed to identify the stability- and performance-vulnerable failures. Based on evaluation of the robust measure, a fault-tolerant robust control will switch itself between one robust control strategy designed under normal operation and another under the faulty condition. It is shown that, under two input-to-state stability conditions, the proposed scheme guarantees not only the desired performance under normal operations but also robust stability and best achievable performance when there is a sensor failure of any kind.     

Reliable H∞ control of discrete-time systems against random intermittent faults

A passive fault-tolerant control strategy is proposed for systems subject to a novel kind of intermittent fault, which is described by a Bernoulli distributed random variable. Three cases of fault location are considered, namely, sensor fault, actuator fault, and both sensor and actuator faults. The dynamic feedback controllers are designed not only to stabilise the fault-free system, but also to guarantee an acceptable performance of the faulty system. The robust H_∞ performance index is used to evaluate the effectiveness of the proposed control scheme. In terms of linear matrix inequality, the sufficient conditions of the existence of controllers are given. An illustrative example indicates the effectiveness of the proposed fault-tolerant control method.     

Robust parameter-dependent fault-tolerant control for actuator and sensor faults

In this article, we study a robust fault-tolerant control (FTC) problem for linear systems subject to time-varying actuator and sensor faults. The faults under consideration are loss of effectiveness in actuators and sensors. Based on the estimated faults from a fault detection and isolation scheme, robust parameter-dependent FTC will be designed to stabilise the faulty system under all possible fault scenarios. The synthesis condition of such an FTC control law will be formulated in terms of linear matrix inequalities (LMIs) and can be solved efficiently by semi-definite programming. The proposed FTC approach will be demonstrated on a simple faulty system with different fault levels and fault estimation error bounds.     

Multisensor fusion fault tolerant control

In this paper, a multisensor fusion fault tolerant control system with fault detection and identification via set separation is presented. The fault detection and identification unit verifies that for each sensor–estimator combination, the estimation tracking errors lie inside pre-computed sets and discards faulty sensors when their associated estimation tracking errors leave the sets. An active fault tolerant controller is obtained, where the remaining healthy estimates are combined using a technique based on the optimal fusion criterion in the linear minimum-variance sense. The fused estimates are then used to implement a state feedback tracking controller. We ensure closed-loop stability and performance under the occurrence of abrupt sensor faults. Experimental validation, illustrating the multisensor fusion fault tolerant control strategy is included.     

Fault-tolerant actuators and drives—Structures, fault detection principles and applications

As fault detection and fault diagnosis methods are more and more finding their way into modern industrial mechatronic products, it is now time to take the next step. Based on the research efforts for fault detection and diagnosis, a status report has been prepared for research on fault management, i.e. automatic reactions of the system to continue operation after the detection of faults. These reactions may employ hardware redundancy (i.e. switching from a faulty actuator to another, intact one) or analytical redundancy (i.e. switching from a faulty sensor to a “model sensor” or “soft sensor”).A total fault-tolerance concept must encompass all components of a system, i.e. the actuators and drives, the process itself, the sensors as well as the controller and communication. In many cases, a degradation of functions has to be accepted after a fault has appeared. Concentrating on some widespread actuation principles, the paper will focus on electric drives and hydraulic actuators.First, a review is given on fault-tolerance principles and general structural considerations, e.g. hot-standby and cold-standby, focusing on the scheme of an overall fault-tolerant control system. Then, fault statistics for existing actuators and drives will be presented. These fault statistics give hints on the parts of the actuators which are most susceptible to faults. Different designs of fault-tolerant actuators and drives, which have been realized as laboratory prototypes or even on an industrial scale, shall be presented and evaluated with respect to their capabilities of withstanding faults. Finally, an outlook for fault-tolerant mechatronic systems will be given.     

一种无线传感器网络中事件区域检测的容错算法

特殊环境中的事件区域检测是无线传感器网络的一种重要应用.由于传感器的错误会导致事件区域检测的不准确,所以相关的容错算法成为近年来的研究热点.已有研究工作都仅考虑了事件的空间相关性,通过相邻传感器之间的数据交换实现容错.文中从事件的空间相关性和时间相关性入手,提出了一种以局部检测为主的分布式事件区域检测算法.该算法通过检验传感器本地采样值构成的时间序列与事件随机过程统计特征的符合程度实现容错.算法分析的结果表明,该算法可以减少传感器之间的数据交换,从而有效地利用传感器的能量.模拟实验表明,当有10%的传感器发生错误时,该算法可以检测到93%的事件区域和88%的错误传感器.     

Fault-tolerant sensor integration for micro flow-sensor arrays and networks

Distributed micro flow-sensor arrays and networks (DMFSA/N), built from collections of spatially scattered, cooperating intelligent and redundant micro flow-sensor nodes, can improve the accuracy and reliability of system. However, it is unrealistic to expect all the sensor nodes and communication links in the system to function properly all the time. This paper is based on an earlier research, in which a DMFSA/N with a cluster architecture and fault-tolerant time-out Protocol (FTTP) was developed. In this paper, a fault-tolerant sensor integration algorithm (FTSIA) is proposed and evaluated in simulations. Experimental results showed that the FTSIA could always give reliable results even when certain portion of the sensors yielded faulty information. Furthermore, the results from FTSIA were significantly more accurate than the mean of sensor readings (popularly applied in industry) if some of the sensors produced faulty readings. Finally, the application of the proposed FTSIA is illustrated by measuring flow pressure using a pressure sensor array of eight sensors.     

双时滞系统的故障诊断和动态最优容错控制

对含有状态时滞和控制时滞的线性时滞系统, 研究系统发生不可直接测量的传感器故障和执行故障时的故障诊断和最优容错控制问题. 首先基于时滞系统的线性变换, 利用Riccati矩阵方程和Sylvester方程设计了故障情况下的最优容错控制律, 并证明了最优容错控制律的存在唯一性. 然后通过构造一种新的含有故障的增广系统的降维状态观测器, 实现了故障的实时在线诊断和系统状态的观测, 解决了最优容错控制的物理不可实现问题. 最后利用故障诊断的结果给出了物理可实现的动态最优容错控制律. 仿真实例验证了故障诊断方法和动态最优容错控制方法的可行性和有效性.     

分布式无线传感器网络容错事件边界检测

事件监测是无线传感器网络的一种重要应用。针对该应用中软故障节点提供的错误数据会降低监测的准确性的问题,提出了一种分布式的容错事件边界检测算法。节点只需与邻节点交换一次传感数据,通过简单地计算识别故障;正常的事件节点利用统计比较的方法判断其是否处于事件边界,边界宽度可根据网络用户的要求调节。该算法执行时所需的通信量小,计算复杂度低,时延小,对大规模网络具有很好的可扩展性。仿真结果表明即使节点故障率很高,应用该算法仍可以获得很好的检测效果。     

Fault-Tolerant Indirect Adaptive Neurocontrol for a Static Synchronous Series Compensator in a Power Network With Missing Sensor Measurements

Identification and control of nonlinear systems depend on the availability and quality of sensor measurements. Measurements can be corrupted or interrupted due to sensor failure, broken or bad connections, bad communication, or malfunction of some hardware or software (referred to as missing sensor measurements in this paper). This paper proposes a novel fault-tolerant indirect adaptive neurocontroller (FTIANC) for controlling a static synchronous series compensator (SSSC), which is connected to a power network. The FTIANC consists of a sensor evaluation and (missing sensor) restoration scheme (SERS), a radial basis function neuroidentifier (RBFNI), and a radial basis function neurocontroller (RBFNC). The SERS provides a set of fault-tolerant measurements to the RBFNI and RBFNC. The resulting FTIANC is able to provide fault-tolerant effective control to the SSSC when some crucial time-varying sensor measurements are not available. Simulation studies are carried out on a single machine infinite bus (SMIB) as well as on the IEEE 10-machine 39-bus power system, for the SSSC equipped with conventional PI controllers (CONVC) and the FTIANC without any missing sensors, as well as for the FTIANC with multiple missing sensors. Results show that the transient performances of the proposed FTIANC with and without missing sensors are both superior to the CONVC used by the SSSC (without any missing sensors) over a wide range of system operating conditions. The proposed fault-tolerant control is readily applicable to other plant models in power systems.      

初级永磁直线电机双动子电流镜像容错控制

为解决双动子无电流传感器控制算法存在参数依赖性高、鲁棒性差等问题,提出一种电流镜像容错控制(current mirror fault-tolerant control,CMFC)策略,在仅采用单动子相电流传感器的条件下完成两台级联动子的控制。双动子系统中动子1为正常动子,采用传统的有限集模型预测控制(finite control set-model predictive control,FCS-MPC)完成电流的跟踪控制。动子2为故障动子,所有电流传感器均发生故障。CMFC控制将动子2虚拟电流与动子1的虚拟电流作为FCS-MPC控制器的输入并完成电流跟踪控制。通过完成两台动子的虚拟电流跟踪,由镜像原理实现两台动子的实际电流跟踪。理论分析和仿真实验证明了CMFC控制能实现动子2实际电流的稳定控制,且具有鲁棒性高的特点。     

Reference governor design for tracking problems with fault detection guarantees

The present paper deals with the reference tracking problem for processes with linear dynamics and multisensor information subject to abrupt sensor faults. A key point for fault tolerance will be the separation between healthy and faulty closed-loop behavior upon a set-characterization approach. This is achieved through set theoretic operations involving the healthy/faulty behavior of residual signals related to the system dynamics. As a main contribution, a reference governor scheme is designed using a receding horizon technique. It is shown that fault detection guarantees can be achieved by appropriate adjusting of the governor's delay/prediction window under mild assumptions on the fault scenario.     

Isolation and handling of sensor faults in nonlinear systems

This work considers the problem of sensor fault isolation and fault-tolerant control for nonlinear systems subject to input constraints. The key idea is to design fault detection residuals and fault isolation logic by exploiting model-based sensor redundancy through a state observer. To this end, a high-gain observer is first presented, for which the convergence property is rigorously established, forming the basis of the residual design. A bank of residuals are then designed using a bank of observers, with each driven by a subset of measured outputs. A fault is isolated by checking which residuals breach their thresholds according to a logic rule. After the fault is isolated, the state estimate generated using measurements from the healthy sensors is used in closed-loop to maintain nominal operation. The implementation of the fault isolation and handling framework subject to uncertainty and measurement noise is illustrated using a chemical reactor example.