Ron John Patton

• PhD Sheffield University
• Professor at University of Hull

Vehicle platoon systems are regarded as autonomous vehicles in the platooning pattern, in which vehicles drive in sequence and maintain the desired inter-vehicle spacing. This paper investigates the platoon control problem of vehicle platoon dynamics under cyber-physical threats through the distributed fault-tolerant consensus control protocol. Com...

This article proposes an actuator fault detection and isolation (FDI) scheme for quadrotor unmanned aerial vehicle (UAV) with a cable-suspended load. First, a linear parameter-varying (LPV) model of quadrotor UAV is established, in which the effects of cable-suspended load are considered. Then, a state boundary-based FDI design is systemically pres...

This paper explores the problem of fault-tolerant control concerning an underactuated unmanned surface vehicle affected by actuator faults and disturbances in the physical layer and multiple cyber threats (time-varying delays, injection attacks, and deception attacks) in the networked layer. Firstly, an extended state observer is designed to estima...

This study addresses the issue of distributed fault‐tolerant consensus control for second‐order multi‐agent systems subject to simultaneous actuator bias faults in the physical layer and deception attacks in the cyber layer. Cyber‐physical threats (malicious state‐coupled nonlinear attacks and physical deflection faults), unknown control gains, ext...

This paper explores the consensus control problem of nonlinear multi-agent systems (MASs) under complex cyber-physical threats (CPTs), which encompass sensor/actuator faults, input/output channel noises, and random cyber-attacks. The multiple sensor/actuator faults are uniformly modeled as an exponential type, while random cyber-attacks are charact...

This study investigates the distributed fault-tolerant consensus issue of multi-agent systems subject to complicated abrupt and incipient time-varying actuator faults in physical hierarchy and aperiodic denial-of-service (DoS) attacks in networked hierarchy. Decentralized estimators are devised to estimate consecutive system states and actuator fau...

This paper proposes a novel active fault tolerant control (FTC) scheme for a 3-degree-of-freedom (3-DOF) helicopter with sensor faults. As a challenge, only attitude angles are considered available, so that when the sensors measuring the elevation/travel angles are faulty, the system with respect to the remaining healthy outputs is not detectable....

The wave energy control competition established a benchmark problem which was offered as an open challenge to the wave energy system control community. The competition had two stages: In the first stage, competitors used a standard wave energy simulation platform (WEC-Sim) to evaluate their controllers while, in the second stage, competitors were i...

To date, one of the main challenges in the wave energy field is to achieve energy-maximizing control in order to reduce the levelized cost of energy (LCOE). This paper presents a model predictive velocity tracking control method based on a hierarchical structure for a Wavestar-like deivce in the WEC-SIM benchmark. The first part of the system struc...

This study proposes a co-design framework of decentralized fault estimation and distributed fault-tolerant tracking control schemes of Lipschitz nonlinear multi-agent systems with external disturbances and unpredicted sensor faults. To begin with, the sensor fault is actively hidden in the extended state through augmented transformation, and the de...

This study explores the leader-following consensus tracking control issue of multiple unmanned surface vehicles (multi-USVs) in the presence of malicious connectivity-mixed attacks in the cyber layer, and concurrent output channel noises, sensor/actuator faults, and wave-induced disturbances in the physical layer. Sensor/actuator faults are initial...

This paper considers fault estimation (FE) and fault-tolerant control (FTC) for linear parameter varying systems with actuator and sensor faults, uncertainties, and disturbances. The inevitable coupling between the FE and FTC functions needs to be taken into account in the design to ensure the overall FE-based FTC closed-loop system performance and...

Vehicle platoon systems are considered as automatous vehicles in a platoon-based driving pattern in which a following vehicle follows the preceding vehicle and maintains the desired vehicle spacing. This study investigates the leader-following tracking issue of vehicle platoon systems under cyber-physical threats with the distributed anti-attack fa...

Offshore wind turbine (WT) rotors are subjected to asymmetrical loads, resulting in enhanced fatigue of the blade structures, which requires reliable load mitigation techniques (e.g. individual pitch control, IPC). The IPC-enhanced pitch motion increases the occurrence of pitch actuator faults. This phenomenon has accelerated the emergence of new r...

This paper presents a robust actuator fault estimation strategy design for a 3-DOF helicopter prototype which can be adapted to aggressive maneuvers. First, considering large pitch angle condition during flight, nonlinear coupling characteristic of the helicopter system is exploited. As the pitch angle can be measured in real time, a polytopic line...

This paper proposes a novel distributed fault-tolerant consensus tracking control design for multi-agent systems with abrupt and incipient actuator faults under fixed and switching topologies. The fault and state information of each individual agent is estimated by merging unknown input observer in the decentralized fault estimation hierarchy. Then...

This chapter presents an adaptive decoupling strategy to separate the FE and FTC designs. An adaptive sliding mode augmented state unknown input observer is designed to actively estimate the perturbations together with the system state and faults. The effects of estimation errors and perturbations are compensated together with the faults using an a...

This chapter summarizes the content in this book and highlights the pros and cons of each robust integration strategy. Potential future research directions are also discussed.

This chapter presents a sequential strategy for robust integration of FE and FTC. An augmented Luenberger state observer is used to estimate the state and faults, and a state feedback FTC controller is used to compensate the faults and stabilize the system. Under this scheme, the FTC controller is designed in the first step and used in the second s...

A sequential strategy (see Fig. 4.1(1)) for robust integration of FE and FTC is proposed in Chap. 3, by taking into account only the unidirectional robustness interaction, i.e. effects of FTC uncertainty on the FE observer. This chapter further presents an iterative integration strategy (see Fig. 4.1 (2)) to account for the bidirectional robustness...

This chapter extends the simultaneous integration strategy in Chap. 5 for Lipschitz nonlinear systems. It also describes application of the proposed strategy to a nonlinear 3-DOF helicopter system with actuator faults and input saturation constraints.

This chapter extends the simultaneous integration strategy in Chap. 5 for large-scale interconnected systems subject to uncertain nonlinear interconnections. Decentralized FE and FTC strategies are developed for large-scale interconnected systems under actuator or sensor faults. The designs are validated on a 3-machine power system with actuator or...

This chapter illustrates the importance and challenges of robust integration. Both theoretic analysis and motivating example are used for illustration. Several important concepts to be used throughout the book are defined, including unidirectional robustness interaction and bidirectional robustness interactions.

It has been shown in Chaps. 3 and 4 that the integration of FE and FTC considered in this book can be formulated as a robust observer-based control problem. This chapter aims to develop a simultaneous integration strategy (see Fig. 5.1 (3)) to obtain optimal FTC controller and FE observer gains in one shot based on a fully LMI formulation.

This chapter presents a robust decoupling strategy for the integration of FE and FTC to avoid the bilinear matrix inequality issue and enjoy more design freedom. The strategy uses the principle of Small Gain Theorem to separate the FE and FTC designs by attenuating the bidirectional robustness interactions between them. An iterative algorithm is pr...

This chapter provides a fault-tolerant wind turbine pitch control example as a simple guide for designing FE-based FTC systems. A new FE observer is also developed for reconstructing the real shapes of multiplicative (component) faults. Simulations are performed on a 4.8 MW benchmark wind turbine with single or multiple pitch actuator faults.

Robust Integration of Model-Based Fault Estimation and Fault-Tolerant Control is a systematic examination of methods used to overcome the inevitable system uncertainties arising when a fault estimation (FE) function and a fault-tolerant controller interact as they are employed together to compensate for system faults and maintain robustly acceptabl...

This paper addresses the challenge of robust simultaneous estimation of state and actuator faults for Lipschitz nonlinear systems with unknown perturbations acting on both the state dynamics and output measurements. The existing methods enhance the estimation robustness by suppressing the perturbations or decoupling them under satisfaction of the m...

This study investigates the consensus problem of multiple 3‐DOF laboratory helicopters modeled with system nonlinearity, uncertainty, and actuator faults. The simultaneous additives and partial loss of effectiveness actuator faults are considered. The fault detection hierarchy, the healthy control hierarchy, and the fault‐tolerant control hierarchy...

Offshore wind turbines suffer from asymmetrical loading (blades, tower, etc), leading to enhanced structural fatigue. As well as asymmetrical loading different faults (pitch system faults etc.) can occur simultaneously, causing degradation of load mitigation performance. Individual pitch control (IPC) can achieve rotor asymmetric loads mitigation,...

Offshore wind turbines suffer from asymmetrical blade loading, resulting in enhanced structural fatigue. Individual pitch control (IPC) is an effective method to achieve blade load mitigation, accompanied by enhancing the pitch movements and thus increased the probability of pitch actuator faults. The occurrence of faults will deteriorate the IPC l...

This paper proposes a data-driven technique to estimate the wave excitation force (WEF) which is an essential signal for wave forecasting and implementing power efficiency maximization control of Wave Energy Converters (WECs). A Bayesian probabilistic model of a WEC hydrodynamic system is described to generate robust WEF estimates. Specifically, th...

This article presents a data-efficient learning approach for the complex-conjugate control of a wave energy point absorber. Particularly, the Bayesian Optimization algorithm is adopted for maximizing the extracted energy from sea waves subject to physical constraints. The algorithm learns the optimal coefficients of the causal controller. The simul...

Several energy maximization control approaches for point-absorber wave-energy converter (PAWEC) systems require knowledge of the wave excitation force (WEF) that is not measurable during the PAWEC operation. Many WEF estimators have been proposed based on stochastic PAWEC modeling using the Kalman filter (KF), extended KF (EKF), or receding-horizon...

This paper investigates the position-tracking and attitude-tracking control problem of close formation flight with vortex effects under simultaneous actuator and sensor faults. On the basis of the estimated state and fault information from unknown input observers and relative output information from neighbors, an integration of decentralized fault...

This paper proposes a novel decentralized output sliding-mode fault-tolerant control (FTC) design for heterogeneous multiagent systems (MASs) with matched disturbances, unmatched nonlinear interactions, and actuator faults. The respective iteration and iteration-free algorithms in the sliding-mode FTC scheme are designed with adaptive upper boundin...

In this work a three dimensional computational fluid dynamic (CFD) model has been constructed based on a 1/50 scale heaving point absorber wave energy converter (PAWEC). The CFD model is validated first via wave tank tests and then is applied in this study to investigate the joint effects of device geometry and power take-off (PTO) damping on wave...

Due to the increasing size of wind turbines, the unbalanced loads caused by the uneven spatial distribution of wind speed and turbulence are becoming larger and larger. As has been proved, individual pitch control (IPC) can mitigate the blade asymmetric loads greatly in region 3. On the other hand, the pitch actuator faults can affect the pitching...

Due to the increasing size of wind turbines, the unbalanced loads caused by the uneven spatial distribution of wind speed and turbulence are becoming larger and larger. As has been proved, individual pitch control (IPC) can mitigate the blade asymmetric loads greatly in region 3. On the other hand, the pitch actuator faults can affect the pitching...

This paper proposes a hierarchical structure-based fault estimation and fault-tolerant control design with bi-directional interactions for nonlinear multi-agent systems with actuator faults. The hierarchical structure consists of distributed multi-agent system hierarchy, undirected topology hierarchy, decentralized fault estimation hierarchy and di...

To achieve optimal power in a wave energy conversion (WEC) system it is necessary to understand the device hydrodynamics. To maximize conversion efficiency the goal is to tune the WEC performance into resonance. The main challenge then to be overcome is the degree to which non-linearity in WEC hydrodynamics should be represented. Although many stud...

Past or/and future information of the excitation force is useful for real-time power maximisation control of Wave Energy Converter (WEC) systems. Current WEC modelling approaches assume that the wave excitation force is accessible and known. However, it is not directly measurable for oscillating bodies. This study aims to provide accurate approxima...

Wave forecasting is an important prerequisite for implementing optimal control of wave energy converters since the control of power take-off problem is dependent on a reference strategy that must be calculated from a time-varying wave excitation force value. The real-time computation of the wave force excitation is a considerable challenge, dependi...

This paper proposes a decoupling approach to the integrated design of fault estimation (FE) and fault-tolerant control (FTC) for linear systems in the presence of unknown bounded actuator faults and perturbations. An adaptive sliding mode augmented state unknown input observer is developed to estimate the system state, actuator faults and perturbat...

Current modelling approaches of Wave Energy Convertors (WECs) assume that the wave excitation force is known and its past/future information is required for some WEC power maximisation control. However, the wave excitation force is not directly measurable for oscillating WECs. This study aims to estimate the wave excitation force from wave elevatio...

Linear modelling approaches are widely applied to predict the hydrodynamics of wave energy conversion systems. One main weakness is that the linearisation near the equilibrium point removes the effects of some important non-linear phenomena, like viscous and friction forces, and hence exaggerates the excursion and power productivity of wave energy...

Three different geometric forms of point absorber wave energy converter (PAWEC) devices have been studied in this work. This paper focuses on suggesting an optimal geometry for improving the efficiency of the wave-PAWEC interaction. Previously, a 1/50 scale cylindrical PAWEC with bluff bottom has been investigated in University of Hull (UoH) via ph...

Abstract—This paper presents a robust control and estimation architecture for a Point Absorber Wave Energy Converter (PAWEC), consisting of a heaving Buoy and a Permanent Magnet Linear Generator. The proposed architecture combines robust control and estimation algorithms in order to achieve high efficiency and reliable PAWEC operation. First, Feedb...

Although the heaving Point Absorber (PA) concept is well known in wave energy conversion research, few studies focus on appropriate modelling of non-linear fluid viscous and mechanical friction dynamics. Even though these concepts are known to have non-linear effects on the hydrodynamic system, most research studies consider linearity as a starting...

This paper proposes a fault-tolerant tracking control for the elevation and pitch angles of a 3-DOF helicopter system, subject to actuator faults and input saturation. The effects of the fault and saturation are combined as a composite actuator fault, which is estimated together with the system state using an adaptive two-step sliding mode observer...

In this paper, a time-domain linear parameter-varying H_/H∞ residual generator or fault detection filter is proposed, which allows a trade-off to be established, between sensitivity and robustness of the residual against the fault and disturbance, respectively. Also, the proposed fault detection filter fits well with the time-domain property of the...

Linear modelling approaches are widely applied to predict the hydrodynamics of wave energy conversion systems. One main weakness is that the linearisation near the equilibrium point removes the effects of some important non-linear phenomena, like viscous and friction forces, and hence exaggerates the excursion and power productivity of wave energy...

This paper proposes a fault-tolerant tracking control for the elevation and pitch angles of a 3-DOF helicopter system, subject to actuator faults and input saturation. The effects of the fault and saturation are combined as a composite actuator fault, which is estimated together with the system state using an adaptive two-step sliding mode observer...

This study proposes a fault estimation (FE)-based fault-tolerant control (FTC) strategy to maintain system reliability and achieve desirable control performance for a 3-DOF helicopter system with both actuator drift and oscillation faults and saturation. The effects of the faults and saturation are combined into a composite non-differentiable actua...

Wind turbine pitch systems are essential for actuating desired blade angles and hence to keep the generator at rated speed in operation region 3. In the presence of parametric pitch actuator faults, pitch systems may have slow dynamics, affecting the pitching performance with the possibility of oscillation on the generator speed and making the turb...

To bridge the gap between model-based fault diagnosis theory and industrial practice, a linear parameter varying H−/H∞ fault estimation approach is applied to a high fidelity nonlinear aircraft benchmark. The aim is to show how the fault estimation can provide robust early warning of actuator fault detection scenarios that can lead to abnormal airc...

In recent years the control of Wave Energy Conversion (WEC) systems has been a challenging research topic. A 1/50 th scale buoy system has been constructed at 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 linea...

This paper describes three numerical methods to study the hydrodynamics of a point absorber wave energy converter (PAWEC), including (i) linear mathematical model based on the boundary element method (BEM), (ii) non-linear finite element method (FEM) simulation and (iii) non-linear state space model considering viscous force. A 1/50 scale prototype...

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,...

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 employe...

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 unce...

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 modelling 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...

This paper proposes an integrated fault estimation and fault-tolerant control (FTC) design for Lipschitz non-linear systems subject to uncertainty, disturbance, and actuator/sensor faults. A non-linear unknown input observer without rank requirement is developed to estimate the system state and fault simultaneously, and based on these estimates an...

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 t...

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 c...

A novel robust fault-tolerant control design for linear descriptor systems is proposed in this paper, with fault tolerant control action achieved via a normal state estimate feedback derived using H∞ optimization and fault compensation. A robust functional (reduced order) observer approach is proposed to estimate the controller directly. Necessary...

A lot of effort has been devoted to the unknown input observer (UIO) research over the past years. However, the strong disturbance decoupling assumption (manifested as some rank constraint) is often implicitly embedded in much of the existing UIO work. With the purpose of state and fault estimation, this fact motivates us to investigate the viabili...

In general, the control of chemical processes that involve unknown disturbances presents interesting challenges. Research issues have been focused on detailed modelling of the involved phenomena in order to use e.g. robust on-line disturbance compensation procedures or attempting to cancel out the disturbance effect in the feedback control of the c...

Over the past decades, substantial progress has been made in fault detection and diagnosis (FDD) and fault tolerant control (FTC) research. Recently, some attention has been paid to the integrated design of fault estimation (FE) and active FTC in a two-stage manner: estimation first and then compensation. Different from the preceding two-stage work...

This paper is concerned with the challenge of developing a fault-tolerant control (FTC) scheme for an inter-connected decentralised system in which the individual subsystems are linear but the inter-connections are non-linear functions of the subsystem states and controls. It is assumed that the subsystems are disturbed by matched faults. The purpo...

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....

This paper investigates a mixed linear parameter varying (LPV) fault estimator using an LPV reference estimator. LMIs are used to calculate the affine parameter-dependent gains of the LPV fault estimator. The design strategy is applied to a high fidelity nonlinear aircraft model provided by AIRBUS for use within the EU-FP7 project ADDSAFE, to estim...

This paper is concerned with multiobjective robust controller design using eigenstructure assignment for multivariable control systems. It considers various performance indices (or cost functions) in the objectives, which are individual eigenvalue sensitivity functions, and the sensitivity and the complementary sensitivity functions in the frequenc...

The control of systems that involve friction presents interesting challenges. Recent research has focused on detailed modeling of friction phenomena in order to use robust on-line friction compensation procedures, attempting to cancel out the friction force effect in the feedback control. The friction modeling problem remains a very difficult chall...

In this work, different model-based procedures exploiting the analytical redundancy principle for the detection and isolation of the input-output sensor faults on a gas turbine simulated process are presented and compared. The contribution of the paper consists of exploiting several identification schemes in connection with linear and nonlinear res...

This paper investigates the development of a new type of dynamic neuro-fuzzy system with neuronal rules and its application to fault detection and isolation (FDI) of components of a dynamic process. Hybrid learning based on fuzzy clustering algorithm and the steepest-descent method, is used to train the proposed neuro-fuzzy system. The experimental...

This paper deals with the problem of fault-tolerant control of a Network Control System (NCS) for the case in which the sensors, actuators and controller are interconnected via various Medium Access Control protocols which define the access scheduling and collision arbitration policies in the network and employing the so-called periodic communicati...

This paper presents a novel approach to integrating quantitative and qualitative information in fault-diagnosis. This paper investigates the development of a supervisory control scheme for a non-linear system with qualitative tasks at the upper level and a lower level comprising quantitative model based non-linear control. A new quantitative approa...

This paper investigates the development of a Supervisory Control System with qualitative tasks at the upper level and simple quantitative models at the lower level to control complex non-linear systems. A new quantitative approach for the stability of non-linear fuzzy inference systems using Takagi-Sugeno (T-S) fuzzy models is presented. The necess...

This paper proposes a new approach for detecting and isolating faults in a non-linear dynamic process using the multiple model approach. The necessary conditions for the assignability of eigenvalues to a region in the s-plane and the necessary conditions to guarantee the stability of fuzzy models for Takagi-Sugeno (T-S) fuzzy observers are derived....

The paper proposes an observer based active fault tolerant control (AFTC) approach to a non-linear large rotor wind turbine benchmark model. A sensor fault hiding and actuator fault compensation strategy is adopted in the design. The adapted observer based AFTC system retains the well-accepted industrial controller as the baseline controller, while...

Multiple myeloma (MM) is the second most common haematological malignancy and results in destructive bone lesions. The interaction between MM cells and the bone microenvironment plays an important role in the development of the tumour cells and MM-induced bone disease and forms a ‘vicious cycle’ of tumour development and bone destruction, intensifi...

Starting with the baseline controller design, this paper proposes an integrated approach of active fault tolerant control based on proportional derivative extended state observer (PDESO) for linear parameter varying descriptor systems. The PDESO can simultaneously provide the estimates of the system states, sensor faults, and actuator faults. The L...

Bone remodelling is a vital process which enables bone to repair, renew and optimize itself. Disorders in the bone remodelling process are inevitably manifested in bone-related diseases, such as hypothyroidism, primary hyperparathyroidism and osteoporosis. In our previous work, a predator-prey based mathematical model was developed to simulate bone...

This paper presents a new approach to active sensor fault tolerant tracking control (FTTC) for offshore wind turbine (OWT) described via Takagi–Sugeno (T–S) multiple models. The FTTC strategy is designed in such way that aims to maintain nominal wind turbine controller without any change in both fault and fault-free cases. This is achieved by inser...

Owing to inherent limitations in different kinds of the well-known fossil fuel and nuclear energy sources, e.g. carbon footprint, rapidly increasing fuel prices or probability of catastrophic effects of nuclear station malfunction, the last two decades have witnessed a rapid growth in the use of wind energy. Although, it is considered a promising s...

Motived by wind turbine pitch actuator component fault estimation problem, a robust adaptive fault estimation procedure is proposed in this paper. The estimation of a component fault which is a multiplicative fault, is not as straightforward a problem as the estimation of an additive fault. The proposed fault estimator is based on an adaptive obser...

This paper proposes an approach to fault tolerant control (FTC) of a wind turbine subject to sensor faults. Both analytical and hardware redundancies are utilized in this approach. A residual generator based on a Takagi-Sugeno (T-S) fuzzy observer is proposed as the fault detection and isolation (FDI) unit. A T-S fuzzy observer design method via on...

In this paper, an integrated active fault tolerant control (AFTC) scheme is proposed within a linear parameter varying (LPV) descriptor system context. The proposed scheme concerns both the response speed and robustness to bounded exogenous disturbance and both modelling uncertainty by combining pole-placement and H∞ optimization. The proposed AFTC...

This work focuses on an improved reconfigurable Fault Tolerant Flight Control (FTFC) strategy based on a traditional model reference Neural Network (NN) adaptive flight control architecture. An expanded control scheme is developed by using a concurrent learning NN strategy combined with the Sliding Mode Control (SMC) theory. The improved NN using c...

This paper proposes an approach to active fault tolerant control (AFTC) of a variable-speed wind turbine subject to single or simultaneous multiple sensor faults. Both analytical and hardware redundancies are used in this approach. A fault estimation observer is proposed for the pitch and generator subsystems. A Takagi-Sugeno (T-S) fuzzy observer i...