Online ISSN
1751-8652
Print ISSN
1751-8644
IET Control Theory & Applications
Volume 1, Issue 5, September 2007
Volumes & issues:
Volume 1, Issue 5
September 2007
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- Author(s): R.V. de Oliveira ; R.A. Ramos ; N.G. Bretas
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1191 –1199
- DOI: 10.1049/iet-cta:20060316
- Type: Article
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The present paper proposes an alternative performance index for the design of robust controllers to damp low-frequency electromechanical oscillations in power systems. The concept of output energy is used as performance index as opposed to the usual criterion of minimum damping ratio. The control problem with both performance indices was structured in the form of linear matrix inequalities and it was verified that the formulation with the output energy is less costly in terms of computational effort when compared to the one with the traditional minimum damping ratio. This characteristic allows the application of the proposed methodology to controller design involving large power system models. The design methodology is based on a multimachine model, without requiring the assumption that some part of the system can be modelled as an infinite bus. Such assumption is usual in control designs based on many modern control techniques, and may modify the dynamics described by the system model and consequently affect the performance of the designed controllers. The design methodology provides controllers that fulfill various practical requirements of the oscillation problem. The methodology has provided effective controllers with acceptable performance as shown in the results, and the gain in computational time was significant. - Author(s): D. Zhang ; L. Wang ; J. Yu
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1200 –1207
- DOI: 10.1049/iet-cta:20060096
- Type: Article
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This paper gives a coordination method for two biomimetic robotic fish in transporting box-like object task. To simplify the difficulty of path planning and action decision when a fish is moving towards the object, a situated-behaviour design method is employed to divide the environment into a set of complete and exclusive situations. For each situation, a specific behaviour is designed. On dealing with the synchronisation and the object orientation control problems in the particular underwater environment, fuzzy logic method is adopted for motion planning of the fish. Experimental results of the box-pushing task performed by two robotic fish validate the effectiveness of the proposed method. - Author(s): Z. Gao and S.X. Ding
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1208 –1218
- DOI: 10.1049/iet-cta:20060389
- Type: Article
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We present a proportional, multiple-integral and derivative (PMID) observer technique that can simultaneously estimate system states, fault signals and the finite times derivatives of the faults for a descriptor system with input and measurement faults. Furthermore for a descriptor system with input and measurement faults and unknown disturbances (including modelling errors), a robust PMID observer is designed to simultaneously estimate system states, fault signals, the derivatives of the faults, and attenuate disturbances successfully. Fault-tolerant design is another important issue in this study. By using the obtained estimates of states and faults, and linear matrix inequality technique, a fault-tolerant control scheme is addressed, which ensures the closed-loop plant to be internally proper stable with prescribed H∞ performance index even as unbounded faults occur. Finally, a numerical example is given to illustrate the design procedures, and simulations show satisfactory tracking and fault-tolerant control performance. - Author(s): N. Hori ; C.A. Rabbath ; P.N. Nikiforuk
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1219 –1223
- DOI: 10.1049/iet-cta:20060413
- Type: Article
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An exact, first-order, discrete-time model that gives correct values at the sampling instants for any sampling interval is derived for a nonlinear system whose dynamics are governed by a scalar Riccati differential equation with constant parameters. The model is derived by transforming the given differential equation into a stable linear form to which the invariant discretisation is applied. This is in contrast with other existing methods which result in a second-order and usually unstable form and which is not suitable for on-line digital control purposes. Simulation results are presented to show that the proposed method is always exact at the sampling instants, whereas the popular forward difference model can be divergent unless the sampling interval is sufficiently small. - Author(s): H.A. Barker ; A.H. Tan ; K.R. Godfrey
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1224 –1233
- DOI: 10.1049/iet-cta:20060292
- Type: Article
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Methods for designing two types of periodic ternary input signal used to identify a system in the presence of both noise and nonlinear distortions have been described here. Signals of the first type have even harmonics suppressed, to eliminate errors in odd-order estimates from even-order distortions, and vice-versa. Signals of the second type have harmonic multiples of both two and three suppressed, to further reduce errors from nonlinear distortions. For both types of signal, three design criteria are defined. The first criterion allows the signal energy-amplitude ratio to be maximised, the second allows the signal spectrum uniformity to be maximised and the third allows a compromise to be made between the first two criteria. With the methods described, ternary signals of both types with a very wide range of periods can be obtained for use in this application. Software for computer-aided design of the signals is available on the internet. The signals and their periods are given in tables, and an example is used to show how they are applied. - Author(s): Z. Wu and W. Zhou
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1234 –1241
- DOI: 10.1049/iet-cta:20060446
- Type: Article
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The problem of delay-dependent robust H∞ control for uncertain singular systems with time delay has been investigated. The considered systems are not assumed to be necessarily regular and impulse free. In terms of linear matrix inequality approach, a delay-dependent stability criterion is given to ensure the nominal system to be regular, impulse-free and stable. Based on the criterion, the problem is solved via state feedback controller, which guarantees that, for all admissible uncertainties, the closed-loop system is not only regular, impulse-free and stable, but also satisfies a prescribed H∞ performance condition. Some numerical examples are provided to demonstrate the efficiency of the proposed methods. - Author(s): C.-W. Park and Y.-W. Cho
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1242 –1254
- DOI: 10.1049/iet-cta:20060265
- Type: Article
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A robust fuzzy feedback linearisation controller is proposed to stabilise the nominal fuzzy system, and a sufficient condition is derived to guarantee the stability of the closed-loop system with bounded parameter uncertainties. For the systems with bounded uncertain parameters, we can design a robust fuzzy controller by choosing the control parameters satisfying the robust stability condition. The design scheme is not a trial and error procedure and it provides us freedom of select the control parameters showing the desired characteristics. The simulation results are given to verify the validity and effectiveness of the proposed control scheme. - Author(s): C.C. Kung and J.Y. Su
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1255 –1265
- DOI: 10.1049/iet-cta:20060415
- Type: Article
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An effective approach is developed to establish affine Takagi-Sugeno (T-S) fuzzy model for a given nonlinear system from its input–output data. Firstly, the fuzzy c-regression model (FCRM) clustering technique is applied to partition the product space of the given input–output data into hyper-plan-shaped clusters. Each cluster is essentially a basis of the fuzzy rule that describes the system behaviour, and the number of clusters is just the number of fuzzy rules. Particularly, a novel cluster validity criterion for FCRM is set up to choose the appropriate number of clusters (rules). Once the number of clusters is determined, the consequent parameters of each IF-THEN rule are directly obtained from the functional cluster representatives (affine linear functions). The antecedent fuzzy sets of each IF-THEN fuzzy rule are acquired by projecting the fuzzy partitions matrix U onto the axes of individual antecedent variable to obtain point-wise defined fuzzy sets and to approximate these point-wise defined fuzzy sets by normal bell-shaped membership functions. Additionally, a check and repartition algorithm is suggested to prevent the inappropriate premise structure where separate regions of data shared the same regression model. Finally, the gradient descent algorithm is included to adjust the fuzzy model precisely. An affine T-S fuzzy model with compact IF-THEN rules could thus be generated systematically. Several simulation examples are provided to demonstrate the accuracy and effectiveness of the affine T-S fuzzy modelling algorithm. - Author(s): A.J. Koshkouei ; K.J. Burnham ; Y. Law
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1266 –1275
- DOI: 10.1049/iet-cta:20060277
- Type: Article
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The sliding mode control (SMC) design for roll reduction of a ship has been addressed. The SMC technique yields the appropriate control with significant roll reduction compared with other controllers such as proportional integrative derivative (PID). The system comprises of three different controllers, fin-roll, rudder-roll and autopilot. Consequently, for each situation along the ship trajectory, the triple controllers need to be designed. It is not necessary to have the same controller structure for all three subsystems. This paper compares SMC controllers individually with PID controllers for ach subsystem, and demonstrates the results of the implementation of controllers with different structures when applied to the entire roll reduction system. - Author(s): J. Wang ; P. Shi ; H. Gao ; J. Wang
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1276 –1285
- DOI: 10.1049/iet-cta:20060463
- Type: Article
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This paper deals with the problem of gain-scheduled stabilisation for linear parameter-varying systems with time-varying input delay. New delay-dependent criteria are developed based on the reduction method combined with the parameter-dependent Lyapunov approach. Sufficient conditions are presented to design gain-scheduled controllers to stabilise the closed-loop systems from past input information in terms of parameterised linear matrix inequalities (LMI). One numerical example is provided to demonstrate the effectiveness of the proposed methods. - Author(s): Z. Gao ; H. Wang ; T. Chai
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1286 –1293
- DOI: 10.1049/iet-cta:20060429
- Type: Article
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In this work, a novel robust fault detection algorithm is investigated for stochastic distribution systems with multiple uncertainties, where the output is characterised by its measured output probability density function. By constructing an auxiliary augmented stochastic descriptor system, the original stochastic distribution system is transferred into a descriptor system subjected to model uncertainties, where a proportional and derivative descriptor estimator is developed to solve the fault detection problem. The system input and the output probability density function are used in the design of this estimator. Furthermore, the derivative gain of the estimator is chosen to attenuate the output uncertainties, and the free parameters embedded inside the proportional gain are selected to generate an optimally robust residual signal for fault detection so as to achieve a situation where this residual signal is sensitive to system faults while insensitive to model uncertainties, input disturbances and output noises. A numerical example is given, and the simulation result shows satisfactory detection performance. - Author(s): H.-P. Wang ; L.-S. Shieh ; Y. Zhang ; J.S.H. Tsai
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1294 –1301
- DOI: 10.1049/iet-cta:20060281
- Type: Article
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A minimal realisation scheme for a class of multiple time-delay transfer function matrices with distinct poles is presented. Also, a simple minimal realisation method is developed for a specific two-input-two-output multiple time-delay system whose poles can be repeated. In addition, a state-space discretisation technique developed for a multivariable system with a single time delay is extended to a multivariable system with multiple time delays. Finally, it should be mentioned that the proposed approach is restricted to systems where multiple time delays arise only in the input and output, and not in the state. Illustrative examples are given to demonstrate the effectiveness of the proposed method. - Author(s): B. Ding and B. Huang
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1302 –1310
- DOI: 10.1049/iet-cta:20060420
- Type: Article
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This paper addresses synthesis approaches to output feedback model predictive control (OFMPC) for systems with Hammerstein–Wiener nonlinearity and bounded disturbance/noise. The Hammerstein nonlinearity is removed (or partially removed) by constructing its inverse (or pseudo-inverse). The remaining nonlinearities in the model are incorporated by polytopic descriptions. At each sampling time, OFMPC finds a feedback gain and an estimator, such that the state of the closed-loop system asymptotically converges to a neighbourhood of the origin. A numerical example is given to illustrate the effectiveness of the controller. - Author(s): F.M. Raimondi and M. Melluso
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1311 –1321
- DOI: 10.1049/iet-cta:20060459
- Type: Article
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A new fuzzy adaptive motion control system including on-line extended Kalman's filter (EKF) for wheeled underactuated cars with non-holonomic constraints on the motion is presented. The presence of parametric uncertainties in the kinematics and in the dynamics is treated using suitable differential adaptation laws. We merge adaptive control with fuzzy inference system. By using fuzzy system, the parameters of the kinematical controller are functions of the lateral, longitudinal and orientation errors of the motion. In this way we have a robust control system where the dynamics of the motion errors is with lower time response than the adaptive control without fuzzy. Also Lyapunov's stability of the motion errors is proved based on the properties of the fuzzy maps. If data from incremental encoders are employed for the feedback directly, sensor noises can damage the performance of the motion control in terms of the motion errors and of the parametric adaptation. These noises are aleatory and denote a kind of non-parametric uncertainties which perturb the nominal model of the car. Therefore an EKF is inserted in the adaptive control system to compensate for the above non-parametric uncertainties. The control algorithm efficiency is confirmed through simulation tests in Matlab environment. - Author(s): R. Vilanova ; I. Serra ; C. Pedret ; R. Moreno
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1322 –1328
- DOI: 10.1049/iet-cta:20060478
- Type: Article
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This paper deals with the realisation of two degrees of freedom (2-DOF) compensators. The advantages of using a 2-DOF compensator are well known: the closed-loop properties can be shaped independently of the reference tracking transfer function. This allows us to consider the separation and independence of properties which will depend on the kind of processing we apply to the reference signal. Depending on the design approach to be applied, separation could be preferred even when independence may seem to be desirable. What we analyse is the kind of reference processing that results from an optimisation problem. It will be seen that the optimal solution involves complete separation and independence. It turns out that the optimal 2-DOF controller that results is seen to have a concise structure that accounts for a complete separation of the reference properties and a complete independence with respect to the feedback controller. - Author(s): P. Wen ; J. Cao ; Y. Li
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1329 –1335
- DOI: 10.1049/iet-cta:20060424
- Type: Article
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The performance of a networked control system (NCS) is affected directly and indirectly by time delays generated in network communication. This paper addresses these time delays, their effects on system performance and the measures taken in an NCS design. For a time delay that is random but less than one sampling interval T, we model the system as a time-invariant control system with constant time delay T. For a time delay that is random and greater than one sampling interval T, we consider the system as a control system with packet drop and model it as a jump linear control system. Based on the above models, we propose a systematic method to improve the control system quality of performance by choosing a proper sampling interval to reduce data transmission, optimally scheduling to minimise packet loss and optimising controller design in case of packet loss. The simulation results and lab experiments demonstrate that the design method results in high performance in networked real-time control system. - Author(s): Z. Mao ; B. Jiang ; P. Shi
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1336 –1343
- DOI: 10.1049/iet-cta:20060431
- Type: Article
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This paper deals with the design of robust fault detection for networked control systems with large transfer delays, in which it is impossible to totally decouple the fault effects from unknown inputs (including model uncertainties and external plant disturbances). First, we employ the multirate sampling method together with the augmented state matrix method to model the long random delay networked control systems as Markovian jump systems. Then, a H∞ fault detection filter is designed based on the model developed. Through the appropriate choice of the filter gain, the filter is convergent if there is no disturbance in the system, meanwhile the effect of disturbances on the residual will satisfy a prescribed H∞ performance. The problem of achieving satisfactory sensitivity of the residual to fault is formulated and its solution is given. Finally, a numerical example is presented to illustrate the effectiveness of the proposed techniques. - Author(s): Y.-L. Wang and G.-H. Yang
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1344 –1354
- DOI: 10.1049/iet-cta:20060489
- Type: Article
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This paper studies the problem of designing H∞ controllers for networked control systems (NCSs) with both network-induced time delay and packet disordering. A delay switching-based method is proposed to model the NCSs with long time delay as switched systems, then by an algorithm involving convex optimisation, H∞ controllers are designed by using the proposed delay switching-based method and the existing parameter uncertainty-based method. Then, prediction-based method is presented to compensate time delay and packet disordering, and H∞ controller design is proposed by using linear matrix inequality (LMI)-based method. The simulation results illustrate the effectiveness of the proposed delay switching-based method and the prediction-based H∞ controller design. - Author(s): S.H. Huh and Z. Bien
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1355 –1363
- DOI: 10.1049/iet-cta:20060440
- Type: Article
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A model reference adaptive-sliding mode control is presented and applied for a variable stiffness actuated (VSA) system. The VSA is a flexible stiffness machine with two coupled actuators in each link, and its safety during the movement can be guaranteed by varying both stiffness and the angular variables. Realisation of precise control of two coupled actuators poses a considerable challenge, however, because of uncertain time-varying parameters and unknown variation bounds. In this paper a neuro-sliding mode approach based on model reference adaptive control (MRAC) is proposed. The proposed MRAC control structure induces the VSA to follow its nominal dynamics with help of sliding mode control efforts. The sliding gain, implemented by a simple neural network (NN), is adaptively updated based on the Lyapunov criterion. A control law and adaptive laws for the sliding mode control as well as the weights in the NN are established so that the closed-loop system is stable in the sense of Lyapunov. The tracking errors of both the angular variables and stiffness are managed to guarantee the system to be asymptotically stable rather than uniformly ultimately bounded. And, the feasibility of the proposed control approach is demonstrated by means of experimental results as well as computer simulations. - Author(s): J.N. Teoh ; C. Du ; L. Xie ; Y. Wang
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1364 –1369
- DOI: 10.1049/iet-cta:20060359
- Type: Article
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Sensitivity function or error rejection function is crucial to determine the disturbance attenuation capability of a closed-loop control system. A nonlinear least-squares optimisation method is applied in sensitivity function shaping to design a feedback controller for a micro-actuator such that its sensitivity function fulfills desired specifications in order to attenuate disturbances at specific frequencies. The micro-actuator is used as a secondary actuator to enhance the positioning accuracy of a servo track writer for hard disk drives. The disturbance attenuation capability of the designed control system is also evaluated for disturbances with varying frequencies. Simulation and experimental results show the effectiveness of this method in designing a controller so that specific conditions imposed on the sensitivity function are satisfied. - Author(s): W. Blajer and K. Kołodziejczyk
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1370 –1379
- DOI: 10.1049/iet-cta:20060439
- Type: Article
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Manipulating payloads with gantry cranes is challenging due to possible undesirable load pendulations induced by the crane motion and external perturbations. When the work environment is cluttered with obstacles, the problem gets increasingly difficult, which must be avoided, resulting in the need for appropriate load trajectory planning and more cautious craning strategy. The trajectory is first sketched by a series of points in the work space, and then approximated by spline functions. A rest-to-rest load motion along the specified trajectory is then imposed, resulting in one coordinated manoeuvre that omits the obstacles. The control of crane executing the load motion is viewed as an inverse dynamics problem, strongly influenced by the underactuated nature of the system. The arising governing differential-algebraic equations enable one for the analysis of crane dynamics and synthesis of its control in the specified motion. The open-loop control obtained this way is enhanced by a closed-loop control with feedback of the actual errors in load position to provide stable tracking of the reference trajectory in presence of perturbations and modelling inconsistencies. Some results of numerical simulations are reported. - Author(s): Y. Liu and W. Zhang
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1380 –1389
- DOI: 10.1049/iet-cta:20060536
- Type: Article
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An analytical two degree-of-freedom decoupling control scheme for two-by-two systems with integrator(s) is proposed. The approach facilitates explicit tuning for both input tracking and load disturbance rejection design goals. In this new scheme, a novel inverse model-based decoupler is first introduced to eliminate interactions. The set-point tracking controller is then analytically derived based on the decoupled process. The disturbance controller that is responsible for rejecting load disturbances is obtained by proposing the desired transfer function for disturbance rejection. Tuning constraints for the proposed disturbance controller are developed based on system robust stability analysis. Simulation examples are used to illustrate the proposed control scheme. Results from the simulation show that a good performance can be obtained using the proposed control scheme. Moreover, it has been demonstrated that the proposed closed-loop for disturbance rejection can also be utilised to reject ramp-type load disturbances. - Author(s): S. Kim ; Y. Kim ; C. Park
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1390 –1397
- DOI: 10.1049/iet-cta:20060537
- Type: Article
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A model-free hybrid fault diagnosis technique is proposed to improve the performance of fault detection and isolation. This is a model-free hybrid method, which combines a parity equation approach with a multi-resolution signal decomposition by using discrete wavelet transform. There exists a required minimum number of measurements to isolate the faulty sensor in a given sensor configuration. The proposed technique can isolate the faulty sensor even when the above condition is not satisfied. To verify the effectiveness of the proposed fault diagnosis method, numerical simulations are performed for a skew-configured inertial sensor system. Experiments using the hardware in a loop simulation system are also performed. - Author(s): K. Belarbi and M. Chemachema
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1398 –1404
- DOI: 10.1049/iet-cta:20050451
- Type: Article
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A state feedback direct adaptive control algorithm for single input single output perturbed nonlinear systems in affine form using single hidden layer neural network is introduced. The weights adaptation laws are based on an estimated control error provided by a fuzzy inference system composed of heuristically determined rules. It provides a bounded estimate of the control error, which affects only the step size of the updating laws. It is shown that under mild conditions the state variables and the control input are bounded and the tracking error and its derivatives converge to a bounded compact set. The method does not require any preliminary off line training of the network weights. All states are supposed to be measurable. Two simulation studies are presented for testing the proposed algorithm. - Author(s): T.-J. Ren and T.-C. Chen
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1405 –1412
- DOI: 10.1049/iet-cta:20060185
- Type: Article
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The modelling and control of a power-assisted mobile vehicle (PAMV) based on a torque observer are presented. In particular, a human, who recognises the environment, plans the trajectory without danger of collision. The mobile vehicle can generate more power than a human. A human-guided powered mobile vehicle is developed. A dynamic model of this vehicle is constructed by Lagrangian's equation. A torque observer, designed using the Lyapunov stability theorem, is applied to estimate the external human thrust. The observer gain could be well designed by the proposed method. According to the estimated thrust, two driving wheels controlled by two servomotors provide appropriate assisted force for the PAMV. The feasibility of the proposed control frame is proven and the experimental results demonstrate that the proposed system has high precision and efficiency. - Author(s): P. Chen ; W. Zhang ; D. Gu
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1413 –1422
- DOI: 10.1049/iet-cta:20060481
- Type: Article
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A quantitative parameter tuning scheme for a class of multiloop control systems is designed by Internal Model Control (IMC) method. IMC method is a common-used design method for multivariable control systems. This design method provides a single controller parameter for each control loop. The existing trial and error method for tuning these parameters are conservative and time-consuming. An analytical tuning scheme is proposed to tune these parameters quantitatively. Differing from the trial and error method, the interaction information is considered quantitatively in the tuning procedure. The proposed tuning scheme consists of calculation method of the tuning bound, parameter estimation method and dominant pole adjustment method. The quantitative relationships between the variation of the dominant pole and the time–domain design specifications are also studied. Numerical examples are given to demonstrate the validity of the proposed tuning scheme. - Author(s): F. Wu and Y. Chen
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1423 –1430
- DOI: 10.1049/iet-cta:20060305
- Type: Article
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A robust receding horizon control (RHC) scheme is proposed for parameter-dependent linear systems with linear fractional parameter dependency and input–output constraints. The cost function is defined over a moving finite horizon as the quadratic performance for future parameter trajectories. The robust stability of the proposed RHC scheme is guaranteed using a parameter-dependent control Lyapunov function as the terminal penalty term, which is available through off-line synthesis procedure. Moreover, it is shown that the domain of attraction will be enlarged and the controlled performance of the RHC scheme will be gradually improved as the upper bound of performance is monotonically decreasing on-line. Both off-line robust control synthesis and on-line RHC computation are formulated and solved using linear matrix inequality optimisation techniques. - Author(s): E.B. Muhando ; T. Senjyu ; A. Yona ; H. Kinjo ; T. Funabashi
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1431 –1440
- DOI: 10.1049/iet-cta:20060448
- Type: Article
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Operation of wind turbine generator (WTG) systems in the above-rated region characterised by high wind turbulence intensities invariably induces fatigue stresses on the drive train components. This demands a trade-off between two performance metrics: maximisation of energy harvested from the wind and minimisation of the damage caused by mechanical fatigue. A learning adaptive controller in the form of a self-tuning regulator (STR) for output power levelling and decrementing fatigue loads is presented. The STR incorporates a hybrid controller of a linear quadratic Gaussian (LQG), neurocontroller and a linear parameter estimator (LPE). The main control objective is to regulate the relationship between rotational speed and wind speed by controlling the generator torque and further, the rotational speed. A pitch actuator ensures system operation geared toward maintaining output at rated power. A second-order model and a stochastic wind field model are used to systematically analyse the dynamical relationship between the WTG subsystems. The LQG is used as a basis upon which the performance of the proposed method in the trade-off studies is assessed. Simulation results indicate the proposed control scheme captures the performance and critical reliability loci thereby ensuring the wind turbine operates optimally in mechanically harmless conditions. - Author(s): O. Santos and G. Sánchez-Díaz
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1441 –1450
- DOI: 10.1049/iet-cta:20060486
- Type: Article
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Recent efforts are encountered to obtain suboptimal controllers using evolutionary algorithms on control of system without delays, including proportional integral derivative (PID) controllers. However, the problem of optimisation on delay control systems has been solved through traditional techniques based on search optimal control. A numerical optimisation problem for a kind of time delay control system is presented. A suboptimal control law is synthesised using a method based on the hill-climbing algorithm, in order to minimise a quadratic index. The stability analysis for the proposed controller is proposed. Finally, experimental results using the proposed method are shown. - Author(s): C.A. Monje ; F. Ramos ; V. Feliu ; B.M. Vinagre
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1451 –1460
- DOI: 10.1049/iet-cta:20060477
- Type: Article
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A new method to control single-link lightweight flexible manipulators in the presence of payload changes is proposed. Undoubtedly, the control of this kind of structures is nowadays one of the most challenging and attractive research areas, being remarkable its application to the aerospace industry, among others. One of the interesting features of the design method presented here is that the overshoot of the controlled system is independent of the tip mass. This allows a constant safety zone to be delimited for any given placement task of the arm, independent of the load being carried, thereby making it easier to plan collision avoidance. Other considerations about noise and motor saturation issues are also presented. To satisfy this performance, the overall control scheme proposed consists of three nested control loops. Once the friction and other nonlinear effects have been compensated, the inner loop is designed to give a fast motor response. The middle loop simplifies the dynamics of the system and reduces its transfer function to a double integrator. A fractional derivative controller is used to shape the outer loop into the form of a fractional order integrator. The result is a constant phase system with, in the time domain, step responses exhibiting constant overshoot, independent of variations in the load, and robust, in a stability sense, to spillover effects. Experimental results are shown, when controlling the flexible manipulator with this fractional order derivator, that prove the good performance of the system. - Author(s): A. Bartoszewicz and A. Nowacka-Leverton
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1461 –1470
- DOI: 10.1049/iet-cta:20060458
- Type: Article
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A new sliding mode control (SMC) algorithm for the third-order uncertain, nonlinear and time-varying dynamic system subject to acceleration constraint is proposed. The algorithm employs a time-varying switching plane. At the initial time t=t0, the plane passes through the point determined by the system initial conditions in the error state space. Afterwards, the plane moves with a constant velocity to the origin of the state space. In order to select the switching plane parameters, the integral of the absolute error is minimised. Two types of the acceleration constraints are considered. First, a conventional constraint expressed by an inequality is analysed and then an elastic (or stretchable) constraint represented by a penalty function is taken into account. In the second case, we assume that the threshold value of the system acceleration is known and exceeding this value is undesirable, however possible if justified by essential improvement of the system performance. In both cases, the switching plane is chosen in such a way that the reaching phase is eliminated, insensitivity of the system to the external disturbance and the model uncertainty is guaranteed from the very beginning of the proposed control action and fast, monotonic error convergence to zero is achieved. - Author(s): D. Llanos ; M. Staroswiecki ; J. Colomer ; J. Meléndez
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1471 –1476
- DOI: 10.1049/iet-cta:20060519
- Type: Article
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The design of control, estimation or diagnosis algorithms most often assumes that all available process variables represent the system state at the same instant of time. However, this is never true in current network systems, because of the unknown deterministic or stochastic transmission delays introduced by the communication network. During the diagnosing stage, this will often generate false alarms. Under nominal operation, the different transmission delays associated with the variables that appear in the computation form produce discrepancies of the residuals from zero. A technique aiming at the minimisation of the resulting false alarms rate, that is based on the explicit modelling of communication delays and on their best-case estimation is proposed. - Author(s): R. Becerril-Arreola ; A.G. Aghdam ; V.D. Yurkevich
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1477 –1486
- DOI: 10.1049/iet-cta:20070020
- Type: Article
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A design method for the decentralised time-varying discrete-time output-feedback control of linear time-invariant plants with unstable unstructured decentralised fixed modes (UDFM) is introduced. The design method uses generalised sampled-data hold functions to eliminate the UDFMs and to decouple the discrete-time equivalent model of the plant into independent input–output channels. Through this structural change, the plant becomes suitable for a stabilising high-sampling-rate controller that induces two-time-scale motions (TTSM) in the closed-loop system. As a result, the discrete-time controller is likewise decoupled into distinct local agents and the TTSM closed-loop system is decentralised. - Author(s): B. Marx ; D. Koenig ; J. Ragot
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1487 –1495
- DOI: 10.1049/iet-cta:20060412
- Type: Article
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A method for state-estimation of Takagi–Sugeno descriptor systems (TSDS) affected by unknown inputs (UI) has been presented here. For ease of implementation's sake, the proposed observers are not in descriptor form, but in usual form. Sufficient existence conditions of the unknown input observers (UIOs) are given and strict linear matrix inequalities are solved to determine the gain of the observers. If the perfect UI decoupling is not possible, the UIO is designed in order to minimise the ℒ2-gain from the UI to the state estimation error. The two previous objectives can be mixed in order to decouple the estimation to a subset of the UI, while attenuating the ℒ2-gain from the other UI to the estimation. The proposed UI observers are used for robust fault diagnosis. Fault diagnosis for TSDS is performed by designing a bank of observers. A simple decision logic and thresholds setting allow to determine the occurring fault. The results are established for both the continuous and the discrete time cases. The proposed method is illustrated by a numerical example. - Author(s): M.V. Moreira and J.C. Basilio
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1496 –1503
- DOI: 10.1049/iet-cta:20060473
- Type: Article
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In a debate paper, Keel and Bhattacharyya have suggested, by means of simple examples taken from the open literature, that optimal and robust controllers can be fragile in the sense that a minute perturbation in the controller parameters can make the closed-loop system unstable. However, is it true that the optimal and robust controllers presented by Keel and Bhattacharyya are actually fragile? It is demonstrated that the particular parametric stability margin used by Keel and Bhattacharyya can be very conservative and to overcome this problem, two non-conservative measures of controller fragility are proposed. In addition, it will be shown that the examples in Keel and Bhattacharyya's paper are very special and the resulting fragility cannot be linked to the H∞ optimisation but to non-appropriate H∞ optimisation criterions and to bad choice of weights. - Author(s): Z. Xi and Z. Ding
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1504 –1511
- DOI: 10.1049/iet-cta:20060432
- Type: Article
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For the first time, a solution to the problem of global decentralised output regulation for a class of large-scale uncertain nonlinear systems with nonlinear exosystem using error information is presented. The proposed constructive approach does not require any matching conditions on the parametric uncertainties with some growth conditions on the interacting output nonlinearities. Two decentralised error feedback adaptive control strategies have been presented under some assumptions. - Author(s): V. Bandal and B. Bandyopadhyay
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1512 –1522
- DOI: 10.1049/iet-cta:20060393
- Type: Article
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In this paper, we propose a power system stabiliser (PSS) design scheme based on robust decentralised output feedback sliding mode control technique. We demonstrate the proposed technique on a 10-machine, 39-bus power system and compare it with classical PSS design. Although the proposed technique is based on linearised model of the nonlinear multimachine power system, the efficacy of the controller has been demonstrated by the simulation using nonlinear model. - Author(s): H. Yang ; B. Jiang ; M. Staroswiecki
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1523 –1532
- DOI: 10.1049/iet-cta:20060406
- Type: Article
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A class of nonlinear systems that are output–input stable in healthy situation is considered. An observer-based fault-tolerant control (FTC) method is proposed to make the origin asymptotically stable in spite of faults. The proposed FTC method can help to construct a family of Lyapunov functions for a class of switched nonlinear systems with unfixed or fixed dwell periods and to design a switching law that guarantees the fault-tolerant asymptotic stability of the origin. Several examples are included to illustrate the design procedures. - Author(s): K.C. Veluvolu ; Y.C. Soh ; W. Cao
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1533 –1540
- DOI: 10.1049/iet-cta:20060434
- Type: Article
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To handle the state estimation of a nonlinear system perturbed by a scalar disturbance distributed by a known nonlinear vector, we incorporate a sliding mode term into a nonlinear observer to realise a robust nonlinear observer. By linking the observability of the unknown input to the output measurement, the so-called matching condition is avoided. The measurable output estimation error is the sliding surface. In the sliding mode, the reduced-order error system is free from the disturbance, and the convergence of the estimation error dynamics is proven. The unknown input/disturbance is estimated from the sliding mode. Under a Lipschitz condition for the nonlinear part, the nonlinear observers are designed under the structural assumption that the system is observable with respect to any control input. The proposed robust nonlinear estimator is applied to state and unknown input estimation of a bioreactor. The simulation results demonstrate the effectiveness of the proposed method. - Author(s): J.C. Geromel ; R.H. Korogui ; J. Bernussou
- Source: IET Control Theory & Applications, Volume 1, Issue 5, p. 1541 –1549
- DOI: 10.1049/iet-cta:20060460
- Type: Article
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Robust dynamic output feedback design is an open problem, computationally speaking, since its determination asks for the solution of nonlinear matrix inequalities, namely bilinear ones. This is particularly the case for polytopic uncertainty. Here, new sufficient conditions for ℋ2 and ℋ∞ robust output feedback control synthesis are proposed by the use of bounds and scaling for completion of squares. The usefulness of the provided conditions stands in the fact that its solution can be performed using the Frank–Wolfe algorithm which runs in only one shot. The ℋ2 robust control design of an inverted pendulum with uncertain friction coefficients and ℋ∞ reliable control systems design illustrate the theory.
Using the output energy as performance index in the design of damping controllers for power systems
Coordinated control of two biomimetic robotic fish in pushing-object task
Fault estimation and fault-tolerant control for descriptor systems via proportional, multiple-integral and derivative observer design
Exact discretisation of a scalar differential Riccati equation with constant parameters
Ternary input signal design for system identification
Delay-dependent robust H∞ control for uncertain singular time-delay systems
Robust fuzzy feedback linearisation controllers for Takagi-Sugeno fuzzy models with parametric uncertainties
Affine Takagi-Sugeno fuzzy modelling algorithm by fuzzy c-regression models clustering with a novel cluster validity criterion
A comparative study between sliding mode and proportional integrative derivative controllers for ship roll stabilisation
Gain-scheduled stabilisation of linear parameter-varying systems with time-varying input delay
A robust fault detection filtering for stochastic distribution systems via descriptor estimator and parametric gain design
Minimal realisation of the transfer function matrix with multiple time delays
Output feedback model predictive control for nonlinear systems represented by Hammerstein–Wiener model
Fuzzy adaptive EKF motion control for non-holonomic and underactuated cars with parametric and non-parametric uncertainties
Optimal reference processing in two-degrees-of-freedom control
Design of high-performance networked real-time control systems
H∞ fault detection filter design for networked control systems modelled by discrete Markovian jump systems
H∞ control of networked control systems with time delay and packet disordering
Robust sliding mode control of a robot manipulator based on variable structure-model reference adaptive control approach
Nonlinear least-squares optimisation of sensitivity function for disturbance attenuation on hard disk drives
Motion planning and control of gantry cranes in cluttered work environment
Analytical design of two degree-of-freedom decoupling control scheme for two-by-two systems with integrator(s)
Failure diagnosis of skew-configured aircraft inertial sensors using wavelet decomposition
Stable direct adaptive neural network controller with a fuzzy estimator of the control error for a class of perturbed nonlinear systems
Modelling and control of a power-assisted mobile vehicle based on torque observer
Quantitative parameter tuning scheme for a class of multiloop control systems
Robust receding horizon control for constrained linear fractional transformation parameter-dependent systems
Disturbance rejection by dual pitch control and self-tuning regulator for wind turbine generator parametric uncertainty compensation
Suboptimal control based on hill-climbing method for time delay systems
Tip position control of a lightweight flexible manipulator using a fractional order controller
SMC without the reaching phase – the switching plane design for the third-order system
Transmission delays in residual computation
Decentralised two-time-scale motions control based on generalised sampling
Design of observers for Takagi–Sugeno descriptor systems with unknown inputs and application to fault diagnosis
Fragility problem revisited: overview and reformulation
Global decentralised output regulation for a class of large-scale nonlinear systems with nonlinear exosystem
Robust decentralised output feedback sliding mode control technique-based power system stabiliser (PSS) for multimachine power system
Observer-based fault-tolerant control for a class of switched nonlinear systems
Robust observer with sliding mode estimation for nonlinear uncertain systems
ℋ2 and ℋ∞ robust output feedback control for continuous time polytopic systems
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