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This paper addresses the exploitation of vector based contraction theory to synchronize the motion of agents in multiagent systems. The convergence analysis of the agents using this theory provides a flexible frame as the components of a vector distance norm follow less stringent conditions than classical contraction analysis. The key feature is that it encompasses the formulation of some comparison system, as a result, the problem of convergence analysis of a complex multiagent system reduces to the convergence analysis of a much simpler comparison system. Hence, despite the nonlinearities, the methods of designing consensus controls remain simple as compared to the existing literature. We address four different cases: 1) consensus of third‐order dynamics multiagent systems subjected to acceleration and input constraints; 2) consensus of multiagent systems with heterogeneous nodes under communication imperfections; 3) synchronization of multiagent systems with connected and disconnected switching topologies; 4) synchronization in networked systems with time‐varying couplings. Moreover, an effective synchronization control scheme for a class of multiagent systems with underactuated agent dynamics is developed using the method of aggregation of comparison systems. Finally, simulation results are illustrated that show the validity of the mathematical results.

This paper proposes a distributed artificially delayed output feedback‐based leader–follower and leaderless consensus control for the uncertain general linear multiagent systems (MASs) with an arbitrary relative degree. Based on the measured relative output and their delayed information with respect to neighbours, two distributed controllers are designed, which relaxes the requirement of all relative states information of agents. Through the Lyapunov–Krasovskii functional, linear matrix inequalities (LMIs) are formulated, and these LMIs are feasible for arbitrary small delays selected by the user. Delay‐dependent sufficient conditions are provided to guarantee the asymptotic convergence of nominal error systems and ultimately uniform boundedness in the case of a perturbed error system, using the input to state stability (ISS) theory. Finally, the efficacy of the proposed method is illustrated through numerical examples.

This paper presents a robust L2-based Static Output Feedback (SOF) controller design for a class of linear continuous-time polytopic systems subject to actuator saturation, which is a feature commo...

Thyristor Controlled Series Capacitor (TCSC) is employed as actuator in an interconnected power system using Supplementary Damping Controller (SDC) to enhance the power transfer capabilities between areas as well as damp out the Inter-Area Low-Frequency (IALF) oscillations by varying the impedance of transmission lines. The time-varying delays in the feedback loop and asymmetric saturation limits at the output of TCSC may reduce the performance of the designed controller and lead to closed-loop instability if these are not considered in the process of controller design. Usually, a Minimum Absolute Saturation Bound technique (MASB) is used to convert asymmetric saturation limits into symmetric one. However, such consideration provides an apparent conservative and degrades the performance of the control system. To reduce the conservative in the control design process, a Normalized Saturation Bound (NSB) technique is used in this paper to convert asymmetric saturation limits of TCSC of time-delayed power system. The L-K functional and generalized sector conditions are utilized in the proposed controller design process to compensate the effect of time-varying delay and converted symmetric saturation limits. Sufficient conditions required for controller design are formulated in LMI form. 2-area 4-machine power model is used to verify the performance of the designed controller. From the simulation results, it is observed that the designed controller is giving superior performance in the present of time-varying delays and asymmetric saturation as compared to the designed controller using MASB technique.

This study is concerned on the design of a quasi-linear parameter varying (qLPV) proportional–integral (PI) controller for twin rotor multiple-input multiple-output systems (TRMS). The non-linear model is represented as a qLPV polytopic plant with an affine dependence on a non-linear parametric function of the pitch angle. This representation retains the exact model as opposed to the conventional linearisation around an operating point. Due to the availability of the pitch angle measurement, the non-linear parameter can be obtained in real-time and the controller is designed using qLPV technique. To deal with limited control input for such systems, the proposed controller design also considers the actuator saturation that yields controller with practical gains without any additional gain bound criterion. Further, the transient tracking performance is also considered in the design by using closed-loop eigenvalues assignment in desired damping regions. The control synthesis problem is formulated in the form of linear matrix inequalities for L 2 gain based performance criterion. The designed controller is validated on a two-degree of freedom helicopter experimental setup. Finally, to demonstrate the effectiveness of the proposed design, a comparative analysis is done with the existing algorithms. Also, the efficacy of the decentralised controller vis-a-vis the centralised one is presented.

A new strategy for the design of controller and state observer is proposed based on the vector based contraction framework. The methodology gives relaxation over the conventional contraction theory as there is no requirement to guarantee the negative definiteness of the complex Jacobian matrix to derive convergence results. The vector framework is used to simplify the problem through the comparison systems. Specifically, suitable choice of comparison system derives the convergence of squared distance between any pair of trajectories in a reduced way. The examples of controller design for duffing system and observer design for Chua’s circuit are illustrated to see the implementation of the proposed results. Furthermore, results are observed through simulation.

This study proposes an output feedback sliding mode control with an artificial delay. The output information-based sliding surface is outlined. An artificial delay as well as an exponential decay term is introduced in the sliding surface, which reflects these additional terms (artificial delay and exponential decay term) in the reduced-order dynamics. The idea and advantage of utilising the artificial delay in the sliding surface are to stabilise the class of systems, which are not able to stabilise with only output feedback. The employment of exponential decay term in the sliding surface provides a reaching phase free behaviour. It implies that the authors' approach is insensitive to external matched disturbances from the very initial time. With the aid of Lyapunov–Krasovskii functional, local input to state stability for the reduced-order dynamics as well as for the closed-loop system is presented. Finally, the simulation results of the translation oscillator with rotating actuator system are presented to validate the effectiveness of the offered technique.

This brief addresses the global stabilization of uncertain single input and single output (SISO) dynamical systems using sliding mode control with multiple delayed partial state feedback. It is shown that using only delayed partial state information, it is possible to stabilize a large class of SISO uncertain dynamical systems. Artificial stabilizing delay is introduced in the partial state feedback to make the reduced-order sliding mode dynamics of a given system asymptotically stable. It is demonstrated that despite the order of dynamical systems, using the information of just three states together with their delayed terms, can asymptotically stabilize the uncertain SISO dynamical system. A numerical example of a ball and wheel system is provided to demonstrate the efficacy of the proposed method.

Inter-area low frequency oscillation in power system is one of the major problems for bulk power transmission through weak tie lines. Use of wide-area signal is more effective than the local area signal in damping out the inter-area oscillations. Wide area measurement system &#x0028 WAMS &#x0029 is convenient to transmit the wide area signal through the communication channel to the remote location. Communication failure is one of the disastrous phenomena in a communication channel. In this paper, a dual input single output &#x0028 DISO &#x0029 H&#x221E controller is designed to build the control resiliency by employing two highest observability ranking wide area signals with respect to the critical damping inter-area mode. The proposed controller can provide sufficient damping to the system and also the system remains stabilized if one of the wide-area signals is lost. The time delay is an unwanted phenomenon that degrades the performance of the controllers. The unified Smith predictor approach is used to design a H&#x221E controller to handle the time delay. Kundur&#x02BC s two-area and IEEE-39 bus test systems are considered to verify the effectiveness of the proposed controller. From the simulation results, it is verified that, the proposed controller provides excellent damping performance at normal communication and improves the controller resiliency to counteract the communication failure.

This paper considers the design of a robust PID controller for higher order MIMO plants. The design problem is first recast into a Static Output Feedback (SOF) controller design problem and then the transformed SOF problem is solved within the framework of Linear Matrix Inequalities (LMIs) through a decomposition of the Lyapunov matrix variable. Sufficient LMI criteria are derived that ensure H∞ performance of the underlying system. By means of a numerical example, it is shown that the designed controller yields less conservative results. Also, a comparative study is done with the existing techniques to demonstrate the efficacy of the proposed method.

This paper addresses the design of static output feedback controller for linear discrete-time systems. New sufficient criteria are derived for designing H∞ and H2 controllers. The correspon...

A dynamic output feedback (DOF) controller design is proposed for an indirect vector-controlled induction motor (IVCIM). The proposed controller is an alternative to the conventional proportional integral (PI) one and can be used for improving the dynamic performance of the IVCIM system. A sequential design method is used in which, first, the inner-loop controllers are designed. Then, the designed inner-loop controller is employed to design the outer speed-loop controller. The procedure incorporates the iron loss dynamics of the induction motor model to fetch the benefit of better performance than conventional controller designs neglecting the same. The DOF controller is designed in an H ∞ control framework by solving the iterative linear matrix inequality that makes stator currents and speed response to be robust against load disturbances and parameter variations. A first-order dynamic controller is tested to highlight its superiority over the PI controller. Comparison between the proposed dynamic and conventional PI controller is shown through several experimental results. It depicts enhanced performance by the proposed controller and suitability to industrial use.

This study addresses the design of static output feedback (SOF) controller for continuous time linear systems. New sufficient conditions are derived for designing SOF controllers. The development involves suitable decomposition of Lyapunov matrices and deriving linear matrix inequality (LMI) criterion that ensures H ∞ performance. LMI criteria for pole placement in the LMI region are also derived. The proposed criteria can be used for restricted SOF controller design effectively. Several numerical examples are presented to demonstrate the effectiveness of the proposed results.

The article analyses possible ways of using predictive controllers to perform control tasks and dynamic decoupling for dynamic systems with Multiple Inputs and Multiple Outputs (MIMO). The results of experiments on the selected reference plant are presented, showing the effectiveness of individual decoupling methods. These are also compared to those obtained in typical control systems with Proportional-Integral-Derivative (PID) controllers. Recommendations are made on how to tune model predictive controllers (MPC) for their effective use for MIMO plants. DOI: 10.5755/j01.eie.25.2.23195

This paper presents the development of a new robust optimal decentralized PI controller based on nonlinear optimization for liquid level control in a coupled tank system. The proposed controller maximizes the closed-loop bandwidth for specified gain and phase margins, with constraints on the overshoot ratio to achieve both closed-loop performance and robustness. In the proposed work, a frequency response fitting model reduction technique is initially employed to obtain a first order plus dead time &#x0028 FOPDT &#x0029 model of each higher order subsystem. Furthermore, based on the reduced order model, a proposed controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed optimal robust decentralized control scheme has been compared with that of a decentralized PI controller. The proposed controller is implemented in real-time on a coupled tank system. From the obtained results, it is shown that the proposed optimal decentralized PI controller exhibits superior control performance to maintain the desired level, for both the nominal as well as the perturbed case as compared to a decentralized PI controller.

This technical note presents the application of simplified contraction analysis using vector framework. In general, conventional approach leads to guaranteeing negative definiteness of the associated Jacobian for ensuring convergence of any pair of trajectories. A vector valued norm is used for simplification of the problem to ensure contraction through the comparison systems. In fact, comparison systems are used for ensuring convergence of the squared distances between any pair of trajectories in a simplified way. We show that by employing this simplified contraction analysis, it is possible to design controller and observer. The methodology is illustrated via a set of representative examples.

In the paper fuzzy logic methods for dynamic decoupling of multi-input multi-output (MIMO) dynamical systems are analysed. A structure of the fuzzy precompensator, which may be used instead classical ideal and inverted decoupling control schemes, is presented. The proposal is illustrated by series of numerical simulations.

In this work, a concurrent proportional integral (PI) controller design technique is addressed for indirect vector controlled induction motor (IVCIM). For this, a full-order induction motor (IM) model is employed that includes the stator current dynamics. The current-loop proportional integral (PI) controllers are tuned to use the attributes of such dynamics. The robustness against load torque and rotor resistance variations are incorporated in the design problem. This method is implemented using a static output feedback scheme in which iterative linear matrix inequality (ILMI) based H-infinity control technique is applied. The simulation and experimental comparison with existing designs show the superiority of proposed method and practical interest for industry use.

Wide-area power system stabilizers (WAPSSs) based on time-synchronized signals are known to be relatively effective in damping inter-area oscillations. However, the use of wide-area signals introduces time-delay in the feedback loop due to the time taken in fetching the feedback information. In general, delays in the feedback loop are detrimental to the performance of the controller and may lead to instability if the control is not sufficiently robust to tolerate the delay variation. It may be the case that one opts for using non-synchronized signals (not time-synchronized) for WAPSS. This paper investigates and compares the effect of delay in synchronized and non-synchronized feedback-based WAPSS. The analysis is carried out using eigenvalue computation for time-delay systems and applied to two study systems. It is shown that non-synchronized signals are less sensitive to delay from the systems stability viewpoint even though comparable damping can be achieved.

This paper deals with non-smooth feedback stabilisation in presence of stochastic unbounded(normally distributed) noise. The integral term of classical proportional-integral controller is replaced by a discontinuous integrator. The overall control effort is still continuous. The behaviour of the proposed scheme under stochastic perturbations is presented. We have given a sound and non-trivial Lyapunov analysis of the closed loop system controlled by the proposed controller on stochastic dynamics.

In this paper, a discretization scheme is proposed for systems with constant delay and the delay is assumed to appear in range. The proposed approach uses simple Lyapunov-Krasovskii functional to derive the robust stability and stabilization criteria. As a result of which the derived criteria become finite-dimensional. Though the criteria give sufficient condition for stability, but they are less conservative than the existing results. To demonstrate the effectiveness of the approach, numerical examples are considered.

Indirect vector-controlled induction motor (IVCIM) dynamics is well known for having different bifurcation behavior, viz., saddle-node bifurcation, Hopf bifurcation (HB), Bogdanov–Takens bifurcation, and zero-HB. A numerical analysis of these bifurcations for proportional–integral-controlled IVCIM is made in this brief using full-order IM model. Some new observations on the bifurcation behavior are made. Simulation and experimental results are presented validating the bifurcation behaviors.

This paper presents a load voltage based (LVB) maximum power point tracking (MPPT) technique using adaptive step-size (ASS) for standalone photovoltaic (PV) systems. The technique improves the convergence speed of the MPPT using a single voltage sensor to measure the load voltage ( V L ) regardless of the nature of load type. The ASS of the MPPT controller is varied according to the slope dV L dD of V L versus duty ratio ( D ) characteristic. The effectiveness of the proposed technique is tested for different insolation level conditions. This ASS based control scheme improves the convergence performance over fixed step-size (FSS) scheme under varying insolation condition. A single-ended primary inductance converter (SEPIC) is used for interfacing the PV system with the resistive load, which increases the operating range of the PV system. The tracking performance of the proposed technique is compared with FSS MPPT, perturb and observe (P&O) and incremental-conductance (IncCond) techniques by simulation. Experimental verification using a developed laboratory prototype is also carried out.

An integral-proportional derivative (I-PD) control strategy for integrating plus time-delay processes is proposed. The proposed scheme consists of an inner PD loop and an outer I-loop for taking care of the servo as well as the regulatory action. Explicit formulas for tuning of the proposed controller are derived in terms of gain margin, phase margin and critical gain. Moreover, pole-placement and frequency loop-shaping design methods are also explored for designing the I-PD controller. Simulation results show the superiority of the proposed I-PD controller over conventional P/PI/PID ones for integrating processes. The design is also validated through experiments on a temperature control process.

It is well known that PD controller, though yields good servo response, fails to provide satisfactory regulatory response for Integrating Plus Time-Delay (IPTD) processes. On the other hand, using an integral control action generally leads to large overshoot or settling time. To achieve good servo as well as regulatory response, a new all-PD control structure is proposed for IPTD processes in this paper. Design formulas are derived in terms of gain-margin and phase-margin specifications. Numerical examples on the design methodology are presented and experimentally validated on a temperature control process.

This paper presents a study on delay robustness improvement ability of a digital Smith predictor based delay compensator for networked control systems with bounded network induced time-varying delays and packet losses. The compensator is considered to be implemented in digital form with time-driven controller and event-driven actuator configuration. The uncertain system model is represented in polytopic form and Lyapunov method is used for stability analysis in terms of linear matrix inequalities. The performance of the digital predictor in terms of delay-tolerability is then tested on two numerical examples and verified with simulation using TrueTime simulator. It is found that the selection of predictor delay can be made based on bounds of network delays to improve the performance of the controller.

This paper addresses a new technique to cater to the nonlinear dynamics involved in a coupled tank system. Earlier approaches to designing a linear controller for a nonlinear system are two-fold. The first considers linearizing the plant around some operating point, thereby ignoring the dynamics posed by higher-order terms while the second approach is to represent the system nonlinearities in the form of model uncertainties, without any approximation of the higher order terms. The latter method forms the basis of design considered in this paper. The nonlinear model of a coupled tank system is represented in the form of a polytopic system that allows for the implementation of a linear controller. The variation in nonlinear term is treated as an uncertain parameter for the system representation. A R∞ based Proportional Integral (PI) controller is designed combined with pole placement in a desired Linear Matrix Inequality (LMI) region to ensure better transient behavior of the system. Experimental results have been provided and compared with conventional design to illustrate the efficacy of the proposed design method.

This work presents a robust LMI tuned PI controller design for the real two degree of freedom (2-DOF) helicopter model with locating poles in a desired region. Experimental results are provided to demonstrate the effectiveness of the proposed design.

Wide area damping controller (WADC) provides the adequate damping to the inter-area modes by using the remote area signal. Wide-Area Measurement System (WAMS) can provide more accurate dynamic data from wide geographical areas. However, the communication time delay in the wide area control loop deteriorates the performance of the controllers and may degrade the system stability. In this paper, speed based power oscillation damping controller, fuzzy logic wide area damping controller and H ∞ controller are designed to provide the damping of the low frequency oscillations. The communication delay is considered in the nonlinear simulation to transmit the wide area remote signal to the controller. Finally, 39 bus power system is considered to verify the efficacious of the designed controllers.

Fixed mode radius is a perturbation measure used to represent how ‘close’ a system is from having at least one fixed mode. In this paper, a catalog of measures for critically delayed fixed mode radius that correspond to critical delays having minimum radius is introduced for systems with input and output delays. Computable formulas are derived using perturbation measures for both centralized and decentralized control systems. Numerical examples are presented to demonstrate the critical delay feature.

To achieve satisfactory set-point tracking and load disturbance rejection, two approaches for PID controller design is presented in this paper. With a PD type controller, conventional IMC techniques fail to provide a satisfactory regulatory response for integrating processes and use of an integral action may lead to a large overshoot in servo response. To address this issue, a modified IMC structure with a second compensation for integrating processes is proposed to achieve desired servo as well as regulatory responses. Next, a frequency loop-shaping based design is proposed and the guidelines for choosing the desired loop-shape are also presented. To obtain the controller parameters in frequency loop-shaping framework, the optimisation problem is solved with primal-dual interior point method. To demonstrate the effectiveness of the proposed controllers, simulation comparisons with some recently developed methods are included. Moreover, the proposed method is experimentally validated on a temperature control process.

This paper presents improved robust delay-range-dependent stability analysis of an uncertain linear time-delay system following two different existing approaches – (i) non-delay partitioning (NDP) and (ii) delay partitioning (DP). The derived criterion (for both the approaches) proposes judicious use of integral inequality to approximate the uncertain limits of integration arising out of the time-derivative of Lyapunov–Krasovskii (LK) functionals to obtain less conservative results. Further, the present work compares both the approaches in terms of relative merits as well as highlights tradeoff for achieving higher delay bound and (or) reducing number of decision variables without losing conservatism in delay bound results. The analysis and discussion presented in the paper are validated by considering relevant numerical examples.

In this paper, a delay-dependent robust stability criterion is proposed for linear systems with two delays. For delay-dependent stable systems, the delays are very small in nature. So, they may overlap each other. This overlapping information may be exploited to obtain a less conservative criterion. To extract such information, a special type of simple Lyapunov–Krasovskii functional is considered. To derive the criterion in form of Linear Matrix inequalities, a matrix variable approach is used. Some numerical examples are presented to validate the less conservativeness of the proposed criterion.

This paper considers the problem of stability analysis of linear systems with a time-varying state delay. A new delay-interval-dependent stability criterion is derived without involving any direct approximation of the integral terms that involve uncertain limit of integration in the time-derivative of the Lyapunov-Krasovskii functional. This development leads to a less conservative LMI criterion as seen through numerical examples.

This paper presents design and real-time implementation of a decentralized active disturbance rejection controller (ADRC) for liquid level regulation of a coupled tank system. To obtain a suitable feasible model of the coupled tank system, in this work system identification approach is employed. Further, based on the identified model, a decoupler has been designed to reduce the coupling effects between input and output. To validate the performance of the controller approach, a real-time experimentation is pursued on the coupled tank system. From the simulation and experimental results, it is found that the ADRC control approach requires less control action to maintain the desired level in both the tanks and also more robust as compared to the other similar reported work in literature.

Decentralized Fixed Mode (DFM) radius is a robustness measure of decentralized control system reflecting how far a system is from having DFM. In this paper, real DFM radius is defined for decentralized control systems with input and output delays, and a computing formula is derived for the same using restricted real perturbation measures. Results of this paper for computing DFM radius of time-delay system are studied with the help of numerical examples.

One of the major issues in an interconnected power system is the low damping of inter-area oscillations which significantly reduces the power transfer capability. Advances in Wide-Area Measurement System (WAMS) makes it possible to use the information from geographical distant location to improve power system dynamics and performances. A speed deviation based Wide-Area Power System Stabilizer (WAPSS) is known to be effective in damping inter-area modes. However, the involvement of wide-area signals gives rise to the problem of time-delay, which may degrade the system performance. In general, time-stamped synchronized signals from Phasor Data Concentrator (PDC) are used for WAPSS, in which delays are introduced in both local and remote signals. One can opt for a feedback of remote signal only from PDC and uses the local signal as it is available, without time synchronization. This paper utilizes configurations of time-matched synchronized and nonsychronized feedback and provides the guidelines to design the controller. The controllers are synthesized using $H_\infty$ control with regional pole placement for ensuring adequate dynamic performance. To show the effectiveness of the proposed approach, two power system models have been used for the simulations. It is shown that the controllers designed based on the nonsynchronized signals are more robust to time time delay variations than the controllers using synchronized signal.

This paper presents design and realization of a robust decentralized PI controller for regulating the level of a coupled tank system. The proposed controller is designed based on a predefined reference transfer function model in which we adopt a frequency matching of actual and reference models. Realization of control algorithms for a multivariable system is often complicated owing to uncertainties in the process dynamics. In this paper, initially a frequency response fitting model reduction technique is adopted to obtain a First Order Plus Dead Time (FOPDT) model of each higher order decoupled subsystem. Further, using the obtained reduced order model, the proposed robust decentralized PI controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed robust decentralized controller has been compared with that of a decentralized PI controller. To validate the performance of the proposed control approach, real-time experimentation is pursed on a Feedback Instrument manufactured coupled tank system.

It is well known that the Decentralized Fixed Mode (DFM) are fixed w.r.t of Linear time-invariant (LTI) decentralized controller. But some modes which are very close to DFM but not exact DFM are called as approximate DFM (ADFM) and a huge control energy is required to shift these modes to a desirable region in complex plane which is not realizable practically. So characterization and determination of these modes are necessary. In this paper, a new quantitative characterization technique of ADFM is proposed by using fixed mode (FM) radius and old characterization techniques are reviewed. ADFM is computed by using proposed method with the help of some numerical examples.

In the paper two different control systems for nonlinear multi-input multi-output MIMO plants are compared and discussed. Their main objective is to reduce the influence of the plant inputs and outputs. A multi-controller control structure, which contains a set of a dynamic decoupling controllers is compared with a synthetized online nonlinear model predictive controller. Pros and cons of both methods are discussed and presented in series of simulations of control of a selected nonlinear MIMO plant. Te paper ends with some final remarks on a practical implementation of decoupling methods for a nonlinear MIMO plants.

This paper presents investigations on a dynamic state feedback controller with state delays that improves tolerable delay margin for systems with input–output delays. Using an iterative pole placement technique for time-delay systems, the effect of introducing state delay in the controller dynamics is studied. It is observed that such a controller improves the tolerable delay margins compared to its static or even simple dynamic counterpart.

This paper presents the design of an output feedback controller for an autonomous underwater vehicle to achieve the task of path following in vertical plane. Using vehicle kinematics, a reference frame is generated which provides desired orientation of the vehicle along the path. An error space is then defined using the reference trajectory and thereby linearized. Based on this linearized model, a static output feedback controller is designed and implemented on the nonlinear plant. Computer simulations have been used to verify the controller design.

The problem of decentralized stabilization of interconnected systems that are delay-dependent for some delays and delay-independent for the remaining ones is addressed in this paper. For the purpose, some of the subsystems are grouped to form new larger subsystems. Such a grouping allows all the interconnection delays present among the smaller subsystems to be divided into two groups in the new subsystem description — (i) intraconnection delays, within the larger subsystem, and (ii) interconnection delays, among the larger subsystems. This facilitates delay-dependent stabilization for the intraconnection delays and delay-dependent stabilization for the interconnection delays. An LMI based stabilization criterion is derived for such mixed delay-dependent/delay-independent stabilization of the overall system. A numerical example is presented demonstrating the effectiveness of the developed criterion.

This paper presents a comparative study of two controllers namely Internal Model control (IMC) decoupling controller and an inverted decoupling controller applied to a coupled-tank liquid level system. These controllers are designed based on identified First Order Plus Dead Time (FOPDT) model of a coupled tank system. The performance of the two decoupling controllers are studied considering input and output multiplicative uncertainties. From the simulation and experimental studies, it is found that the inverted decoupling approach is more robust compared to IMC.

Decoupling of the stator currents is important for smoother torque response of indirect vector controlled induction motors. Typically, feedforward decoupling is used to take care of current coupling that requires exact knowledge of motor parameters, additional circuitry and signal processing. In this paper, a method is proposed to design the regulating proportional-integral gains that minimize coupling without any requirement of the additional decoupler. The variation of the coupling terms for change in load torque is considered as the performance measure. An iterative linear matrix inequality based H∞ control design approach is used to obtain the controller gains. A comparison between the feedforward and the proposed decoupling schemes is presented through simulation and experimental results. The results show that the proposed scheme is simple yet effective even without additional block or burden on signal processing.

This paper demonstrates synthesis of a robust wide-area controller for damping inter-area power system oscillation. A wide-area damping controller is more effective in damping inter-area modes in power system as it takes remote signal as feedback in which inter-area oscillations strongly observable. However, with the involvement of remote signal time-delay is introduced in the feedback loop causing limitation in performance and design. An H ∞ controller with regional pole placement controller is designed in this paper. Time-delay is Pade approximated for controller synthesis. Finally, the designed controller is validated through a two-area power system.

In a modern power system, damping of an inter-area mode is crucial as it limits the power transfer capability. With the progress in Wide-Area Measurement System (WAMS), now dynamic data from wide geographical areas are available readily. The accuracy of such data motivates to be used as feedback for controllers, which can have better performance. The placement of such controllers and the signals to be considered as feedback with the redundancy, such that action will be effective is an interesting idea to deal. The paper deals with the issue of wide-area loop selection in a detailed manner. The selection considers not only being strongly controllable/observable but also the interaction and robustness issue. A static controller performance is compared with dynamic controllers (Lead-Lag compensator, PI Controller, Multi-Objective Controller). The controllers are synthesized so as to minimize the norm. The designed controllers are validated through a four machine case study.

SUMMARY This paper addresses the controller synthesis problem of linear time-delay systems subjected to saturating control. Delay-dependent regional stabilization criteria are derived based on Lyapunov–Krasovskii approach by using both the polytopic or dead-zone representation of the saturation function. The main contribution of the paper lies in developing less conservative convex criterion in terms of LMIs to obtain superior results. On the basis of the derived stabilization criterion, an optimization problem is defined to compute the stabilizing state feedback gains with an aim to maximize the stabilizing region while guaranteeing the asymptotic stability of the closed-loop system. Considering three numerical examples, an assessment of the polytopic and dead-zone nonlinearity approaches is made. Copyright © 2012 John Wiley & Sons, Ltd.

This paper considers the problem of power system load frequency control design incorporating the effect of using open communication network instead of a dedicated one for the area control error signals. To have this, we appropriately consider time-delays in the ACE signals. A delay-dependent two-term H∞ controller design has then been proposed using linear matrix inequalities. Comparison of effectiveness of the proposed two-term controller with that of existing one-term and two-term controller designs establishes the superiority as well as applicability of the present design for the LFC problem.