Showing papers on "Robust control published in 2007"
TL;DR: In this article, a decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) was proposed to detect the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions.
Abstract: This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL
1,169 citations
TL;DR: Several new conditions are obtained for the asymptotic stability of discrete-time systems with time-varying state delay by defining new Lyapunov functions and by making use of novel techniques to achieve delay dependence.
Abstract: This note is concerned with the stability analysis of discrete-time systems with time-varying state delay. By defining new Lyapunov functions and by making use of novel techniques to achieve delay dependence, several new conditions are obtained for the asymptotic stability of these systems. The merit of the proposed conditions lies in their less conservativeness, which is achieved by circumventing the utilization of some bounding inequalities for cross products between two vectors and by paying careful attention to the subtle difference between the terms Sigmam=k-dk k-1(middot) and Sigma m=k-dM k-1(middot), which is largely ignored in the existing literature. These conditions are shown, via several examples, to be much less conservative than some existing result
667 citations
TL;DR: Improved delay-dependent stochastic stability and bounded real lemma (BRL) for Markovian delay systems are obtained by introducing some slack matrix variables and the conservatism caused by either model transformation or bounding techniques is reduced.
Abstract: This paper deals with the problems of delay-dependent robust Hinfin control and filtering for Markovian jump linear systems with norm-bounded parameter uncertainties and time-varying delays. In terms of linear matrix inequalities, improved delay-dependent stochastic stability and bounded real lemma (BRL) for Markovian delay systems are obtained by introducing some slack matrix variables. The conservatism caused by either model transformation or bounding techniques is reduced. Based on the proposed BRL, sufficient conditions for the solvability of the robust Hinfin control and Hinfin filtering problems are proposed, respectively. Dynamic output feedback controllers and full-order filters, which guarantee the resulting closed-loop system and the error system, respectively, to be stochastically stable and satisfy a prescribed Hinfin performance level for all delays no larger than a given upper bound, are constructed. Numerical examples are provided to demonstrate the reduced conservatism of the proposed results in this paper.
525 citations
01 Aug 2007
TL;DR: In this paper, an observer-based feedback controller is designed to robustly exponentially stabilize the networked system in the sense of mean square and also achieve the prescribed Hinfin disturbance-rejection-attenuation level.
Abstract: In this paper, the robust Hinfin control problem Is considered for a class of networked systems with random communication packet losses. Because of the limited bandwidth of the channels, such random packet losses could occur, simultaneously, in the communication channels from the sensor to the controller and from the controller to the actuator. The random packet loss is assumed to obey the Bernoulli random binary distribution, and the parameter uncertainties are norm-bounded and enter into both the system and output matrices. In the presence of random packet losses, an observer-based feedback controller is designed to robustly exponentially stabilize the networked system in the sense of mean square and also achieve the prescribed Hinfin disturbance-rejection-attenuation level. Both the stability-analysis and controller-synthesis problems are thoroughly investigated. It is shown that the controller-design problem under consideration is solvable if certain linear matrix inequalities (LMIs) are feasible. A simulation example is exploited to demonstrate the effectiveness of the proposed LMI approach.
480 citations
TL;DR: This note uses not only the time-varying-delayed state x(t-h(t)) but also the delay-upper-bounded state x([email protected]?) to exploit all possible information for the relationship among a current state x (t), an exactly delayed state x h, a marginally delayed state X([email-protected]?), and the derivative of the state [email protected]?(t).
442 citations
TL;DR: It is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable, and the effectiveness of the novel networked predictive control scheme is shown.
Abstract: The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme
436 citations
TL;DR: The method proposed can be applied to determine homogeneous parameter-dependent matrix solutions to a wide variety of PD-LMIs by transforming the infinite-dimensional LMI problem described in terms of uncertain parameters belonging to the unit simplex in a sequence of finite- dimensional LMI conditions which converges to the necessary conditions for the existence of a homogeneous polynomially parameter- dependent solution of arbitrary degree.
Abstract: This note investigates the robust stability of uncertain linear time-invariant systems in polytopic domains by means of parameter-dependent linear matrix inequality (PD-LMI) conditions, exploiting some algebraic properties provided by the uncertainty representation. A systematic procedure to construct a family of finite-dimensional LMI relaxations is provided. The robust stability is assessed by means of the existence of a Lyapunov function, more specifically, a homogeneous polynomially parameter-dependent Lyapunov (HPPDL) function of arbitrary degree. For a given degree , if an HPPDL solution exists, a sequence of relaxations based on real algebraic properties provides sufficient LMI conditions of increasing precision and constant number of decision variables for the existence of an HPPDL function which tend to the necessity. Alternatively, if an HPPDL solution of degree exists, a sequence of relaxations which increases the number of variables and the number of LMIs will provide an HPPDL solution of larger degree. The method proposed can be applied to determine homogeneous parameter-dependent matrix solutions to a wide variety of PD-LMIs by transforming the infinite-dimensional LMI problem described in terms of uncertain parameters belonging to the unit simplex in a sequence of finite-dimensional LMI conditions which converges to the necessary conditions for the existence of a homogeneous polynomially parameter-dependent solution of arbitrary degree. Illustrative examples show the efficacy of the proposed conditions when compared with other methods from the literature.
428 citations
TL;DR: In this paper, the adaptive nature of the guidance method makes its stability independent of vehicle velocity, and the stability analysis is also extended to show robust stability in the presence of saturated lateral acceleration, which is an inherent limitation of flight vehicles.
Abstract: Performance and stability are demonstrated for a nonlinear path-following guidance method for unmanned air vehicles. The method was adapted from a pure pursuit-based path following, which has been widely used in ground based robot applications. The method is known to approximate a proportional-derivative controller when following a straight line path, but it is shown that there is also an element of anticipatory control that enables tight tracking when following curved paths. Ground speed is incorporated into the computation of commanded lateral acceleration, which adds an adaptive capability to accommodate vehicle speed changes due to external disturbances such as wind. Asymptotic Lyapunov stability of the nonlinear guidance method is demonstrated when the unmanned air vehicle is following circular paths. The adaptive nature of the guidance method makes its stability independent of vehicle velocity. The stability analysis is also extended to show robust stability of the guidance law in the presence of saturated lateral acceleration, which is an inherent limitation of flight vehicles. Flight tests of the algorithm, using two small unmanned air vehicles, showed that each aircraft was controlled to within 1.6 m root mean square when following circular paths. The method was used to perform a rendezvous of the two aircraft, bringing them into very close proximity, within 12 m of along track separation and 1.4 m root mean square relative position errors.
389 citations
TL;DR: This paper overviews several selected topics in this popular area, specifically, recent extensions of the basic concept of robust counterpart of an optimization problem with uncertain data, tractability of robust counterparts, links between RO and traditional chance constrained settings of problems with stochastic data, and a novel generic application of the RO methodology in Robust Linear Control.
Abstract: Robust Optimization is a rapidly developing methodology for handling optimization problems affected by non-stochastic “uncertain-but- bounded” data perturbations. In this paper, we overview several selected topics in this popular area, specifically, (1) recent extensions of the basic concept of robust counterpart of an optimization problem with uncertain data, (2) tractability of robust counterparts, (3) links between RO and traditional chance constrained settings of problems with stochastic data, and (4) a novel generic application of the RO methodology in Robust Linear Control.
339 citations
TL;DR: This paper presents a formulation for distributed model predictive control (DMPC) of systems with coupled constraints that divides the single large planning optimization into smaller sub-problems, each planning only for the controls of a particular subsystem.
Abstract: This paper presents a formulation for distributed model predictive control (DMPC) of systems with coupled constraints. The approach divides the single large planning optimization into smaller sub-problems, each planning only for the controls of a particular subsystem. Relevant plan data is communicated between sub-problems to ensure that all decisions satisfy the coupled constraints. The new algorithm guarantees that all optimizations remain feasible, that the coupled constraints will be satisfied, and that each subsystem will converge to its target, despite the action of unknown but bounded disturbances. Simulation results are presented showing that the new algorithm offers significant reductions in computation time for only a small degradation in performance in comparison with centralized MPC.
336 citations
27 Jul 2007
Abstract: Preface. Notation. 1 Introduction. 1.1 Systems and Control 1.2 Modern Control Theory 1.3 Stability 1.4 Optimal Control 1.5 Optimal Control Approach 1.6 Kharitonov Approach 1.7 H- and H2 Control 1.8 Applications 1.9 Use of This Book 2 Fundamentals of Control Theory. 2.1 State Space Model 2.2 Responses of Linear Systems 2.3 Similarity Transformation 2.4 Controllability and Observability 2.5 Pole Placement by State Feedback 2.6 Pole Placement Using Observer 2.7 Notes and References 2.8 Problems 3 Stability Theory. 3.1 Stability and Lyapunov Theorem 3.2 Linear Systems 3.3 Routh-Hurwitz Criterion 3.4 Nyquist Criterion 3.5 Stabilizability and Detectability 3.6 Notes and References 3.7 Problems 4 Optimal Control and Optimal Observers. 4.1 Optimal Control Problem 4.2 Principle of Optimality 4.3 Hamilton-Jacobi-Bellman Equation 4.4 Linear Quadratic Regulator Problem 4.5 Kalman Filter 4.6 Notes and References 4.7 Problems 5 Robust Control of Linear Systems. 5.1 Introduction 5.2 Matched Uncertainty 5.3 Unmatched Uncertainty 5.4 Uncertainty in the Input Matrix 5.5 Notes and References 5.6 Problems 6 Robust Control of Nonlinear Systems. 6.1 Introduction 6.2 Matched Uncertainty 6.3 Unmatched Uncertainty 6.4 Uncertainty in the Input Matrix 6.5 Notes and References 6.6 Problems 7 Kharitonov Approach. 7.1 Introduction 7.2 Preliminary Theorems 7.3 Kharitonov Theorem 7.4 Control Design Using Kharitonov Theorem 7.5 Notes and References 7.6 Problems 8 H and H2 Control. 8.1 Introduction 8.2 Function Space 8.3 Computation of H2 and H- Norms 8.4 Robust Control Problem as H2 and H- Control Problem 8.5 H2/H- Control Synthesis 8.6 Notes and References 8.7 Problems 9 Robust Active Damping. 9.1 Introduction 9.2 Problem Formulation 9.3 Robust Active Damping Design 9.4 Active Vehicle Suspension System 9.5 Discussion 9.6 Notes and References 10 Robust Control of Manipulators. 10.1 Robot Dynamics 10.2 Problem Formulation 10.3 Robust Control Design 10.4 Simulations 10.5 Notes and References 11 Aircraft Hovering Control. 11.1 Modelling and Problem Formulation 11.2 Control Design for Jet-borne Hovering 11.3 Simulation 11.4 Notes and References Appendix A: Mathematical Modelling of Physical Systems. References and Bibliography. Index.
TL;DR: This paper studies a methodology for group coordination and cooperative control of n agents to achieve a target-capturing task in 3D space based on a cyclic pursuit strategy, where agent i simply pursues agent i+1 modulo n.
TL;DR: This paper introduces a robust current-control scheme for a permanent-magnet synchronous motor (PMSM) with a simple adaptive disturbance observer that provides an efficient solution for torque-ripple minimization in PMSM drives.
Abstract: This paper introduces a robust current-control scheme for a permanent-magnet synchronous motor (PMSM) with a simple adaptive disturbance observer. The robust controller is realized by including an adaptive element in the reference-voltage-generation stage using the feedforward control. Due to the time-varying nature and the high-bandwidth property of the uncertainties in a practical PMSM drive system, the adaptive element is simply chosen as the estimated uncertainty function, which adaptively varies with different operating conditions. Subsequently, the frequency modes of the uncertainty function are embedded in the control effort, and a robust current-control performance is yielded. Furthermore, the inclusion of the estimated uncertainty function provides an efficient solution for torque-ripple minimization in PMSM drives. This is because the frequency modes of the disturbances to be eliminated, i.e., the flux harmonics, are included in the stable closed-loop system. To provide a high-bandwidth estimate of the uncertainty function, a simple adaptation law is derived using the nominal current dynamics and the steepest descent method. To guarantee the system's convergence and to properly tune the proposed observer, a stability analysis based on a discrete-time Lyapunov function has been used. Comparative evaluation experiments are presented to demonstrate the effectiveness of the proposed control scheme under different operating conditions.
TL;DR: Criteria for verifying robust stability are formulated as feasibility problems over a set of frequency-dependent linear matrix inequalities and can be equivalently formulated as semi-definite programs (SDP) using Kalman-Yakubovich-Popov lemma.
TL;DR: The robust stabilization method via the dynamic surface control (DSC) is proposed for uncertain nonlinear systems with unknown time delays in parametric strict-feedback form and it is proved that all the signals in the closed-loop system are semiglobally uniformly bounded.
Abstract: The robust stabilization method via the dynamic surface control (DSC) is proposed for uncertain nonlinear systems with unknown time delays in parametric strict-feedback form. That is, the DSC technique is extended to state time delay nonlinear systems with linear parametric uncertainties. The proposed control system can overcome not only the problem of ldquoexplosion of complexityrdquo inherent in the backstepping design method but also the uncertainties of the unknown time delays by choosing appropriate Lyapunov-Krasovskii functionals. In addition, we prove that all the signals in the closed-loop system are semiglobally uniformly bounded. Finally, an example is provided to illustrate the effectiveness of the proposed control system.
TL;DR: When the results obtained are applied to stabilization of combustion in the chamber of a liquid monopropellant rocket motor, it is found that the combustion can be robustly stabilized over larger variation intervals of pressure parameter and time-delay parameter.
TL;DR: A loop-shaping design method is developed from a study of fundamental differences between interaction control and the more common servo problem, using a computational approach to search parameter spaces and displaying variations in performance as control parameters are adjusted.
Abstract: Robots intended for high-force interaction with humans face particular challenges to achieve performance and stability. They require low and tunable endpoint impedance as well as high force capacity, and demand actuators with low intrinsic impedance, the ability to exhibit high impedance (relative to the human subject), and a high ratio of force to weight. Force-feedback control can be used to improve actuator performance, but causes well-known interaction stability problems. This paper presents a novel method to design actuator controllers for physically interactive machines. A loop-shaping design method is developed from a study of fundamental differences between interaction control and the more common servo problem. This approach addresses the interaction problem by redefining stability and performance, using a computational approach to search parameter spaces and displaying variations in performance as control parameters are adjusted. A measure of complementary stability is introduced, and the coupled stability problem is transformed to a robust stability problem using limited knowledge of the environment dynamics (in this case, the human). Design examples show that this new measure improves performance beyond the current best-practice stability constraint (passivity). The controller was implemented on an interactive robot, verifying stability and performance. Testing showed that the new controller out-performed a state-of-the-art controller on the same system
TL;DR: This paper studies the problem of designing a robust fault-detection system for uncertain Takagi-Sugeno fuzzy models and the worst case fault sensitivity measure is formulated in terms of linear matrix inequalities.
Abstract: This paper studies the problem of designing a robust fault-detection system for uncertain Takagi-Sugeno fuzzy models. The worst case fault sensitivity measure is formulated in terms of linear matrix inequalities. The existence of a robust fault detection system that guarantees i) the L2-gain from a fault signal to a residual signal greater than a prescribed value and ii) the L2-gain from an exogenous input to a residual signal less than a prescribed value is given in terms of the solvability of linear matrix inequalities. Numerical examples are used to illustrate the effectiveness of the proposed design techniques.
TL;DR: The controller design method is presented based on a delay-dependent approach, and the robust Hinfin controller gain matrices are obtain by solving a set of linear matrix inequalities (LMIs).
Abstract: This paper concerns a problem of robust Hinfin control for a class of uncertain nonlinear networked control systems (NCSs), which can be represented by a T-S fuzzy model with uncertainties. Both network-induced delay and packet dropout are addressed. The controller design method is presented based on a delay-dependent approach, and the robust Hinfin controller gain matrices are obtain by solving a set of linear matrix inequalities (LMIs). Moreover, a general Lyapunov-Krasovskii functional is used, and some slack matrices, which bring much flexibility in solving LMIs, are introduced during the proof. Simulation results show the validity of the proposed method.
TL;DR: A nonlinear controller is designed, obtained by suitably combining feedforward control actions and high-gain and nested saturation feedback laws, which succeeds in enforcing the desired trajectories robustly with respect to uncertainties characterizing the physical and aerodynamical parameters of the helicopter.
TL;DR: This paper develops the idea of min-max robust experiment design for dynamic system identification and proposes a convex optimisation algorithm that can be applied more generally to a discretised approximation to the design problem.
TL;DR: An adaptive fuzzy sliding-mode control system for an indirect field-oriented induction motor drive to track periodic commands and an adaptive algorithm, derived in the sense of Lyapunov stability theorem, is utilized to adjust the fuzzy parameter for further assuring robust and optimal control performance.
Abstract: This study mainly deals with the key problem of chattering phenomena on the conventional sliding-mode control (SMC) and investigates an adaptive fuzzy sliding-mode control (AFSMC) system for an indirect field-oriented induction motor (IM) drive to track periodic commands. First, an indirect field-orientation method for an IM drive is introduced briefly. Moreover, a fuzzy logic inference mechanism is utilized for implementing a fuzzy hitting control law to remove completely the chattering phenomena on the conventional SMC. In addition, to confront the uncertainties existed in practical applications, an adaptive algorithm, which is derived in the sense of Lyapunov stability theorem, is utilized to adjust the fuzzy parameter for further assuring robust and optimal control performance. The indirect field-oriented IM drive with the AFSMC scheme possesses the salient advantages of simple control framework, free from chattering, stable tracking control performance, and robust to uncertainties. Furthermore, numerical simulation and experimental results due to periodic sinusoidal commands are provided to verify the effectiveness of the proposed control strategy, and its advantages are indicated in comparison with the conventional SMC system and the SMC system with a boundary layer
TL;DR: In this paper, a 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), is presented.
Abstract: 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 Hinfin 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 Hinfin 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.
TL;DR: In this paper, a shunt active power filter based on a pulsewidth modulation dc-to-ac voltage source converter has been designed to compensate harmonic currents of nonlinear loads connected to the mains.
Abstract: This paper presents the detailed design, analysis, and application of the controller for a shunt active power filter based on a pulsewidth modulation dc-to-ac voltage source converter. The controller is mainly tailored to compensate harmonic currents of nonlinear loads connected to the mains. However, it can also achieve reactive-power compensation and mains-current balancing when required. The controller has a two-layer structure. The outer layer generates the current references for the inner layer. The former uses a plug-in discrete-time repetitive algorithm for current-harmonic compensation, a proportional-integral algorithm to maintain the dc-capacitor voltage in spite of unmodeled losses and a reactive-power-reference generator. The inner layer uses state-feedback with integral action for current control. The repetitive controller is justified to improve the tracking of the periodic current references required by the active filters. The stability of the resulting closed-loop system is studied and some indication of the system robustness is given. The proposed controller has been tested in a prototype with balanced and unbalanced nonlinear loads. A discrete-time model of the filter has been used from the beginning. The microcomputer delay when calculating the controller output and the delay due to the anti-aliasing filters have been included in the inner system state-variable model
TL;DR: Integral sliding mode approach is extended to high-order sliding modes (HOSMs), and allows choosing transient dynamics, or assigning a transient-time function of initial conditions, which is robust and capable of controlling outputs of uncertain smooth SISO systems of a known permanent relative degree.
Abstract: Integral sliding mode approach is extended to high-order sliding modes (HOSMs), and allows choosing transient dynamics, or assigning a transient-time function of initial conditions. The resulting controller is robust and capable of controlling outputs of uncertain smooth SISO systems of a known permanent relative degree. The control smoothness can be deliberately increased.
TL;DR: In this article, the authors introduce integral resonant control (IRC), a simple, robust and well-performing technique for vibration control in smart structures with collocated sensors and actuators.
Abstract: This paper introduces integral resonant control, IRC, a simple, robust and well-performing technique for vibration control in smart structures with collocated sensors and actuators. By adding a direct feed-through to a collocated system, the transfer function can be modified from containing resonant poles followed by interlaced zeros, to zeros followed by interlaced poles. It is shown that this modification permits the direct application of integral feedback and results in good performance and stability margins. By slightly increasing the controller complexity from first to second order, low-frequency gain can be curtailed, alleviating problems due to unnecessarily high controller gain below the first mode. Experimental application to a piezoelectric laminate cantilever beam demonstrates up to 24 dB modal amplitude reduction over the first eight modes.
TL;DR: It is shown that the proposed controller can guarantee stability, but also transient performance, in a class of uncertain dynamic nonlinear systems preceded by unknown backlash nonlinearity.
Abstract: In this note, we consider a class of uncertain dynamic nonlinear systems preceded by unknown backlash nonlinearity. The control design is achieved by introducing a smooth inverse function of the backlash and using it in the controller design with backstepping technique. For the design and implementation of the controller, no knowledge is assumed on the unknown system parameters. It is shown that the proposed controller not only can guarantee stability, but also transient performance
TL;DR: In this paper, the authors provide an overview of computationally efficient approaches for quantifying the influence of parameter uncertainties on the states and outputs of nonlinear dynamical systems with finite-time control trajectories, focusing primarily on computing probability distributions.
Journal Article•
TL;DR: In this article, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system.
Abstract: In this paper, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system. Through a simple selection of weighting functions, the synthesized Hinfin controller would exhibit significant gains in the vicinity of positive- and negative-sequence fundamental frequencies, and therefore, it would be able to regulate both positive- and negative-sequence components effectively, with explicit robustness in the face of system parameter variations. A detailed discussion of Hinfin controller weighting function selection, inner current loop tuning, and system disturbance rejection capability is presented. Finally, the designed control scheme is extensively tested on a laboratory 10-kV MV-level DVR system with varying voltage sag (balanced and unbalanced) and loading (linear/nonlinear load and induction motor load) conditions. It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.
TL;DR: It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.
Abstract: In this paper, a robust control scheme with an outer Hinfin voltage control loop and an inner current control loop is designed and implemented on a medium-voltage (MV)-level dynamic voltage restorer (DVR) system. Through a simple selection of weighting functions, the synthesized Hinfin controller would exhibit significant gains in the vicinity of positive- and negative-sequence fundamental frequencies, and therefore, it would be able to regulate both positive- and negative-sequence components effectively, with explicit robustness in the face of system parameter variations. A detailed discussion of Hinfin controller weighting function selection, inner current loop tuning, and system disturbance rejection capability is presented. Finally, the designed control scheme is extensively tested on a laboratory 10-kV MV-level DVR system with varying voltage sag (balanced and unbalanced) and loading (linear/nonlinear load and induction motor load) conditions. It is shown that the proposed control scheme is effective in both balanced and unbalanced sag compensation and load disturbance rejection, as its robustness is explicitly specified.