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This paper presents a disturbance observer-based robust optimal flight control strategy for near space vehicle (NSV) attitude system with external time-varying disturbance generated by an exogenous system. For the purpose of eliminating the effect of the disturbance, nonlinear disturbance observer (NDO) technique is used and the disturbance estimation error is guaranteed to be globally exponential convergence. Then, based on the disturbance estimation result and desired trajectory signal, a steady state control input is presented and the optimal tracking problem of original system with external disturbance can be converted into the optimal regulation problem of a nominal error system. Furthermore, a single network-based adaptive dynamic programming (ADP) method is applied to obtain the corresponding optimal feedback control law. Finally, all the signals in closed-loop system are proved to be uniformly ultimately bounded (UUB) and the tracking error can converge to a sufficiently small bound. Simulation tests about NSV attitude system are given to verify the effectiveness of proposed robust optimal flight control scheme. [ABSTRACT FROM AUTHOR]

This work proposes a robust control scheme of a three-phase induction motor using a new Backstepping approach based on variable gains. Because of the saturation blocks that are essential to protect the control system, the use of conventional integral Backstepping could lead to a modest performance represented by overshooting and strong vibrations in transitional regimes that cause overcurrent. To develop an efficient and simple control algorithm, the variable gains propriety is used in the speed controller to offer a quick response without overshooting with good robustness against external disturbances. The same property has been introduced in current regulation by a different mean in order to develop a new solution to solve obstacles related to very low-speed operations. The asymptotic stability of the global control is proven by Lyapunov theory. The improvement of the new version compared with the classical one was verified by a brief comparative study based on simulation results. The proposed algorithm has been implemented in a dSPACE DS 1104 card, to analyze the real-time motor performance, and to test control sensitivity against parametric variations. The obtained results show a remarkable improvement of the new control concerning rapidity and stability of transient regimes, overtaking elimination and reduction of starting current, with a low algorithm sensitivity against parametric variations. We have also been able to confirm that the new current control method can guarantee optimal regulation in order to achieve a high-performance operation at very low-speed zones, in the presence of various internal and external disturbances. [ABSTRACT FROM AUTHOR]

Due to the sensitivity of gas turbines' power generation in Iran, robustness is considered as a crucial matter and the controllers play an essential role in this objective. The common controllers used in gas turbines are usually based on standard performance. Whereas, robust controllers demonstrate acceptable performance in the presence of adverse factors such as uncertainties, disturbances, and input step changes. In this study, dynamic structures and various robust control design scenarios for an MGT-30 three-shaft gas turbine have proposed. Input-output matrices have been presented based on the dynamic model structures, and a standard robust controller structure has been used to design and present transfer matrices. Four scenarios have been considered in the robust control design according to the number of control variables, uncertainties, and disturbance effects, evolutionally, respectively. H ∞ and H 2 / H ∞ methods were used in the controller design when presenting the results of using the existing PID controller. The results show that with the increase and develop in parameters influencing the production of the actual system behavior and the controller responses improve noticeably. Finally, the fourth scenario was proposed as a scenario with more desirable robustness features than other scenarios, which provide a complete array of robust controllers. [ABSTRACT FROM AUTHOR]

This article deals with field-oriented control of induction machine squirrel cage. A robust fractional-order controller is applied and investigated to control the induction machine currents isd and isq. The fractional-order gives better fit in regulation operation. For this purpose, this controller form is recommended, especially in industrial systems, thanks to his flexibility, robustness and efficiency to solve complex problems such as electrical parameters changes (i.e. uncertain parameter) caused by the temperature effect. Based on frequency specification and several constraints, the fractional-order controller is designed. The fmincon toolbox optimization is used to adjust ki, kp and α values. In order to show the reliability of the developed controller in the induction machine behavior, several simulation results are carried out and illustrated. [ABSTRACT FROM AUTHOR]

Position control of piezoelectric actuators is greatly affected by nonlinearities such as hysteresis and creep. Therefore, precise position sensors must be utilized which have high cost and complicated structures in micro scales. Charge-based position estimation is an alternative method which resorts to piezoelectric linear charge-position property to estimate the actuator position, but in low-impedance actuators, there is a charge leakage caused by actuator internal resistance which deteriorates the position estimation and closed-loop control performance. In this article, the leakage is considered as a sensor fault. Therefore, a combination of charge measurement method and an appropriate observer is designed to detect and isolate the mentioned fault and estimate the actuator position properly. In addition, an adaptive sliding mode control procedure is proposed for trajectory tracking in the presence of estimated states. The required analysis is carried out to guarantee the closed-loop stability. Finally, experimental results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Ground resonance (GR) in helicopters is a potentially catastrophic instability commonly caused by coalescence of the regressive cyclic blade lag mode with the fuselage motion in certain rotor speed ranges. It can limit the helicopter operational envelope and the design of this type of vehicle can become a difficult task. Although a broad class of actuators allows the use of active and semi-active techniques to design feedback-based control systems, a limited number of works in the literature introduce formulations to compute the controller gain to suppress this phenomenon. Also, commonly, a control approach defines a feedback, particularly to a specific rotor speed. In this context, this work introduces an alternative methodology to design an active control system to stabilize GR of a helicopter. The proposed approach can suppress this instability in all rotor speed ranges by using only one control gain. Two strategies are proposed based on linear matrix inequalities (LMIs). The Lyapunov stability criteria are used and the unstable rotor speed is considered as an uncertain parameter to define an associated convex space. Using convex optimization, a robust control gain is computed until all the unstable rotor speed range is stabilized. Numerical simulations are carried out to demonstrate the effectiveness of this methodology. The results confirm the viability of the proposed approach to design active and semi-active controllers. [ABSTRACT FROM AUTHOR]

In this paper, a three-degree-of freedom (3 DOF) integrated vehicle lateral, yaw, roll dynamics model with optimal control design have been proposed to improve the bus lateral stability and handling performance. First, a 3 DOF vehicle model for a passenger bus is introduced. The 3 DOF model dynamics include the vehicle steering wheel angle, forward speed, yaw motion, sideslip angle, lateral acceleration and the rolling motion. Then, the presented 3 DOF model is used to design the robust static output feedback H ∞ controller for both nominal system and uncertain system. The proposed controller is designed to improve the bus lateral stability and handling performance by controlling the yaw rate during normal driving and maneuvers. For the robust static output feedback H ∞ controller, the norm bounded uncertainty is considered to simulate the variation of vehicle forward velocity uncertainty. The robust controller is designed to check the lateral stability of the bus at different forward velocity and at different velocity uncertainty. The controllers are synthesized within the H ∞ control approach and the controllers' design conditions are given within the Linear Matrix Inequalities (LMIs) framework. Numerical simulations have been carried out to demonstrate the effectiveness of the proposed controllers. The obtained simulation results show that the designed nominal and robust controllers enhance the lateral stability of the bus by reducing the amplitude of the yaw rate, lateral acceleration and rolling motion. Hence, the improvements in bus lateral stability and handling performance are achieved. [ABSTRACT FROM AUTHOR]

This paper proposes a robust event-driven control for attitude regulation in flexible spacecraft affected by inertial parametric uncertainties and external disturbances. The bandwidth constraint of the communication channel between controller and system requires an event-based control design. Under the action of proposed control law, the system trajectories are ensured to be uniformly ultimately bounded (UUB) in a small vicinity of their equilibrium points. Apart from the boundedness of states, the proposed event-triggered controller also satisfies bandwidth restrictions by achieving a substantially low control usage. The results obtained from numerical simulations are indeed encouraging. It demonstrates the proposed controller as a potential alternative to the periodically sampled data controllers. Moreover, the proposed control strategy successfully eludes the unwanted unwinding phenomenon encountered in quaternion based attitude control of the spacecraft. [ABSTRACT FROM AUTHOR]

The aim of this research is to attenuate the vibrations of a blade structure with an attached piezoelectric actuator using robust multi-objective control. The force obtained from a piezoelectric patch loading has uncertainties due to the complicated shape (airfoil) of the blade element. A parameter-dependent model of the force equation is developed to understand the possible variation range of the actuation force. The modal analysis of the blade is performed to find vibration mode frequencies, and an aerodynamic load is generated experimentally to create steady-state vibration on the blade. A state-space model is obtained by considering certain vibration modes and the parameter-dependent part of the force in the input vector is taken outside of the plant model. The robust stability filter is modified with parameter dependency to have a cluster of the filter. Two different multi-objective controllers are designed with different design objectives. The designed controllers are implemented in experiments and performances of the controllers are compared using frequency and time domain responses. It is shown that the flexible blade vibrations are successfully suppressed with the proposed mixed norm robust controllers under the effect of steady-state aerodynamic disturbance with different air speeds. It is observed in experimental results that the performances of the H ∞ / H 2 controller are better than the H 2 / H ∞ controller. [ABSTRACT FROM AUTHOR]

This paper defines the research area of Diversity-enhanced Autonomy in Robot Teams (DART), a novel paradigm for the creation and design of policies for multi-robot coordination. Although current approaches to multi-robot coordination have been successful in structured, well-understood environments, they have not been successful in unstructured, uncertain environments, such as disaster response. Although robot hardware has advanced significantly in the past decade, the way we solve multi-robot problems has not. Even with significant advances in the field of multi-robot systems, the same problem-solving paradigm has remained: assumptions are made to simplify the problem, and a solution is optimized for those assumptions and deployed to the entire team. This results in brittle solutions that prove incapable if the original assumptions are invalidated. This paper introduces a new multi-robot problem-solving paradigm which uses a diverse set of control policies that work together synergistically within the same team of robots. Such an approach will make multi-robot systems more robust in unstructured and uncertain environments, such as in disaster response, environmental monitoring, and military applications, and allow multi-robot systems to extend beyond the highly structured and highly controlled environments where they are successful today. [ABSTRACT FROM AUTHOR]

This work presents a novel robust control design approach for missile longitudinal autopilot under multiple disturbances and uncertainties. The uncertainties and disturbances of the missile dynamics are treated as a lumped disturbance based on the concept of equivalent input disturbance. Then a generalized extended state observer is employed to estimate the system states and the equivalent input disturbance in an integrated manner. These estimates are used to construct the state-feedback controller as well as to attenuate the effect of the exogenous disturbances and endogenous uncertainties. The state-feedback controller is obtained by solving the linear matrix inequalities of mixed H 2 / H ∞ control problem, which provides an impressive flexibility to tune the controller to compromise between H 2 performance and H ∞ performance. Closed-loop stability of the system under the presented controller-observer structure is also established. The proposed design tactfully circumvents the engineering implementation problems encountered by mixed H 2 / H ∞ control, achieves strong robustness against disturbances and uncertainties, and does not involve any complicated nonlinear control methodologies. Numerical simulation results of nominal and perturbed performance comparisons with classic methods sufficiently demonstrate the feasibility and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

Model reference adaptive control is one of the popular methods that simultaneously deals with uncertainties and reduces conservatism. However, it usually suffers from slow convergence and poor tracking at the beginning of the adaptation. On the other hand, attaining fast convergence by increasing the learning rate could cause oscillation in the control response, which results in system instability. Some of the solutions that have been presented so far use prediction error, low-pass filter, or normalizing the control signal. In this article, a novel robust normalized Lyapunov design is proposed for model reference adaptive control to achieve fast convergence and to avoid oscillatory response. In contrast to the other solutions, it uses a new Lyapunov function to guarantee the global asymptotic stability and to prove the robustness of the closed-loop system against bounded uncertainties. The performance of the proposed method is compared with two other model reference adaptive controls using simulations. In addition, an industrial selective compliance assembly robot arm is used for further verification. Results indicate that that the proposed normalized Lyapunov design reduces the tracking error by 62.4% on average; it also has faster convergence and shows robustness against uncertainties such as payload changes. [ABSTRACT FROM AUTHOR]

The active suspension has drawn considerable attention due to its superiority in improving the vehicle vertical dynamics. This paper investigates robust nonfragile H ∞ optimal control for the vehicle active suspension with time-varying actuator delay. Firstly, the dynamic equation of an active suspension system with actuator delay is established in terms of the main performance objectives, that is, ride comfort, handling ability, and road holding. Then, a robust nonfragile H ∞ optimal controller is proposed to deal with the problem of active suspension control with time delay and actuator uncertainty, which is based on Lyapunov theory, convex optimization, and the linear matrix inequality approach. Finally, a quarter-car test rig is used for an experiment to illustrate the effectiveness of the proposed controller. Simulation and experimental results demonstrate that the proposed controller can ensure the asymptotic stability of the closed-loop system with bounded time-varying actuator delay, while managing the tradeoff between the conflicting performances and achieving performance optimization for the active suspension. [ABSTRACT FROM AUTHOR]

Aircraft loss of control is an acute phenomenon that has far reaching consequences irrespective of the class and type of aircraft. In order to ensure safe aircraft operation, loss of control problem has to be addressed efficaciously. This paper investigates various factors that trigger the onset of loss of control events and recovery solutions for the same. Rather than relying on statistics alone, this paper concentrates on simulation-based investigation towards various loss of control scenarios and subsequent recovery schemes. Through bifurcation analysis, distinct abnormal dynamics have been identified and their contributions in driving the aircraft towards loss of control have been examined. The effect of steady wind on aircraft dynamics and the evolution of chaotic dynamics as a precursor to loss of control are presented. Aircraft loss of control under actuator impairment conditions are also probed into. Various loss of control recovery schemes have been investigated and a robust loss of control recovery solution based on sliding mode control is also presented. [ABSTRACT FROM AUTHOR]

This paper studies the performance of the classical integral force feedback (IFF) controller for suppressing the forced response of a single degree of freedom (SDOF) system. An ℋ∞ optimization criterion is used to derive the optimal feedback gain of the IFF controller contributed as a complement for the state of the art. This optimal gain is calculated in the closed-form based on a SDOF system which is then applied to a two degrees of freedom system to study its adaptability. It is found that the ℋ∞ optimal gain can be easily transposed into multi-degrees of freedom applications without introducing too many errors. An equivalent mechanical model is also developed to enable a straightforward interpretation of the physics behind the IFF controller. [ABSTRACT FROM AUTHOR]

Complex-order differintegral (COD) is the extended version of fractional-order one in which the differintegral order can be a complex number rather than a real number. In comparison with fractional-order differintegral (FOD), the distinguishing feature of the COD is that the phase slope of its Bode diagram is a function of imaginary part of the complex order of the COD. In this paper, by the use of this property of the COD, a robust control system is proposed. The design procedure and the realization of the proposed COD-based closed-loop control system are discussed. Since the phase of COD's frequency response is a nonsymmetric function of frequency, stability analysis of the proposed control system is considered a problematic task. It is proven that for the stability of the control system, it is essential that the COD be applied in a limited frequency band that is derived by the use of the Nyquist stability criterion. Finally, some numerical examples are given to demonstrate the validity and superiority of the proposed complex-order control system. [ABSTRACT FROM AUTHOR]

This paper studies the tracking control of a convoy of multiple autonomous cars or car-like robots in the planar motion without any collision with a prescribed performance that has not been addressed sufficiently in the literature yet. Toward this end, a coordinate transformation is initially employed to transform the posture errors between each two successive cars in a group from the earth-fixed frame into their relative distance and angle errors that should satisfy some predefined transient and steady-state constraints. By employing the prescribed performance technique, a nonlinear transformation is used to transform the constrained relative distance and angle errors and to obtain an unconstrained kinematic error equation. Then, a novel kinematic controller is designed to satisfy the prescribed transient and steady-state performance specifications without any collision and any controller singularity. Next, the Dynamic Surface Control technique is effectively used to simplify the convoy controller design at the dynamic level by using a first-order filter. An adaptive neural network is used to maintain the control system robustness against modelling errors and external disturbances. The Lyapunov theory proves the stability of the convoy control system and, finally, simulation examples verify the controller performance for multiple autonomous cars in intelligent transportation applications. [ABSTRACT FROM AUTHOR]

This paper focuses on a challenging problem in the internal model control (IMC) strategy: the model inversion to design the IMC controller for non-square systems. Several existing approaches for the synthesis of a specific inversion of the identified model will be presented in this paper to deal with the differences between the system's inputs and outputs numbers. The non-square effective relative gain is firstly presented. It consists of the measurement of interactions between the loops of the system in order to square the system and make it invertible. The equivalent transfer function method is presented as well. It is based on tuning the pseudo-inverse of the process to design the internal model controller. These methods are then compared with a novel proposed model inversion approach based on virtual outputs method. Virtual adding is considered in order to obtain an invertible square transfer matrix to design the internal model controller. This simple yet effective method ensures robust control performance. Its efficiency and availability, as compared with other presented methods, is illustrated through simulations on an overactuated system with three inputs/two outputs. [ABSTRACT FROM AUTHOR]

With the gradually increasing usage of high-response proportional solenoid valve in the middle- and high-end electronic hydraulic system, to possess a superior performance controller is always most important for high-response proportional solenoid valve. Thus, many novel nonlinear control algorithms, such as sliding mode control and adaptive robust control, are researched and applied to high-response proportional solenoid valve. However, the strict condition of full-state feedback usually cannot be met, since there are no velocity and acceleration measurements available in high-response proportional solenoid valve. Therefore, we proposed an extended disturbance observer to observe the velocity of the high-response proportional solenoid valve's spool assembly at first. Or rather, the extended disturbance observer is designed to observe the disturbances in the model of high-response proportional solenoid valve and the velocity is also obtained as a by-product. And then, a nonlinear cascade controller based on the extended disturbance observer is designed. The proposed extended disturbance observer is driven by both the estimation error and the virtual input discrepancy of nonlinear cascade controller. The nonlinear cascade controller is designed by utilizing backstepping technique. The stability of the overall closed-loop system is proved according to the Lyapunov theory. As a comparison, a desired compensation nonlinear cascade controller is also applied to the same high-response proportional solenoid valve. The experiment results demonstrate that the proposed nonlinear cascade controller based on extended disturbance observer has an excellent performance under multiple working conditions. Even when the supply pressure has severe fluctuations, the nonlinear cascade controller based on extended disturbance observer can still maintain high performance. [ABSTRACT FROM AUTHOR]

The control problem of underactuated systems with external perturbations is investigating in this paper. Using the super-twisting-based global sliding mode control (GSMC) method, an original control law is proposed to guarantee removal of the reaching mode and obtain the robustness and exponential stability of the underactuated systems. Via the offered scheme, a robust control law is designed so that the state trajectories of the underactuated systems are convergent to the global sliding surface in an exponential manner. Moreover, this article develops an adaptive super-twisting algorithm for these systems. The adaptive-tuning controller eliminates the need of the knowledge about upper bound of the exterior disturbance. The discontinuous sign function appears in the controller derivative; as a result, the actual control signal reached after integration is continuous and free of chattering. Demonstrative simulations on a cart–inverted pendulum system as well as an experimental study are presented to show the effectiveness and applicability of the proposed technique. [ABSTRACT FROM AUTHOR]

Collaborative object transportation using multiple MAV with limited communication is a challenging problem. In this paper, we address the problem of multiple MAV mechanically coupled to a bulky object for transportation purposes without explicit communication between agents. The apparent physical properties of each agent are reshaped to achieve robustly stable transportation. Parametric uncertainties and unmodeled dynamics of each agent are quantified and techniques from robust control theory are employed to choose the physical parameters of each agent to guarantee stability. Extensive simulation analysis and experimental results show that the proposed method guarantees stability in worst-case scenarios. [ABSTRACT FROM AUTHOR]

An adaptive hybrid controller is proposed for reducing the unbalanced vibration response of a flexible rotor/active magnetic bearing system. It is observed that conventional adaptive feedforward controller (AFFC) normally used in the active noise control is very sensitive in performance for changes in rotor spin frequencies. Although frequency updating is a part of its architecture, a small practical variation in the rotor spin frequency can reduce its effectiveness drastically. A smart combination of adaptive notch filter and Goertzel filter is proposed for the frequency estimation. During changes of the rotor spin frequency, fundamental harmonics of the flexible rotor are excited. By using hybrid controllers that combine feedback control and AFFC, the amplitude of these fundamental harmonics is reduced significantly. By applying the multi-harmonic hybrid control, the multiple harmonics generated due to coupling misalignment are compensated efficiently. Fourier transform of the control signal is further used to detect the presence of the coupling misalignment. [ABSTRACT FROM AUTHOR]

This paper puts forward a switching rule stabilization design of the robust integral sliding mode control for uncertain switched systems. A kind of common robust integral sliding mode (CRISM) is firstly designed and the system matrices of subsystems under the sliding mode comprise a robust stable matrix set. The stability of the switched system (SS) under the sliding mode is then analyzed by multiple Lyapunov functions (MLF) method. Based on the presented design of CRISM, a sliding mode controller is devised so that the sliding mode can be reached. Finally, the correctness of the proposed method is verified through results of numerical and application simulations. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of reliable finite–time stochastic stability (FTSS) for uncertain networked control systems (NCSs). A Markovian jump system (MJS) model with partly unknown transition probabilities (TPs) for the NCSs with random delays, data packet dropouts (disorders as well) and stochastic actuator faults is established to describe the closed–loop system. A mode-dependent static output feedback controller is designed taking only the measured outputs into account. A new criterion is also derived in terms of linear matrix inequalities (LMIs) to ensure reliable FTSS of the closed–loop system, based on the stochastic stability theory. Simulation studies on a benchmark numerical example, as well as an unstable numerical example can verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article is devoted to the modeling, performance evaluation and robust control of the railway transport network in Sahel Tunisia. The regular increase in the number of passengers makes the management of transportation systems more and more complex. Railway transport requires specific needs. Indeed, many decision and optimization problems occur from the planning phase to the implementation phase. Railway transport networks can be considered as discrete event systems with time constraints. The time factor is a critical parameter, since it includes schedules to be respected in order to avoid overlaps, delays and collisions between trains. The uncertainties affect the service and the availability of transportation resources and, consequently, the transport scheduling plan. Petri nets have been recognized as powerful modeling and analysis tools for discrete event systems with time constraints. Consequently, they are suitable for railway transport systems. In this article, stochastic P-time Petri nets are used for the railway transport networks in Sahel Tunisia. A global model is first detailed. Then, this model is used to analyze the network traffic and evaluate the performance of the system. Robustness again disturbances is introduced and a control strategy is developed to reduce the consequences of the disturbances in order to maintain the expected schedule. [ABSTRACT FROM AUTHOR]

A robust H ∞ observer-based static state-feedback controller is designed for the path following of autonomous ground vehicles in this paper. Considering the lateral velocity of vehicle is usually difficult to measure, an observer is designed to estimate the value of lateral velocity first. Then, a robust controller is proposed to cope with the modeling uncertainty and disturbance, such as the variation of road coefficient and lateral disturbance. Numerical simulations using a high-fidelity and full-vehicle model based on a CarSim–Simulink joint platform have verified the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicles (AUVs) are highly nonlinear underactuated systems with uncertain dynamics and a challenging control problem. The main focus of this paper is to present a control law that shows desirable performance in the presence of modeling uncertainties. In this study, uncertainties are considered to be bounded and the AUV mathematical model is obtained in the presence of such uncertainties. Forces and torques applied to the AUV are also designed using a nonlinear dynamic controller. Appropriate adaptive rules are also presented to overcome system uncertainties and external disturbances. The adaptive nonlinear dynamic controller is designed based on upper bounds of system uncertainties and its stability is proven using the Lyapunov theory. In this article, the performance of the proposed control algorithm for tracking reference trajectories in an obstacle-rich environment is investigated. Therefore, the control algorithm is combined with potential fields for obstacle avoidance. Obtained results show the efficiency of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper proposes a new robustification strategy of a primary H ∞ controller based on a systematic selection of adequate fractional weights. Its robust performance (RP) margin is well enhanced with respect to unstructured multiplicative uncertainties presented in linear feedback systems. The proposed robustification strategy provides a robustified H ∞ controller when following proposed hierarchical control is well respected. First, the primary H ∞ controller is synthesized from solving a weighted-mixed sensitivity H ∞ problem using initial integer weights. Thus, an initial RP margin is obtained. Second, an automatic selection of adjustable fractional weights is performed by the particle swarm optimization algorithm, in which some proposed tuning rules are accordingly well satisfied. Third, frequency response data of these weights are computed and then fitted by corresponding approximated integer weights using a frequency identification technique. Finally, these weights reformulate a new weighted-mixed sensitivity problem. The optimal solution to this problem updates the previous initial RP margin. These last three steps are repeated as the updated RP margin is diminished. Otherwise, the proposed hierarchical control is achieved by selecting the best adjustable fractional weights, providing, therefore, the best approximated integer weights and leading, therefore, to the robustified H ∞ controller. In order to confirm the effectiveness of our proposed hierarchical control, primary and robustified H ∞ controllers are applied on a permanent magnet synchronous motor where its actual behavior is modeled by an unstructured multiplicative uncertain model. The results obtained are compared in frequency domains using the singular value plots of their sensitivity functions. Otherwise, the same results are compared in time domains using the Powersim ® software. [ABSTRACT FROM AUTHOR]

This article presents an improved robust tracking control for uncertain robot manipulators. An approximate terminal sliding mode control is proposed by integrating a terminal sliding surface with a novel nonlinear function. Lyapunov stability theory is employed to prove the global approximate finite-time stability ensuring that the tracking errors can globally converge to an arbitrary small ball centred at the origin within a finite time and thereafter arrive at the origin asymptotically. The benefits of this integrated design are that it can ensure fast transient and high steady-state tracking precision. Extensive simulations and experimental results are presented to demonstrate the effectiveness and improved performance of the proposed approach. [ABSTRACT FROM AUTHOR]

This article focuses on an integrated chassis control algorithm design for path tracking utilizing four-wheel steering and direct yaw-moment control. The designed integrated chassis control algorithm mainly consists of three parts: (1) taking the parametric uncertainties, external disturbances, measurement noise and unmodeled dynamics into consideration, a robust controller is designed for path tracking utilizing μ synthesis approach; (2) the control allocation algorithm is proposed to distribute the output torque requirements to each in-wheel motor based on the weighted least square; and (3) considering that vehicle lateral velocity is a critical state variable for path-tracking control, while it is not easy to measure with low-cost sensors, a state observer is designed for lateral velocity estimation using unscented Kalman filter. To verify the performance of the designed integrated chassis control algorithm, three simulation maneuvers including the single-lane change, curve and the double-lane change are carried out in MATLAB/Simulink with a high-fidelity, full-vehicle model built in CarSim. The proposed integrated chassis control algorithm is compared with other three control algorithms, that is, active front steering, four-wheel steering and active front steering + direct yaw-moment control, and simulation results indicate that the integrated chassis control algorithm has superior path-tracking performance and handling stability. The robust performance of the integrated chassis control algorithm is also verified under the variation of vehicle velocity and different road conditions. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive robust control algorithm for the nonlinear dynamics of robot manipulators with unknown backlash in gears. The basic nonlinear model of a serial manipulator robot is used for the controller design, and this is combined with the nonlinear proposed dead zone model, based on the input and output torque. The main idea of providing this model is to achieve a dynamic model of the system considering the backlash of the robot joint gears, and having less complexity such that the developed controller does not need the inverse backlash model. The adaptive robust controller is developed, without using the inverse backlash model. The proposed controller is designed based on an unknown dead zone parameter and it guarantees the stability and path tracking of the robot trajectory with unknown dead zone parameter in the desired range. Numerical simulations are conducted to show the effectiveness of the proposed controller. Finally, the efficiency and capability of the proposed controller in dealing with the unknown backlash nonlinearities in gears of the manipulator are demonstrated by experimental results with a five-bar manipulator. [ABSTRACT FROM AUTHOR]

It is seen that when the hook mass is larger than the load mass or the load has distributed mass property, the load sway of the crane system presents as double-pendulum effect. In this situation, crane system has two different natural frequencies so that the sway characteristic becomes more complex and greatly increases the difficulty of the dynamic performance analysis and controller design. Moreover, the rope length changes significantly affect the stability and control performance of the crane system. In order to solve the aforementioned problems, the linear dynamics of a two-dimensional overhead crane with double-pendulum effect is derived based on a disturbance observer, and is decoupled for controller design by modal analysis. Next, a state feedback controller is presented to achieve robust control performance for a given range of rope length changes. The controller gains are obtained via linear matrix inequality optimization method. Finally, numerical simulations and experimental results validate that the proposed method has superior control performance. [ABSTRACT FROM AUTHOR]

This paper presents a robust dynamic sliding mode control for electrically driven robot manipulators. The control law computes the motor voltages based on the voltage control strategy. Uncertainties are estimated using the Fourier series expansion and the truncation error is compensated. The Fourier coefficients are tuned based on the stability analysis. The contribution of this paper is designing a robust controller using a novel adaptive Fourier series expansion. In comparison with previous related works based on the Fourier series expansion, the superiority of this paper is presenting an adaptation law for the fundamental frequency of the Fourier series expansion and, consequently, relaxing the need for trial and error procedure in its tuning. The case study is a SCARA (Selective Compliant Articulated Robot for Assembly) robot manipulator actuated by permanent magnet DC electrical motors. The influence of uncertainty estimation based on the Fourier series expansion instead of using sign function is studied. Simulation results verify robust and satisfactory performance of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper presents the collective operation and comparative assessment of artificial neural network (ANN)-based adaptive controller with detuned-inductor capacitor (LC) filter facility in grid-tied voltage source control (VSC) system. In order to facilitate proper shaping of VSC outputs and to avoid voltage surge or current surge issues that may occur during the synchronization, the controlling action should reflect importance of total impedance (Zt) effect for: (i) accurate online weight updating, (ii) generation of correct references for proper shaping of VSC outputs, (iii) accurate assessment and exclusion of current harmonics and (iv) robust in defending any system perturbation. This impedance is taken into consideration during the run-time weight updation process through extended control steps in order to pass over various losses that certainly occurs in transformers, filters, line parameters and so forth. Performance of the system is well improved with an inclusion of total impedance (Zt) measured between the VSC and point of common coupling (PCC). A detuned-LC filter is predominantly intended for reactive power compensation, power factor correction, prompt and accurate alleviation of the harmonics. A comparative assessment in between enhanced and conventional adaptive controllers that are designed in MATLAB/Simulink clarifies the robust performances of the proposed control design under sundry system turbulences. The verification of the proposed enhanced controller is approved with the hardware results obtained using dSPACE RTI 1202 kit. [ABSTRACT FROM AUTHOR]

This paper proposes a robust controller for semi-active suspension system with actuator dynamics using the quantitative feedback theory. It solves the vehicle vibration attenuation problem using the novel cascade approach. The proposed cascade quantitative feedback theory control approach consists of the inner and outer loop. The damping force tracking of the magneto-rheological damper is chosen as the inner loop, while the outer loop is for the vibration attenuation. The inner loop is added to the control structure to enhance damping force tracking capabilities. The damping force of the magneto-rheological damper depends on the many factors, such as the complex and nonlinear (hysteresis) dynamics and operating temperature. The actuator (magneto-rheological damper) dynamics is well approximated by a first-order model with an uncertain time constant which captures the essential dynamics. The simulation case study is conducted on a realistic quarter car suspension system to show the effectiveness of the proposed cascade control method. The proposed method is found to deliver superior performances, in terms of ride comfort and road holding, over the skyhook, H ∞ control, and single-loop quantitative feedback theory control under the bump, sine, and random road disturbances. [ABSTRACT FROM AUTHOR]

To guarantee convergent state estimates and exact approximations, it is highly desirable that observers can independently dominate the effects of unmodelled dynamics. Based on adaptive nonlinear approximation, this paper presents a robust H ∞ gain neuro-adaptive observer (R H ∞GNAO) design methodology for a large class of uncertain nonlinear systems in the presence of time-varying unknown parameters with bounded external disturbances on the state vector and on the output of the original system. The proposed R H ∞GNAO incorporates radial basis function neural networks (RBFNNs) to approximate the unknown nonlinearities in the uncertain system. The weight dynamics of every RBFNN are adjusted online by using an adaptive projection algorithm. The asymptotic convergence of the state and parameter estimation errors is achieved by using Lyapunov cogitation under a well-defined persistent excitation condition, and without recourse to the strictly positive real condition. The repercussions of unknown disturbances are reduced by integrating an H ∞ gain performance criterion into the proposed estimation approach. The condition imposed by this proposed observer approach, such that all estimated signals are uniformly ultimately bounded, is expressed in the form of the linear matrix inequality problem and warrants the demanded performances. To evaluate the performance of the proposed observer, various simulations are presented. [ABSTRACT FROM AUTHOR]

This paper addresses the non-fragile control problem for a class of uncertain linear systems subject to model uncertainty, controller perturbations, fault signals and input constraints. The controller to be designed is supposed to have additive gain perturbations. A novel state feedback controller is proposed based on the exact available expectation of a Bernoulli random variable, which is introduced to model the feature of the controller gain perturbation that randomly occurs. By using Lyapunov stability theory, new sufficient conditions are derived to design non-fragile controller for a class of uncertain linear systems considering input constraints. Compared with the existing non-fragile state feedback controller methods, the non-fragile property is fully considered to improve the tolerance of uncertainties in the controller, where the conservativeness can be reduced via the Bernoulli random variable. The effectiveness of the proposed control strategy is illustrated by two numerical examples. [ABSTRACT FROM AUTHOR]

This paper presents a new robust decentralized control of nonlinear interconnected systems, which is applied and validated on a large scale power system. Our work is performed in three steps. Firstly, we have developed the polynomial description of the nonlinear uncertain and interconnected system using odd Kronecker power of state vectors, which is an easy-manipulation model for such complex systems. Then we applied Lyapunov's direct method of stability analysis, associated with a quadratic function, in order to determine a sufficient condition for global asymptotic stability by applying a nonlinear, decentralized and optimal polynomial control. Finally, we carried out a simulation study on a nonlinear uncertain power system with three interconnected machines. We considered different cases of perturbations on its state variables as well as different cases of fault locations. We prove via advanced simulations, the effectiveness of the proposed control technique which is able to mitigate the successive amplitudes of the oscillations, to limit the control actions and to enhance the power system transient stability. [ABSTRACT FROM AUTHOR]

For a class of complex interconnected nonlinear disturbed systems, a proportional integral (PI) decentralized observer-based feedback robust decentralized controller technique is proposed, relying on H∞ synthesis for disturbance mitigation and linear matrix inequality (LMI) tools to achieve asymptotic stabilization and stability analysis within the Lyapunov framework. The proposed design method draws on a prominent optimization problem that can be tackled in terms of LMI constraints to evaluate the decentralized controller and PI observer gain matrices jointly, to maximize the nonlinearity coverage tolerated by the system without destabilization and to improve the robustness of the proposed control strategy by minimizing an H∞ criterion despite exogenous disturbances and strong nonlinear interconnections affecting the subsystems. The efficacy and high performance of the proposed control approach, compared with a renowned decentralized guaranteed cost control strategy from the literature, are validated by numerical simulations on a greatly interconnected three-machine power system. [ABSTRACT FROM AUTHOR]

This article proposes a novel gain scheduled control technique for a class of linear parameter varying (LPV) systems with main emphasis on reducing the cross coupling interaction in dynamics using the Hadamard weight. By employing the Hadamard and the conventional H ∞ performance weighting, an extended H ∞ closed loop norm LPV theorem is derived that involves traditional H ∞ weights for input output shaping control and Hadamard weight for decoupling control. Furthermore, a robust dynamic output feedback gain scheduled control law is designed to solve the control optimization problem in the proposed theorem using the linear matrix inequality (LMI) approach. It is shown that the proposed theorem is suitable for the multivariable control of multiple input multiple output (MIMO) coupled non-linear systems. In particular, in presence of cross coupled dynamics, external disturbances, changing operating conditions and time varying parameters. The effectiveness of the proposed technique is demonstrated in simulation as well as validated with experiments. [ABSTRACT FROM AUTHOR]

This paper presents a robust nonlinear H∞ output-feedback control approach for attitude manoeuvring of flexible spacecraft with external disturbances, inertia matrix perturbation and input constraints. By applying Lyapunov stability theory and using the generalized S-procedure and sum of squares (SOS) techniques, the robust H∞ output-feedback attitude control problem is converted into a convex optimization problem with SOS constraints when the flexible spacecraft is modelled as a polynomial state-space equation with polytope uncertainties. As a result, it overcomes the difficulty in constructing Lyapunov function and implementing numerical computation caused by the non-convexity of output-feedback H∞ control design for nonlinear systems. Moreover, it enables the state-observer and the controller to be designed independently and hence the complexity of the control algorithm is reduced remarkably. A numerical example illustrates the effectiveness and feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, the stability issue and tracking control problem for a class of switched nonlinear systems with uncertain input delay and disturbance are investigated. First, it is assumed a piecewise Lyapunov function exists for the nominal system (system without input delay and disturbance), and then, under the terms of the hypothetical piecewise Lyapunov function, a new Lyapunov-Krasovskii functional is constructed. By employing this new function and a switching signal which satisfies the average dwell time, the delay-dependent input-to-state stability under a certain delay bound is provided; also, a mechanism is invented to find the upper bound for input delay of switched system. In the next step, tracking control problem for this system is studied. Finally, a kind of state feedback control law which ensures conditions of aforesaid hypothetical piecewise Lyapunov function is proposed to guarantee the input-to-state stability and the robust model reference tracking performance. Simulation examples are given to illustrate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Large-scale morphing aircraft can adaptively alter configuration according to the different flight conditions or a variety of missions to ensure the optimal aerodynamic performance. However, this will certainly put forward a higher request to modeling method and controller performance. In this paper, we propose an adaptive sliding mode control strategy with bounded L2 gain performance based on linear-parameter-varying methodology for the robust control of a morphing aircraft with variable span and variable sweep angle. Using the Kane method, the longitudinal dynamic model of the morphing aircraft is derived. Moreover, the linearized linear-parameter-varying model of the aircraft in the wing varying process is formulated for controller synthesis. The adaptive sliding mode control synthesis for this uncertain linear-parameter-varying system consists of two steps. Firstly, based on the full block S-procedure, the sufficient condition in form of linear matrix inequality constrains is derived for the existence of a reduced-order sliding mode dynamics. Then, the synthesized adaptive sliding mode control is proved to drive the linear-parameter-varying system trajectories onto the predefined switching surface without the information of upper bound of external disturbances. The performance and robustness of the proposed controller are verified by the numerical results. [ABSTRACT FROM AUTHOR]

We aim to control the differential mobile robot system to follow a class of pre-specified constraints sufficiently closely in the presence of system uncertainties. The mass and the moment of inertia of the differential mobile robot are considered as the uncertain parameters, which are (possibly) fast time-varying. In the first step, based on Udwadia and Kalaba's approach, an adaptive robust control scheme is proposed to deal with the system uncertainties. The adaptive law is of leakage type, which can adjust itself based on the tracking error. Using this adaptive robust control scheme, we can obtain the desired armature currents of the two direct current (DC) motors, which are not the real control inputs. In the second step, taking the motor dynamics into account, a Lyapunov Minimax approach for the required actual control inputs (i.e., the input voltages of the two DC motors) is proposed to generate the desired armature currents. This two-step control methodology guarantees uniform boundedness and uniform ultimate boundedness, and renders the system to follow a class of pre-specified constraints approximately. [ABSTRACT FROM AUTHOR]

The design of a robust maneuver load alleviation (MLA) system for a high-performance aircraft is studied in this paper. First, the aeroservoelastic (ASE) models of a high-performance military aircraft in climbing maneuver at varying Mach numbers are established. Then, a linear parameter-varying (LPV) model of the ASE systems is constructed and an H∞ robust controller is designed based on the LPV model. The robust control is realized via a pair of outboard ailerons to alleviate the wing-root bending moments in the climbing maneuvers. To compensate the loss of performance in the load alleviation, a controller based on recurrent neural networks is designed in the flight control. Finally, some numerical simulations are made to testify the performance and robustness of the MLA system. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive robust fault-tolerant control scheme is developed for attitude tracking control of a medium-scale unmanned autonomous helicopter with rotor flapping dynamics, external unknown disturbances and actuator faults. For the convenience of control design, the actuator dynamics with respect to the tail rotor are introduced. The adaptive fault observer and robust item are employed to observe the actuator faults and eliminate the effect of external disturbances, respectively. A backstepping-based robust fault-tolerant control scheme is designed with the aim of obtaining satisfactory tracking performance and closed-loop system stability is proved via Lyapunov analysis, which guarantees the convergence of all closed-loop system signals. Simulation results are given to show the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Electromagnetic actuated active suspension (EAAS) benefits energy harvesting while providing active control. However, the inertia of the actuator introduces an equivalent mass coupled with the sprung and unsprung mass. In addition, the specific structure of the suspension features structure non-linearity, which results in the perturbation of the equivalent mass of the actuator, the variation of the transmission ratio of the actuator output torque to the actuator force at the wheel side and an extra force to be compensated with. A dynamic model of active control considering the equivalent mass and the structure non-linearity is proposed. Based on a gearbox type EAAS, respective non-linearity is studied. For multi-objective optimization, a robust controller is designed with proper weighting functions. A virtual prototype of the EAAS is built and simulated with a bump/pothole and random excitation road profiles. Results show that neglecting the structure non-linearity effects influences the accuracy of active control. The investigation of this paper provides a fundamental methodology for the control design of actual applications of EAASs. [ABSTRACT FROM AUTHOR]

This paper presents an improved robust tracking control for uncertain robot manipulators. An approximate fast terminal sliding mode control is proposed by integrating a nonsingular fast terminal sliding surface with an exponential reaching law. Lyapunov stability theory is employed to prove the global approximate finite-time stability ensuring that the tracking errors converge to an arbitrary small ball centered at zero within a finite time and thereafter arrive at zero asymptotically. The benefits of this integrated design are that it can ensure faster transient and higher steady-state tracking precision with lower chattering. Simulations and experiments are presented to demonstrate the effectiveness and improved performances of the proposed approach. [ABSTRACT FROM AUTHOR]

Designing a controller for multi-body systems including flexible and rigid bodies has always been one of the major engineering challenges. Equations of motion of these systems comprise extremely nonlinear and coupled terms. Vibrations of flexible bodies affect sensors of rigid bodies and might make the system unstable. Introducing a new control strategy for designing control systems which do not require the rigid–flexible coupling model and can dwindle vibrations without sensors or actuators on flexible bodies is the purpose of this paper. In this study, a spacecraft comprising a rigid body and a flexible panel is used as the case study, and its equations of motion are extracted using Lagrange equations in terms of quasi-coordinates. For oscillations on a rigid body to be eliminated, a frequency estimation algorithm and an adaptive filtering are used. A controller is designed based on the rigid model of the system, and then robust stability conditions for the rigid–flexible system are obtained. The conditions are also developed for the spacecraft with more than one active frequency. Finally, the robust adaptive vibration control system is simulated in the presence of resonance. Simulations' results indicate the advantage of the control method even when several active frequencies simultaneously resonate the dynamics system. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of designing a non-fragile polynomial fuzzy controller for a class of polynomial fuzzy models subjected to persistent bounded disturbances and system uncertainty. The proposed controller is considered to satisfy the input saturation constraint. Furthermore, the resilient controller is affected by linear fractional uncertainties. The overall structure of the controller is obtained by the polynomial parallel distributed compensation concept. The sufficient conditions guarantee an L1 performance of the perturbed system and exponential stability of the non-perturbed system is achieved in terms of sum-of-squares decomposition conditions. Subsequently, the sum-of-squares-based conditions lead to minimization of the L1 performance such that the above-mentioned hard constraints on the control input and robustness of the closed-loop system against the system and controller uncertainties will be guaranteed. The controller gain matrices will be achieved by numerically solving the sum-of-squares-based conditions with the third-party MATLAB toolbox 'SOSTOOLS'. Finally, extensive studies and hardware-in-the-loop simulations on a ball-and-beam system are presented, which illustrate the proposed controller can accurately and smoothly track the set point frequency. Furthermore, the proposed control approach is more robust over prior-art controllers for all the simulation scenarios. [ABSTRACT FROM AUTHOR]