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In the field of unmanned aerial vehicle control, the pursuit of robustness and optimality in the presence of uncertainties and disturbances remains a paramount challenge, particularly for small-scale helicopters. This study addresses the robust optimal control of longitudinal and lateral flight dynamics using the mixed sensitivity H∞ norm approach. The focus lies on achieving a control system that not only stabilizes but also excels in performance under various flight conditions, including hovering and translational maneuvers. The adopted methodology commences with the derivation of a mathematical model reflecting the system dynamics, characterized by six degrees of freedom and nonlinearities with inherent unstable coupling dynamics. Subsequent linearization of this model employs a Taylor approximation near an operational point, effectively transforming the complex nonlinear system into a more tractable linear form. To incorporate real-world applicability, this model is augmented with representations of uncertainties and external disturbances, acknowledging the unpredictable nature of aerial environments. The crux of this research lies in the implementation of the mixed sensitivity design method for H∞ feedback control. This approach is meticulously applied to the longitudinal and lateral motion subsystems, with a critical emphasis on maintaining system robustness in the face of the aforementioned uncertainties and disturbances. The evaluation of the controller's efficacy is based on qualitative performance metrics, such as response speed and overshoot characteristics. Simulation results demonstrate that the designed controller adeptly manages the intricate multi-input multi-output system, maintaining commendable control performance even under deterministic disturbances and noise. These findings contribute significantly to the unmanned aerial vehicle field, offering a robust control solution for small-scale helicopters that navigate complex environments. The methodology and results presented here hold promise for broader applications in unmanned aerial systems, where stability and adaptability in uncertain conditions are crucial. [ABSTRACT FROM AUTHOR]

During the brushless DC (BLDC) motor working process, the system encounters inevitable uncertainties. These ambiguities stem from potential fluctuations, random occurrences, measurement inaccuracies, varying operational conditions, environmental shifts such as temperature alterations, among other factors. Uncertainties, an inherent aspect of any real control system, can be broadly classified into two categories: sensor signal uncertainties and discrepancies between the mathematical and actual models due to parameter perturbations. To mitigate the impact of sensor noise and parameter perturbations on the BLDC motor, a robust control strategy utilizing infinite norm mixed sensitivity based on PI control strategy (PI-H∞-MIX) is proposed in this paper. Firstly, the closed-loop control structure and transfer function model of the BLDC motor control system current loop are analyzed based on the current loop circuit topology, and then, the model parameters perturbation is analyzed, and the multiplicative uncertainty bound is given. In addition, the appropriate weighting function is selected to ensure the robustness of the system. In this case, the controller design problem is transformed into the H∞ standard control problem, and then, the system augmentation matrix is established, and the controller is solved by Matlab/Simulink. Finally, the performances of the traditional PI control strategy and the PI-H∞-MIX are compared and analyzed. The results show that (1) the proposed PI-H∞-MIX strategy can improve the control system robustness under the parameter perturbation condition effectively, and (2) the proposed PI-H∞-MIX strategy can suppress the noise signal of the sensor. [ABSTRACT FROM AUTHOR]

A rigorous study on optimized robust control is presented for non-preview (nulling-type) high-speed tilting rail vehicles. The scheme utilizes sensors on the vehicle's body, contrary to that of preview tilt (which uses prior rail track information). Tilt with preview is the industrial norm nowadays but is a complex scheme (both in terms of inter-vehicle signal connections and when it comes to straightforward fault detection). Non-preview tilt is simple (as it essentially involves an SISO control structure) and more effective in terms of (the localization of) failure detection. However, the non-preview tilt scheme suffers from performance limitations due to non-minimum-phase zeros in the design model (due to the compound effect of the suspension dynamic interaction and sensor combination used for feedback control) and presents a challenging control design problem. We proposed an optimized robust control design offering a highly improved non-preview tilt performance via a twofold model representation, i.e., (i) using the non-minimum phase design model and (ii) proposing a factorized design model version with the non-minimum phase characteristics treated as uncertainty. The impact of the designed controllers on tilt performance deterministic (curving acceleration response) and stochastic (ride quality) trade-off was methodically investigated. Nonlinear optimization was employed to facilitate fine weight selection given the importance of the ride quality as a bounded constraint in the design process. [ABSTRACT FROM AUTHOR]

Aero-engine control system is an important mechanism of aircraft, the uncertainty of control gain attenuation and unmodeled dynamics of aero-engine can affect its control performance, therefore, a controller combining H∞ adaptive control and compensation control is designed.Firstly, the H∞ adaptive controller is designed based on the mixed sensitivity theory.And then, based on Lyapunov strict stability theory, the radial basis function (RBF)neural network compensation controller is designed to compensate the uncertainty, and the fitting speed is adjusted by the linear function related to the error.Finally, the normalized aero-engine model is taken as the controlled object to carry out the multi-variable simulation test.The results show that the adaptive controller designed in this paper can effectively compensate the uncertainty and reduce the overshoot and adjusting time compared with the H∞controller.

The relative position between the laser beam and the nozzle is controlled by laser-focus-controlled magnetic actuators to achieve non-coaxial laser cutting and improve laser cutting efficiency. In this paper, a 3-DOF (degrees of freedom) magnetic actuator is designed to solve the inconsistency of the laser beam focus and the nozzle focus in off-axis laser cutting. A mixed sensitivity robust controller is designed, and its simulation analysis and experimental research are carried out. First, the kinetic mathematical equations are established according to the structure of the actuator. Then, a mixed sensitivity robust controller is designed and analyzed using MATLAB/Simulink. The control performance is simulated and analyzed under 20% parameter variation and pulse disturbance with an uncertain mathematical model and external disturbance, respectively. Finally, the experimental study of the step response of the actuator is carried out. The experimental results show that the step response of the actuator in the Y, X, and θ directions can quickly reach the steady-state value. Furthermore, the steady-state error in the X is 1.6%; the steady-state error in the Y is 0.39%; the steady-state error in the θ is 0.45%. Their errors are all less than 0.025 mm, so they meet the position performance requirements. It can provide technical support for laser off-axis cutting. [ABSTRACT FROM AUTHOR]

A rigorous study on optimized robust control is presented for non-preview (nulling-type) high-speed tilting rail vehicles. The scheme utilizes sensors on the vehicle’s body, contrary to that of preview tilt (which uses prior rail track information). Tilt with preview is the industrial norm nowadays but is a complex scheme (both in terms of inter-vehicle signal connections and when it comes to straightforward fault detection). Non-preview tilt is simple (as it essentially involves an SISO control structure) and more effective in terms of (the localization of) failure detection. However, the non-preview tilt scheme suffers from performance limitations due to non-minimum-phase zeros in the design model (due to the compound effect of the suspension dynamic interaction and sensor combination used for feedback control) and presents a challenging control design problem. We proposed an optimized robust control design offering a highly improved non-preview tilt performance via a twofold model representation, i.e., (i) using the non-minimum phase design model and (ii) proposing a factorized design model version with the non-minimum phase characteristics treated as uncertainty. The impact of the designed controllers on tilt performance deterministic (curving acceleration response) and stochastic (ride quality) trade-off was methodically investigated. Nonlinear optimization was employed to facilitate fine weight selection given the importance of the ride quality as a bounded constraint in the design process.

A two-axis gimbaled stabilization system in air vehicles must stabilize the line of sight of the payload toward a target against the external motion induced by air vehicle maneuvering and aerodynamic forces. The target tracking and pointing performances of the air vehicles are largely affected by air vehicle motion decoupling capability. In this work, the H ∞ controller design is carried out for a two-axis gimbal system. The plant model is generated using experimental frequency response data and mathematical formulation of the system. The mixed sensitivity problem is posed and weighting functions are selected so that they not only fulfill all the design goals but also accommodate the modeling uncertainties. The stabilization loop is designed and implemented in digital signal processor-based hardware for only one axis (in azimuth). [ABSTRACT FROM AUTHOR]

Recent analytical solutions to Mixed Sensitivity Control (MSC) are developed and compared with standard MSC based on γ-iteration. The proposed MSC solution gives conditions for strong stability and overcomes the pole-zero cancellations between the plant and the controller of non-iterative solutions, keeping the low-computational effort advantage of non-iterative solutions. The proposed MSC is based on the minimization of the most common closed-loop sensitivity functions in low-frequencies and the free-parameters of the stabilizing-controllers solve an algebraic equation of restriction that assigns the same value to the infinity-norms of the sensitivity functions at low and high-frequencies, guaranteeing robust stability and robust performance. It is assumed that the plant state dimension is double the plant input dimension and that the linear time-invariant nominal plant has a stabilizable and detectable realization and is strongly stabilizable. This MSC problem is solved in a one-parameter observer-controller configuration and reference tracking-control of positions is realized on a two-degrees of freedom feedback-configuration. An approximated optimal value of the location of the closed-loop poles is proposed based on Glover and McFarlane's optimal stability margin [(1989)] which in turn is based on Nehari's Theorem. Simulations of a mechanical system illustrate the results.

The voltage control performance of the voltage source inverter (VSI) in a microgrid may change under different load conditions. However, in the case of traditional control strategies, the robustness of VSI is insufficient. In response to the above problems, a novel robust control scheme for VSI in the microgrid based on H∞ hybrid sensitivity is proposed in this study. The grid-side interference during the VSI operation is taken as the variable, and the sensitivity function is designed to build a H∞ robust voltage controller for VSI. In addition, an adaptive virtual impedance group is designed to further improve the voltage control robustness under a variety of operation conditions. Finally, comparative simulation experiments are carried out to verify the anti-interference ability of the proposed control strategy under different working conditions.

The relative position between the laser beam and the nozzle is controlled by laser-focus-controlled magnetic actuators to achieve non-coaxial laser cutting and improve laser cutting efficiency. In this paper, a 3-DOF (degrees of freedom) magnetic actuator is designed to solve the inconsistency of the laser beam focus and the nozzle focus in off-axis laser cutting. A mixed sensitivity robust controller is designed, and its simulation analysis and experimental research are carried out. First, the kinetic mathematical equations are established according to the structure of the actuator. Then, a mixed sensitivity robust controller is designed and analyzed using MATLAB/Simulink. The control performance is simulated and analyzed under 20% parameter variation and pulse disturbance with an uncertain mathematical model and external disturbance, respectively. Finally, the experimental study of the step response of the actuator is carried out. The experimental results show that the step response of the actuator in the Y, X, and θ directions can quickly reach the steady-state value. Furthermore, the steady-state error in the X is 1.6%; the steady-state error in the Y is 0.39%; the steady-state error in the θ is 0.45%. Their errors are all less than 0.025 mm, so they meet the position performance requirements. It can provide technical support for laser off-axis cutting.

With the problem of lightweight for body-in-white, a parametric optimization method based on mixed sensitivity analysis was proposed. The bending stiffness and modal properties of body-in-white were calibrated through the finite element simulation. Then the model was used to do mixed sensitivity analysis about stiffness and modal by experiment design, and related parts that have little influence on stiffness and modal properties were screened out. Takes thickness of related parts as design variables, the body-in-white quality and bending and torsion stiffness as the optimization targets, modal properties as constraint. The body-in-white lightweight of multi-objective optimization design was carried out by NSGA-II. Then simulate calculation was carried out by Isight to optimize the thickness of those parts, so as to realize the lightweight optimization design of the body-in-white structure. The simulation results show that its stiffness and modal performance were guaranteed after the parametric optimization, and the weight of the body-in-white was reduced by 5.7% of the original structure.

Aiming at the problem that the output voltage of relay inductive coupled power transfer (ICPT) system is susceptible to changes due to the influence of system load changes, frequency perturbations, and input voltage fluctuations, an H∞ mixed sensitivity robust control method is adopted to relay ICPT system to regulate the output voltage. First, the working principle of the relay ICPT system is analyzed. Then, the GSSA model of the relay ICPT system is established. By constructing the S/R/T mixed sensitivity function, a suitable weighting function is selected from the frequency domain perspective and converted into H∞ standard control problem to get a robust controller. Finally, an experimental platform is built to verify the control effect of the controller on the system output voltage. Experimental results show that the designed controller in this paper stabilizes the system output voltage and obtains good tracking performance, suppression parameter perturbation performance, anti-interference performance, and improves system robustness simultaneously. [ABSTRACT FROM AUTHOR]

Multi-Input Multi-Output (MIMO) Linear Time-Invariant (LTI) controllable and observable systems where the controller has access to some plant outputs but not others are considered. Analytical expressions of coprime factorizations of a given plant, a solution of the Diophantine equation and the two free parameters of a two-degrees of freedom (2DOF) controller based on observer stabilizing control are presented solving a pole placement problem, a mixed sensitivity criterion, and a reference tracking problem. These solutions are based on proposed stabilizing gains solving a pole placement problem by output feedback. The proposed gains simplify the coprime factorizations of the plant and the controller, and allow assigning a decoupled characteristic polynomial. The 2DOF stabilizing control is based on the Parameterization of All Stabilizing Controllers (PASC) where the free parameter in the feedback part of the controller solves the mixed sensitivity robust control problem of attenuation of a Low-Frequency (LF) additive disturbance at the input of the plant and of a High-Frequency (HF) additive disturbance at the measurement, while the free parameter in the reference part of the controller assures that the controlled output tracks the reference at LF such as step or sinusoidal inputs. With the proposed expressions, the mixed sensitivity problem is solved without using weighting functions, so the controller does not increase its order; and the infinite norm of the mixed sensitivity criterion, as well as the assignment of poles, is determined by a set of control parameters. [ABSTRACT FROM AUTHOR]

Recent analytical solutions to Mixed Sensitivity Control (MSC) are developed and compared with standard MSC based on γ-iteration. The proposed MSC solution gives conditions for strong stability and overcomes the pole-zero cancellations between the plant and the controller of non-iterative solutions, keeping the low-computational effort advantage of non-iterative solutions. The proposed MSC is based on the minimization of the most common closed-loop sensitivity functions in low-frequencies and the free-parameters of the stabilizing-controllers solve an algebraic equation of restriction that assigns the same value to the infinity-norms of the sensitivity functions at low and high-frequencies, guaranteeing robust stability and robust performance. It is assumed that the plant state dimension is double the plant input dimension and that the linear time-invariant nominal plant has a stabilizable and detectable realization and is strongly stabilizable. This MSC problem is solved in a one-parameter observer-controller configuration and reference tracking-control of positions is realized on a two-degrees of freedom feedback-configuration. An approximated optimal value of the location of the closed-loop poles is proposed based on Glover and McFarlane's optimal stability margin [(1989)] which in turn is based on Nehari's Theorem. Simulations of a mechanical system illustrate the results. [ABSTRACT FROM AUTHOR]

In this paper, a new method based on signal flow graph is proposed for modeling a Cuk converter. Furthermore, the original signal flow graph based method suggested in literature is also implemented on the Cuk converter. The proposed method is very simple in the process, compared to other methods of modeling and the old method of signal flow graph. By using signal flow graph approach the three models of small signal, large signal and steady state are extracted. Also, without adding any additional computation, the desired transfer function between any two state variables of the circuit is extractable. After modeling the converter, a controller design problem for the Cuk converter will be discussed. A robust control method is proposed for controlling the system. It will be shown that, although the switching converter has a nonlinear nature, but this does not affect the controller design problem. By using a linear controller with parameters tuned with a robust method of mixed sensitivity type, controlling the converter is possible.

Considering the load frequency fluctuation in the shipboard integrated power system caused by such stochastic uncertainty as wind, wave and current, the battery is adopted here to compensate for the difference between diesel generator output power and ship demand power, and the secondary frequency control is used for the diesel generator to guarantee the power balance in the shipboard integrated power system and suppress the frequency fluctuation. The load frequency control problem is modeled as a state space equation, the robust controller is designed by selecting the appropriate sensitivity function and complementary sensitivity function based on the H∞ mixed sensitivity principle, and the controller is solved by the linear matrix inequality(LMI)approach. The amplitude frequency characteristics denote the reasonability of the designed controller and the design requirement is satisfied by the impact of the impulse signal. The simulation results show that, compared with the classical PI controller, the controller designed by the H∞ robust method can significantly suppress frequency fluctuation under stochastic uncertainty, and improve the power variation of the diesel generator, battery and state of charge(SOC). The robust stability and robust performance of the power system are also advanced.

Real-time hybrid simulation (RTHS), dividing the emulated structure into numerical substructures (NS) and physical substructures (PS), is a powerful technique to obtain responses and then to assess the seismic performance of civil engineering structures. A transfer system, a servo-hydraulic actuator or shaking table, is used to apply boundary conditions between the two substructures. However, the servo-hydraulic actuator is inherently a complex system with nonlinearities and may introduce time delays into the RTHS, which will decrease the accuracy and stability of the RTHS. Moreover, there are various uncertainties in RTHS. An accurate and robust actuator control strategy is necessary to guarantee reliable simulation results. Therefore, a mixed sensitivity-based H∞ control method was proposed for RTHS. In H∞ control, the dynamics and robustness of the closed-loop transfer system are realized by performance weighting functions. A form of weighting function was given considering the requirement in RTHS. The influence of the weighting functions on the dynamics was investigated. Numerical simulations and actual RTHSs were carried out under symmetric and asymmetric dynamic loads, namely sinusoidal and earthquake excitation, respectively. Results indicated that the H∞ control method used for RTHS is feasible, and it exhibits an excellent tracking performance and robustness.

• Efficient controller was applied for a linear MIMO granulation model with time delay. • Smith predictor & Reference updating were keys in applying the robust controller. • Uncertainties in model parameters & time delay were studied successfully. • Proposed controller managed time delay, physical constraints & model mismatch. Model-based feedback control is developed for a continuous granulation process addressing the challenge of time delay and physics-based input-output constraints. The process plant is a multi-input multi-output (MIMO) linear model with time delay. A robust H ∞ controller is designed using the mixed sensitivity loop shaping design. A framework has been laid down to insure the robustness of the Smith predictor by incorporating the model mismatch as an additive uncertainty in the predictor's structure. The control performance and robustness is assessed by simulations for regulation and reference tracking problems. We show significant performance gains by employing a Smith predictor and the technique of reference updating: The control is coping significantly better with time delay, physical constraints and model mismatch. The proposed control approach is more efficient as compared to other widely used methods such as model predictive control (MPC); obtaining a stable behaviour of the response and control effort while forcing them to remain within the desired bounds. [ABSTRACT FROM AUTHOR]

Balancing control of a rotary double inverted pendulum system is a challenging research topic for researchers in dynamics control field because of its nonlinear, high degree-of-freedom, under actuated and unstable characteristics. The system always works under uncertainties and disturbances. Many control algorithms fail or ineffectively control the rotary double inverted pendulum system. In this article, mixed sensitivity H∞control is proposed to balance the rotary double inverted pendulum system. The controller is proposed to ensure the robust stability and enhance the time domain performance of the system under uncertainties and disturbances. Structure of the system, dynamics model and controller synthesis are presented. For performance evaluation, the proposed mixed sensitivity H∞controller is compared with linear quadratic regulator from both simulation and experiment on the rotary double inverted pendulum system. The results show high performance of the proposed controller on the rotary double inverted pendulum system with model uncertainties and external disturbances. [ABSTRACT FROM AUTHOR]

DC-DC Quadratic Buck Converter (QBC) is largely used in applications where the high step-down conversion ratio is required. In the practical implementation, QBC is subject to uncertainties, disturbance, and sensor noise. To address the QBC control problems, a two-degree of freedom PID (2-DOF PID) is designed in the robust control framework. Further, for comparison purpose, a one-degree of freedom PID (1-DOF PID) and mixed sensitivity loop-shaping (MS-LS) controller are also proposed. Considering QBC parasitic components, the QBC small-signal transfer function is derived based on a practical approach. Sensitivity functions are used to specify the desired design requirements, and non-smooth optimization is used to tune both PID's parameters. The three control structures are implemented and tested in the Matlab/Simulink environment. As attested by simulation results, the 2-DOF PID exhibits a better regulation accuracy with enhanced robust stability and robust performance for a wide range of supply voltage/load variation and sensor noise effect.

An intelligent robust controller, which combines a shuffled frog-leaping algorithm (SFLA) and an H∞ control strategy, is designed for a semi-active control system with magnetorheological (MR) dampers to reduce seismic responses of structures. Generally, the performance of mixed-sensitivity H∞ (MSH) control highly depends on expert experience in selecting the parameters of the weighting functions. In this study, as a recently-developed heuristic approach, a multi-objective SFLA with constraints is adopted to search for the optimal weighting functions. In the proposed semi-active control, firstly, based on the Bouc–Wen model, the forward dynamic characteristics of the MR damper are investigated through a series of tensile and compression experiments. Secondly, the MR damper inverse model is developed with an adaptive-network-based fuzzy inference system (ANFIS) technique. Finally, the SFLA-optimized MSH control approach integrated with the ANFIS inverse model is used to suppress the structural vibration. The simulation results for a three-story building model equipped with an MR damper verify that the proposed semi-active control method outperforms fuzzy control and two passive control methods. Besides, with the proposed strategy, the changes in structural parameters and earthquake excitations can be satisfactorily dealt with. [ABSTRACT FROM AUTHOR]

The nonlinear behaviour of suspension elements is substantial when the vehicles experience large road disturbances. These nonlinearities lead to performance deterioration of active suspension systems, which in turn degrades ride comfort, road holding and road handling. Standard control trends on the active suspension count on linear models to benefit from the well established linear control theory, while neglecting the nonlinear dynamics of the suspension systems. In this study, the quarter-car model has a nonlinear suspension spring with a hysteretic nature. The presented design is based on the combination of feedback linearisation (FBL) and H∞ controller. This approach is selected to take in consideration the nonlinear behaviour of the suspension system, while maintaining the opportunity to conduct the linear control theory. The main objective is maximising the ride comfort while keeping the suspension stroke, tyre dynamic load, and actuator force bounded. To assess the efficiency of the proposed design, simulations are performed on two types of road disturbances. The time and frequency domain simulations show the superiority of the proposed feedback controller in providing ride comfort in comparison with the passive suspension system. Moreover, the proposed design guarantees an agreement between the ride comfort and the other design constraints. [ABSTRACT FROM AUTHOR]

The three-port converter (TPC) obtains major attention due to its power density and ability to dispose different electric powers flexibly. Since the control models of the TPC are derived from particular steady state work point through small signal modeling method, the model parameters usually be deviated from their normal values with the change of operation and load conditions. Furthermore, there are couplings and interactions in power delivery between different ports, which have a significant influence in the dynamic control performance of the system. In this paper, the H∞ mixed sensitivity method is employed to design robust controllers for a TPC control system. Simulation results are given to demonstrate the effectiveness of the proposed scheme, and experimental studies are conducted on a prototype circuit to further validate the developed method. Compared to a traditional PI controller, it shows that a mixed sensitivity based robust controller manifest balanced performance in model parameters changes attenuation and dynamic control performance.

In this article,optimal feedback control of the twin rotor multiple input–multiple output (MIMO) system is investigated. The twin rotor MIMO system is a benchmark aero-dynamical laboratory model having strongly nonlinear characteristics and unstable coupling dynamics which make the control of such system for either posture stabilization or trajectory tracking a challenging task. This article first briefs the mathematical model of the twin rotor MIMO system and then illustrates the basic idea and technical formulation for controller design. The paper briefly explains the mixed sensitivity design method forfeedback control of the twin rotor multiple input–multiple output system laboratory model. This approach has been considered in order to assure high control performance of the system. The simulation results show that the investigated controller has both static and dynamic performance, therefore the stability and the quick control effect can be obtained simultaneously for the twin rotor MIMO system. [ABSTRACT FROM PUBLISHER]

DC-DC Quadratic Buck Converter (QBC) is largely used in applications where the high step-down conversion ratio is required. In the practical implementation, QBC is subject to uncertainties, disturbance, and sensor noise. To address the QBC control problems, a two-degree of freedom PID (2-DOF PID) is designed in the robust control framework. Further, for comparison purpose, a one-degree of freedom PID (1-DOF PID) and mixed sensitivity loopshaping (MS-LS) controller are also proposed. Considering QBC parasitic components, the QBC smallsignal transfer function is derived based on a practical approach. Sensitivity functions are used to specify the desired design requirements, and non-smooth optimization is used to tune both PID's parameters. The three control structures are implemented and tested in the Matlab/Simulink environment. As attested by simulation results, the 2-DOF PID exhibits a better regulation accuracy with enhanced robust stability and robust performance for a wide range of supply voltage/load variation and sensor noise effect. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and robust H ∞ control of a novel ultra-quiet spacecraft which employs the non-contact Stewart platform to actively control its support module (SM) and payload module (PM). The SM and PM are mechanically separated such that the disturbances and vibrations from the SM can be perfectly suppressed. However, this novel spacecraft has internal instability. To overcome the instability, this paper derives the dynamics model of the non-contact Stewart spacecraft using Newton–Euler approach at first. Then, the mixed sensitivity robust H ∞ control is developed to guarantee both the attitude stability and precision pointing. Finally, simulation studies are provided to validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

SUMMARY The mixed sensitivity minimization problem is revisited for a class of single-input-single-output unstable infinite dimensional plants with low order weights. It is shown that H ∞ controllers can be computed from the singularity conditions of a parameterized matrix whose dimension is the same as the order of the sensitivity weight. The result is applied to the design of H ∞ controllers with integral action. Connections with the so-called Hamiltonian approach are also established. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we analyzed uncertainty problems for the system of clamping force control on the condition that its model had been established. To oppose the uncertainty problems caused by many reasons, sensitivity method is mixed based on the control theory of H∞ and robust controller. Then, its control effects were studied by MATLAB. The simulation results showed the effectiveness of this method. They manifested that fault-tolerant, robustness and dynamic performance of the system are improved. It will be able to promote the application of pneumatic manipulator in the field of ultra-precision control. [Copyright &y& Elsevier]

Analytical expressions for the parameterization of all one- and two-degrees-of-freedom stable controllers stabilizing full state information systems are presented. It is assumed that the strictly proper, lumped, and linear time-invariant nominal plant has a stabilizable realization and is strongly stabilizable, and that the number of entries of the plant state is even and is double the number of entries of the plant input. Right and left coprime factorizations of the transfer function of the plant in terms of the matrices of the plant realization are proposed, the Diophantine equation is solved, and stabilizing controllers are obtained using Youla parameterization. Conditions for strong stability are given, and the free parameters of the stabilizing controllers solving the mixed sensitivity problem are established. The results are illustrated through simulation examples of a half-car active suspension system and a two-degrees-of-freedom planar rotational robot. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a systematic control-oriented robust identification procedure which produces a parametric/nonparametric set of models is applied to a duct, in order to design a feedback active noise control (ANC) based on robust analysis and control. In addition, practical problems encountered in applying such a robust identification and feedback control approaches to ANC are pointed out. These are mainly derived from the compromises between identification and control, performance and robustness, the inherent limitations of feedback when applied to ANC, model and controller order, and implementation issues. Theoretical and experimental results on a real duct are compared using two different noise sources, a speaker and a fan. [Copyright &y& Elsevier]

Real-time hybrid simulation (RTHS), dividing the emulated structure into numerical substructures (NS) and physical substructures (PS), is a powerful technique to obtain responses and then to assess the seismic performance of civil engineering structures. A transfer system, a servo-hydraulic actuator or shaking table, is used to apply boundary conditions between the two substructures. However, the servo-hydraulic actuator is inherently a complex system with nonlinearities and may introduce time delays into the RTHS, which will decrease the accuracy and stability of the RTHS. Moreover, there are various uncertainties in RTHS. An accurate and robust actuator control strategy is necessary to guarantee reliable simulation results. Therefore, a mixed sensitivity-based H∞ control method was proposed for RTHS. In H∞ control, the dynamics and robustness of the closed-loop transfer system are realized by performance weighting functions. A form of weighting function was given considering the requirement in RTHS. The influence of the weighting functions on the dynamics was investigated. Numerical simulations and actual RTHSs were carried out under symmetric and asymmetric dynamic loads, namely sinusoidal and earthquake excitation, respectively. Results indicated that the H∞ control method used for RTHS is feasible, and it exhibits an excellent tracking performance and robustness. [ABSTRACT FROM AUTHOR]

The current article presents a design procedure for obtaining robust multiple-input and multiple-output (MIMO) fractional-order controllers using a μ -synthesis design procedure with D–K iteration. μ -synthesis uses the generalized Robust Control framework in order to find a controller which meets the stability and performance criteria for a family of plants. Because this control problem is NP-hard, it is usually solved using an approximation, the most common being the D–K iteration algorithm, but, this approximation leads to high-order controllers, which are not practically feasible. If a desired structure is imposed to the controller, the corresponding K step is a non-convex problem. The novelty of the paper consists in an artificial bee colony swarm optimization approach to compute the nearly optimal controller parameters. Further, a mixed-sensitivity μ -synthesis control problem is solved with the proposed approach for a two-axis Computer Numerical Control (CNC) machine benchmark problem. The resulting controller using the described algorithm manages to ensure, with mathematical guarantee, both robust stability and robust performance, while the high-order controller obtained with the classical μ -synthesis approach in MATLAB does not offer this. [ABSTRACT FROM AUTHOR]

The three-port converter (TPC) obtains major attention due to its power density and ability to dispose different electric powers flexibly. Since the control models of the TPC are derived from particular steady state work point through small signal modeling method, the model parameters usually be deviated from their normal values with the change of operation and load conditions. Furthermore, there are couplings and interactions in power delivery between different ports, which have a significant influence in the dynamic control performance of the system. In this paper, the H∞ mixed sensitivity method is employed to design robust controllers for a TPC control system. Simulation results are given to demonstrate the effectiveness of the proposed scheme, and experimental studies are conducted on a prototype circuit to further validate the developed method. Compared to a traditional PI controller, it shows that a mixed sensitivity based robust controller manifest balanced performance in model parameters changes attenuation and dynamic control performance. [ABSTRACT FROM AUTHOR]