H-infinity Synthesis Research Articles

An Approach to Robust Control of Aircraft Motion

The article deals with approaches to designing aircraft control systems based on the robust synthesis. The mathematical model of the aircraft control system both for deterministic and stochastic cases is considered. The Dryden filter models are represented. The state-space conception is applied. The concept of robust designing based on H-infinity synthesis, function of the mixed sensitivity, and loop shaping is represented. The features of Robust Control Toolbox necessary for automated designing of aircraft control systems are studied. The weighting transfer functions are proposed. Results of simulation of the synthesized robust control system are shown in the form of transient processes in lateral and longitudinal motions. The proposed approach is directed on providing the possibility of the aircraft to function in conditions of influence of disturbances. The possible applications of obtained results is control of aircraft motion in civil aviation.

Fixed-order H-infinity controller design for port-Hamiltonian systems

We present a new fixed-order H-infinity controller design method for potentially large-scale port-Hamiltonian (pH) plants. Our method computes controllers that are also pH (and thus passive) such that the resulting closed-loop systems is again passive, which ensures closed-loop stability simply from the structure of the plant and controller matrices. In this way, we can avoid computationally expensive eigenvalue computations that would otherwise be necessary. In combination with a sample-based objective function which allows us to avoid multiple evaluations of the H-infinity norm (which is typically the main computational burden in fixed-order H-infinity controller synthesis), this makes our method well-suited for plants with a high state–space dimension.In our numerical experiments, we show that applying a passivity-enforcing post-processing step after using well-established H-infinity synthesis methods often leads to a deteriorated H-infinity performance. By contrast, our method computes pH controllers, that are automatically passive and simultaneously aim to minimize the H-infinity norm of the closed-loop transfer function. Moreover, our experiments show that for large-scale plants, our method is significantly faster than the well-established fixed-order H-infinity controller synthesis methods.

Simulation of an Active Suspension Control for Frequency Response from Road Vibrations Using H-Infinity Synthesis and Validation for Robust Operation Using Μ-Synthesis

In a general suspension system ride comfort and suspension performance are inversely related.Whenever the vibrations are damped in a periodic and slow manner, the ride comfort improves but the suspension performance degrades. This project presents a frequency-based controller for active suspension using the H-infinity algorithm. The implementation includes performing the analysis using a general quarter car model. This is done to reduce the complexity of the model and at the same time helps to carry out the analysis without any compromise. In the implementation, the quarter car model is converted into a state-space model to make further analysis easier. The next part includes the development of a robust controller so that the system response is acceptable even in the case of uncertain input. In the model developed, the output states to be monitored are taken as suspension deflection and body acceleration. The input state to the controller is taken as the actuator force input. Intent of the model development is to mitigate the general trade-off between ride comfort and suspension performance.

On the existence of Equivalent-Input-Disturbance and multiple integral augmentation via H-Infinity Synthesis for unmatched systems

In this paper, the existence of a solution for the transformation of the disturbances from the unmatched cases to the matched one is investigated. The usage of matched/unmatched disturbance notions and the underlying assumptions are clarified. Then, a simplified definition is introduced to obtain a set of performance metrics to be used in observer design. Using bilinear pole shifting and multiple integral augmentation to the plant, not only the stabilizability/detectability conditions but also infinity-norm bounds for unstable MIMO systems are derived. Then, the solvability of the augmented Hamiltonian matrices to get stabilizing solutions via standard H∞-Synthesis is explained. Finally, the solutions, definitions, and assumptions are validated through numerical examples.

H∞ robust control design for coupled Ciscrea AUV model

Objective The multi input multi output (MIMO) robust controller was proposed to realize the trajectory tracking and the yaw control for the four-DoF Ciscrea Autonomous Underwater Vehicle (AUV) model. Methods The parameter uncertainty of the inertia matrix and quadratic damping affection was formulated as an uncertain structure by the perturbation method, the general system was derived by linear fraction transformation (LFT). The H-infinity synthesis method was proposed to solve the MIMO robust controller for AUV general system, and the structure singular value analysis method was applied to compute the robust stability margin. To validate the robust yaw controller, the paper simulated AUV trajectory tracking as well as the yaw control scenario with MATLAB. The tracking performance was compared between interference and non-interference control condition. Results The upper bound and lower bound of the structure singular value was analyzed for the stable robust controller, and the elimination of the perturbation on AUV output showed effective anti-jamming performance. Conclusion The proposed control method is available for parameter uncertainty and nonlinearity issues on the AUV model. This paper provides a specific application for AUV motion and attitude control problem in the complicated ocean environment.

Dynamics modeling and motion control for high-speed underwater vehicles using H-infinity synthesis with anti-windup compensator

The control synthesis of a high-speed supercavitating vehicle (HSSV) faces many difficulties such as the stability, control, and maneuvering with dynamical uncertainties due to parameter perturbations, external disturbances, unmodeled dynamics, measurement noises, and actuator constraints. Inspired by the HSSV dynamical analysis, this paper proposes the H∞ (i.e. "H-infinity") robust control synthesis to generate a robust low-order controller, which is intended for real implementations to ensure active control actions. Particularly, the presented control scheme includes a feedback component and an anti-windup compensator. The anti-windup synthesis is to provide system stability under actuator saturations. Extensive simulations show that the designed controller provides good performances with high robustness for vertical plane manoeuver while effectively eliminating planning forces, exogenous disturbances and noises as well as overcoming cavitator saturations.

Robust Compensating Function Scheme for Adequate Electrical Power System Stabilization

This work centers on robust compensating function scheme for adequate electrical power system stabilization. There has been high level of disturbances in the power line and lack of adequate compensation technique to cancel the effects of the resultant instability which has caused power failures. The problem was addressed by the consideration of disturbances in the power line during the design of the compensating function for the improvement of the power system performance and stability. H-Infinity synthesis robust compensating function design method was used to design an adequate compensator that can improve the performance and stability of the power system. From the results, the H-infinity Synthesis Controlled Generating Plant (HCGP) recorded an overshoot of 0%, settling time of 1.04 seconds, tracking error of 0dB, gain margin of 21.7dB and phase margin of 79.6 degrees. The simulation was repeated by varying the value to k to -0.3, and the generating plant produced same results. This shows that the system can maintain performance and stability equilibrium even when there is change in its parameters. Since the HCGP satisfied the performance and stability robustness, therefore it was concluded that power system robust compensating function scheme for improved performance and stability robustness was achieved using H-Infinity synthesis method.

Explicit parallel co-simulation approach: analysis and improved coupling method based on H-infinity synthesis

Co-simulation is widely used in the industry for the simulation of multidomain systems. Because the coupling variables cannot be communicated continuously, the co-simulation results can be unstable and inaccurate, especially when an explicit parallel approach is applied. To address this issue, new coupling methods to improve the stability and accuracy have been developed in recent years. However, the assessment of their performance is sometimes not straightforward or is even impossible owing to the case-dependent effect. The selection of the coupling method and its tuning cannot be performed before running the co-simulation, especially with a time-varying system.In this work, the co-simulation system is analyzed in the frequency domain as a sampled-data interconnection. Then a new coupling method based on the H-infinity synthesis is developed. The method intends to reconstruct the coupling variable by adding a compensator and smoother at the interface and to minimize the error from the sample-hold process. A convergence analysis in the frequency domain shows that the coupling error can be reduced in a wide frequency range, which implies good robustness. The new method is verified using two co-simulation cases. The first case is a dual mass–spring–damper system with random parameters and the second case is a co-simulation of a multibody dynamic (MBD) vehicle model and an electric power-assisted steering (EPAS) system model. Experimental results show that the method can improve the stability and accuracy, which enables a larger communication step to speed up the explicit parallel co-simulation.

An Innovative Aerial Manipulator with Tandem Ducted Fans: Modeling, Control, and Simulation

This paper proposes an innovative ducted fan aerial manipulator, which is particularly suitable for the tasks in confined environment, where traditional multirotors and helicopters would be inaccessible. The dynamic model of the aerial manipulator is established by comprehensive mechanism and parametric frequency-domain identification. On this basis, a composite controller of the aerial platform is proposed. A basic static robust controller is designed via H-infinity synthesis to achieve basic performance, and an adaptive auxiliary loop is designed to estimate and compensate for the effect acting on the vehicle from the manipulator. The computer simulation analyses show good stability of the aerial vehicle under the manipulator motion and good tracking performance of the manipulator end effector, which verify the feasibility of the proposed aerial manipulator design and the effectiveness of the proposed controller, indicating that the system can meet the requirements of high precision operation tasks well.

Closed-form H-infinity optimal control for a class of infinite-dimensional systems

H-infinity optimal control and estimation are addressed for a class of systems governed by partial differential equations with bounded input and output operators. Diffusion equations are an important example in this class. Explicit formulas for the optimal state feedback controller as well as the optimal state estimator are given. Unlike traditional methods for H-infinity synthesis, no iteration is needed to obtain the optimal solution. Moreover, the optimal performance for both the state feedback and state estimation problems are explicitly calculated. This is shown to be useful for problems of H-infinity optimal actuator and sensor location. Furthermore, the results can be used in testing and bench-marking of general purpose algorithms for H-infinity synthesis. The results also apply to finite-dimensional systems.

Robust Control for a 3DOF Articulated Robotic Manipulator Joint Torque under Uncertainties

This research work emphasizes on design of a robust control for a 3DOF robotic manipulator under uncertainties. The plant model was achieved using the independent joint method and the uncertainty problem was addressed by designing a robust controller using H-Infinity synthesis which was compared with PID. This was achieved with algorithms implemented in MATLAB. The H-Infinity controller recorded 0dB, while PID controller recorded 0.117dB and 0.061dB for joints I and II respectively in Complementary Sensitivity (T) graph at low frequencies. H-Infinity controller achieved better disturbance rejection characteristics with sensitivity (S) graph recording peak sensitivity of 0.817dB and 1.79dB at joints I and II respectively than PID controller which achieved 3dB and 1.86dB at joints I and II respectively. H-Infinity controller achieved better noise rejection characteristics with T graph recording lower gains at joints I and II respectively at high frequencies than PID controller which recorded higher gains at joints I and II respectively. Thus, it was concluded that the H-Infinity controller achieved better performance and stability robustness characteristics for the joint torque control than the PID.

Inversion Based Adaptive Feedforward Control for Multivariable Systems

This paper presents a novel adaptive feedforward control (AFC) method for rejecting sinusoidal disturbances with known frequencies acting on multi-input-multi-output (MIMO) discrete time linear systems based on the H-infinity synthesis. First, the gradient AFC (GAFC) for MIMO systems is reviewed, and the linear time invariant (LTI) equivalent form of the GAFC is approximated for stability analysis. For single-input-single-output (SISO) systems, this paper shows small adaptation gains guarantee the stability of GAFC for any disturbance frequency. Then inspired by the stability of SISO GAFC, the inversion based AFC (IAFC) is proposed for MIMO systems. In this method, the GAFC is compensated by an H-infinity model matching filter, which renders nearly decoupled systems with fixed time delays. The LTI analysis, simulation study and experimental results from an open-loop unstable MIMO Active Magnetic Bearing Spindle (AMBS) are presented to demonstrate the stability and effectiveness of the proposed IAFC in rejecting narrow-band disturbances.

H-infinity controller with graphical LMI region profile for liquid slosh suppression

This paper presents a H-infinity synthesis with pole clustering based on LMI region schemes for liquid slosh control. Using LMI approach, the regional pole placement known as LMI region combined with design objective in H-infinity controller guarantee a fast input tracking capability and very minimal liquid slosh. A graphical profile of the transient response of liquid slosh suppression system with respect to pole placement is very useful in giving more flexibility to the researcher in choosing a specific LMI region. With the purpose to confirm the design of control scheme, a liquid slosh model is considered to represent the lateral slosh movement. Supremacy of the proposed approach is shown by comparing the results with hybrid model-free fuzzy-PID controller with derivative filter. The performance of the control schemes is examined in terms of time response specifications of lateral tank tracking capability and level of liquid slosh reduction.

Multivariable Disturbance Observer Based Control with the Experiment on an Active Magnetic Bearing Spindle

This paper presents a new method of disturbance observer based control (DOBC) for multi-input-multi-output (MIMO) highly-coupled unstable systems based on the game theory and the H-infinity synthesis. First motivated by the Youla parameterization of full order state observer feedback control, a full order state observer (FOSO) based DOBC is proposed for single-input-single-output (SISO) systems. Then inspired by the FOSO based DOBC design, a disturbance decoupling method is proposed for MIMO systems using game theoretic observer design. By using error dynamics from the proposed observers, single-input-multi-output (SIMO) virtual plants are constructed. Inverses of those virtual plants for a certain bandwidth are found by solving the model matching problem using H-infinity solver. The proposed DOBC is applied to an open loop unstable MIMO Active Magnetic Bearing Spindle (AMBS). Simulation and experimental results show that the disturbances are effectively estimated and compensated.

Mixed adaptive control architecture for a novel coaxial-ducted-fan aircraft under time-varying uncertainties

This paper is concerned with a kind of mixed adaptive control architecture for a novel tandem coaxial-ducted-fan aircraft in the presence of relative large time-vary uncertainties and external disturbances. For the proposed aircraft, elementary analysis is first performed to evaluate the system's inherent sensitivity to uncertainty. The control architecture includes mainly two parts: a robust decoupling controller and a L1 adaptive augmentation. The robust decoupling controller designed via H-infinity synthesis mainly provides states decoupling and ensures baseline performance; while the L1 adaptive augmentation based on L1 adaptive theory is mainly responsible for large uncertainty estimation and compensation. Numerical simulations of this novel unmanned aerial vehicle (UAV) are applied to illustrate the performances of the proposed control architecture. The simulation results reveal that compared to the classic robust method, the proposed controller is more effective and shows much improvement even under relative serious uncertainties and external disturbances.

A frequency-shaping methodology for discrete-time sliding mode control

ABSTRACTThis paper proposes a frequency shaping methodology for performance enhancement of discrete-time sliding mode control for systems with narrow band disturbances. This approach augments the sliding mode surface as a dynamic feedback system and designs an ‘optimal’ shaping filter in the feedback loop based on H-infinity synthesis, which assures both the stability and the desired frequency-response characteristics of the sliding mode surface. Furthermore, this frequency-shaping technique is advanced to be parameter-dependent to improve the efficiency and flexibility. The methodology enables the design of sliding mode control in frequency domain, which is critically important for high-precision systems that are subjected to high-frequency disturbances. The proposed frequency-shaped sliding mode control is applied onto a hard disk drive in the presence of vibrations with multiple peak frequencies; effective vibration suppression is demonstrated through comprehensive simulation study.

LADRC-based attitude decoupling control for helicopter and parameters tuning

To meet the ADS-33E-PRF flight quality and effectively overcome the influence of external disturbance,an attitude control strategy based on a linear active disturbance rejection control( LADRC) is proposed for helicopter. Flight dynamics model of UH-60 A and the wind model were established. UH-60 A was trimmed for verifying accuracy of dynamic model and trim algorithm. Helicopter attitude decoupling control loop based on the single input / single output second-order LADRC controller was set up with stabilization feedback loop. The controller parameter tuning problem was transformed into constrained optimization problem in time and frequency domain according to quality requirement of ADS-33E-PRF. Combining H-infinity synthesis algorithm and steepest descent algorithm,the optimization of parameters was calculated. Quality assessment of attitude control was made and the control loop was applied to the attitude hold control simulation in atmospheric disturbance. The results of simulation and quality evaluation show that the attitude control system based on LADRC has good decoupling performance and capability of anti-disturbance.

Stall Flutter Suppression for Absolutely Divergent Motions of Wind Turbine Blade Base on H-Infinity Mixed-Sensitivity Synthesis Method

This paper is devoted to solve the problem of stall flutter suppression for an absolutely divergent blade of small scale wind turbine. The blade is specially designed with absolutely divergent motions for the purpose of determining the most effective methods of active control for stall flutter suppression. A 2-DOF blade section is considered, with a simplified stall nonlinear aerodynamic model being applied. H-infinity mixed-sensitivity synthesis method with a new three-weight regulation is designed to control the time-domain instability of aeroelastic equations, with a third weight being chosen to weight complementary sensitivity for tracking problems and noise attenuation to robust stabilization in H-infinity control. Effects on flutter suppression are investigated based on different structural and external parameters. Apparent effects of H-infinity mixed-sensitivity method are displayed in the paper, when the other common intelligent control methods fail. The research provides a control way for absolutely divergent turbine blade motions.

Modeling and control of an anti-lock brake and steering system for cooperative control on split-mu surfaces

The brake and steering systems in vehicles are the most effective actuators that directly affect the vehicle dynamics. In general, the brake system affects the longitudinal dynamics and the steering system affects the lateral dynamics; however, their effects are coupled when the vehicle is braking on a non-homogenous surface, such as a split-mu road. The yaw moment compensation of the steering control on a split-mu road is one of the basic functions of integrated or coordinated chassis control systems and has been demonstrated by several chassis suppliers. However, the disturbance yaw moment is generally compensated for using the yaw rate feedback or using wheel brake pressure measurement. Access to the wheel brake pressure through physical sensors is not cost effective; therefore, we modeled the hydraulic brake system to avoid using physical sensors and to estimate the brake pressure. The steering angle controller was designed to mitigate the non-symmetric braking force effect and to stabilize the yaw rate dynamics of the vehicle. An H-infinity design synthesis was used to take the system model and the estimation errors into account, and the designed controller was evaluated using vehicle tests.

H-Infinity Controller Based on LMI Region for Flexible Robot Manipulator

This study presents investigations into the development of H-infinity controller with LMI region schemes for trajectory tracking and vibration control of a Flexible Robot Manipulator System. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the assume mode method. H-infinity synthesis with pole clustering schemes is used to control the hub angle with very minimal vibration at the end-point of the manipulator. The performance of the flexible robot manipulator system is examined in terms of time response specifications of hub angle, minimal vibration at the end-point of the manipulator and minimal control input torque. To examine the effectiveness of the proposed controller, it is compared with hybrid input shaping with collocated PD controller schemes. The implementation results show that H-infinity controller with confined closed-loop poles based on LMI region produce a fast tracking capability with very minimal end-point vibration and smooth control input torque.