Structure Model Reference Adaptive Control Research Articles

Precise orientation control of gimbals with parametric variations using model reference adaptive controller

AbstractThis study focuses on a model reference adaptive control method that ensures identical orientation outputs for different prototypes of a two‐axis gimbal produced in mass production. In this method, unlike traditional MRAC structures, an MRAC structure is used in conjunction with state feedback control. First, the reasons for the need for an adaptation mechanism in gimbals and why Model Reference Adaptive Control (MRAC) alone won't be sufficient have been discussed. In the first section, various applications of MRAC have also been mentioned. Then, the mathematical foundation of the model reference adaptive controller used in this study is elaborately explained, followed by stability analyses. In the next step, an ideal reference model exhibiting desired behavior and a real system model with different dynamics are created in a simulation environment. This allows a comparison of the adaptation capabilities of only MRAC and MRAC+State Feedback controllers. Based on the information gathered in this section, the recommended approach in the article is tested on a real gimbal system, and the results are shared. The obtained results demonstrate that the MRAC+State Feedback control structure significantly reduces the error in the gimbal's orientation response compared to the reference model.

AnesthesiaGUIDE: a MATLAB tool to control the anesthesia

The goals of this paper are: (a) to investigate adaptive and fractional-order adaptive control algorithms for an automatic anesthesia process, using a closed-loop system, and (b) to develop an easy-to-use tool for MATLAB/Simulink to facilitate simulations for users with less knowledge about anesthesia and adaptive control. A model reference adaptive control structure was chosen for the entire system. First of all, to control the patient’s state during the surgery process, the patient mathematical model is useful, or even required for simulation studies. The pharmacokinetic/pharmacodynamics (PK/PD) model was determined using MATLAB’s SimBiology tool, starting from a previously available block diagram, and validated through simulation. Then, to achieve the desired control performances, two controllers are designed: a PI adaptive controller and a PIλ (PI-fractional) adaptive controller, using the MIT algorithm. The time response during anesthetic drug infusion for each patient can be plotted with the AnesthesiaGUIDE tool, which is also designed in MATLAB/Simulink. The tool was tested on data from 12 patients, subjected to general anesthesia, with successful results. Through this tool, the article provides a good opportunity for any user to experience with adaptive control for the anesthesia process.

Direct fractional order MRAC adaptive control design for a class of fractional order commensurate linear systems

In this paper, we introduce a direct fractional order adaptive control design based on model reference adaptive control (MRAC) structure for a class of commensurate fractional order linear systems with an arbitrary relative degree, and whose parameters are unknown. By generalising the application of standard direct MRAC strategy to plants described by fractional order models, we develop a fractional adaptive control scheme (FOMRAC) based on the output feedback. We also define an adaptation control law ensuring the stability of the closed-loop system and the good tracking of the reference trajectory. The asymptotic stability of the fractional order control system is proven using an extension of the Lyapunov theorem. Simulation results show the effectiveness of the proposed control method even for plants with model parametric variations and additive noises.

A Model Reference Adaptive Sliding Mode Control Method for Aero-Engine

Abstract In this paper, a model reference adaptive sliding mode control method is proposed for a variable cycle engine (VCE) which is a MIMO system with uncertainties and external disturbances. The reference model is designed based on optimal LQR method to provide ideal reference states. An adaptive sliding mode controller (ASMC) is designed for model reference adaptive control structure, which the adaptive law is derived based on Lyapunov function to estimate the unknown upper bound of uncertainties and external disturbances. Simulation results for VCE demonstrate the performance and fidelity of the proposed method.

Model reference adaptive tracking control for hydraulic servo systems with nonlinear neural-networks

It is well known that hydraulic systems typically suffer from heavy disturbances including parametric uncertainties and unknown disturbances. In order to attain high performance tracking control, this paper proposes a composite design of nonlinear neural-networks (NN) and continuous robust integral of the sign of the error (RISE) feedback controller. The control development incorporates a NN feedforward component to have a compensation for unknown state-dependent disturbances and to further improve the accuracy of feedforward compensation, meanwhile input parameter is updated online. To achieve asymptotic stability, a novel RISE term with NN-based feedforward component is developed for the first time to enable the incorporation of model reference adaptive control structure where acceleration signal is not employed. The proposed controller guarantees controlled hydraulic system a semi-global asymptotic stability. For the experimental results, the prescribed transient performance is tested under rectangular trajectory and the steady state performance is tested under sinusoidal trajectory.

Multi-loop Model Reference Adaptive PID Control for Fault-Tolerance

This study demonstrates application of multi-loop model reference adaptive control (MRAC) structure to enhance fault tolerance performance of closed-loop PID control systems. The proposed multi-loop MRAC-PID structure can transform a conventional PID control system to an adaptive control system by combining an outer adaptation loop that employs MIT rule. This control structure can be used to improvement of fault tolerance and fault detection performance of the existing closed-loop PID control systems. One of the advantages of this structure originates from the reference input shaping technique that allows adaptive control without modifying any coefficients of the existing PID controllers. Numerical and experimental studies are presented to illustrate the application of the multi-loop MRAC-PID control structure for rotor control applications.

Time-varying parameter model reference adaptive control and its application to aircraft

A new Second Order (SO) adaptive control approach, that accounts for both matched and unmatched unknown time-varying uncertainties, is proposed in this paper. It is developed based on the Predictor based Model Reference Adaptive Control (PMRAC) structure. In this approach, the estimated parameter dynamics is composed of a σ-modified PMRAC update law and a predicted parameter dynamics, with projection operator. The predicted parameter dynamics consists of a stable known eigendynamics, a feedback of an approximate parameter error, and the remaining part linearly parameterized by a set of known regressor functions combined with an adaptive estimate of unknown second-order parameters, which are updated by a Lyapunov design. Due to the estimation of time derivatives of the parameters, the proposed predictor based SO-MRAC is hence capable of capturing the rapid parameter variations in system dynamics. Furthermore, a generalized ultimate boundedness formulation based on the Lyapunov theory is presented for its stability analysis. This formulation provides separate bounds for each of the state vector partitions, mainly tracking and parameter estimation errors. Finally, this proposed approach is applied to control of lateral dynamics of an unmanned aircraft to illustrate the usefulness of the proposed approach. The simulation results are found to be quite satisfactory both in terms of tracking and adaptation performance.

Reference tracking control and attenuation of unknown periodic disturbances in the presence of noise for unknown minimum‐phase LTI plants

SummaryThe rejection of unknown periodic disturbances in the plant output through adaptive feedback has been an active area of research. In most successful efforts, it is assumed that the plant model is a known LTI stable system. In this paper, we relax the assumption of stable known plant and consider the case where the plant model can be unstable with unknown parameters. We do assume, however, that the plant model is minimum phase and use the model reference adaptive control structure to meet the objectives of reference tracking and unknown periodic disturbance rejection without amplifying the effect of broadband noises. The cost of achieving these objectives is the use of overparameterization that adds to the number of computations. The main contribution of this paper is that it shows that the problem of rejecting unknown periodic disturbances can be solved for unstable plants with unknown parameters as long as they are minimum phase. Numerical examples illustrate the effectiveness of the proposed control methodology.

A novel reconfigurable control method for an aircraft with potential actuator failures

This paper presents a novel reconfigurable control method for an aircraft with potential actuator failures. A Variable Structure Model Reference Adaptive Control (VS-MRAC) scheme is deployed to counteract the adverse effects when the actuator failure occurs. Combined with exponential reaching law, the convergence rate is improved and the chattering is reduced. This approach ensures that the reference input value can be tracked rapidly and accurately. The safety and stability of the aircraft is much improved during the event of actuator failures. Finally, the simulation results are given to show the effectiveness and performance of the developed method.

A novel reconfigurable control method for an aircraft with potential actuator failures

This paper presents a novel reconfigurable control method for an aircraft with potential actuator failures. A Variable Structure Model Reference Adaptive Control (VS-MRAC) scheme is deployed to counteract the adverse effects when the actuator failure occurs. Combined with exponential reaching law, the convergence rate is improved and the chattering is reduced. This approach ensures that the reference input value can be tracked rapidly and accurately. The safety and stability of the aircraft is much improved during the event of actuator failures. Finally, the simulation results are given to show the effectiveness and performance of the developed method.

BLDC Multi-Motor Speed Synchronization by Leader Following Multi-Agent and Hybrid Control

In this article, a unique and innovative design for addressing the speed synchronization problem in a multi-motor system using Brush less DC (BLDC), motors is presented by utilizing motor back emf equation and rotor position commonly called sensor less technique. In the proposed method, the system is modelled as a consensus problem of leader following multi-agent system (MAS), and a hybrid controller is designed by using Model Reference Adaptive Control (MRAC) along with Variable Structure (VS) control technique of Sliding Mode Control (SMC), herein called Variable Structure Model Reference Adaptive Control (VS-MRAC). The consensus algorithm of MAS (reformed w.r.t motor speed data), is fused with the hybrid controller to reach consensus on speed regulated by proposed hybrid controller. The stability of a system is endorse by designing a Lyapunov function. The efficiency of the proposed methodology is proven by simulations performed in MATLAB and the acquired results validate the success of proposed design methodology.

Discrete variable structure model reference adaptive control using only input-output measurements

Designing an adequate controller for a plant with an arbitrary relative degree is still an active area of research. In this paper, a discrete variable structure model reference adaptive control using only input-output measurements (DVS-MRAC-IO) for not strictly positive real systems with a relative degree of two is proposed. In order to show the effectiveness of the proposed controller, a detailed stability analysis is studied using Lyapunov theory. Further, a straightforward generalization of DVS-MRAC-IO for systems with arbitrary relative degree is presented. Numerical results are used to show the effectiveness of the proposed methods.

From adaptive control to variable structure systems – seeking harmony

From adaptive control to variable structure systems – seeking harmony

Lyapunov based PD/PID in model reference adaptive control for satellite launch vehicle systems

This paper proposes a Lyapunov based model reference adaptive PD/PID controller for Satellite Launch Vehicle (SLV) systems. SLV is an open loop unstable plant with time varying characteristics and in general it is handled with the help of gain scheduling controllers. To improve the tracking performance, Lyapunov based adaptive PD and PID controllers are designed for model reference adaptive control structure and the performances are compared with existing gain scheduling PD/PID controller. In particular, we show that an adaptive PID controller outperforms in the presence of unmodelled dynamics and wind disturbance conditions.

Robust control of robotic manipulators based on left inverse system and variable structure model reference adaptive control

SummaryThis work proposes a control structure to be applied to robotic manipulators, which are articulated mechanical systems composed of links connected by joints. The proposed controller can be divided into two parts. The first one is a left inverse system, which is used to decouple the dynamic behavior of the joints. The second is a sliding mode controller, which is applied for each decoupled joint. It is important to note that the proposed structure, using only input/output measurements, reduces the control signal ‘chattering’, and it is robust to parametric uncertainties. Besides all the characteristics presented, the proposed structure simplifies the design of sliding mode controller to be applied in robotic manipulators. All these features are verified by simulations. Copyright © 2016 John Wiley & Sons, Ltd.

MRAC-based Fault Tolerant Control of a SISO Real Process Application

In this paper, a modified version of Variable Structure Model Reference Adaptive Controller (VS-MRAC) scheme is developed for an application in Fault Tolerant Control (FTC) of a Single Input-Single Output (SISO) process. As a result of steady state error and oscillations when faults are induced in sensor and actuator of the process, the original VS-MRAC is modified by adding a Saturation Function and a PI controller (VS-MRAC-SAT-PI). The new scheme performance is compared against a classical PID and two other MRAC-based FTC schemes in a Coupled-Tank System. Different types of additive faults (abrupt and gradual faults) were induced in the process and results showed better fault accommodation capabilities of the VS-MRAC-SAT-PI.

A new model reference adaptive control structure for uncertain switched systems with unmodeled input dynamics

In this paper, a new model reference adaptive controller (MRAC) for uncertain switched linear systems is developed. A class of uncertain switched linear systems with parametric mismatched and input matched uncertainties, control input effectiveness and unmodeled dynamics is studied in this paper. The difference in input matrix for different switching modes which means the input channel degradation is investigated through this paper. By using common Lyapunov function method and developing new linear matrix inequality based sufficient conditions, uniform ultimate boundedness of the reference tracking error is guaranteed by switched MRAC and by using a novel nonlinear controller term, the size of the uniform ultimate bounded region can be made arbitrarily small which could enhance the performance of the overall control structure. Modified versions of MRAC systems using low-frequency learning adaptation MRAC is also used for better transient performance at switching instants. An illustrative numerical example demonstrates the performance of the proposed approach. Results also show that for the cases without parametric uncertainty in the linear part, asymptotic stability of the reference tracking error is guaranteed.

Robust Control Applied to Multiple-Input Multiple-Output Nonlinear Systems

Many of practical systems (for example: robotic systems, power systems and electronic circuits) are multiple-input multiple-output nonlinear systems and some of them have coupling between inputs and outputs. Besides all that, these systems can suffer with parametric uncertainties and external disturbances. Any control techniques applied to these systems are complex. This work presents a control structure, based on the union between a modified version of the variable structure model reference adaptive control and a left-inverse decoupling technique, to transform a multiple-input multiple output nonlinear system into a set of single-input single-output linear systems. In that case each input affects only one output and with a desired closed-loop performance. The proposed structure transforms the variable structure model reference adaptive control, which is usually applied to single-input single-output linear systems, into a controller to be applied to a class of multiple-input multiple-output nonlinear systems. It is important to note that proposed structure, using only input/output measurements, presents fast transient performance, reduces the output “chattering” and it is robust to parametric uncertainties and disturbances. All these features are verified by simulation results of an electronic circuit that exhibits chaotic behavior (Chua’s circuit).

Multiple spacecraft formation reconfiguration using solar radiation pressure

In this paper the use of solar radiation pressure for spacecraft formation reconfiguration at the L2 Sun–Earth/Moon collinear libration point is presented. The system consisting of a leader and three follower spacecraft is considered. The leader spacecraft is assumed to be in a fixed halo trajectory and the follower spacecraft position relative to the leader satellite is controlled using two angles and area; these are varied based on a variable structure model reference adaptive control technique to achieve the desired formation reconfiguration. This approach ensures that all follower spacecraft complete the required maneuver in the same time. An intertially fixed circular trajectory, which is suitable for interferometer missions, is used in this paper. The stability of the proposed controller is established using Lyapunov theory. The performance of the proposed controller is tested through numerical simulation of the governing nonlinear equations of motion and is applied for formation initialization, resizing, retargeting, and rotation. The numerical results demonstrate the effectiveness of the proposed control technique for spacecraft formation reconfiguration using solar radiation pressure at the L2 libration point. Furthermore, control inputs on the order of 15degrees and 2m2 for area change are sufficient to execute the maneuvers.

State derivative-free variable structure model reference adaptive control of linear parabolic systems

The problem of constructing a model reference adaptive control law for an uncertain 1-dimensional parabolic system is considered in this article. The controller designed here involves only the plant state but no its derivatives. A priori bounds on the plant’s uncertain parameters are used to propose switching laws which serve as an adaptive mechanism. The exponential decay to zero of the state error with any prescribed rate is guaranteed by choosing a controller parameter correspondingly. Numerical studies are also presented to illustrate the applicability of the control law.