Large Control Signals Research Articles

Optimal Position Control for Linearized Robot Arm.(Dept.E)

This paper investigates the lementation of optimal controllers to dynamic control systems and addresses their causality. First, a one-link robot arm system is introduced as the model for which the optimal controller will be designed. This model is used in a discrete linearized for so as to ease the mathematics involved, however no generality is lost due to this simplification as dictated by the obtained results. Then a proposed time-optimal controller is first adopted in which the control requirements are reduced to merely reaching a specified set-point in the shortest possible time. This, of course, gives rise to large control signals that may not be physically attained resulting in a fictitious controller. Then a relaxation is made to overcome this problem by applying a performance index to be minimized through the use of the minimum principle of Pontryagen. Finally, a comparative analysis is briefly made supported by the response curves.

A New Quadratic Spacing Policy and Adaptive Fault-Tolerant Platooning With Actuator Saturation

This article investigates a fault-tolerant control problem for heterogeneous vehicular platoons with actuator faults and saturation. The occurrence of actuator faults may yield large control signals to avoid performance loss, which can potentially lead to saturation of the actuator that may cause further performance deterioration or even instability. To compensate for the effects of actuator faults and saturation, an adaptive fault-tolerant control method is proposed based on nonlinear vehicle dynamics and a new quadratic spacing policy. The improved quadratic spacing policy is introduced to remove the assumption of zero initial spacing errors. The nonlinear vehicle dynamics is approximated by a radial basis function neural network (RBFNN). The adaptive fault-tolerant platoon control method is developed in the context of PID-type sliding mode control technique, and proved to be capable of guaranteeing individual vehicle stability, string stability and traffic flow stability. The effectiveness of the method is verified through comparison simulation studies.

An auxiliary control aided modified sliding mode control for a PMSG based wind energy conversion system

Purpose This study proposes a modified sliding mode control technique having a proportional plus integral (PI) sliding surface aided by auxiliary control applied to a wind turbine driven permanent magnet synchronous generator. This paper aims to realize real and reactive power control, keeping the voltage under the desired limit during transients. Design/methodology/approach First, a PI sliding surface type sliding mode control (PISMC) is formulated, which is capable of dragging the system to the desired state and stability. Then a saturation function-based auxiliary controller is incorporated with PISMC to enhance its performance during wind speed and system parameter variations. Findings The proposed controller can tackle the problems faced while using a PI controller and the conventional sliding mode controller (CSMC) such as lack of robustness and requirement of unnecessary large control signals to overcome the parametric uncertainties and problem of chattering. Originality/value To justify the superior performance of the proposed controller in terms of robustness, reliability and accuracy a comparative study is done with the CSMC and PI controllers. The simulations are performed using MATLAB.

Comparison controllers for inverter operating in island mode in microgrids with linear and nonlinear loads

This paper presents the design and implementation of a resonant controller into a PI-P control configuration (PI-P+Resonant controller). The design of this controller is conducted for inverter operation in island mode within the context of microgrids The main PI-P control is avoid that large control signal causing the saturation phenomena in the systems. The Resonant controller allows providing high gain at the frecuency of the harmonics, in order to mitigate these harmonics. If both controller are combiate (PI-P-Resonant controllers) turns out to be an adequate solution to reduce total armonic distortion in the output voltage (THDv) of a single-phase inverter due to nonlinear loads.

Adaptive integral dynamic surface control of a hypersonic flight vehicle

In this article, non-linear adaptive dynamic surface air speed and flight path angle control designs are presented for the longitudinal dynamics of a flexible hypersonic flight vehicle. The tracking performance of the control design is enhanced by introducing a novel integral term that caters to avoiding a large initial control signal. To ensure feasibility, the design scheme incorporates magnitude and rate constraints on the actuator commands. The uncertain non-linear functions are approximated by an efficient use of the neural networks to reduce the computational load. A detailed stability analysis shows that all closed-loop signals are uniformly ultimately bounded and the tracking performance is guaranteed. The robustness of the design scheme is verified through numerical simulations of the flexible flight vehicle model.

Anti-windup-based dynamic controller synthesis for nonlinear systems under input saturation

This paper describes the design of dynamic controller and static anti-windup compensator (AWC) for Lipschitz nonlinear systems under input saturation. Global and local AWC-based control schemes for stabilization of the nonlinear systems are proposed, and necessary conditions for feasibility of the control approaches are investigated. A one-step approach for simultaneous design of H∞ controller and AWC by means of linear matrix inequalities (LMIs) is presented herein, which supports multi-objective synthesis to attain stabilization or tracking, robustness against disturbance and noise, and penalization of large and high frequency control signals. This multi-objective synthesis can be accomplished by incorporating design weights, as commonly used in the standard H∞ control theory, to design a performance-oriented anti-windup-based control scheme. LMIs for the global control of the nonlinear systems subject to input saturation are derived by application of a quadratic Lyapunov function, the Lipschitz condition, the global sector condition, L2 gain reduction, substantial matrix algebra and variable transformation. In order to cope with unstable and oscillatory nonlinear systems, LMI-based local results are established using a local sector condition. Additional conditions are derived, by incorporating properties of the saturation function, to ensure well-posedness of the controller. Two simulation examples are provided to show the effectiveness of the proposed control schemes for control of stable and chaotic nonlinear systems under input saturation.

Random Delay Compensation for Nonlinear Systems

This paper presents the digital controller design for nonlinear system with random delay. First, the delay-free nonlinear system is linearized through optimal linearization. Then, based on this optimal linear model, an analog state-feedback controller is designed via linear quadratic regulation (LQR) to achieve a satisfactory performance in the delay-free case. Lastly, an input delay compensation technique via digital redesign is applied. The resulting digital controller can maintain the essential performance of the analog counterpart in the presence of random input delay, and also possesses the features practical for implementation, like large control period and small control signal in the transient. The proposed method is verified by the simulation results on the balance control of single rotary inverted pendulum (SRIP) as well as the physical experiments.

Adaptive dynamic surface control of a hypersonic flight vehicle with improved tracking

AbstractThis work presents a nonlinear adaptive dynamic surface air speed and a flight path angle control design procedure for the longitudinal dynamics of a generic hypersonic flight vehicle. The proposed design scheme takes into account the magnitude, rate, and bandwidth constraints on the actuator signals. A new approach is used to enhance tracking performance and avoid a large initial control signal. The uncertain nonlinear functions in the flight vehicle model are approximated by using radial basis function neural networks. A detailed stability analysis of the designed controllers shows that all the signals of the closed‐loop system are uniformly ultimately bounded. The robust performance of the design scheme is verified through numerical simulations of the flight vehicle model for various parameter variation test cases.Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Exact Analytic Solutions for Optimal Control Problems Under Multiplicative Noise

AbstractControl-dependent (multiplicative) noise makes it difficult to achieve optimal control because large control signals amplify noise. This paper considers a minimal (one-dimensional) system that includes multiplicative noise and solves the optimal control problem for arbitrary cost functions. In a limit when the control-cost approaches zero, this formulation becomes analytically solvable. The analysis reveals several important properties that are absent in traditional LQ anlysis. In particular, multiplicative noise makes optimal solutions depend on the global features of cost functions.

An optimal adaptive H-infinity tracking control design via wavelet network

In this paper, an optimal adaptive H-infinity tracking control design method via wavelet network for a class of uncertain nonlinear systems with external disturbances is proposed to achieve H-infinity tracking performance. First, an alternate tracking error and a performance index with respect to the tracking error and the control effort are introduced in order to obtain better performance, especially, in reducing the cost of the control effort in the case of small attenuation levels. Next, H-infinity tracking performance, which attenuates the influence of both wavelet network approximation error and external disturbances on the modified tracking error, is formulated. Our results indicate that a small attenuation level does not lead to a large control signal. The proposed method insures an optimal trade-off between the amplitude of control signals and the performance of tracking errors. An example is given to illustrate the design efficiency.

A new approach to model reference adaptive control

In classical model reference adaptive control, the goal is to design a controller to make the closed-loop system act like a prespecified reference model in the face of significant plant uncertainty. Typically, the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that asymptotic matching is achieved. However, the controller is typically highly nonlinear, and the closed loop system can exhibit undesirable behavior, such as large transients or a large control signal, especially if the initial parameter estimates are poor. Furthermore, its ability to tolerate time-varying parameters is typically limited. Here, we propose an alternative approach. Rather than estimating the plant or parameters, instead we estimate what the control signal would be if the plant parameters and plant state were known and the ideal LTI compensator were applied. We end up with a linear periodic controller. Our assumptions are reasonably natural extensions of the classical ones to the time-varying setting; we allow rapid parameter variations, although we add a compactness requirement. We prove that we can obtain arbitrarily good tracking, explore the benefits and limitations of the approach, and provide a simulation study.

A new approach to adaptive control: no nonlinearities

In adaptive control the goal is to design a controller to control an uncertain system whose parameters may be changing with time. Typically the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that good asymptotic behaviour is achieved, such as model matching (for minimum phase systems) or stability. However, a typical adaptive controller does not track time-varying parameters very well, and it is often highly nonlinear, which can result in undesirable behaviour, such as large transients or a large control signal. Furthermore, most adaptive controllers provide only asymptotic tracking, with no ability to design for a pre-specified settling time. Here we propose an alternative approach, which yields a linear periodic controller. Rather than estimating the plant or compensator parameters, instead we estimate what the control signal would be if the plant parameters were known. In this paper we argue the utility of this approach and then examine the first order case in detail, including a simulation. We also explore the benefits and limitations of the approach.

Enhanced direct adaptive fuzzy control of robot manipulators

In this article, an enhanced direct adaptive fuzzy robot controller is developed to overcome problems of high-frequency oscillations across the boundary of the constraint set and large control signals. The direct adaptive fuzzy robot control algorithm employs tracking errors of the joint motion to drive the parameter adaptation. The predominant concern of the adaptation law is to reduce the tracking errors, and closed-loop stability is ensured by appending a supervisory controller. This adaptive controller, appended with the supervisory controller, does not require the exact robot dynamics, but only the boundary of the dynamics. Theoretical results and simulation studies on a two-link robot manipulator show that by modifying the activation function of the supervisory controller, the enhanced direct adaptive fuzzy robot controller is as robust as before and the problems of high-frequency oscillations across the boundary of the constraint set and large control signals are alleviated. ©1999 John Wiley & Sons, Inc.

Optical timing, trigger and control distribution for LHC detectors

At CERN's future Large Hadron Collider, timing, trigger-accept and control signals must be distributed from a small number of sources to many thousands of front-end electronics destinations located on the ATLAS and CMS detectors. The LHC timing reference must be delivered with sub-nanosecond jitter and programmable phase. First-level trigger decisions must be broadcast from the central trigger processor to all the front-end pipeline controllers and delivered synchronously with the appropriate bunch identification, compensated for particle flight times and detector, electronics and propagation delays. In addition, broadcast control signals and individually-addressed controls and parameters such as calibration data have to be distributed. This paper describes how it is planned to broadcast all the signals over entirely passive multichannel optical fiber networks with uncontrolled path lengths. It reviews some of the technology options which are currently available and those which are likely to mature within the time frame of LHC preparation. It discusses how synchronization can be established over the system and describes how different distribution network configurations, laser transmitters and encoding methods can be used to deliver the signals using optoelectronic receivers which are becoming affordable for extensive deployment. >

Variance constrained self-tuning control

A self-tuning regulator for a variance constrained optimal control problem is given. The criterion for control is to minimize the stationary variance of the output. In the cases when the regulator which gives minimum variance requires too large control signals an inequality constraint on the input variance is introduced. In practice it is easier to select a constraint on the variance of the input than to choose the relative weights in a quadratic loss function. The self-tuning regulator applies the Robbins-Monro scheme to adjust the Lagrange multiplier of the variance constrained control problem. The behaviour of the algorithm is illustrated by a simulated example. The asymptotic behaviour of the regulator is studied using a set of associated ordinary differential equations.

Alternating current control of the half-wave bridge magnetic amplifier

RECENT developments in transistors indicate great promise for a high-gain, high-power-output servo amplifier consisting of a transistor preamplifier in combination with a fast-response half-wave bridge magnetic power amplifier. Existing literature on this type of magnetic amplifier does not discuss certain problems inherent in applying this device as an output stage fed by an a-c pre-amplifier.1,2 Among these are the problems of reduced output as a result of large control signals, and variation in operation caused by different types of load.