Volume 9, Number 5, 2012
The paper addresses the adaptive behaviour of parallel fuzzy proportional plus fuzzy integral plus fuzzy derivative (FP+FI+FD) controller. The parallel FP+FI+FD controller is actually a non-linear adaptive controller whose gain changes continuously with output of the process under control. Two non-stationary processes, whose characteristics change with time, are considered for simulation study. Simulation is performed using software LabVIEWTM. The set-point tracking response of parallel FP+FI+FD is compared with conventional parallel proportional plus integral plus derivative (PID) controller, tuned with the Ziegler-Nichols (Z-N) tuning technique. Simulation results show that conventional PID controller fails to track the set-point and becomes unstable as the process changes its characteristic with time. But the parallel FP+FI+FD controller shows considerably much better set-point tracking response and does not deviate from steady state. Also, a huge spike is observed in the output of PID controller as the reference set-point and process parameters are changed, while the FP+FI+FD controller gives spike free control signal.
A mobile satellite communication system (MSCS) is a device installed on a moving carrier for mobile satellite communication. It can eliminate disturbance and maintain continuous satellite communication when the carrier is moving. Because of many advantages of mobile satellite communication, the MSCSs are becoming more and more popular in modern mobile communication. In this paper, a typical ship-mounted MSCS is studied. The dynamic model of the system is derived using the generalized Lagrange method both in the joint space and in the workspace. Based on the dynamic model, a nonlinear computed torque controller with trajectory planning is designed to track an aimed satellite with a satisfied transient response. Simulation results in two different situations are presented to show the tracking performance of the controller.
In network service systems, satisfying quality of service (QoS) is one of the main objectives. Admission control and resource allocation strategy can be used to guarantee the QoS requirement. Based on partially observable Markov decision processes (POMDPs), this paper proposes a novel admission control model for video on demand (VOD) service systems with elastic QoS. Elastic QoS is also considered in resource allocation strategy. Policy gradient algorithm is often available to find the solution of POMDP problems, with a satisfactory convergence rate. Through numerical examples, it can be shown that the proposed admission control strategy has better performance than complete admission control strategy.
The mathematical models for dynamic distributed parameter systems are given by systems of partial differential equations. With nonlinear material properties, the corresponding finite element (FE) models are large systems of nonlinear ordinary differential equations. However, in most cases, the actual dynamics of interest involve only a few of the variables, for which model reduction strategies based on system theoretical concepts can be immensely useful. This paper considers the problem of controlling a three dimensional profile on nontrivial geometries. Dynamic model is obtained by discretizing the domain using FE method. A nonlinear control law is proposed which transfers any arbitrary initial temperature profile to another arbitrary desired one. The large dynamic model is reduced using proper orthogonal decomposition (POD). Finally, the stability of the control law is proved through Lyapunov analysis. Results of numerical implementation are presented and possible further extensions are identified.
This paper gives a novel delay-dependent admissibility condition of discrete-time singular systems with time-varying delays. For convenience, the time-varying delay is assumed to be the sum of delay lower bound and the integral multiples of a constant delay. Specially, if the constant delay is of unit length, the delay is an interval-like time-varying delay. The proposed admissibility condition is presented and expressed in terms of linear matrix inequality (LMI) by Lyapunov approach. Generally, the uncertainty of time-varying delay would lead to conservatism. In this paper, this critical issue is tackled by accurately estimating the time-varying delay. Consequently, the proposed admissibility condition is less conservative than the existing results, which is demonstrated by a numerical example.
This paper is concerned with the stabilization problem for a class of nonlinear systems with disturbance. The disturbance model is unknown and the first derivative of disturbance is bounded. Firstly, a general disturbance observer is proposed to estimate disturbance approximatively. Secondly, since the bound of the disturbance observer error is unknown, an adaptive sliding mode controller is designed to guarantee that the state of system asymptotically converges to zero and the unknown bound can be adjusted by an adaptive law. Finally, an example is given to illustrate the effectiveness of the proposed method.
For a sampled-data control system with nonuniform sampling, the sampling interval sequence, which is continuously distributed in a given interval, is described as a multiple independent and identically distributed (i.i.d.) process. With this process, the closed-loop system is transformed into an asynchronous dynamical impulsive model with input delays. Sufficient conditions for the closed-loop mean-square exponential stability are presented in terms of linear matrix inequalities (LMIs), in which the relation between the nonuniform sampling and the mean-square exponential stability of the closed-loop system is explicitly established. Based on the stability conditions, the controller design method is given, which is further formulated as a convex optimization problem with LMI constraints. Numerical examples and experiment results are given to show the effectiveness and the advantages of the theoretical results.
Considering the situation that the least-squares (LS) method for system identification has poor robustness and the least absolute deviation (LAD) algorithm is hard to construct, an approximate least absolute deviation (ALAD) algorithm is proposed in this paper. The objective function of ALAD is constructed by introducing a deterministic function to approximate the absolute value function. Based on the function, the recursive equations for parameter identification are derived using Gauss-Newton iterative algorithm without any simplification. This algorithm has advantages of simple calculation and easy implementation, and it has second order convergence speed. Compared with the LS method, the new algorithm has better robustness when disorder and peak noises exist in the measured data. Simulation results show the efficiency of the proposed method.
With the development of manufacturing, numerical control (NC) machining simulation has become a modern tool to obtain safe and reliable machining operations. Although some research and commercial software about NC machining simulations is available, most of them is oriented for GM code. It is a low-level data model for computer numerical control (CNC), which has inherent drawbacks such as incomplete data and lack of accuracy. These limitations hinder the development of a real simulation system. Whereas, standard for the exchange of product data-compliant numerical control (STEP-NC) is a new and high-level data model for CNC. It provides rich information for CNC machine tools, which creates the condition for an informative and real simulation. Therefore, this paper proposes STEP-NC based high-level NC machining simulations solution integrated with computer-aided design/computer-aided process planning/computer-aided manufacturing (CAD/CAPP/CAM). It turned out that the research provides a better informed simulation environment and promotes the development of modern manufacturing.
In this paper, the problem of increasing information transfer authenticity is formulated. And to reach a decision, the control methods and algorithms based on the use of statistical and structural information redundancy are presented. It is assumed that the controllable information is submitted as the text element images and it contains redundancy, caused by statistical relations and non-uniformity probability distribution of the transmitted data. The use of statistical redundancy allows to develop the adaptive rules of the authenticity control which take into account non-stationarity properties of image data while transferring the information. The structural redundancy peculiar to the container of image in a data transfer package is used for developing new rules to control the information authenticity on the basis of pattern recognition mechanisms. The techniques offered in this work are used to estimate the authenticity in structure of data transfer packages. The results of comparative analysis for developed methods and algorithms show that their parameters of efficiency are increased by criterion of probability of undetected mistakes, labour input and cost of realization.
With regard to the failure and cancellation of business logic of web services composition (WSC), this paper propose a novel web services transaction compensation mechanism based on paired net which can dynamically establish agile compensation-triggered process (CSCP-Nets), and satisfy prospective compensation requirements. The related execution semantics of five usual composition compensation patterns based on paired net are analyzed in the situations of successful execution, failure compensation and failure recovery. Paired net based application of trip reservation process (TRP) shows that it is feasible.
To overcome the disadvantages of the location algorithm based on received signal strength indication (RSSI) in the existing wireless sensor networks (WSNs), a novel adaptive cooperative location algorithm is proposed. To tolerate some minor errors in the information of node position, a reference anchor node is employed. On the other hand, Dixon method is used to remove the outliers of RSSI, the standard deviation threshold of RSSI and the learning model are put forward to reduce the ranging error of RSSI and improve the positioning precision effectively. Simulations are run to evaluate the performance of the algorithm. The results show that the proposed algorithm offers more precise location and better stability and robustness.
In this paper, adaptive dynamic surface control (DSC) is developed for a class of nonlinear systems with unknown discrete and distributed time-varying delays and unknown dead-zone. Fuzzy logic systems are used to approximate the unknown nonlinear functions. Then, by combining the backstepping technique and the appropriate Lyapunov-Krasovskii functionals with the dynamic surface control approach, the adaptive fuzzy tracking controller is designed. Our development is able to eliminate the problem of explosion of complexity inherent in the existing backstepping-based methods. The main advantages of our approach include: 1) for the n-th-order nonlinear systems, only one parameter needs to be adjusted online in the controller design procedure, which reduces the computation burden greatly. Moreover, the input of the dead-zone with only one adjusted parameter is much simpler than the ones in the existing results; 2) the proposed control scheme does not need to know the time delays and their upper bounds. It is proven that the proposed design method is able to guarantee that all the signals in the closed-loop system are bounded and the tracking error is smaller than a prescribed error bound, Finally, simulation results demonstrate the effectiveness of the proposed approach.
A quad-rotor aircraft is an under-actuated, strongly coupled nonlinear system with parameter uncertainty and un-modeled disturbance. In order to make the aircraft track the desired trajectory, a nested double-loops control system is adopted in this paper. A position error proportional-derivative (PD) controller is designed as the outer-loop controller based on the coupling action between rotational and translational movement, and an adaptive backstepping sliding mode control algorithm is used to stabilize the attitude. Finally, both the numerical simulation and prototype experiment are utilized to demonstrate the effectiveness of the proposed control system.