Online process estimation using fuzzy logic for dead time compensator design

A novel active disturbance rejection control (ADRC) solution and a particular tuning method are presented for a class of time delay system (TDS) with uncertainty. First, the complicated process dynamics is modeled as a simple first order plus large time delay (FOPTD) plant, with the difference between the actual dynamics and its model treated as disturbances to be rejected. Then the reduced order linear extended state observer (RLESO) with input delay is proposed to estimate the time delay state and disturbance. It is shown how the time delay could be eliminated from the characteristic equation of the closed-loop system by manipulations of controller parameters. Secondly, the one parameter tuning (OPT) technique is developed where all controller parameters are made function of a single coefficient. In comparison with optimal proportional-integral-derivative (PID) controller and twice optimum controller (TOC), the simulation results show that the proposed method not only has better accuracy and faster response, but also ensures better robustness and adaptability against uncertain model parameters and external disturbances, especially for the plant with very large time delays.

The modified Smith predictor is well known as an effective time-delay compensator for a plant with large time delays, and several papers on the modified Smith predictor have been published. The parametrization of all stabilizing modified Smith predictors for minimum-phase time-delay plants is obtained by Yamada and Matsushima. In addition, Yamada et al. expanded the result by Yamada and Matsushima and proposed the parametrization of all stabilizing modified Smith predictors for non-minimum-phase time delay plants. However, no paper examines the parametrization of all stabilizing 2-degree-of-freedom modified Smith predictors that can specify the input-output characteristic and the feedback characteristic separately. From the practical point of view, it is desirable that the input-output characteristic and the feedback characteristic are specified separately. In this paper, we propose the parametrization of all stabilizing 2-degree-of-freedom modified Smith predictors for time-delay plants that can specify the input-output characteristic and the feedback characteristic separately.

In this paper, we examine a design method for a modified Smith predictor for a class of non-minimum-phase time-delay plants. The modified Smith predictor is well known as an effective time-delay compensator for a plant with large time delays. Several papers on the modified Smith predictor have been published. However, the parametrization of all stabilizing modified Smith predictors has not been obtained. The purpose of this paper is to propose the parametrization of all stabilizing modified Smith predictors for a class of non-minimum-phase time-delay plants and present a design method of modified Smith predictors. At first, the definition of modified Smith predictor is given. Next, we propose the parametrization of all stabilizing modified Smith predictors for a class of non-minimum-phase system which is not necessarily stable. The control characteristics of the control system using the parametrization of all stabilizing modified Smith predictors are also given. The obtained parametrization of all stabilizing modified Smith predictor has a free-parameter which is used to specify control specification. Next, in order to specify input-output characteristics, we present a design method of modified Smith predictor using the fusion of obtained parametrization of all stabilizing modified Smith predictors and the model matching methods. Finally, a numerical example for unstable plant is illustrated to show the effectiveness of the proposed method.

Bifurcation analysis on a turning system with large and state-dependent time delay

Time delay is an important issue when dealing with control system design and analysis in mechanical, aerospace and civil engineering. The unavoidable existence of time delays will hamper the controller, and even amplify undesired responses. It is difficult to design a controller that compensates for the influence of large time delays. Accordingly this study will investigate the design of, and experimental verification of, controllers that take into account such time delays. A single-degree-of-freedom system was analyzed and time delay compensated velocity and displacement feedback control algorithms were designed. Additionally, a new method was developed to take advantage of the time delay when large time delays occur. A one story shear-type structure was set up to experimentally verify the proposed time-delayed control algorithms. Numerical simulation and experimental results demonstrated that the proposed time-delayed control algorithm was effective in reducing the maximum response of the system and that the system stability can be guaranteed despite large time delays.

The modified Smith predictor is well known as an effective time-delay compensator fora plant with large time-delays, and several papers on the modified Smith predictor have been published.Recently, the parameterization of all stabilizing modified Smith predictors for time-delay plantswas obtained by Yamada et al. But, their method cannot specify the input-output characteristic andthe feedback characteristic separately. From the practical point of view, it is desirable that the inputoutputcharacteristic and the feedback characteristic are specified separately. In this paper, we proposethe parameterization of all stabilizing two-degree-of-freedom modified Smith predictors for multipleinput/multiple-output time-delay plants.

In this paper, a new strategy for robust control of temperature in a steel slab reheating furnace with large time delay uncertainty based on fractional-order controllers combined with a Smith predictor is proposed. A time delay model of the preheating zone of this process is used, obtained from an identification procedure applied in a real industrial furnace. It is shown that this process experiences very large time delay changes. A fractional-order integral controller embedded in a Smith predictor structure (FI-SP) is designed, which is robust to changes in such time delay. Simulated results of a standard Proportinal Integral Derivative (PID) controller, a PID controller embedded in a Smith predictor and the proposed FI-SP controller are compared. Six performance indexes have been used in this comparison. The analysis of these indexes shows that the designed FI-SP controller exhibits the most robust behavior (lowest indexes averaged in all the range of time delay variation) for ranges that include large time delays. Then the robustness features of the FI-SP controller outperform the other integer order controllers in the time responses both to set-point changes and to step disturbances. Therefore, this controller guarantees the best accuracy of temperature control. The designed FI-SP guarantees system stability and robust performance for a high range of plant time delay uncertainties.

When developing a wide class of on-line parameter estimation scheme for estimating the unknown parameter vector that appears in certain general linear and bilinear parametric model will be parametrizations of LTI processes or plants as well as of some special classes of nonlinear processes or plants. The resuls is used to design one of the important tools in control, i.e., adaptive observer and for stable LTI processes or plants. In this paper it will consider the design of schemes that simultaneously estimate the plant state variables and parameters by processing the plant I/O measurements on-line and such schemes is refered to as adaptive observers. The design of an adaptive observer is based on the combination of a state observer that could be used to estimate the state variables of aparticular plant state-space representation with an on-line estimation scheme. The choice of the plant state-space representation is crucial for the design and stability analysis of the adaptive observer. The paper will discuss a class of observer called Adaptive Luenberger Observer and its application. Begin with observable canonical form one can find observability matrix of n linear independent rows. By using this fact or their linear combination chosen as a basis, various canonical forms known also as Luenberger canonical form can be obtained. Also,this formation will leads to various algorithm for computing including computation of observable canonical form, observable Hessenberg form and reduced-order state observer design.

Stabilization Strategy for Unstable First Order Linear Systems with Large Time Delay

Нестационарное запаздывание установления нелинейных колебаний в системе двух связанных осцилляторов. Часть 3. Определяющее уравнение.

The light curves of solar coronal loops often peak first in channels associated with higher temperatures and then in those associated with lower temperatures. The delay times between the different narrowband EUV channels have been measured for many individual loops and recently for every pixel of an active region observation. The time delays between channels for an active region exhibit a wide range of values. The maximum time delay in each channel pair can be quite large, i.e., >5000 s. These large time delays make-up 3%–26% (depending on the channel pair) of the pixels where a trustworthy, positive time delay is measured. It has been suggested that these time delays can be explained by simple impulsive heating, i.e., a short burst of energy that heats the plasma to a high temperature, after which the plasma is allowed to cool through radiation and conduction back to its original state. In this paper, we investigate whether the largest observed time delays can be explained by this hypothesis by simulating a series of coronal loops with different heating rates, loop lengths, abundances, and geometries to determine the range of expected time delays between a set of four EUV channels. We find that impulsive heating cannot address the largest time delays observed in two of the channel pairs and that the majority of the large time delays can only be explained by long, expanding loops with photospheric abundances. Additional observations may rule out these simulations as an explanation for the long time delays. We suggest that either the time delays found in this manner may not be representative of real loop evolution, or that the impulsive heating and cooling scenario may be too simple to explain the observations, and other potential heating scenarios must be explored.

It is difficult to identify the unstable processes with time delay, especially with large time delay. In this paper, a new relay feedback identification method for open-loop unstable processes with time delay is proposed. The exact expressions for the periods and amplitudes of limit cycles under the biased relay feedback are derived for unstable processes which can be modeled by first-order plus dead-time dynamics. Furthermore, for the unstable processes with large time delay, an additional PD controller is incorporated in the relay feedback system to relax the constraint on the ratio of delay to the unstable time constant, so that the exact model parameters of unstable processes can be identified. The numerical simulation examples demonstrate the validity of the proposed identification method.

For complex systems with time-varying, nonlinearity, and large time delay, the IMC-PID controller designed using the internal mode control strategy can be used to improve the control performance. Different setting formulas for IMC-PID controller parameters can be obtained by using different approximation methods for processing the time-delay process. These methods have a great influence on the control effect. The first-order Taylor, the first-order Pade, the second-order symmetric Pade and the second-order asymmetric Pade and all-pole approximation are used to obtain the parameter setting formulas, respectively. Their adaptabilities to large time-delay, large-inertia process and to large time-delay, small-inertia process are studied. The simulation results show that the all-pole approximation is more adaptive to the application of large time delay. The second-order symmetric Pade approximation is more effective in the large time-delay, small-inertia process, whereas the second-order asymmetric Pade approximation is more adaptive to large time-delay, large-inertia process.

Auto-tuning of fuzzy logic controllers for self-regulating processes

Series elastic actuation for improved transparency in time delayed haptic teleoperation