Static Decoupling Research Articles

Continuous Time Identification and Decentralized Pid Controller of an Aerothermic Process

Abstract The interactions between input/output in multivariable processes represent a major challenge in the design of decentralized controllers. In this paper, a simple method for the design of decentralized PID controller is proposed. It consists to combine the conventional PID controller with the static decoupler approach. For each single loop, the individual controller is independently designed by applying the internal model control (IMC) tuning rules. To demonstrate the effectiveness of the proposed method, the PID controller with and without decoupling is implemented on an aerothermic process. It is a pilot scale heating and ventilation system equipped with a heater grid and a centrifugal blower, fully connected through the Humusoft MF624 data acquisition system for real time control. The outcome of the experimental results is that the main control objectives, such as set-point tracking and interactions rejection are well achieved. The experimental results have shown that the proposed method provides a significant improvement compared to conventional PID controller.

Research on Non-Linear Decoupling for Multi-Dimensional Force Sensor

Based on the integrated design of structure, multi-dimensional force sensor has severe dimension coupling interference. Besides, two-order non-linear coupling error exists generally. This paper focuses on a six-axis force sensor of strain gauge balance, and uses a P normative decoupling network to compute the decoupling matrix. Then the static non-linear decoupling parameters are solved by multi-step least square so that the morbidity in the process of computing the decoupling matrix is avoided.

Minimizing cross-talk in high-precision motion systems using data-based dynamic decoupling

To minimize cross-talk in high-precision motion systems, the possibilities of data-based dynamic decoupling are studied. Atop a model-based and static decoupling, a multi-input multi-output (MIMO) and finite impulse response (FIR) dynamic decoupling structure is considered for machine-specific and performance-driven fine tunings. The coefficients of the FIR filters are obtained via data-based optimization, whilst the machine operates under nominal and closed-loop conditions. The FIR filters provide the ability to generate zeros outside the origin. These zeros are needed in the description of the low-frequency inverted plant dynamics. In addition, a low-pass filter structure supports the ability to generate poles outside the origin as to account for plant zeros. Both filter structures are effectively used in the high-precision motion control of a state-of-the-art scanning stage system and an industrial vibration isolation system.

A new control method for MIMO first order time delay non-square systems

This paper proposes a new method using internal model control (IMC) to design Smith delay compensation decoupling controller for multivariable non-square systems with transfer function elements consisting of first order + time delay. This proposed method is applied to a shell control problem in multiple-input–multiple-output (MIMO) first order plus dead time non-square systems in which the number of input variables exceeds the number of output variables, with input and output variables being 3 and 2 respectively. This method does not only dynamically compensate for shortcoming caused by static decoupling but also overcomes the impact of model error on system performance caused by model approximation and uncertainty. In other words, the design method proposed in this paper is capable of significantly improving dynamic quality and robustness of the control system as can be seen from the simulation results. Moreover, this new method is simple and easy to implement. Integral of squared error (ISE) performance criterion is employed to quantitatively evaluate the design method.

Optimal Static Decoupling for the Decentralized Control: an Experimental Study

AbstractA three Degrees-Of-Freedom (DOF) vibration isolation system with a certain degree of symmetry shows significant cross coupling. The decentralized control is intended and it demands excellent decoupling performance. The Vaes optimization algorithm is applied to find the optimal static decoupling matrices. However, experiments show that the measured μ interaction measure is not consistent with calculation results and thus not optimized. An iterative procedure based on the Vaes algorithm is proposed to obtain the optimal static decoupling matrices. The Vaes algorithm is also modified to improve the numerical stability and to speed up the optimization process. The proposed iterative procedure and the modified Vaes optimization algorithm are validated on the 3-DOF vibration isolation system.

Multivariable control with adjustment by decoupling using a distributed action approach in a distillation column

Abstract Abstract This paper presents an approach which uses a multivariable control strategy with distributed action in order to minimize operation transients in distillation columns when a disturbance in the temperature feed is introduced. Experiments were carried out adjusting multivariable PID controllers by static decoupling of the temperature loops of the bottom and distillate trays, characterizing a 2 × 2 system. The dynamics was compared to the distributed approach (same controllers on the bottom and top and an additional control loop on a tray). The controllers adjustment of this new system (3 × 3) was carried out considering the temperature control loop stage in two different ways: decentralized and coupled with the bottom and top temperature control loops. The minimization of transients was verified in both distributed approaches.

A DESIGN OF MULTILOOP PID CONTROLLERS WITH A NEURAL-NET BASED DECOUPLER

In process industries, PID control schemes have been widely used due to their simple structures and easiness of comprehending the physical meanings of control parameters. However, the good control performance cannot be obtained by simply using PID controlschemes, since most processes are considered as nonlinear multivariable systems with mutual interactions. In this paper, a design method of multiloop PID controllers neural-net based decoupler is proposed for nonlinear multivariable systems with mutual interactions. The proposed method consists of a decoupler given by the sum of a static decoupler and a neural-net based decoupler, and multi-loop PID controllers. Finally, the effectiveness of the proposed control scheme is evaluated on the simulation examples.

POLE-ASSIGNMENT BASED SELF-TUNING PID CONTROLLERS FOR MULTIVARIABLE SYSTEMS WITH UNCERTAIN TIME-DELAYS

PID control schemes have been widely still used in process industries. However, the good control performance can not be obtained by simply using PID control schemes, since most processes are considered as multivariable systems with mutual interactions, time variation, and uncertain time-delays. In this paper, pole-assignment based self-tuning PID control system is newly proposed for multivariable systems whose system parameters and time-delays can not be exactly obtained beforehand. Then, the proposed PID control system is composed of a static decoupler, improved Smith compensators, pole-assignment based PID gain tuners and recursive parameter estimators. Finally, the effectiveness of the proposed control scheme is evaluated on a simulation example.

Feedback Approach for Reproduction of Field Measurements on a Hydraulic Four Poster

The study of vibrations in agriculture is performed to assess the efficiency of machinery, lifetime of components, drivers’ comfort, damage of crop during harvest and transport. An important source of vibrations is the soil. Owing to the stochastic character and visco-elastic behaviour of the soil, it is very difficult to create repeatable testing conditions. Experiments on vibration test rigs, also called shakers, in combination with time waveform replication (TWR) can solve this problem. The objective of TWR is to determine the inputs to the shakers in order to obtain the same sensor readings as during the field experiments. The classical TWR method consists of an iterative procedure that can be time consuming. This paper presents a feedback approach, thereby reducing the number of iterations. As in general, several sensor signals need to be reproduced, a multiple-input multiple-output (MIMO) controller needs to be designed, which is often a time consuming and difficult process. A methodology based on static decoupling is introduced such that the MIMO controller design reduces to the synthesis of several single-input, single-output (SISO) controllers. Experiments on a tractor indicate that with the present procedure, compared to the classical TWR procedure, the number of iterations can be reduced and a better accuracy can be achieved.

Comparison of Different Multivariable Control Design Methods Applied on Half Car Test Setup

The multivariable tracking accuracy on an automotive vibration test rig can be improved by extending the current industrial off-line iterative feedforward procedure with a real time feedback controller. This article compares three MIMO feedback control design procedures with respect to design complexity and obtained performance: (1) DK-iteration, the most common μ-synthesis method to design robust MIMO-controllers, (2) a control design based on static decoupling, which is a combination of a static input – output transformation to decouple the system, and independent SISO-controllers designed for the diagonal elements of the transformed system and (3) an inverse-based control design, which is also based on a decoupling transformation, but the decoupling is performed by a dynamic precompensator. The performance of these controllers is compared experimentally on a half car test setup. The tracking performance of the controller designs based on static or dynamic decoupling is comparable with the performance of the controller based on μ-synthesis. The decoupling-based controller designs, using standard SISO H∞ techniques, are however much simpler and more straightforward.

Multivariable feedback design to improve tracking performance on tractor vibration test rig

The multivariable tracking accuracy on an automotive vibration test rig can be improved by extending the current industrial off-line iterative feedforward procedure with a real-time multiple-input-multiple-output (MIMO) feedback controller. This paper shows that for the considered 4 × 4 application, the two most common approaches, namely full MIMO identification and μ -synthesis on one hand and decentralised control on the other hand fail to design a robust MIMO controller with acceptable performance. Therefore, a control design based on static decoupling is applied. This is a combination of (1) a transformation of the inputs and the outputs to decouple the system, and (2) independent single-input-single-output (SISO) controllers designed for the diagonal elements of the transformed system, using standard SISO identification and H ∞ -techniques. To optimise the closed-loop performance, a new decoupling algorithm is developed. The new presented algorithm outperforms the existing decoupling algorithms, yielding satisfactory multivariable closed-loop performance.

Static decouplers for control of multivariable processes

AbstractDecouplers can be used to improve performances of multiloop control systems by compensating for process interactions, but they are sensitive to process changes and require fairly detailed process models, which are hard to obtain. These disadvantages of decouplers hinder their successful applications in industry. On the other hand, static decouplers can be designed from process steady‐state gains, which are easier to obtain and can be tuned in the field. However, static decouplers can introduce undesirable effects on loop interactions at high frequencies for some processes. Here it is shown that static decouplers are better applied to the integral control modes for such processes. Because the integral mode is dominant at low frequencies and its magnitude decreases as frequency increases, the static decoupler implemented only on the integral mode will not disturb the frequency response of a control system at high frequencies. A simple antireset windup scheme, guaranteeing given control performances under process input saturations or failures, is provided. For online tuning of the proposed control system, a closed‐loop identification method to find process steady‐state gains is also presented. © 2005 American Institute of Chemical Engineers AIChE J, 2005

A Neural-Net based PID Controllers for Nonlinear Multivariable Systems

In process industries, PID control schemes have been popular because of their simple structures and ease of comprehension of the physical meanings of the control gains. However, good control performance cannot be obtainedby simply using PID control schemes, as most processes are considered as nonlinear multivariable systems with mutual interactions. The authors propose a design method of neural-net based PID controllers for nonlinear multivariable systems with mutual interactions. The proposed method consists of a static decoupler that plays a role of roughly decoupling the controlled object, multiloop PID controllers, and some multilayered neural networks used in order to improve decoupling and linearize the approximately decoupled controlled object. Finally, the effectiveness of the proposed control scheme is evaluated on some simulation examples.

Application of Total Least Square Algorithm in Static Decoupling of NGMIMU

The linear coupling of Non-gyro Micro Inertial Measurement Unit (NGMIMU) is a kind of system error that affects the accuracy of measurement seriously. In this article, the author puts forward a new linear decoupling algorithm which simultaneously considers the error of standard input signal and output of accelerators when the coupling parameters are calculated. The Total Least Square (TLS) solutions of coupling parameters own the minimum characteristic to the input and output values. Then these parameters are used to reconstruct the outputs of accelerators so as to realize the decoupling. The emulation result show that the ratio of decoupling error is less than 8% and verify the feasibility of this algorithm.

385. 大型高速炉炉心の核的ディカップリング特性

It was made clear by critical experiments (called JUPITER) that nuclear characteristics of large-sized fast reactor cores were quite different from those of small-sized cores. For instance, radial neutron flux distributions are significantly changed by perturbations, control rod reactivity interaction effects are large, etc. These phenomena are interpreted to be commonly caused by the spatial neutronic decoupling of large core. The changeability and instability of flux distribution, which might cause a power peaking and a flux tilting, is a new problem for the development of large core. The paper shows measured results of static decoupling characteristics, interprets them physically, and considers a reactor physics system of large core. The paper also investigates a nuclear core design method, in which the decoupling characteristics are taken into account. A neutronic stability is a new requirement for the nuclear design of large core, which the design policy is to promote and secure together with the performance and the safety. The more tightly coupled the core, i.e., the smaller the degree of decoupling, the better the neutronic stability.

Design of decoupled PI controllers for two-by-two systems

The design of PI controllers for systems with interacting loops is discussed. It is advantageous to deal with the interaction at the loop level, because supervisory control seldom has sufficient bandwidth. A new scheme based on modified scalar PI design and static decoupling is developed, in which the frequency characteristic of the coupling between the lower-level loops is taken into account. This leads to a design method emphasising the trade-off between the individual loop performances and the interaction indices introduced in the paper. The controller is easily implemented, due to its simple configuration based on standard components. A useful observation is that the interaction can be reduced substantially by using set-point weighting. The method is applied to three examples, including a model of a new laboratory system called the quadruple-tank process.

Nonlinear decoupling method in the case of fast varying parameters

Static and dynamic state feedback decoupling and linearization methods are presented in the case of fast varying parameters. The computation of the static and dynamic feedback laws are given in the case of nonlinear decoupling, linearization and rejection of perturbations. An example in robotics is given.

Advanced Control of an Industrial Closed-Loop Grinding Circuit

This paper gives an industrial application of advanced control strategies using basic functions available in distributed control systems (DCS). The process under study is an industrial full-scale closed-loop grinding circuit where pulp solid mass fraction is to be controlled at the mill and at the cyclones. An algebraic implementation of a Kalman filter is used to evaluate the unmeasured pulp solid mass fraction at the mill discharge using mass balance relations. A static decoupler is used to eliminate the interaction between the two controlled variables. Open-loop adaptation is used to take into account the non-linearity of the process in conjunction with an internal model controller.

Experimental evaluation of a multivariable adaptive nonlinear predictive controller

Abstract A new multivariable adaptive nonlinear predictive controller is designed using a general nonlinear input-output model and variable transformations. The controller is similar in form to typical linear predictive controllers can be tuned analogously or by specifying a single parameters for each controlled variable. In addition, the design procedure is computationally efficient. The new controller is compared to a multi-loop proportional-integral (PI) controller with one-way static decoupling and to an adaptive linear predictive controller through tests on a simulated nonlinear distillation column. The new controller performed well in an experimental application to a multicomponent distillation column.

New results about Morgan's problem

Some aspects of the nonsquare Morgan's problem are considered. In particular, it is shown that the condition given by J. Descusse et al. (1986) to solve this problem is not sufficient. It is also shown that the essential orders are not necessarily preserved in the static decoupling problem. A necessary and sufficient condition for static decoupling of a system without modifying the essential orders is given for the case k=p-1. where p is the number of outputs and k is the rank at infinity of the proper part of the interactor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>