MODEL-BASED FUZZY LOGIC CONTROL OF A NONLINEAR PLANT

A full-envelope controller for nonlinear systems is developed based on a novel model-based fuzzy logic control (MBFLC) approach. This approach envisages a bank of linear compensators, with each compensator optimized for a different operating point throughout the operational envelope. The fuzzy logic module properly blends the compensator outputs into a composite control signal, and avoids instability when none of the individual compensators are valid. In general practice, in the strongly nonlinear system under consideration, the fuzzy element of the MBFLC dominates due to the extremely small regions of validity of perturbation models of the strongly nonlinear plant. The MBFLC, with the composite control input smoothed by a linear compensator, provides full-envelope control of the benchmark plant. © 1997 by John Wiley & Sons, Ltd. This paper was produced under the auspices of the US Government and it is therefore not subject to copyright in the US.     

Some results in nonlinear QFT

Nonlinear QFT (quantitative feedback theory) is a technique for solving the problem of robust control of an uncertain nonlinear plant by replacing the uncertain nonlinear plant with an ‘equivalent’ family of linear plants. The problem is then finding a linear QFT controller for this family of linear plants. While this approach is clearly limited, it follows in a long tradition of linearization approaches to nonlinear control (describing functions, extended linearization, etc.) which have been found to be quite effective in a wide range of applications. In recent work, the authors have developed an alternative function space method for the derivation and validation of nonlinear QFT that has clarified and simplified several important features of this approach. In particular, single validation conditions are identified for evaluating the linear equivalent family, and as a result, the nonlinear QFT problem is reduced to a linear equivalent problem decoupled from the linear QFT formalism. In this paper, we review this earlier work and use it in the development of (1) new results on the existence of nonlinear QFT solutions to robust control problems, and (2) new techniques for the circumvention of problems encountered in the application of this approach. Copyright © 2001 John Wiley & Sons, Ltd.     

FLEXIBLE FUZZY PRIORITY SCHEDULING OF THE CAN BUS

With the increasing complexity of distributed real‐time systems, the need for improved CAN bus performance is continually increasing. Normally, a scheduling scheme with static‐priority has low network schedulability/utilization; while using dynamic priority will improve the QoS of the network at the cost of a narrow service range or a high overhead, compared with the fixed priority scheduling schemes. Actually, because of the fluctuation of network traffic, these priority policies may not guarantee flexibility for different kinds of messages. Based on the broadcast nature of the CAN bus, a closed‐loop fuzzy scheduling scheme is proposed in this paper. Compared with the dynamic priority schemes, this fuzzy scheduling scheme uses fewer bits to encode fewer priority levels, which widens the service range of the network without increasing overhead. Based on game theory, a fuzzy parameter updating algorithm for the fuzzy scheme is developed to improve the adaptation of the scheme, which guarantees the required QoS of the network even with traffic fluctuation. Simulation results well demonstrate the abilities of the fuzzy scheme to guarantee high schedulability for real‐time messages, as well as the fairness and the same QoS for non‐real‐time messages in networks.     

Interval QFT: a mathematical and computational enhancement of QFT

The paper presents an overview of a mathematical and computational enhancement of Horowitz's QFT design procedure. The enhancement uses methods of interval analysis and is called as interval QFT, or IQFT. IQFT addresses and solves some of the fundamental issues in QFT, concerning selection of design frequencies, selection of controller phases in bound generation, approximation of plant templates with finite plant sets, and generation of plant templates and controller bounds with reliability and to a prescribed accuracy. An example is presented to illustrate the key features of IQFT. Copyright © 2002 John Wiley & Sons, Ltd.     

APPLICATION OF QFT TO CONTROL SYSTEM DESIGN—AN OUTLINE FOR ENGINEERS

Control system design is an interdisciplinary and multistage process, and is not a sub-area of mathematics but rather an engineering endeavour. It behoves the engineer to reduce the real world control task to a tractable mathematical problem. The required simplifying assumptions and the attendant mathematical modelling effort require sound engineering knowledge and judgement. Furthermore, the mathematical solution of the control problem needs to be implemented, and the validity and applicability of the modelling assumptions need to be verified, by the engineer. Hence, in this paper the process of applying the QFT robust control system design method is presented from this broad perspective and it is shown that it is uniquely suited to address and solve engineering control system design problems. © 1997 by John Wiley & Sons, Ltd. This paper was produced under the auspices of the US Government and it is therefore not subject to copyright in the US.     

采掘机器人的模糊监督——神经网络控制器技术

介绍一种基于规则的自学习神经网络控制器在采掘机器人上的应用。它根据实时执行的结果，采用多步学习－模糊监督学习方法，修正神经网络的教师信号，使控制算法简化，提高了计算的实时性，加快了学习速度实验验证了采用该方法取得的一些结果。     

FAULT TOLERANT CONTROL SYSTEM: QFT DESIGN

This paper addresses flight control system synthesis and the accommodation of controlled plant variation in an aircraft design envelope by using the frequency domain based quantitative feedback theory (QFT) robust control system design method. Plant variations considered include varying flight conditions in the flight envelope and damage to aerodynamic control surfaces. A robust flight control system is designed for the aircraft's longitudinal and lateral directional channels and validated with simulations containing nonlinear saturation elements. © 1997 by John Wiley & Sons, Ltd. This paper was produced under the auspices of the US Government and it is therefore not subject to copyright in the US.     

一类模糊非线性系统自适应输出反馈控制

针对一类未知非线性系统,利用模糊逻辑系统、H∞控制和高增益观测器,提出了一种模糊自适应输出反馈控制方法.证明了所设计的输出反馈控制器可以获得状态反馈控制器的性能.仿真结果证明了所提出方法是有效的.     

弹性飞机的QFT控制器设计

以某弹性飞机纵向模型为例,考虑模型的不确定性及外部扰动,应用定量反馈理论设计了其俯仰姿态保持系统.仿真结果表明,利用该理论方法设计的控制器能很好地抑制弹性飞机的结构弹性变形,具有良好的鲁棒性,并取得了满意的控制效果,证明了该方法在弹性飞机控制律设计中的有效性和实用性.     

Simultaneous meeting of robust control specifications in QFT

Simultaneous meeting of different‐nature feedback control specifications requires special attention, particularly in the presence of uncertainties. This paper introduces some ideas to obtain a feasible set of QFT bounds, analysing the compatibility of the desired control specifications and the model uncertainty. It studies general robust feedback requirements and their mapping on QFT bounds through quadratic inequalities. Analysing them, it is possible to infer the bound typology with dependence on the model of each particular specification and the uncertainty size. Two bound typologies (amongst three categories: upper, outer and lower bounds) are possible for each type of control objective. On this basis, some general hints are established to guarantee compatible bounds at each frequency, before designing the controller. Copyright © 2003 John Wiley & Sons, Ltd.     

ECOLOGICAL SYSTEMS CONTROL BY FUZZY LOGIC CONTROLLER

The application of fuzzy logic control in the long‐term management of an ecological system is proposed. The ecological systems are subject to unpredictable but bounded disturbances due to changes in climatic conditions, disease, migrating species, etc. By applying the fuzzy logic controller, the biomasses of exploited and continually disturbed ecological systems will converge in a comparatively short time and keep the biomasses within a small neighborhood of the unique nontrivial optimal equilibrium state of the undisturbed exploited ecosystem. Demonstration through examples reveals that the accumulated yield with fuzzy logic control is better than that with state feedback control or no control.     

一类时变非线性系统的参数反馈模糊控制器分析与设计

本文针对工业控制中一类常见的非线性时变系统，提出了一种利用参数反馈在线修正 规则的模糊控制器；在全面介绍控制器结构与功能的同时，详细阐述了模糊规则修正器的原 理和设计方法，并采用基于功能评价的方法进行系统分析．在这个控制系统中，基本模糊控 制器简单实用；模糊规则修正器能充分利用对被控对象的分析成果；GA寻优算法能进一步简 化设计，提高性能．仿真结果表明，这种控制器的效果是令人满意的．     

Simultaneous automated design of structured QFT controller and prefilter using nonlinear programming

This paper describes a nonlinear programming‐based robust design methodology for controllers and prefilters of a predefined structure for the linear time‐invariant systems involved in the quantitative feedback theory. This controller and prefilter synthesis problem is formulated as a single optimization problem with a given performance optimization objective and constraints enforcing stability and various specifications usually enforced in the quantitative feedback theory. The focus is set on providing constraints expression that can be used in standard nonlinear programming solvers. The nonlinear solver then computes in a single‐step controller and prefilter design parameters that satisfy the prescribed constraints and maximizes the performance optimization objective. The effectiveness of the proposed approach is demonstrated through a variety of difficult design cases like resonant plants, open‐loop unstable plants, and plants with variation in the time delay. Copyright © 2016 John Wiley & Sons, Ltd.     

基于客户满意度的模糊调度模型及其应用

本文对有时间窗的调度问题进行了分析,针对传统模型不能表达调度问题中所存在 的不确定因素,无法利用人的经验知识的缺点,提出了基于模糊理论的调度模型．本模型考 虑了调度中存在的不确定因素,并以各个客户的满意度作为目标函数,运用遗传算法求解, 确定有多个任务同时要求服务时的调度策略．最后作为一个实例,将本文提出的基于客户满 意度的模糊调度模型应用于某混凝土公司的调度,取得了满意的结果,验证了模型的可行性 ．     

Analytical formulation to compute QFT bounds: The envelope method

This paper describes an analytical formulation to compute quantitative feedback theory (QFT) bounds in one‐degree‐of‐freedom feedback control problems. The new approach is based on envelope curves and shows that a QFT control specification can be expressed as a family of circumferences. Then, the controller bound is defined by the envelope curve of this family and can be obtained as an analytical function. This offers the possibility of studying the QFT bounds in an analytical way with several useful properties. Gridding methods are avoided, resulting in a lower computational effort procedure. The new formulation improves the accuracy of previous methods and allows the designer to calculate multivalued bounds. Copyright © 2009 John Wiley & Sons, Ltd.     

基于多环QFT的高超声速飞行器鲁棒控制

阐述了定量反馈理论(QFT)的基本原理和设计方法,针对超燃冲压发动机不同工作状态时高超声速飞行器不确定性模型,应用多环QFT设计了高超声速飞行器纵向飞行控制系统;仿真结果表明,运用QFT方法设计的控制系统不仅具有良好的跟踪性能和抗干扰性能,而且能够很好地解决飞行控制系统由于模型参数具有不确定性而造成的控制系统鲁棒性设计问题,并从工程应用角度为高超飞行器纵向飞行控制系统提供了一种鲁棒控制设计方案。     

Efficient algorithm for computing QFT bounds

This article presents an efficient algorithm for computing quantitative feedback theory (QFT) bounds for frequency-domain specifications from plant templates which are approximated by a finite number of points. To develop the algorithm, an efficient procedure is developed for testing, at a given frequency, whether or not a complex point lies in the QFT bound. This test procedure is then utilised along with a pivoting procedure to trace out, with a prescribed accuracy or resolution, the boundary of the QFT bound. The developed algorithm for computing QFT bounds has the advantages that it is efficient and can compute QFT bounds with multi-valued boundaries. A numerical example is given to show the computational superiority of the proposed algorithm.     

A QFT SUBSONIC ENVELOPE FLIGHT CONTROL SYSTEM DESIGN

An aircraft's response to control inputs varies widely throughout its full flight envelope. Furthermore, the aircraft configuration impacts control response through variations in centre of gravity and moments of inertia. Quantitative feedback theory (QFT) is a robust control system design method which provides a full-envelope flight control system design and gives the engineer direct control over compensator order and gain. A full subsonic flight envelope FCS is designed for using QFT for four representative aircraft configurations. Flying qualities are embedded in the longitudinal design by using a control variable which varies with the aircraft's energy state throughout the flight envelope. Linear simulations with realistically large control inputs are used to validate the design. © 1997 by John Wiley & Sons, Ltd. This paper was prepared under the auspices of the US Government and it is therefore not subject to copyright in the US.     

DISCRETIZING CONTINUOUS‐TIME CONTROLLERS WITH FUZZY LOGIC SYSTEMS AND ITS STABILITY ANALYSIS

In this paper, a new method, applying the fuzzy logic system, is proposed to discretize the continuous‐time controller in computer‐controlled systems. All the continuous‐time controllers can be reconstructed by the proposed method under the Sampling Theorem. That is, the fuzzy logic systems are used to add nonlinearity and to approximate smooth functions. Hence, the proposed controller is a new smooth controller that can replace the original controller, independent of the sampling time under the Sampling Theorem. Consequently, the proposed controller not only can discretize the continuous‐time controllers, but also can tolerate a wider range of sampling time uncertainty. Besides, the input‐output stability is proposed for discretizing the continuous‐time controller of the fuzzy logic systems. Finally, computer simulation shows that the proposed method can easily reconstructthe continuous‐time controller and has very good robustness for different sampling times.     

基于多环QFT的飞行仿真转台鲁棒控制

阐述了定量反馈理论(QFT)的基本原理及设计方法,并给出了某型飞行仿真转台的QFT控制器设计实例。为了有效地抑制高频测量噪声对系统的干扰,以及避免系统的高频不确定性,在单环QFT控制的基础上,引入了基于多环QFT的鲁棒控制。理论分析和仿真实验表明,这种多环QFT控制可以明显地缩减控制器的带宽,使系统具有很强的抗高频测量噪声的性能,达到了理想的控制效果。该方法在转台的控制上取得了成功的应用,具有广泛的应用价值。