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.     

DESIGN OF AN AIR-TO-AIR AUTOMATIC REFUELING FLIGHT CONTROL SYSTEM USING QUANTITATIVE FEEDBACK THEORY

Quantitative feedback theory is developed for the design of an automatic station-keeping flight control system to regulate the position of an aircraft receiving fuel relative to the tanker aircraft during air-to-air refueling. A robust flight control system is designed for automating the station-keeping task. A simple outer loop feedback control system is developed that achieves stable position regulation in the presence of wind gusts and fuel transfer related disturbances. The modelling and analysis clearly show the usefulness of QFT in the design of flight control systems for aircraft with large structured parametric uncertainty. Linear and nonlinear simulations are performed to validate the design. © 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.     

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.     

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Matlab语言定量反馈控制器的分析与设计

对定量反馈理论（QFT）的基本原理进行了介绍和利用Matlab语言工具箱进行设计的基本方法，Matlab通用QFT工具箱为用户进行QFT控制器的设计提供了有利的工具，文章就以典型二阶系统为例进行QFT控制器的设计，仿真的结果表明定量反馈理论在不确定系统设计中有着经典控制理论无法替代的性能。     

融合GPC和QFT对不确定性系统的鲁棒控制

针对广义预测控制(GPC)与定量反馈理论(QFT)的特点,提出了把两种算法融合的鲁棒控制算法。该方法是在对QFT进行修改的基础上,采用双回路控制。内回路采用QFT控制器实现对系统不确定性的控制;外回路采用GPC控制器,实现对系统的各种性能要求并且提高鲁棒性。该方法可以充分利用两种控制理论的优点。最后的仿真结果显示,融合的算法比单独采用其中的任何一种控制算法所取得的控制效果都好。     

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.     

定量反馈理论发展综述

定量反馈理论是一种基于频域的鲁棒控制理论,可以用于具有高度不确定性的单变量线性/非线性系统、多变量线性/非线性系统控制器设计.本文概述了定量反馈理论的基本原理、设计过程以及特点.总结了近年来QFT在提高系统性能、鲁棒稳定性、自动设计以及应用等方面的最新研究进展,并且给出了一些已有的理论应用成果.最后讨论了进一步的研究方向.     

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。     

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.     

基于QFT的无人机纵向飞行控制系统设计

介绍了定量反馈理论(QFT)的基本原理和设计步骤;定量反馈理论作为一种新颖的频率域鲁棒控制技术,综合考虑了对象的不确定性范围和系统的性能指标要求,以定量方式进行分析设计,从而保证了设计结果具有稳定鲁棒性和性能鲁棒性;无人机飞行过程中具有较强的不确定性,气动参数会不断发生变化,运用QFT对无人机纵向飞行控制系统进行设计,可以很好解决飞行控制系统中的不确定性问题;仿真结果显示,QFT设计的控制器能够很好地满足无人机鲁棒稳定性指标和跟踪性能,符合纵向控制的要求。     

MIMO QFT CAD PACKAGE (VERSION 3)

The MIMO/QFT CAD package is capable of carrying through a multivariable control system robust design, for tracking and the rejection of external disturbance signals, from problem set-up to a frequency domain analysis of the compensated system. The package automates: the selection of the weighting matrix; the discretization of the plants; the formation of the square effective plants; the polynomial matrix inverse required to form the equivalent plants; the generation of templates; the selection of a nominal plant; the generation of stability, tracking, cross-coupling effects, external disturbance rejection, gamma and composite bounds; the loop shaping; and the design of the prefilter elements. This is followed by a frequency-domain analysis of the completed design, and export of this design to the MATLAB SIMULINK® toolbox in order to validate the frequency domain design by time-domain simulations. © 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.     

COMPARISON OF FLIGHT CONTROL SYSTEM DESIGN METHODS IN LANDING

Intelligent control theory usually involves the subjects of neural control and fuzzy logic control. The great potential of intelligent control in control designs has recently been realized in the literature. In this survey paper, we attempt to employ this subject and provide the reader with an overview of related topics, such as conventional, fuzzy logic‐based, neural net‐based adaptive control techniques. Practical control schemes realistically applicable in the area of control system design are introduced. The control laws are demonstrated on a three‐degree‐of‐freedom simulation with linearized aerodynamic and engine models. This paper deals the issue of aircraft landing maneuvers. Generally this part of flight needs to be strongly assisted by human pilot.     

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。     

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.     

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.     

QFT与神经网络并行控制研究

阐述了定量反馈理论(Quantitative Feedback Theory,简称QFT)的基本原理及设计步骤,并给出了设计实例。在QFT的基础上,提出了一种QFT和神经网络并行控制的方案,以QFT为主控制器,神经网络进行动态误差补偿。QFT控制能克服对象的参数不确定性,保障系统的鲁棒性;神经网络可以进一步提高系统的跟踪精度。仿真表明,这种方法实现了QFT控制和神经网络控制的完美结合,很适合高精度伺服系统的鲁棒控制。     

Construction of linear time‐invariant equivalent plants for nonlinear continuous‐time and sampled‐data systems

In this paper, a technique is presented for constructing the so‐called linear time‐invariant equivalent (LTIE) plants used in the nonlinear quantitative feed back theory (QFT) approach. The proposed technique is applicable equally well to both continuous‐time and sampled‐data nonlinear plants described by nonlinear integro‐differential equation and nonlinear autoregressive moving average with exogenous inputs (NARMAX) models, respectively. The technique uses inclusion function and interval integration tools of interval analysis. A nonlinear chemical reactor example is used to illustrate the procedure for both nonlinear continuous‐time and sampled‐data systems, and found to yield satisfactory results in both cases. Copyright © 2003 John Wiley & Sons, Ltd.