Quantitative Feedback Theory Methodology Research Articles

Disturbance Rejection Design for a Bank-to-Turn Missile using Decoupling Quantitative Feedback Theory

Multivariable Quantitative Feedback Theory (QFT) is applied to a bank-to-turn missile plant for disturbance rejection specifications. The plant is first partially decoupled over the plant uncertainty to reduce the interaction index to below unity for frequencies around and higher than the expected closed-loop system bandwidth. QFT methodology is then applied to design a diagonal controller to meet the disturbance rejection specifications. The resulting fully populated controller is able to meet the design specifications, which was not achievable using a diagonal controller because of the interaction and delay in the system.

A fully autonomous unmanned aerial vehicle landing controller synthesis: quantitative feedback theory and H∞ technique comparison

This article presents an overview of the design of an autonomous landing controller. The flight control system must be robust against the effects of wind and must control the height accurately enough to support an autoland function. This study design and compare two different altitude command tracker controllers for an unmanned air vehicle using H∞ and quantitative feedback theory (QFT) techniques during the landing phase. The different stages of QFT methodology have been done with help of software tool quantitative feedback theory interactive tool. This is a free software tool that is characterized by its easy of use and interactive nature. QFT is standing as a viable control design method that can be applied to practical problems and produce implementable results. Tests with realistically large control inputs are used to validate and compare both designs.

Frequency domain control based on quantitative feedback theory for vibration suppressionin structures equipped with magnetorheological dampers

This paper addresses the problem of designing quantitative feedback theory (QFT) basedcontrollers for the vibration reduction in a structure equipped with an MR damper. In thisway, the controller is designed in the frequency domain and the natural frequencies of thestructure can be directly accounted for in the process. Though the QFT methodology wasoriginally conceived of for linear time invariant systems, it can be extended to nonlinearsystems. A new methodology is proposed for characterizing the nonlinear hystereticbehavior of the MR damper through the uncertainty template in the Nichols chart. Theresulting controller performance is evaluated in a real-time hybrid testing experiment.

An interactive approach to template generation in quantitative feedback theory methodology

AbstractThe calculation of templates associated with plant uncertainty at some frequencies is one of the first steps in the design of robust controllers using the quantitative feedback theory (QFT) methodology. If the QFT designer does not calculate the templates correctly, the design will be unnecessarily conservative, or even erroneous. This paper describes the main features of Template Interactive Generator (TIG), a new, free software tool that calculates the templates of plants with special parameter dependences, such as interval plants and plants with affine parametric uncertainty. The paper also includes two examples that illustrate the ease of use and the high level of interactivity of TIG. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

QFT Based Robust Control of a Single-Link Flexible Manipulator

This article presents the application of multi-input multi-output (MIMO) quantitative feedback theory (QFT) to the control of a single-link flexible manipulator. The manipulator employs an actuation scheme comprised of a DC motor that provides spatially discrete actuation and a surface bonded piezoelectric ceramic that provides spatially distributed actuation. The efficacy of the sequential MIMO QFT methodology for articulating flexible structure control is investigated using the flexible manipulator testbed, with the control system designed to achieve rapid, rest-to-rest positioning of the manipulator tip in the presence of significant parametric and non-parametric structured uncertainty. Numerical simulations and experiments are employed to validate the synthesised control system and the combined discrete-distributed actuation scheme. Conservatisms in the MIMO QFT methodology are identified and partly alleviated using recent theoretical and design improvements.

Interactive computer-aided control design using quantitative feedback theory: the problem of vertical movement stabilization on a high-speed ferry

In a first approximation, the vertical acceleration associated with pitch motion can be considered as the main cause of motion sickness, which is without a doubt one of the most unpleasant disadvantages of maritime transport. The reduction of motion sickness can be stated as a monovariable regulation problem of a highly perturbed system. This work presents the design of a monovariable robust controller with quantitative feedback theory (QFT) for reducing the vertical movement on a high-speed ferry. The different stages of QFT methodology have been done with the help of the software tool QFTIT (Quantitative Feedback Theory Interactive Tool). This is a free software tool that is characterized by its ease of use and interactive nature. The designed regulator is validated experimentally in sea behaviour trials with a scaled down replica 1/25 the size of a high-speed ferry. The designed regulator is also compared with a gain-scheduling scheme using a proportional and derivative controller (PD).

Parametric model development and quantitative feedback design for automotive torque converter bypass clutch control

Customer demands for large high-performance vehicles in the face of increasingly stringent fuel economy targets have led automobile makers to seek innovative ways of meeting these requirements, especially in the North American market. One of the most critical elements in automotive powertrain systems is the torque converter bypass clutch which is now in almost universal use in automatic transmission-equipped vehicles. The clutch is used to bypass the fluid coupling of the torque converter during steady state conditions (i.e. highway cruise), thus eliminating a 15–20 percent loss of efficiency. Generally, the clutch is disengaged during dynamic events (e.g. vehicle launch, braking and gear changes) when the torque converter functionality is required. Further gains in fuel economy can now be realized through modulation of the bypass clutch in some situations where it had been considered necessary that the clutch be disengaged (i.e. during gear changes). In this case, the clutch is operated in a state of continuous slip; the transmitted torque is controlled through modulation of the clutch apply pressure. The dynamics of this system, however, exhibit considerable complexity. Characterization of this behaviour has been of considerable interest among automobile makers in recent years. However, investigation of the non-linear dynamics of this system is beyond the scope of this paper; a more in-depth treatment generally requires bifurcation analysis and/or exhaustive simulation studies. The focus in this paper is upon the detailed development of a linear parametric differential equation model and the design of a linear robust feedback control system. Parametric uncertainty is included to capture the effects of variations in system damping, bulk modulus, coefficient of friction and constants of linearization. Based upon a specific operating point, a linear robust controller is developed using the quantitative feedback theory (QFT) technique. The QFT methodology is aimed at designing feedback controllers so that pointwise frequency response specifications on closed-loop tracking and disturbance rejection are met in spite of large parametric plant uncertainty. The local stability and performance of the non-linear feedback system are subsequently verified by simulation. Since the feedback design is based upon a linear parametric model, no specific guarantees can be made as to the performance of the non-linear closed-loop system, although the results are found to be satisfactory in this case.

Introduction to Quantitative Feedback Theory for lateral robust flight control systems design

Quantitative Feedback Theory (QFT), is a frequency-domain-based robust control design approach that was developed in the early 1970s and has received considerable attention over the past two decades. In the last few years, its application to aircraft flight control systems design has been widely investigated. In this paper the basic concepts, principles, design procedure, and features of QFT are reviewed and summarized for single-input single-output systems. Its application to a lateral flight control system design is then considered. A robust roll-attitude control system is designed to cover a certain operating range using the QFT methodology, and certain eigenstructure-assignment results. The integration of QFT with eigenstructure methods results in a controller with the stability and performance robustness of QFT design, and the decoupled dynamic responses of an eigenstructure-assignment approach. The results indicate QFT has significant potential in robust flight control systems design. The combination of techniques should be applicable to other industrial sectors.

Robust Stability of Plants With Mixed Uncertainties and Quantitative Feedback Theory

Quantitative Feedback Theory (QFT) has often been criticized for lack of a rigorous mathematical theory to support its claims. Yet it is known to be a very effective design methodology. In this paper, we re-examine QFT and state several results that confirm the validity of this highly effective framework proposed by Horowitz. Also provided are some additional insights into the QFT methodology that may not be immediately apparent. We consider three important fundamental questions: (i) whether or not a QFT design is robustly stable, (ii) does a robust stabilizer exist, and (iii) does a controller assuring robust QFT performance exist. The first two are obvious precursors for synthesizing controllers for performance robustness. We give necessary and sufficient conditions that unambiguously resolve the question of robust stability under mixed uncertainty, thereby, confirming that a properly executed QFT design is automatically robustly stable. Also given is a sufficiency condition for a robust stabilizer to exist which is derived from the well known Nevanlinna-Pick theory in classical analysis. Finally, we give a sufficiency theorem for the existence of a QFT controller and deduce that when the uncertain plant set is minimum phase with no unstructured uncertainty there always exists a controller satisfying robust performance specifications in the sense of QFT.