Robust Multivariable Control Research Articles

Integrated Propulsion-based Flight Control System Design for a Civil Transport Aircraft

We describe results of a study carried out at the University of Leicester in collaboration with Volvo Aero Corporation, on the design of integrated flight and propulsion control systems for a large civil transport aircraft. The use of the aircraft engines (via differential thrust and/or thrust vectoring) for the purposes of emergency flight control is examined in detail. An industry standard modelling and simulation tool (IFPClab), containing a detailed model of the Boeing 747-100 transport aircraft, was developed for the study using the MATLAB/SIMULINK software environment. IFPClab has a flexible, modular structure, which can easily be adapted to different aircraft and engine configurations. Propulsion based flight control systems, for use in the event of a partial or total failure of the traditional aerodynamic control surfaces, are designed using modem robust multivariable control methods. Evaluation of these control systems in non-linear simulations indicates that large civil transport aircraft may be effectively controlled using only collective and differential thrust. The addition of thrust vectoring, however, is seen to significantly improve the flying qualities that may be achieved.

Robust multivariable control design for HVDC back to back schemes

A robust multivariable control design procedure for HVDC back-to-back schemes is presented. HVDC links are commonly controlled with a decentralised structure, whereby in normal operation the rectifier may track direct current and the inverter may track direct voltage, firing angle or extinction angle. In the case of a back-to-back HVDC link the measurements of control variables of both sides are physically close, hence it is possible to apply a true multivariable controller whereby current and voltage are controlled by rectifier and inverter together. H-infinity control theory is used for a systematic tuning procedure which incorporates robustness against uncertainty in the short-circuit levels of both rectifier and inverter side AC systems. The linear control transfer functions for rectifier and inverter controllers are arrived at simultaneously thereby removing iterative design steps to find the best combination of control parameters for both rectifier and inverter controllers. The decoupling effect resulting from the multivariable controller structure reduces the interaction between tracking of direct current and direct voltage. It is verified by nonlinear EMTDC simulation that the designed controller is robust and can contribute to good fault recovery when integrated with other control loops and nonlinear control functions as implemented in manufactured controls.

Plasma multivariable robust control system design and simulation for a thermonuclear tokamak-reactor

The paper reports results on the design and analysis of the multivariable feedback Hinfin; robust system for plasma current, position and shape control in the fusion energy advanced tokamak (FEAT) developed in the International Thermonuclear Experimental Reactor (ITER) project. The system contains the fast loop with the SISO plasma vertical speed robust controller and the slow loop with the MIMO plasma current and shape robust controller. The goal is to study the resources of the system robustness to achieve a higher degree of the FEAT operation reliability. Two Hinfin; block diagonal controllers {K SISO, K MIMO} were designed by a mixed sensitivity approach in the framework of the disturbance rejection configuration. These controllers were compared with block diagonal decoupling, PI and LQG controllers at the set of FEAT key scenario points according to the multiple-criterion: nominal performance at minor disruptions, robust stability and robust performance. The Hinfin; controllers showed larger multivariable stability margin and better nominal performance.

Multivariable robust control of an integrated nuclear power reactor

The design of the main control system of the CAREM nuclear power plant is presented. This plant is an inherently safe low-power nuclear reactor with natural convection on the primary coolant circuit and is self-pressurized with a steam dome on the top of the pressure vessel (PV). It is an integrated reactor as the whole primary coolant circuit is within the PV. The primary circuit transports the heat to the secondary circuit through once-through steam generators (SG). There is a feedwater valve at the inlet of the SG and a turbine valve at the outlet of the SG. The manipulated variables are the aperture of these valves and the reactivity of the control rods. The control target is to regulate the primary and secondary pressures and to monitor steam flow reference ramps on a range of nominal flow from 100% to 40%. The requirements for the control system are robust stability, low-order simple controllers and transient/permanent error bounding. The controller design is based on a detailed RETRAN plant model, from which linear perturbed open-loop dynamic models at different powers are identified. Two low-order nominal models with their associated uncertainties are chosen for two different power ranges. Robust controllers with acceptable performances are designed for each range. Numerical optimization based on the loop-shaping method is used for the controller design. The designed controllers are implemented in the RETRAN model and tested in simulations achieving successful results.

Dynamic second-order sliding mode control of the hovercraft vessel

A suitable combination of the differential flatness property and the second-order sliding mode controller design technique is proposed for the specification of a robust dynamic feedback multivariable controller accomplishing prescribed trajectory tracking tasks for the earth coordinate position variables of a hovercraft vessel model.

Multivariable robust controller design for a boiler system

In an industrial boiler system, multiloop (decentralized) proportional-integral (PI) control is used because of its implementational advantages. We show that such control schemes sacrifice robustness and performance of the overall system. In particular, under normal boiler operating conditions, we design a robust multivariable controller using H/sub /spl infin// loop-shaping techniques; for consideration in implementation, we then reduce this controller to a multivariable PI controller. Both the H/sub /spl infin// controller and its PI approximation are tested extensively in letdown the frequency domain as well as in the time domain, using a valve complex nonlinear simulation software; the results show that the designed controllers are superior in robustness and performance to the existing multiloop controller.

Design and experimental testing of a robust multivariable controller on a tokamak

Describes the design and the experimental validation of a multivariable digital controller for a Tokamak, the Tokamak a configuration variable (TCV). The design of the controller is based on a linearized model of the plasma confined in the Tokamak. The plant is multiple-input-multiple-output (MIMO) and the various outputs are strongly coupled. Moreover the plant is open-loop unstable. The scope of the controller is to stabilize the plasma and to guarantee some closed-loop performance in terms of decoupling among the plant outputs. The proposed controller is composed of two nested loops: one is devoted to the vertical stabilization, the other, designed using the /spl Hscr//sub /spl infin// technique, guarantees the control of the plasma current and of the plasma shape. After massive simulations, this controller has been successfully tested on the plant. The experimental results show a significant improvement of the performance with respect to those obtained with a proportional integral derivative (PID) MIMO controller, that was used before on the plant.

Design and testing of track-following controllers for dual-stage servo systems with PZT actuated suspensions

This paper discusses the design and testing of two track-following controllers for dual-stage servo systems in hard disk drives. The first controller is designed using the μ-synthesis multivariable robust optimal controller design methodology. The second is designed using classical single-input-single-output (SISO) frequency shaping design techniques, based on sensitivity transfer functions decoupling of the dual-stage actuator. The controllers were implemented and tested on a disk drive with a PZT actuated suspension based dual-stage servo system. The position error signal (PES) for the servo system was obtained by measuring the slider displacement using an LDV and injecting simulated track runout. In the experiment, both designs achieved a track-mis-registration (TMR) less than 10 nm.

A MULTIVARIABLE H∞ CONTROLLER FOR A ROTARY DRYER

This paper describes the design of a multivariable robust controller for a drying process. The plant consists of a co-current rotary dryer to evaporate moisture from a waste product, called alp eorujo or two phase cake, generated by olive-oil mills. A methodology to design a multivariable H∞ controller is shown, including the selection of appropriate weigh ting functions for a mixed sensitivity control formulation. The performance obtained with this control strategy has been validated under simulation, using a very accurate nonlinear simulator developed in Dymola.

Robust Multivariable Flutter Suppression for Benchmark Active Control Technology Wind-Tunnel Model

The Benchmark Active Controls Technology (BACT) project is part of NASA Langley Research Center''s Benchmark Models Program for studying transonic aeroelastic phenomena. In January of 1996 the BACT wind-tunnel model was used to successfully demonstrate the application of robust multivariable control design methods (H infinity and mu-synthesis) to flutter suppression. This paper addresses the design and experimental evaluation of robust multivariable flutter suppression control laws with particular attention paid to the degree to which stability and performance robustness was achieved.

Design and Implementation of µ Controllers for Real Industrial Plants

This paper considers the design and implementation of robust multivariable controllers for a real process control plant. The plant used for experimental tests is intended to control output flow rate and level of a product tank. First, a detailed description of a method for finding and representing uncertainties is presented. Next, a robust control is designed using the µ synthesis. Comparisons of uncertainties (structured) parametric and non-parametric are also presented. They show how conservative the µ analysis could be and, in some cases, how to reduce the conservatism.

Controller order reduction for robust control of parallel operating dc/dc converters

A useful straightforward controller order reduction procedure for multivariable robust control is presented. Reduced controllers regarding robust stability criterion and robust performance criterion are developed. Weighted Balanced Truncation is used as the concept for the real reduction work. The procedure is applied to Loop Shaping Design Procedure, Internal Model Control and Decentralized robust controllers of parallel operating dc/dc converters. Uncertainty robustness and performance of the closed-loop systems with reduced controllers are investigated. The reduction procedure efficiently decreases high controller orders, from which robust theory suffers, preserving at the same time closed-loop robust stability and robust performance at a desired level.

A finite-dimensional robust controller for systems in the CD-algebra

Robust multivariable controllers for stable infinite-dimensional systems in the Callier-Desoer (CD) algebra are discussed. In particular, the following robust regulation problem is solved. Given reference and disturbance signals, which are linear combinations of signals of the form t/sup j/ sin(/spl omega//sub k/t+/spl phi//sub k/), j/spl ges/0, k=0, /spl middot//spl middot//spl middot/, n, find a low-order finite-dimensional controller so that the outputs asymptotically track the reference signals, asymptotically reject the disturbance signals, and the closed-loop system is stable and robust with respect to a class of perturbations in the plant. The proposed controller consists of a positive scalar gain /spl epsi/ and certain polynomial matrices K/sub k/(s) for k=0, /spl middot//spl middot//spl middot/, n. The main result of the paper shows that the matrices K/sub k/(s) must satisfy certain stability conditions involving the values of the plant transfer function only at the reference and disturbance signal frequencies /spl omega//sub k/ for k=0, /spl middot//spl middot//spl middot/, n. The controller has unstable poles on the imaginary axis. The behavior of these poles as a function of the scalar parameter /spl epsi/ in the form of a Puiseux series is given.

Robust feedback control of flow-induced structural radiation of sound

The paper presents the robust multivariable control of noise radiation from panels driven by turbulent flow. The controlled inputs are point forces to the panel and the feedback signals are panel accelerations. Collocated actuator/sensor locations on the panel are chosen such that vibration control will lead to a reduction in the radiated sound pressure levels. The multivariable controller is realized though a sequential loop closure approach. Each controller is designed in the frequency domain where the impact of system uncertainty and closed-loop sensitivity can be analyzed. The proposed frequency domain approach will also facilitate the design of feedback controllers that employ the natural dynamics of the panel for noise control purposes. The proposed design technique is experimentally validated on a panel subjected to turbulent flow in a quiet wind tunnel. Active control of the sound radiation was achieved at frequencies as high as 1000 Hz. Sound pressure level reductions of as much as 15 dB were achieved at the resonant frequencies of the panel modes. Overall reductions over the 100-1000 Hz band were approximately 5 dB.

Synthesis of robust multivariable iterative learning controllers with application to a wafer stage motion system

Iterative Learning Control (ILC) is a powerful control concept that iteratively improves the transient behaviour of processes that are repetitive in nature. Although most of the published ILC schemes are heuristic in nature, some initial research has been performed on the formulation of the ILC problem in the H

Fuzzy wide-range control of fossil power plants for life extension and robust performance

This paper presents a fuzzy-logic-based methodology of life extending control (LEC) for robust wide-range operation of fossil power plants including load-following, scheduled shutdown, and hot startup. The objectives of the LEC are performance enhancement and structural durability of both aging and new fossil power plants. The proposed control system has a two-tier architecture, which explores and optimizes the plant performance and structural durability trade-off. The lower tier consists of a feedforward control policy and a family of linear multivariable robust feedback controllers, which are gain-scheduled for wide-range operation. The sampled-data feedback control laws are synthesized based on an induced L 2-norm technique that minimizes the worst-case gain between the energy of the exogenous inputs and the energy of the regulated outputs. The supervisory controller at the upper tier makes decisions on plant operations with due consideration to structural durability of critical plant components (e.g., steam generators, steam headers, and turbines). The supervisory controller is synthesized based on approximate reasoning embedded with rule-based expert knowledge of the power plant and analytical models of structural damage. Using the fuzzy logic, the plant operation strategy is modified on-line for trade-off between plant performance and structural damage in critical components. The fuzzy algorithm facilitates bumpless controller switching for gain scheduling under wide-range operation and control. It also adds robustness to the control system especially if the lower tier of gain-scheduled controllers is not able to maintain stability under plant perturbations.

905 遺伝的アルゴリズムによるモデル規範多変数ロバストモデル規範形制御の設計(機械力学・計測制御VIII)

905 遺伝的アルゴリズムによるモデル規範多変数ロバストモデル規範形制御の設計(機械力学・計測制御VIII)

Robust resilient dynamic controllers for systems with parametric uncertainty and controller gain variations

One of the fundamental problems in feedback control design is the ability of the control system to maintain stability and performance in the face of system uncertainties. To this end, elegant multivariable robust control design frameworks such as H control, L control and mu synthesis have been developed to address the robust stability and performance control problem. An impl1icit assumption inherent in these design frameworks is that the controller will be implemented exactly. In a recent paper by Keel and Bhattacharyya, it was shown that even though such frameworks are robust with respect to system uncertainty, they are extremely fragile with respect to errors in the controller coefficients. In this paper, we extend the robust fixed-structure controller synthesis approach to develop controllers which are robust to system uncertainties and non-fragile or resilient to controller gain variations.

Application of Parameter-Dependent Robust Control Synthesis to Turbofan Engines

Recent results in multivariable robust control synthesis forlinearparameter-varying (LPV)systems are applied to the control of a turbofan engine over a wide range of power codes. Seven linear, time-invariant models are used in the control design. The resulting LPV controller consists of seven linear controllers, gain scheduled via linear interpolation. This gain-scheduled controller is obtained directly as part of the described design process, as opposed to conventional processes, where the gain schedules are developed after the fact to connect point designs. A model matching approach is employed such that the resulting closed loop resembles a decoupled set of secondordersystems with specie ed rise timesand overshoots. The performanceoflinear H1 point designs arecompared with the LPV controller at e xed operating points. A nonlinear simulation is performed with the turbofan engine and LPV controller schedules as a function of the power code. The LPV controller exhibits excellent tracking of reference commands as the power code varies in time.

Robust Damage-Mitigating Control of Mechanical Systems: Experimental Validation on a Test Apparatus

The goal of damage-mitigating control is to achieve high performance of operating machinery without overstraining the mechanical structures and the potential benefit is an increase in the component service life with no significant loss of performance. This paper presents the design of a test apparatus, the synthesis of a damage-mitigating control system, and the results of experimentation where the objective is to demonstrate the concept of fatigue damage reduction as an extension of multivariable robust feedback control. The test apparatus is built upon a three-degree-of-freedom, two-input three-output mechanical structure. The methodology of the damage-mitigating control synthesis is built upon the principles of: (i) frequency-domain identification of the plant dynamics and modeling of uncertainties in the state-space setting; and (ii) robust control based on the H∞ approach by taking both plant dynamic performance and material degradation of structural components into consideration. Case studies on the test apparatus indicate that fatigue life of specimens can be substantially extended with no appreciable degradation in the dynamic performance of the mechanical system.