Two-input one-output compensators

Two-input one-output compensators can be used for decoupling and exact model-matching design. They are more general than the well-known output feedback and observer-controller-type feedback. However, the design of two-input one-output compensators is also difficult. In this paper we present a design procedure for a two-input one-output compensator for multivariable systems. In the design, we only require an added dynamic to ensure the solution-existence condition. Thus the design of two-input one-output compensators is put on the same level as the familiar output feedback and observer-controller-type feedback designs.     

Squaring down by static and dynamic compensators

Given a system, which is not necessarily invertible and which has an unequal number of inputs, a method of `squaring down', that is a method of designing pre-compensators and postcompensators such that the resulting system has an equal number of inputs and outputs and is invertible, is presented. The compensators are, in general, dynamic and have the property that the additional finite zeros induced by them are assignable to the open left-half complex plan. Furthermore, the compensators are asymptotically stable, and hence do not deteriorate the robustness and performance of an eventual feedback design. Also, the compensator design preserves the stabilizability, detectability, and minimum-phase properties and the infinite zero structure of the original system. Thus, a method of designing nonsquare systems by converting them to square invertible systems is introduced. Two applications of such a design philosophy, (1) diagonal decoupling with state feedback; and (2) almost disturbance decoupling with output feedback, are pointed out     

H-Infinity Static Output-feedback Control for Rotorcraft

The problem of stabilization of an autonomous rotorcraft platform in a hover configuration subject to external disturbances is addressed. Necessary and sufficient conditions are presented for static output-feedback control of linear time-invariant systems using the H-Infinity approach. Simplified conditions are given which only require the solution of two coupled matrix design equations. This paper also proposes a numerically efficient solution algorithm for the coupled design equations to determine the output-feedback gain. A major contribution is that an initial stabilizing gain is not needed. The efficacy of the control law and the disturbance accommodation properties are shown on a rotorcraft design example. The helicopter dynamics do not decouple as in the fixed-wing aircraft case, so that the design of helicopter flight controllers with a desirable intuitive structure is not straightforward. In this paper an output feedback approach is given that allows one to selectively close prescribed multivariable feedback loops using a reduced set of the states. Shaping filters are added that improve performance and yield guaranteed robustness and speed of response. This gives direct control over the design procedure and performance. Accurate identification of the System parameters is a challenging task for rotorcraft control, addition of loop shaping facilitates implementation engineers to counteract unmodeled high frequency dynamics. The net result yields control structures that have been historically accepted in the flight control community.     

Noninteracting control of 2-D systems

Necessary and sufficient conditions for the existence of a decoupling bicausal precompensator for multivariable 2-D systems are derived in state-space and frequency domains. In general, the decoupling problem for 2-D systems can be solved by feedback compensators if suitable injectivity assumptions are introduced on the input-state matrices. The structure of dynamic compensators is derived for this case, and the 2-D decoupling problem with stability is solved     

Direct Adaptive Dynamic Compensation for Minimum Phase Systems With Unknown Relative Degree

We consider parameter-monotonic direct adaptive control for single-input-single-output minimum-phase linear time-invariant systems with knowledge of the sign of the high-frequency gain (first nonzero Markov parameter) and an upper bound on the magnitude of the high-frequency gain. The first part of the paper is devoted to fixed-gain analysis of single-parameter high-gain-stabilizing controllers. Two novel fixed-gain dynamic compensators are presented for stabilizing minimum-phase systems. One compensator stabilizes systems with arbitrary-but-known relative degree, while the other utilizes a Fibonacci series construction to stabilize systems with unknown-but-bounded relative degree. Next, we provide a general treatment of parameter-monotonic adaptive control, including a result that guarantees state convergence to zero. This result is then combined with the high-gain-stabilizing controllers to yield parameter-monotonic direct adaptive dynamic compensation for minimum-phase systems with either arbitrary-but-known or unknown-but-bounded relative degree     

离散时间奇异系统的可测扰动解耦

为离散时间广义非线性控制系统的可测扰动提供一种反演算法．运用一类正则动态补偿器解决了系统的解耦问题，并且证明系统既可利用动态反馈进行解耦，也可利用拟表态反馈进行解耦．     

一类非线性系统的输出反馈半局鲁棒镇定

从半局镇定角度研究了一类非线性系统的输出反馈镇定问题,这类系统具有较强的非线性增长特征.利用高增益观测器,把非分离设计原则应用于输出反馈半局镇定控制器设计.在不需系统具有一个一致完全可观状态反馈控制器情况下,给出了输出反馈控制器的设计方法.对任意给定紧子集,所设计的反馈控制器使闭环系统是渐近稳定的且吸引域包含指定的紧子集.最后的仿真实例说明了设计方法的有效性.     

A constructive approach to local stabilization of nonlinear systems by dynamic output feedback

The note considers the problem of local stabilization of nonlinear systems by dynamic output feedback. A new concept, namely, local uniform observability of feedback control law, is introduced. The main result is that if a nonlinear system is Nth-order approximately stabilizable by a locally uniformly observable state feedback, then it is stabilizable by dynamic output feedback. Based on the approximate stability, a constructive method for designing dynamic compensators is presented. The design of the dynamic compensators is beyond the separation principle and can handle systems whose linearization might be uncontrollable and/or unobservable. An example of nonminimum phase nonlinear systems is presented to illustrate the utility of the results.     

Mini Rotorcraft Flight Formation Control Using Bounded Inputs

In this paper, the flight formation control and trajectory tracking control design of multiple mini rotorcraft systems are discussed. The dynamic model of a mini rotorcraft is presented using the Newton-Euler formalism. Our approach is based on a leader/follower structure of multiple robot systems. The centroid of the coordinated control subsystem is used for trajectory tracking purposes. A nonlinear controller based on separated saturations and a multi-agent consensus algorithm is developed. The analytic results are supported by simulation tests. Experimental results include yaw coordination and tracking only.     

Smooth Switching Output Tracking Control for LPV Systems

This paper is concerned with the problem of smooth switching state feedback controller design for aircraft dynamic systems with multiple operating points. Based on the theory of robust control, a single state feedback controller which considers smooth switching is constructed. With the constant controller, the output response can be considerably improved in the switching process when the flight condition changes. An example for autopilot design of an F‐18 aircraft is given to illustrate the effectiveness of the proposed approach.     

An adaptive vision-based autopilot for mini flying machines guidance,navigation and control

The design of reliable navigation and control systems for Unmanned Aerial Vehicles (UAVs) based only on visual cues and inertial data has many unsolved challenging problems, ranging from hardware and software development to pure control-theoretical issues. This paper addresses these issues by developing and implementing an adaptive vision-based autopilot for navigation and control of small and mini rotorcraft UAVs. The proposed autopilot includes a Visual Odometer (VO) for navigation in GPS-denied environments and a nonlinear control system for flight control and target tracking. The VO estimates the rotorcraft ego-motion by identifying and tracking visual features in the environment, using a single camera mounted on-board the vehicle. The VO has been augmented by an adaptive mechanism that fuses optic flow and inertial measurements to determine the range and to recover the 3D position and velocity of the vehicle. The adaptive VO pose estimates are then exploited by a nonlinear hierarchical controller for achieving various navigational tasks such as take-off, landing, hovering, trajectory tracking, target tracking, etc. Furthermore, the asymptotic stability of the entire closed-loop system has been established using systems in cascade and adaptive control theories. Experimental flight test data over various ranges of the flight envelope illustrate that the proposed vision-based autopilot performs well and allows a mini rotorcraft UAV to achieve autonomously advanced flight behaviours by using vision.     

Comparative Results on Stabilization of the Quad-rotor Rotorcraft Using Bounded Feedback Controllers

In the recent years autonomous flying vehicles are being increasingly used in both civil and military areas. With the advancement of the technology it has become possible to test efficiently and cost-effectively different autonomous flight control concepts and design variations using small-scale aerial vehicles. In this paper the stabilization problem of the quad-rotor rotorcraft using bounded feedback controllers is investigated. Five different types of nonlinear feedback laws with saturation elements, previously proposed for global control of systems with multiple integrators, are applied and tested to control the quad-rotor rotorcraft roll and pitch angles. The results obtained from autonomous flight simulations and real time experiments with the Draganflyer V Ti four-rotor mini-rotorcraft are analyzed with respect to the structural simplicity of the control schemes and the transient performance of the closed-loop system.     

Cooperative Containment Formation for Discrete-time Heterogeneous Networks by Double Compensators

In this paper, two practical distributed observers are constructed to solve the cooperative robust containment formation problem for discrete-time linear multi-agent systems. The dynamics of the systems contain uncertain parts. A containment error is presented to guarantee all the outputs of followers converge to the convex hull spanned by the outputs of the leaders. There are two compensators in this paper, we first present a distributed compensator to estimate the information of convex hull, and use an internal compensator to solve the problem of uncertain parts in dynamics. Further more, based on the both compensators, a distributed dynamic output feedback controller is designed to solve the containment control problem for the discrete-time multi-agent systems. Finally, a numerical example is given to verify the effectiveness of the main results.     

Robust optimization of multivariable feedback systems with time-varying nonlinear uncertainties

A design criterion is developed to achieve the input-output decoupling of multivariable feedback systems and the robust stabilization of systems with time-varying nonlinear uncertainties. Moreover, an effective design algorithm is derived to achieve the robust optimization of multivariable feedback systems subjected to time-varying nonlnear uncertainties. The theory of minimum H^∞ -norm and the optimal interpolation technique are employed to solve this robust optimization problem. Since the requirements of internal stability are satisfied, this design algorithm performs appropriately, even if the plant is unstable and/or non-minimum phase. From the result of the robust optimization, we can predict the maximum sector bounds of nonlinear uncertainties that can be tolerated in the multivariable feedback system.     

Design and Implementation of a Flight Control System for an Unmanned Rotorcraft using RPT Control Approach

In this paper, we apply a so‐called robust and perfect tracking (RPT) control technique to the design and implementation of the flight control system of a miniature unmanned rotorcraft, named HeLion. To make the presented work self‐contained, we will first outline some background knowledge, including mainly the nonlinear flight dynamics model and the inner‐loop flight control system design. Next, the highlight of this paper, that is, the outer‐loop flight control system design procedure using RPT control technique, will be detailed. Generally speaking, RPT control technique aims to design a controller such that (i) the resulting closed‐loop system is asymptotically stable, and (ii) the controlled output almost perfectly tracks a given reference signal in the presence of any initial conditions and external disturbances. Since it makes use of all possible information including the system measurement output and the command reference signal together with all its derivatives (if available) for control, RPT control technique is particularly useful for the outer‐loop layer of an unmanned aircraft. Both simulation and flight‐test results will be presented and analyzed at the end of this paper, and the efficiency of the RPT control approach will be evaluated comprehensively.     

Design of sensitivity-reducing compensators using observers

In this paper the design of compensators for output feedback systems which satisfy a sensitivity, reduction criterion is considered for the case when the dynamic compensator is an observer. Using the conditions for comparison sensitivity design of output feedback systems derived by Naeije and Bosgra [4], it is shown that for arbitrary stable state-observers (full or reduced order) there exist feedback gains multiplying the system output and observer states for which the system is stable and the sensitivity reduction criterion is satisfied. Use of observers enables direct control over some of the feedback system eigenvalues and leads to a useful interpretation of the sensitivity weighting matrix. A design procedure is described and illustrated by an example of an aircraft control. The results are graphically compared with results obtained by a conventional design procedure.     

Design of dynamic output feedback controller for power system stabilization

A computational method of designing dynamic compensators for stabilization of power systems is described. The control strategy only employs feedback from the available system output variables. A design procedure which would result in a stable closed-loop system over wide operating points is also included.     

Noninteracting control by output feedback and dynamic compensation

The design of noninteracting multivariable control systems by slate feedback has received considerable attention recently, and an extensive theory is now available. One area, however, that requires further clarification concerns the case where the state vector is not accessible to measurement, and feedback of output is inadequate for the purpose of decoupling. In this paper a new technique is described by means of which it is possible to decouple a system which is not olherwise decouplable by proportional feedback of the output vector. The technique is based on the addition of a dynamic controller in the forward path, and is analogous to cascade compensation in single-loop systems. It is shown that a necessary and sufficient condition for the success of this method of decoupling control is that the Original system should satisfy the condition for state feedback decoupling.     

Design of optimal constrained dynamic compensators for non-stationary linear stochastic systems

This paper deals with the design of fixed-order dynamic compensators for non-stationary linear stochastic systems with noisy observations, where the observation noise need not necessarily be white. An integral quadratic performance index defined over a finite time interval is employed and this yields a matrix variational problem in the compensator parameters. It is shown how the optimal, possibly time-varying, compensator parameters rnay be determined by direct solution of this variational problem using a conjugate-gradient technique. Consideration is also given to finding suboptimal compensators that are simpler to implement. In particular, an algorithm is proposed for designing compensators having gains that are constrained to be piecewise-constant functions of time, with provision for optimally choosing the instants at which gains changes occur. An illustrative numerical example is included.     

Fixed-structure controller design for systems with actuator amplitude and rate non-linearities

In this paper we develop output feedback controllers and fixed-order (i.e., full- and reduced-order) dynamic compensators for systems with actuator amplitude and rate saturation constraints. The proposed design methodology employs a rate limiter as part of the controller architecture. The problem of simultaneous control amplitude and rate saturation is embedded within an optimization problem by constructing a Riccati equation whose solution guarantees closed-loop global/local asymptotic stability in the face of sector bounded actuator amplitude and rate non-linearities. Application of the proposed framework is demonstrated via a flight control example involving actuator amplitude and rate saturation constraints.