Stabilization and disturbance rejection for the beam equation

We consider a system described by the Euler-Bernoulli beam equation. For stabilization, we propose a dynamic boundary controller applied at the free end of the system. The transfer function of the controller is a marginally stable positive real function which may contain poles on the imaginary axis. We then give various asymptotical and exponential stability results. We also consider the disturbance rejection problem     

An exponential stability result for the wave equation

We consider a system described by the one-dimensional linear wave equation in a bounded domain with appropriate boundary conditions. To stabilize this system, we propose a dynamic boundary controller applied at the free end of the system. The transfer function of the proposed controller is a proper rational function which consists of a strictly positive real function and some poles on the imaginary axis. We then show that under some conditions the closed-loop system is exponentially stable.     

The location of the continuous-time stationary Kalman filter poles

It is shown that the closed-loop poles of the continuous-time Kalman filter reside in a region in the left half of the complex plane that is confined by two concentric circles whose radii depend on the system matrices and the signal-to-noise ratio. This region includes the system open-loop poles and excludes the imaginary axis. In the case where the system dynamic matrix has a simple eigenstructure, this region possesses an additional boundary, that is parallel to the imaginary axis at a distance that varies with the signal-to-noise ratio.     

基于高阶干扰观测器的极点配置控制器及应用

本文设计了一种可以对外部干扰进行估计的高阶干扰观测器,并针对一类具有外部干扰的单输入单输出离散时间线性系统,提出了一种基于高阶干扰观测器的极点配置控制方法.该方法由常规极点配置控制器和高阶干扰观测器组成.常规极点配置控制器用来保证闭环系统稳定,并将闭环系统的极点配置到理想位置,高阶干扰观测器用来补偿外部干扰对闭环系统的影响.理论分析以及仿真和水箱液位系统中的实验结果表明了所提方法的有效性和优越性.     

Fundamental design limitations of the general control configuration

The theory of fundamental design limitations is well understood for the case that the performance variable is measured for feedback. In the present paper, we extend the theory to systems for which the performance variable is not measured. We consider only the special case for which the performance and measured outputs and the control and exogenous inputs are all scalar signals. The results of the paper depend on the control architecture, specifically, on the location of the sensor relative to the performance output, and the actuator relative to the exogenous input. We show that there may exist a tradeoff between disturbance attenuation and stability robustness that is in addition to the tradeoffs that exist when the performance output is measured. We also develop a set of interpolation constraints that must be satisfied by the disturbance response at certain closed right half plane poles and zeros, and translate these constraints into generalizations of the Bode and Poisson sensitivity integrals. In the absence of problematic interpolation constraints we show that there exists a stabilizing control law that achieves arbitrarily small disturbance response. Depending on the system architecture, this control law will either be high gain feedback or a finite gain controller that depends explicitly on the plant model. We illustrate the results of this paper with the problem of active noise control in an acoustic duct.     

一类线性系统区域极点配置静态输出反馈可靠控制

考虑连续线性系统,在连续增益故障模型的前提下,提出带有执行器故障的圆形区域极点配置的静态输出反馈的可靠控制问题。本文利用线性矩阵不等式(LMI) 在考虑执行器故障模型的基础上,给出圆形区域极点配置的静态输出反馈的可靠控制器存在的充分条件。通过成果的仿真,并进一步说明当系统发生故障时,正常控制的闭环系极点可能离开所给定的圆形区域,而可靠控制的闭环系统仍然会保持极点在给定的圆形区域内。从而看出对系统进行极点配置的静态输出反馈的可靠控制的必要性。     

VIBRATION ATTENUATION OF AN AXIALLY MOVING STRING VIAACTIVE IN-DOMAIN CONTROL METHODS

A study of active vibration control of axially moving string-like system is presented in this paper. The approach is based on the concept of wave absorption or impedance matching through placement of both sensors and actuators in domain. A classical model-matching framework for disturbance rejection is used to solve the control laws. For SISO cases, perfect wave absorption can be achieved if one of the boundary conditions is known. Further, by moving both the sensor and actuator to the boundary, the in-domain control laws become the boundary controllers derived by previous researchers. To avoid the requirement of knowing the boundary condition precisely, a two-sensor control law is then proposed. The resulting controller, though boundary independent, contains an infinite number of poles on the imaginary axis, and the closed-loop system is not internally stable. A simple “notch filter” is added to the control law, and the stability of as well as deterioration in performance are analyzed. Numerical results for a moving string system under external excitation are presented to demonstrate the effectiveness of this controller.     

Exact computation of infimum for a class of continuous-time H∞ optimal control problem with a nonzero direct feedthrough term from the disturbance input to the controlled output

A noniterative method for the computation of infimum for a class of continuous-time H_∞ optimal control problem is considered in this paper. The problem formulation is fairly general and does not place any restrictions on any direct feedthrough terms of the given systems. The method is applicable to systems where (i) the transfer function from the disturbance input to the measurement output is free of imaginary axis invariant zeros and left invertible, and (ii) the transfer function from the control input to the controlled output of the given system is free of imaginary axis invariant zeros and right invertible. The result presented in this paper is a continuation of the previous work of the author and his co-workers (Chen et al., 1992), in which the direct feedthrough term from the disturbance input to the measurement output of the given system are required to be zero.     

Some considerations for estimator-based compensator design

In this paper some criteria are presented for dividing the closed-loop system poles of a feedback system between the estimator and the controller when using an estimator-based compensator. The criteria are based on frequency response considerations, but are related to some well-known facts in the time domain. It is well known, for example, that the closed-loop system poles are the poles of the estimator in union with the controller poles. It is also well known that the time response of the closed-loop plant states due to a command depends only on the closed-loop control poles, and the response of the estimate error depends only on the closed-loop estimator poles. In the frequency domain, the following can be said: the open-loop compensator transfer function from the sensor measurement to the control and the closed-loop transfer function from the sensor measurement to the system output are both independent of how the closed-loop poles are distributed between the controller and the estimator, but the closed-loop transfer function from the command to the control or system output is not. Placing the slower closed-loop poles in the controller causes the control gains to be smaller, which in turn causes the effect of the command signal to be attenuated, both at the control and at the closed-loop system output. Making use of these facts allows the closed-loop poles to be divided between the controller and the estimator on a more intelligent basis than ‘the estimator poles should be three times faster than the controller poles’. In an example, these concepts are applied to the design of a platform despin control system for a dual-spin satellite.     

干扰解耦和极点配置组合问题的研究*

本文用代数方法研究了干扰解耦和极点配置组合问题,导得了存在一个状态反馈控制器使得干扰—输出完全解耦且同时配置闭环系统全部(或部分)极点的充分条件,给出了实现干扰解耦和极点配置的状态反馈阵的一个检验算法。     

Computation of general inner-outer and spectral factorizations

In this paper, we solve two problems in linear systems theory: the computation of the inner-outer and spectral factorizations of a continuous-time system considered in the most general setting. We show that these factorization problems rely essentially on solving for the stabilizing solution a standard algebraic Riccati equation of order usually much smaller than the McMillan degree of the transfer function matrix of the system. The proposed procedures are completely general, being applicable for a polynomial/proper/improper system whose transfer function matrix could be rank deficient and could have poles/zeros on the imaginary axis or at infinity. As an application we discuss the extension to the case of rational matrices of the complete orthogonal decomposition of a constant matrix. Numerical refinements and examples illustrating the proposed approach, are discussed in detail     

Input-output stability degrees for undamped constant coefficients linear partial differential equations

It is an established fact that systems which have transfer matrices with poles converging to the imaginary axis cannot have exponentially stable time responses. Recently it was proved that for a class of partial differential equations with such a structure of poles it is possible to have a fast decay in time, uniformly in space, as arbitrary polynomials if the initial conditions are smooth enough and with an appropriate decay at infinity. The non-homogeneous version of this result which we present here can be summarized as follows: 'arbitrary regularity in space of the input function leads to arbitrary polynomial convergence in time towards the steady state'. The relation between the properties of the input function and the rate of convergence of the poles to the imaginary axis is quantitative and we indicate methods for computing this rate. We also provide conditions for exponential stability in this context. Due to some limitations in exponential stabilization by feedback a natural alternative to stability enhancement is this polynomial one. Therefore it is useful to investigate when it can be recovered in more practical situations (bounded space, boundary control, etc). Possible applications include the control of distributed oscillatory phenomena (e.g. in large flexible structures, plates), and more recently the control of some advanced materials.     

Extremal pole placement in control systems with a low order controller

We develop an optimizational approach to the design of linear control systems with a low order controller. The objective function is given by the right boundary of the location of poles in the closed-loop system, which depends on the values of controller parameters. We specify the types of mutual pole placements (root diagrams) corresponding to singular manifolds of such functions in the space of parameters and, in particular, their critical points. We establish the exact number of critical root diagrams depending on the dimension of the parameter space. With the example of finding a stabilizing control for a triple mathematical pendulum, we demonstrate the algebraic approach to finding the global minimum of the objective function.     

Perturbation of strongly and polynomially stable Riesz-spectral operators

In this paper we consider bounded and relatively bounded finite rank perturbations of a Riesz-spectral operator generating a polynomially stable semigroup of linear operators on a Hilbert space. We concentrate on a commonly encountered situation where the spectrum of the unperturbed operator is contained in the open left half-plane of the complex plane and approaches the imaginary axis asymptotically. We present conditions on the perturbing operator such that the spectrum of the perturbed operator is contained in the open left half-plane of the complex plane and additional conditions for the strong and polynomial stabilities of the perturbed semigroup. We consider two applications of the perturbation results. In the first example we apply the results to the perturbation of a polynomially stabilized one-dimensional wave equation. In the second example we consider the perturbation of a closed-loop system consisting of a distributed parameter system and an observer-based feedback controller solving the robust output regulation problem related to an infinite-dimensional signal generator.     

SIMO和MISO系统绝对稳定性问题的一个猜想和几个推论

首先分析了具有多个非线性特性的 SIMO 和 MISO 系统的绝对稳定性问题, 指出应用已知的频域判据来解决上述问题很难奏效. 然后, 基于所有孤立部分传递函数都正实的充分必要条件给出了上述系统为稳定的一个猜想, 当传递函数的零极点都位于虚轴上时, 由这一猜想得到了一个已知的结论; 当传递函数的零极点都位于实轴上时, 由这一猜想得到了一个新的结论, 本文证明该结论是正确的; 最后, 根据这一猜想, 给出了传递函数极点位于复平面的一个例子, 它涉及到一类系数矩阵为时变正定矩阵的振动方程的稳定性问题, 值得去深入研究.     

Arbitrarily fast and robust tracking by feedback

The output of a singe-input-single-output linear feedback system with more than one pole in excess over the zeros in the loop transmission cannot track arbitrarily fast its input (by the root locus). In this work we extend the linear feedback so that some of the open loop poles may depend on the open loop gain; we call this new class quasi-linear feedback systems. We then derive time domain, pole-zero, and frequency domain conditions which ensure arbitrarily fast and robust tracking by quasi-linear feedback, for an arbitrary number of poles in excess over the zeros. We prove that in a particular case these conditions are equivalent, and that the boundedness in frequency of the closed loop transfer function is no longer necessary for achieving arbitrarily fast tracking. The robustness is to external disturbances and initial conditions, and the open loop has to be minimum phase. Some examples are presented which illustrate these results. They also show that this good performance can be obtained with a reduced control effort, and that quasi-linear feedback can alleviate the limitation on performance of non-minimum phase open loops.     

Dahlin控制器的根轨迹研究

本文研究了针对一阶时滞对象的Dahlin控制器的根轨迹。该根轨迹以闭环系统时间常数为参数。研究表明，随着闭环系统时间常数的减小，除了静止的极点外，控制器的所有的极点都将远离原点；其中，位于实轴上方的极点沿逆时针方向运动；位于实轴下方的极点沿顺时针方向运动。可以通过根轨迹的性质来研究算法的鲁棒性。     

Pole assignment using dynamic compensators with prespecified poles

The paper describes a simple method for the design of physically realizable dynamic output feedback compensators with prespecified poles to achieve pole assignment in single-input, single-output and multivariable systems. In this method, the numerator parameters of the compensator transfer function are used to position the poles of the augmented closed-loop system consisting of the plant and the compensator at specified locations in the complex plane. It is shown that some or all poles of the closed-loop system can be positioned arbitrarily depending on the order of the compensator. The method is first developed for single-input systems. It is then shown to apply directly to single-output systems and is extended to multivariable systems by restricting the compensators to have unity rank. A number of illustrative numerical examples are given     

Relatively optimal control with characteristic polynomial assignment and output feedback

A relatively optimal control is a stabilizing controller such that, if initialized at its zero state, produces the optimal (constrained) behavior for the nominal initial condition of the plant (without feedforwarding and tracking the optimal trajectory). In this paper, we prove that a relatively optimal control can be obtained under quite general constraints and objective function, in particular without imposing 0-terminal constraints as previously done. The main result is that stability of the closed-loop system can be achieved by assigning an arbitrary closed-loop characteristic stable polynomial to the plant. An explicit solution is provided. We also show how to choose the characteristic polynomial in such a way that the constraints (which are enforced on a finite horizon) can be globally or ultimately satisfied (i.e., satisfied from a certain time on). We provide conditions to achieve strong stabilization (stabilization by means of a stable compensator) precisely, we show how to assign both compensator and closed-loop poles. We consider the output feedback problem, and we show that it can be successfully solved by means of a proper observer initialization (based on output measurements only). We discuss several applications of the technique and provide experimental results on a cart-pendulum system.     

The area enclosed by the (oriented) Nyquist diagram and theHilbert-Schmidt-Hankel norm of a linear system

It is shown that the Hilbert-Schmidt-Hankel norm (HSH-norm) of a transfer function of a stable system is equal, up to a constant factor, to the square root of the area enclosed by the oriented Nyquist diagram of the transfer function (multiplicities included). A generalization is presented for the case of systems which have no poles on the stability boundary, but otherwise have no restrictions on the pole locations