Reliable decentralized integral-action controller design

Reliable stabilizing controller design with integral-action is considered for linear time-invariant, multi-input-multi-output decentralized systems with stable plants. Design methods are proposed to achieve reliable closed-loop stability with integral-action in each output channel for asymptotic tracking of step-input references applied at each input. The design approaches guarantee stability and integral-action in the active channels when all controllers are operational and when any of the controllers is set equal to zero due to failure     

Nearly decoupled multivariable control systems design Part 2. Multi-loop control systems design

The design technique proposed in Part 1 is successfully developed to deal with multiloop control systems design. The inner loop is used to extend the frequency range of sensitivity reduction. In the case of a ‘square’ plant this inevitably leads to an excessive noise-response bandwidth. However, it is discovered that the noise response within the inner loop can be reduced considerably by the use of extra output measurements. Again, the standard model-matching problem plays a vital role in the design of a control system with a ‘tall’ plant.     

Feedback design in control reconfigurable systems

This paper is concerned with the design of reconfigurable control laws for fault-tolerant systems. From the control design point of view the issue of performance robustness during the system normal operation versus failure sensitivity at the time of a system component failure is addressed. To achieve a balanced design, a parametrized set of controllers satisfying a prescribed performance level is first constructed, and then the parameter is optimized under a detection criterion that sensitizes the measurements to some specific failures. An example involving aircraft surface impairment is given to explain the procedure for obtaining the optimized design.     

Limitations in tracking systems

In this paper, we obtain information theoretical conditions for tracking in linear time-invariant control systems. We consider the particular case where the closed loop contains a channel in the feedback loop. The mutual information rate between the feedback signal and the reference input signal is used to quantify information about the reference signal that is available for feedback. This mutual information rate must be maximized in order to improve the tracking performance. The mutual information is shown to be upper bounded by a quantity that depends on the unstable eigenvalues of the plant and on the channel capacity. If the channel capacity reaches a lower limit, the feedback signal becomes completely uncorrelated with the reference signal, rendering feedback useless. We also find a lower bound on the expected squared tracking error in terms of the entropy of a random reference signal.We show a misleading case where the mutual information rate does not predict the expected effect of nonminimum phase zeros. However, mutual information rate helps generalize the concept that there is a tradeoff when tracking and disturbance rejection are simultaneous goals, and a constraint communication channel is present in the feedback loop. Examples and simulations are provided to demonstrate some of the results.     

Probabilistic design of LPV control systems

This paper presents an alternative approach to design of linear parameter-varying (LPV) control systems. In contrast to previous methods, which are focused on deterministic algorithms, this paper is based on a probabilistic setting. The proposed randomized algorithm provides a sequence of candidate solutions converging with probability one to a feasible solution in a finite number of steps. The main features of this approach are as follows: (i) The randomized algorithm gives a method for general LPV plants with state space matrices depending on scheduling parameters in a nonlinear manner. That is, the probabilistic setting does not need a gridding of the set of scheduling parameters or approximations such as a linear fractional transformation of the state space matrices. (ii) The proposed algorithm is sequential and, at each iteration, it does not require heavy computational effort such as solving simultaneously a large number of linear matrix inequalities.     

Optimization problems arising in control systems design

Control design is naturally formulated as an optimization problem in which the constraints may be conventional, non-differentiable (e.g. constraints on singular values for robustness or eigenvalues for stability) or infinite-dimensional (e.g. time domain constraints on step responses or frequency domain constraints for performance) and the design variables may be finite dimensional (e.g. parameters of a controller) or infinite dimensional (e.g. a non-linear control law). This paper concentrates on the latter type of problem, a typical problem being the simultaneous determination of a Lyapunov function and non-linear control law to stabilize a non-linear system. An outer approximation algorithm is presented and shown to produce converging subsequences. The algorithm is illustrated by its application to a simple non-linear control problem.     

Architecture design for internet-based control systems

The Internet is playing an important role in information retrieval, and additionally industrial process manipulation. This paper describes an approach to writing requirements specifications for Internet-based control systems, from which architectures can be derived. The requirements specifications developed are described in terms of a functional model, which is then extended to form an information architecture. Distinct from the functional model, the information architecture provides an indication as to the architectural structure of subsequently developed Internet-based control systems. Three general control structures are generated from the analysis of an information architecture. An integrated-distributed architecture is derived as an ideal implementation, in which a control system is linked to the Internet at all levels of a control system hierarchy.     

Networked control design for linear systems

In this paper we study a systematic networked control method designed specifically to handle the constraints of the networked realization of a linear time invariant control system. The general structure of the proposed controller requires switching between the open loop and closed loop subsystems of the controller which is dictated by the behaviour of the communication network.     

Overlapping control design for multi-channel systems

This paper deals with the decentralized overlapping control of interconnected systems. The notion of a quotient overlapping fixed mode (QOFM) is first introduced and it is shown that a mode of an interconnected linear time-invariant system can be shifted by means of a general decentralized overlapping controller if and only if it is not a QOFM. It is then asserted that any interconnected system with no unstable QOFM can be stabilized by using an appropriate finite-dimensional linear time-varying controller. It is also shown how the existing results aiming at designing a decentralized controller of a certain type such as generalized sampled-data hold function, finite-dimensional linear time-varying, and sampled-data can be utilized to design a decentralized overlapping controller of a desired form, in order to achieve any design specification. The efficacy of the results is elucidated through two numerical examples.     

挠性系统的鲁棒控制设计

提出一种新的鲁棒设计思想：将挠性模态部分的Nyquist图线安排到右半平面。由于综合运用了频域分析、极点配置、正实性引理、线性矩阵不等式等概念和算法，使得这种鲁棒控制设计得以实现，且简单直观。通过两个算例说明了该设计方法的有效性。     

Analysis and design of oscillatory control systems

This paper presents analysis and design results for control systems subject to oscillatory inputs, i.e., inputs of large amplitude and high frequency. The key analysis results are a series expansion characterizing the averaged system and various Lie-algebraic conditions that guarantee the series can be summed. Various example systems provide insight into the results. With regards to design, we recover and extend a variety of point stabilization and trajectory tracking results using oscillatory controls. We present novel developments on stabilization of systems with positive trace and on tracking for second order underactuated systems.     

Parameter space design of robust control systems

Find a state or output feedback with fixed gains such that nice stability (defined by a region in the eigenvalue plane) is robust with respect to large plant parameter variations, sensor failures, and quantization effects in the controller. Keep the required magnitude of control inputs small in this design. A tool for tackling such problems by design in the controller parameter spaceKis introduced. Pole placement is formulated as an affine map from the spacePof characteristic polynomial coefficients to theKspace. This allows determining the regions in theKspace, which place all eigenvalues in the desired region in the eigenvalue plane. Then tradeoffs among a variety of different design specifications can be made inKspace. The use of this tool is illustrated by the design of a crane control system. Several open research problems result from this approach: graphical computer-aided design of robust systems, algebraic robustness conditions, and algorithms for iterative design of robust control systems.     

The design of distributed control computer systems

The top-down approach in the design of Distributed Control Computer Systems, DCCS, is presented. The starting point of the study is three statements: (i) the design approach should be production process control oriented; (ii) for real time process control applications, computer networks require an efficient communication subsystem, the most important features of which are high reliability and short message transmission times and (iii) recent research has shown that the tools and methodologies used in both computing and control should be complementary to each other in order to solve some of the distributed control computer system/distributed computer control system design problems. The paper contains the design problems of distributed control computer systems, the presentation of the methods and tools for the study and design of the DCCS, the top-down approach in the design of the DCCS, and examples of two design stages.     

带扰动控制系统的形式化设计

利用有限抽象进行控制系统的形式化分析与设计是目前研究较多的一类控制系统分析与设计方法.本文提出两种方法,使用有限抽象,构造出两种控制器,使带扰动的控制系统满足时序逻辑规范.为此,首先在时序逻辑规范上引入"弱化"转换函数和"强化"转换函数.进而,利用"弱化"转换函数提出一种方法用于构造控制器,使原系统近似满足给定规范;利用"强化"转换函数,提出另一种方法用于构造控制器,使原系统严格满足给定规范.本文分析比较上述两种方法与文献中已有的方法,指出各自的优缺点和适用范围.最后给出仿真实验,说明上述两种方法的有效性并展示这些方法的不同适用范围.     

Digital design of variable structure control systems

Reachability conditions are developed for discrete single-input-single-output variable structure control systems described by linear mathematical models in general state-space form to reach a switching function from anywhere in state space. Stability conditions of a sliding mode are investigated. A modified algorithm is proposed to simplify the design procedure. Practical application to a thermal process has been achieved by using the modified algorithm to show the potential for development and practical results are compared with those using the classical PID controller design.