锅炉汽包水位的多模态仿人智能控制

分析了汽包水位的动态特性和传统的控制方法,以及仿人智能控制理论。针对锅炉汽包水位调节系统提出一种基于特征辨识的多模态仿人智能控制方法.这种方法模仿操作人员的操作过程,根据对象动态特性适时改变控制策略,使控制作用及时、准确。通过与传统方法的对比仿真表明,该方法能够较好地克服虚假水位现象,控制效果良好。     

汽包水位粒子群-PID优化控制

对循环流化床锅炉汽包水位控制系统,采用串级三冲量PID控制,应用粒子群优化算法对PID控制器进行参数整定,并获得了最优参数。仿真结果表明,与传统整定方法相比,这种参数整定方案使汽包水位控制系统具有更好的控制品质,提高了系统的静动态特性。     

Convergence of discrete-time Kalman filter estimate to continuous time estimate

This article is concerned with the convergence of the state estimate obtained from the discrete-time Kalman filter to the continuous time estimate as the temporal discretisation is refined. The convergence follows from Martingale convergence theorem as demonstrated below; however, surprisingly, no results exist on the rate of convergence. We derive convergence rate estimates for the discrete-time Kalman filter estimate for finite and infinite dimensional systems. The proofs are based on applying the discrete-time Kalman filter on a dense numerable subset of a certain time interval [0, T].     

Digital flight control design for a tandem-rotor helicopter

Methods and results in the continuing development of a digital flight control system (DFCS) for a CH-47B helicopter are presented. The helicopter is the research vehicle for the NASA VTOL Approach and Landing Technology (VALT) Program, and it equipped with comprehensive equipment for the investigation of navigation, guidance, and control requirements for future VTOL aircraft. Two control modes (attitude-command and velocity-command) are implemented, and each mode provides ‘Type 1’ response to guidance commands. DFCS design is based upon optimal estimation and control methods, which are found to provide flexible and efficient means for defining practical digital control systems.     

Networked iterative learning control design for discrete-time systems with stochastic communication delay in input and output channels

This paper develops two kinds of derivative-type networked iterative learning control (NILC) schemes for repetitive discrete-time systems with stochastic communication delay occurred in input and output channels and modelled as 0-1 Bernoulli-type stochastic variable. In the two schemes, the delayed signal of the current control input is replaced by the synchronous input utilised at the previous iteration, whilst for the delayed signal of the system output the one scheme substitutes it by the synchronous predetermined desired trajectory and the other takes it by the synchronous output at the previous operation, respectively. In virtue of the mathematical expectation, the tracking performance is analysed which exhibits that for both the linear time-invariant and nonlinear affine systems the two kinds of NILCs are convergent under the assumptions that the probabilities of communication delays are adequately constrained and the product of the input–output coupling matrices is full-column rank. Last, two illustrative examples are presented to demonstrate the effectiveness and validity of the proposed NILC schemes.     

Using discrete models with continuous design packages

An algorithm is derived for converting a discrete state-space model to an equivalent continuous form. Both approximate and exact solutions are presented. A new discrete model is also derived, for which the continuous design will be valid. The principles are illustrated using an example of optimal control, and the discrete and continuous designs are compared. These techniques have particular relevance for computer aided design of feedback control systems.     

PID controller design for nonlinear systems represented by discrete-time local model networks

This paper deals with proportional–integral–derivative (PID) controller design for nonlinear systems represented by local model networks. The proposed method is based on the concept of parallel distributed compensators where the scheduling of the local model network is adopted for the PID parameters. The proposed design method for nonlinear PID controllers considers closed-loop stability by means of a Lyapunov stability criterion as well as closed-loop performance. All PID parameters are determined by a multi-objective genetic algorithm (multiGA), which handles the trade-off between stability and performance. A simulation example demonstrates the effectiveness of the proposed method.     

An impulsive‐switched‐system approach to aperiodic sampled‐data systems with time‐delay control

This paper devotes to the stability of aperiodic sampled‐data systems with time‐delay control, where the delays can impose a positive effect on the stability of the systems. The systems are modeled as impulsive switched systems with fixed switching laws. A novel separation theorem is presented to determine the Schur property of a matrix product and then used to obtain a less conservative stability criterion for the impulsive switched systems with fixed switching laws. By the separation theorem and a loop‐functional approach, some new stability and stabilization criteria for aperiodic sampled‐data systems with time‐delay control are provided in terms of linear matrix inequalities. Finally, the stability and stabilization results are tested on some classical numerical examples to illustrate the efficiency of the proposed method.     

HIFU医疗系统中介质水水温水位的智能控制

为了满足HIFU医疗系统要求,在分析常用水温水位单一控制方式存在问题的基础上提出了水温水位智能控制系统。阐述了系统的硬件设计、控制方案及原理,并给出了水温水位控制原理图和部分软件流程图。仿真实验结果表明,采用该系统对水温水位进行控制,取得了良好的效果,而且调节过程平稳。     

Discrete-time optimal control of systems with unilateral time-delays

Industrial plants which contain unilateral flow of material are considered. First, it is shown that such plants can be represented by finite-dimensional difference equations after sampling. Then, the design of discrete-time optimal control systems is studied based on the difference equations. The main difficulty in this design problem is the high dimensionality resulting from the discretization of long delays. In this paper, a new algorithm to solve the discrete Riccati equation for this class of systems is proposed. An example is given to illustrate how the computational difficulties are effectively reduced.     

Dynamic scaling and observer design with application to adaptive control

A constructive algorithm for designing an observer for a class of nonlinear systems is presented. We follow the invariant manifold based approach which allows one to shape the dynamics of the estimation error. However, this shaping relies on the solution of a partial differential equation, which becomes difficult for multi-output systems. In this paper we remove this restriction by adding to the reduced-order observer an output filter and a single dynamic scaling parameter. We show that this method can be applied to systems with unknown parameters, leading to a new class of adaptive controllers. As an application, we consider two examples: an induction motor with unknown load and a longitudinal controller for an aircraft with unknown aerodynamic properties.     

New design of linear discrete-time predictor using covariance information

A discrete one-stage predictor algorithm using covariance information in linear systems is derived. The algorithm is obtained for white Gaussian observation noise. The signal is a nonstationary or stationary stochastic process. The auto-covariance function of the signal is expressed using a semi-degenerate kernel of discrete-time systems. The semi-degenerate kernel can represent general covariance functions of random processes by a finite sum of nonrandom functions.     

Sampled‐data control of nonlinear networked systems with time‐delay and quantization

In this paper, the stabilization problem of a class of nonlinear networked systems with time‐delay and quantization through sampled‐data control is investigated. With sampled‐data control, sufficient conditions to guarantee the trivial solution of the nonlinear networked system to be asymptotically stable without any quantization or with uniform quantization are derived. Finally, an example of a continuous‐time nonlinear system controlled through a digital controller and a communication channel is given to illustrate the effectiveness of the proposed control methods. Copyright © 2015 John Wiley & Sons, Ltd.     

On analysis and design of discrete-time constrained switched systems*

This paper presents novel design techniques for discrete-time constrained switched systems. Two problems are considered: the first one is centred at determining a set of switching rules for which the system is unconditionally stable; the second one focuses on the design of a stabilising state-dependent switching function that is subject to structural constraints. Convex optimisation is the kernel of the devised procedures and, thus, these techniques are computationally viable.     

Linear-quadratic discrete-time control and constant directions

The general linear-quadratic discrete-time minimization problem is studied, in which no restrictions are placed on the singularity or otherwise of certain matrices, or the appearance of cross-product terms in the performance indices. Constant directions are characterized in a number of ways, and an algorithm is presented for replacing a prescribed problem with constant directions by one of lower state and/or control dimension, lacking constant directions. The replacement is achieved using a series of state and input co-ordinate basis changes, and allows simplification of the calculations obtaining the optimal control law and performance index of the original problem.     

锅炉汽包水位三冲量控制的水位补偿计算及应用

锅炉汽包水位主要采用三冲量控制,但是汽包中汽液的密度变化造成水位测量不准,从而导致控制效果变差。本文采用多测孔技术各增设了三块现场仪表来分别测量汽包的实时温度和压力,进而对汽包水位进行补偿计算,并在DCS系统进行了组态和现场应用。实际应用效果表明提高了水位测量精度,满足了汽包控制及联锁的要求。     

非线性PID控制在液位控制系统中的应用

针对液位控制系统的大时滞、不稳定性,常规PID控制很难满足要求,提出带有死区的非线性PID控制,实际运行验证了该方法的有效性.     

Sampled‐data output feedback stabilization for a class of switched stochastic nonlinear systems

This paper investigates a global sampled‐data output feedback stabilization problem for a class of switched stochastic nonlinear systems whose output and system mode are available only at the sampling instants. An observer is designed to estimate the unmeasurable state and thus a sampled‐data controller is constructed with the sampled estimated state. As a distinctive feature, a merging virtual switching signal is introduced to describe the asynchronous switching generated by detecting the system mode via a sampler. By choosing an appropriate piecewise Lyapunov function, it is proved that the proposed sampled‐data controller with allowable sampling period can stabilize the considered switched stochastic nonlinear systems under an average dwell‐time condition. Finally, two simulation results are presented to illustrate the effectiveness of the proposed method.     

A stability criterion for asynchronously switched linear systems via sampled‐data control

This paper considers an asynchronous problem for sampled‐data control of switched linear systems, which are described as switched linear systems with an input delay. To handle the problem, this paper proposes a stability criterion for the systems by constructing a novel Lyapunov‐Krasovskii functional dependent not on system modes but on controller modes. The functional continuously remains when the system modes are switched but discontinuously changes whenever the controller mode moves to the current system mode at the sampling instants. Furthermore, the functional is allowed to increase or decrease up to a certain level when the functional discontinuously changes and to increase up to a certain level when the system modes and the controller modes are asynchronous. Based on the functional, this paper derives an average dwell time associated with the interval of samplings and the incremental level of the functional for guaranteeing the stability of the systems. A numerical example illustrates the validation of the proposed method.     

Deterministic and stochastic control of discrete-time bilinear systems

Optimal control of a class of time invariant single-input, discrete bilinear systems is investigated in this paper. Both deterministic and stochastic problems are considered.

In the deterministic problem, for the initial state in a certain set ∑₀, the solution is the same as the solution to the associated linear system. The optimal path may be a regular path or a singular path.

The stochastic control problem is considered with perfect state observation, and additive and multiplicative noise in the state equation. It is demonstrated that the presence of noise simplifies the analysis compared to that in the determinstic case.