Time-Delay Systems
Time-Delay Systems
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DOI：
10.1007/978-1-84628-531-8_1
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Qing‐Guo Wang;Tong-heng Lee;K. Tan
中科院分区：
文献类型：
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作者：
Qing‐Guo Wang;Tong-heng Lee;K. Tan
在过程控制系统中，时间延迟可以定义为从控制信号的应用到过程变量中任何可观察到的变化的时间间隔。时间延迟一直是过程控制中遇到的最困难的问题之一。它可能因各种原因和不同程度而发生。这可能归因于过程变量测量的延迟。一个这样的例子是轧钢过程，其中测量点位于钢压机下游的某个距离处，使得在向压机控制器反馈板厚度时总是存在时间延迟。时间延迟可能是由于控制延迟，典型的涉及管道和输送机系统中的材料运输的过程，例如热、合成和蒸馏过程。对于这些过程，致动装置在物理上是有限的，使得瞬时的脉冲状动作是不可能实现的。在现代数字控制系统中，时间延迟也可能以采样间隔的形式出现，或者以多路访问现场网络系统避免冲突所涉及的固有轮询和等待状态的形式出现。消除时间延迟的最佳方法是通过仔细和适当的系统和工业工程实践来完全避免它。在过程设计中，必须仔细考虑传感器和控制设备的放置，以尽量减少死区时间。然而，在实际执行这些系统时受到实际、空间和业务方面的限制，这一点的实现程度相当有限。因此，时滞系统的控制代表了一类重要的问题，它已经并将继续对过程控制工程师提出强烈的挑战。
Atime-delayunder the context of process control systems may be defined asthe time interval from the application of a control signal to any observable change in the process variable. Time delays have always been among the most difficult problems encountered in process control. It could occur for various reasons and in different magnitudes. It may be attributed to a delay in measurement of the process variable. One such example is the steel rolling process where the measurement point is located at some distance downstream of the steel press so that there is always a time delay in the feedback of plate thickness to the press controller. The time delay could be due to a delay in control, typical of processes involving transportation of materials in pipelines and conveyor systems such as thermal, composition and distillation processes. For these processes, the actuating devices are physically limited, so that instantaneous impulse-like action is not realizable. In modern digital control systems, time-delay can also arise in the form of sampling intervals, or the inherent polling and waiting states involved in collision avoidance for multiple access field-network systems. The best approach to eliminate time-delay is to avoid it altogether, through careful and proper system and industrial engineering practices. In the design of processes, careful considerations must be given to placement of sensors and the control devices to minimize dead times. However, under physical, spatial and operational constraints in the practical implementation of these systems, the extent to which this is realizable is fairly limited. Therefore, control of time-delay systems represents one important class of problems which has and will continue to pose a strong challenge for process control engineers.