The delay operator z-1 - inappropriate for use in recursive digital filters?Goodall, R.M.
doi: 10.1177/014233129001200503pmid: N/A
The paper questions the appropriateness of using the delay operator z-1 for recursive digital filters, particularly when applied to the realisation of digital control. The well known problems of coefficient sensitivity at high sample frequencies are reviewed, and the fundamental reason for this lack of robustness is identified. An analogy is used to argue that the approach whereby digital filters are designed using discrete transfer functions in z is, in fact, mathematically dubious, perhaps unperceived by their users, and that the sensitivity problems are inevitable when z is used. The analogy is extended to argue strongly for using an alternative, the δ operator, which inherently avoids the problem. Some of the implications of using the new operator are assessed, but the main purpose of the paper is to challenge the established practice of using the z operator.
On-line steady-state optimisation of nonlinear constrained processes with slow dynamicsZhang, H.; Roberts, P.D.
doi: 10.1177/014233129001200504pmid: N/A
A scheme for on-line optimisation of constrained nonlinear processes with slow dynamics is suggested and applied to a continuous reactor process. A two-model adaptive mechanism, dynamic and steady state, is used in the scheme. The dynamic model is used to approximate the process locally at each working point for the purpose of estimating steady-state derivatives, and the steady-state model is used for model-based optimisation. The performance lost caused by the inaccuracy of the steady-state model is compensated for by derivatives information which is obtained from dynamic data. The correct optimum can be achieved on-line even if both models are very rough. As shown in applications, the scheme is suited to various types of constraints and nonlinearities and is noise-insensitive.
Interconnected spatially distributed systemsWhalley, R.
doi: 10.1177/014233129001200505pmid: N/A
In this paper system models arising from process-plant installations are derived in the form of an interconnected series of mixed, distributed and lumped-parameter realisations. The terminal characteristics of these models is shown to be a rational, multidimensional function of a finite set of transformed discrete time-delay variables which may be used in feedback-control studies. By employing a linear mapping of the support of the model it is established that stability can be assessed using a corresponding algebraic function to that of the denominator of the system model. Simple worked examples are used to illustrate the procedure.
The control and supervision of groups of lifts using the blackboard architecture approachBrandin, B.; Chen, T.; Derventzis, C.; Pang, G.
doi: 10.1177/014233129001200506pmid: N/A
An artificial-intelligence technique, namely blackboard architecture, is used to confront the problem of controlling and supervising groups of lifts.With the construction of high-rise buildings, transportation efficiency has become an important consideration in lift systems design. The variety of constraints, and especially the constraints related to traffic, make the design of lift systems and lift traffic supervision and control a complex task.The paper is divided into two main sections: the first considers the design and development of the shell of the blackboard system presented; the second describes the implementation of the problem solving framework. Simulation results follow as well as a discussion and conclusions.