Showing papers by "Derek P. Atherton published in 2001"

Smith predictor design by CDM

Abstract: Good control of processes with a long dead time is often achieved using a Smith predictor structure. Typically a PI or PID controller is used in this configuration. In this paper, controller design is considered for a recently proposed modified form of the Smith predictor. The design is done using the Coefficient Diagram Method (CDM) to achieve a good step response to a set point change. The proposed method is compared with some other existing methods to illustrate its value.

Exact parameter estimation from. relay autotuning under static load disturbances

Abstract: Obtaining the parameters for PID controllers based on limit cycle information from the process in a relay controlled feedback loop has become an accepted practical procedure. If the form of the plant transfer function is known, exact expressions for the limit cycle frequency and amplitude can be derived in terms of the plant parameters, so that their measurements, assumed error free, can be used to calculate the parameter values. In the literature to date the solutions have only been considered for odd symmetrical limit cycles which will not be the situation when constant disturbances exist. Use of these expressions will lead to errors when the limit cycle is not odd symmetrical. The paper reports on exact parameter estimation for stable and unstable FOPDT or SOPDT plant transfer functions from relay autotuning under static load disturbances where the limit cycles are asymmetrical.

A Model-Based Method for an Online Diagnostic Knowledge-Based System

Abstract: Fault diagnosis is very important for modern production technology and has received increasing theoretical and practical attention during the last few years. This paper presents a model-based diagnostic method for industrial systems. An online, real-time, deep knowledge based fault detection system has been developed by combining different development environments and tools. The system diagnoses, predicts and compensates faults by coupling symbolic and numerical data in a new environment suitable for the interaction of different sources of knowledge and has been successfully implemented and tested on a real hydraulic system.

Relay feedback and wavelet based estimation of plant model parameters

Abstract: The paper presents a relay feedback and wavelet based method for the estimation of completely unknown processes for autotune purposes. From a single symmetrical relay feedback analysis a set of general expressions are presented for on-line process identification. Using these expressions the exact parameters of open loop stable and unstable first order plus time delay (FOPDT) and second order plus time delay (SOPDT) transfer function models may be obtained from simple measurements made on the limit cycle. However, noise in limit cycle output results in inaccurate estimate of the process model parameters. This paper proposes an effective mother wavelet for tracking the critical points of a noisy output signal. Further, using the wavelets based noise reduction it has been shown how accurate measurements can be made on the noisy limit cycle signal. Simulation studies illustrate the value of the proposed identification method.

Bode envelopes of multilinear affine systems

Abstract: The paper deals with the problem of computing the Bode envelope of an uncertain transfer function whose numerator and denominator polynomials are multiples of independent uncertain polynomials of the form P(s, q) = l 0 (q) + l 1 (q)s +………+ l n (q)sn whose coefficients depend linearly on q = [q 1 , q 2 ,…, q q ]T and the uncertainty-box is Q = {q : q i ∊[q i , q i ], i = 1,2,…, q} Using the geometric structure of the value set of P(s, q), a powerful edge elimination procedure is proposed for computing the magnitude and phase envelopes of these uncertain systems A numerical example is included to illustrate the benefit of the method presented

A new control strategy for integrating and unstable time delay processes

Abstract: This paper presents a novel control strategy for open-loop integrating and unstable processes with time delay and shows that on it the Smith predictors are not absolutely necessary to overcome the control problems caused by long dead time in these processes. An inner feedback loop with a proportional (P) or proportional and derivative (PD) controller plays an important role in stabilizing the integrating and unstable processes. Then the feedforward controller in the outer loop is designed to control the stabilized process efficiently. Simple tuning formulae have been derived for the controllers based on user-specified gain and phase margins. A comparison of the performance of the proposed design settings with those given by earlier workers is presented.