A modified relay-based technique for improved critical point estimation in process control

Modern methods of design, analysis, optimization and implementation of conventional control algorithms for processes with finite and infinite degrees of freedom

“…   By using these principles a lot of methods for estimation of process parameters u u p , , (0) kG  and corresponding models have been developed [3][4][5][6][7][8][9][10]. Then, methods of the critical experiment based on the PLL (Phase Locked Loop) principle for process characterization have been developed [11,12], etc.…”

“…method of the critical experiment suggested by ZN, is still actual and inspiring for process dynamics estimation regardless if it is performed in the time or in the frequency domain. These two directions in the process characterization through critical experiment under certain conditions imply analysis of the process response in the time domain (the first direction) and in the frequency domain (the second direction) for assumed form of the transfer function of the process model [3][4][5][6][7][8][9][10][11][12][13][14]. Many of developed methods are referred to uncontrolled process (open-loop system), so their application is limited.…”

Enhanced frequency response estimator to guarantee pre-specified phase angle and static disturbance rejection with all harmonics removed

“…Modified relay feedback methods using a two-level signal, a saturation-relay or a preload relay have been proposed to increase the accuracy of the identified frequency data set, by reducing the high order harmonic terms of the relay output [4][5][6]. Also, a modified relay-based technique and a phase-locked loop identifier using sinusoidal signals have been proposed to remove the harmonics completely [7][8][9].…”

“…All previous relay feedback methods except two [7,9] were unable to completely reject the effects of the harmonics, inevitably resulting in some errors in estimating the frequency data of the process. Also, the two previous approaches [7,9] have some drawbacks even though they can remove the harmonics completely in ideal situations. One method [7] cannot guarantee a desirable cycle under the circumstances of static disturbances.…”

PID Controller Tuning Based on the Classification of Stable, Integrating and Unstable Processes in a Parameter Plane

“…This drawback is eliminated by Aström and Hägglund (1984). The factors influencing the critical point estimation accuracy in this conventional relay setup are: the use of describing function method is faced with the fact that higher harmonics are not efficiently filtered out by the process, presence of the load disturbance d, and presence of the measurement noise n. The first drawback of the conventional relay experiment is eliminated by the modified relay setup (Lee et al, 1995). Due to its simplicity, the relay-based setup proposed by Aström and Hägglund (1984) is still a basic part of different methods developed in the area of process dynamics characterization.…”