Enhanced Dynamic Set-point Weighting Design for Two-Input-Two-Output (TITO) Unstable Processes

2019 ◽  
Vol 15 (1) ◽  
Author(s):  
Purushottama Rao Dasari ◽  
A. Seshagiri Rao
Keyword(s):  
Pid Control ◽  
Time Delays ◽  
Closed Loop ◽  
Control Law ◽  
Unstable Systems ◽  
Set Point ◽  
Point Tracking ◽  
Unstable Processes ◽  
Tito Systems ◽  
Independent Loops

Abstract Control of unstable systems with time delays usually result in overshoots in the closed loop responses. The intricacy involved in multivariable unstable processes further makes the problem more challenging. In industry, set-point weighting is one of the recommended methods to minimize the overshoot. However, design of the set-point weighting parameters determines the percentage of minimization of the overshoot. In this paper, a method is proposed to design the set-point weighting parameters for unstable multivariable processes which is relatively simple and also reduces the overshoot. Weighting is considered for both proportional (β) and derivative (γ) terms in the PID control law. In the closed loop relation for set-point tracking, the coefficients of ‘s’ and ‘s3’ both in the numerator and denominator are made equal in order to find dynamically β and γ. The obtained expressions for β and γ are simple and dynamically depends on the controller parameters and are applied to TITO systems in present work. Decouplers are used in TITO systems mainly to reduce the interaction between the loops so that they can be viewed as independent loops. Decoupler design suggested by (Hazarika and Chidambaram [1] has been used in this work and two TITO unstable processes with time delays are illustrated here. Comparison with the reported methods available in literature verifies that the proposed method gives improved closed loop performance.

Two Degree of Freedom Model Driven PID Control for Unstable Process with Time Delays

2013 ◽  
Vol 339 ◽  
pp. 45-49
Author(s):  
Li Xiang Zhang
Keyword(s):  
Control System ◽  
Control Systems ◽  
Pid Control ◽  
Time Delays ◽  
Degree Of Freedom ◽  
Control Technology ◽  
Model Driven ◽  
Unstable Process ◽  
Unstable Processes ◽  
Two Degree Of Freedom

PID control systems are the most commonly used control technology in industries. However, there are issues on control performances for the unstable process with time delays. In order to improve the control performances of PID control systems, a new two degree of freedom model driven PID control system is introduced in this paper and it is used to the unstable processes with time delay. The model driven PID control is capable of stabilizing with unstable processes by using PD feedback, regulating quickly for disturbance and tracking quickly to the change of set point. With case studies comparing with conventional PID control systems was done.

scholarly journals Design of modified 2-degree-of-freedom proportional–integral–derivative controller for unstable processes

2020 ◽  
Vol 53 (7-8) ◽  
pp. 1465-1471
Author(s):  
Ziwei Li ◽  
Zheng Xu ◽  
Ridong Zhang ◽  
Hongbo Zou ◽  
Furong Gao
Keyword(s):  
Control Method ◽  
Direct Synthesis ◽  
Degree Of Freedom ◽  
Proportional Integral Derivative ◽  
Outer Loop ◽  
Set Point ◽  
Proportional Integral ◽  
Point Tracking ◽  
Disturbance Suppression ◽  
Unstable Processes

Concerning first-order unstable processes with time delays that are typical in chemical processes, a modified 2-degree-of-freedom proportional–integral–derivative control method is put forward. The system presents a two-loop structure: inner loop and outer loop. The inner loop is in a classical feedback control structure with a proportional controller intended for implementing stable control of the unstable process; the outer loop is in a 2-degree-of-freedom structure with feedforward control of set points, where the system’s tracking response of set points is separated from its disturbance response. To be specific, the system has a feedforward controller that is designed based on the controlled object models and mainly used for regulating the system’s set point tracking characteristics; besides, it has a feedback controller that is designed on the ground of direct synthesis of disturbance suppression characteristics to improve the system’s disturbance rejection. To verify the effectiveness, the system is put into a theoretical analysis and simulated comparison with other methods. Simulation results show that the system has good set point tracking characteristics and disturbance suppression characteristics.

scholarly journals Stabilization of Unstable Second-Order Delay Plants under PID Control: A Nyquist Curve Analysis

Actuators ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 227
Author(s):  
Li Sun ◽  
Dan Ma
Keyword(s):  
Control Systems ◽  
Pid Control ◽  
Time Delays ◽  
Closed Loop ◽  
Second Order ◽  
Control Algorithms ◽  
Special Cases ◽  
Communication Links ◽  
Nyquist Stability ◽  
Real Poles

Time delays arise in various components of control systems, including actuators, sensors, control algorithms, and communication links. If not properly taken into consideration, time delays will degrade the closed-loop performance and may even result in instability. This paper studies the stabilization problem of the second-order delay plants with two unstable real poles. Stabilization conditions under PD and PID control are derived using the Nyquist stability criterion. Algorithms for computing feasible PD and PID parameter regions are proposed. In some special cases, the maximal range of delay for stabilization under PD control is also given.

scholarly journals Set-Point Tracking Analysis of Controllers Designed for a Trickle-Bed Catalytic Reactor

2020 ◽  
Vol 5 (2) ◽  
Author(s):  
A Aharram ◽  
◽  
P. K. Juneja ◽  
M Chaturvedi ◽  
R. Mishra ◽  
...  
Keyword(s):  
Closed Loop ◽  
Industrial Process ◽  
Optimal Controller ◽  
Catalytic Reactor ◽  
Third Order ◽  
Set Point ◽  
Point Tracking ◽  
Performance Benchmarks ◽  
Trickle Bed ◽  
Delayed Model

Set-point tracking is one of the key performance benchmarks for a controller. In an industrial process, it is important to choose the optimal controller that offers the best performance. In this work, set-point tracking of 3 different controllers designed by different methods has been evaluated by comparing the closed-loop responses for a selected third-order delayed model.

scholarly journals Set-Point Tracking and Multi-Objective Optimization-Based PID Control for the Goethite Process

IEEE Access ◽  
2018 ◽  
Vol 6 ◽  
pp. 36683-36698 ◽  
Author(s):  
Xiaojun Zhou ◽  
Jiajia Zhou ◽  
Chunhua Yang ◽  
Weihua Gui
Keyword(s):  
Pid Control ◽  
Multi Objective Optimization ◽  
Set Point ◽  
Multi Objective ◽  
Point Tracking

Simplified tuning of IMC based modified smith predictor for UFOPDT processes

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Somak Karan ◽  
Chanchal Dey
Keyword(s):  
Closed Loop ◽  
Performance Enhancement ◽  
Chemical Reactor ◽  
Internal Model Control ◽  
Smith Predictor ◽  
Tuning Parameter ◽  
Set Point ◽  
Point Tracking ◽  
Model Control ◽  
Modified Smith Predictor

AbstractA simplified tuning guideline for internal model control (IMC) based modified Smith predictor technique is reported here for unstable lag dominated first-order processes with dead time (UFOPDT). Pole location in right half section of s-plane signifies the unstable behaviour of UFOPDT processes. Mostly, chemical processes like isothermal chemical reactor, bioreactor, dimerization reactor, fluid catalytic cracker etc. are found to be lag dominated and unstable along with considerable time delay. Smith predictor technique based control methodology is considered to be a well-accepted approach for such cases. However, conventional Smith predictor technique is not capable enough for controlling UFOPDT processes. Whereas modified Smith predictor is found to be quite competent in such cases as its design involves more than one controller. Modified Smith predictor structure is capable to provide desirable closed loop response during set point tracking along with the load recovery phases. To mitigate the tuning complexity of multiple controllers involved in modified Smith predictor designing, suggested IMC structure employs single tuning parameter λ i.e. closed loop time constant for all three controllers concerned. Noticeable performance enhancement is reported by the proposed scheme as no overshoot is observed during set point tracking. Moreover, smooth and efficient load rejection behaviour is also obtained. Supremacy of the proposed tuning is established through closed loop performance comparison with others’ reported modified Smith predictor based tuning relations for chemical reactor and bioreactor in terms of performance indices as well as stability margins.

scholarly journals A Modified 2-DOF Control Framework and GA Based Intelligent Tuning of PID Controllers

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 423
Author(s):  
Gun-Baek So
Keyword(s):  
Disturbance Rejection ◽  
Pid Controller ◽  
Weighting Function ◽  
Pid Controllers ◽  
Set Point ◽  
Tuning Method ◽  
Point Tracking ◽  
Load Disturbance ◽  
Control Framework ◽  
Feedforward Controller

Although a controller is well-tuned for set-point tracking, it shows poor control results for load disturbance rejection and vice versa. In this paper, a modified two-degree-of-freedom (2-DOF) control framework to solve this problem is proposed, and an optimal tuning method for the pa-rameters of each proportional integral derivative (PID) controller is discussed. The unique feature of the proposed scheme is that a feedforward controller is embedded in the parallel control structure to improve set-point tracking performance. This feedforward controller and the standard PID con-troller are combined to create a new set-point weighted PID controller with a set-point weighting function. Therefore, in this study, two controllers are used: a set-point weighted PID controller for set-point tracking and a conventional PID controller for load disturbance rejection. The parameters included in the two controllers are tuned separately to improve set-point tracking and load dis-turbance rejection performances, respectively. Each controller is optimally tuned by genetic algo-rithm (GA) in terms of minimizing the IAE performance index, and what is special at this time is that it also tunes the set-point weighting parameter simultaneously. The simulation results performed on four virtual processes verify that the proposed method shows better performance in set-point tracking and load disturbance rejection than those of the other methods.

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