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In this paper, stabilization and control of linear time-invariant systems with two unstable poles and time delay are looked at. It is well known that time delays make it harder to analyze stability and come up with good control strategies. Because of this, suggest a simple control strategy based on “dynamic optimization” to stabilize this type of system. In this work, dynamic optimization (DO) to figure out the PID controller parameters for a process that is unstable in second order plus time delay (SOPTD). In particular, the process model is used to figure out the controller parameters so that integral performance criteria and controller variations are kept to a minimum (such as ISE, IAE and TV). The controller responses looked at both the set-point following the load disturbance rejection. Robustness studies have been carried out for uncertainties in the process parameters. Lastly, some examples are given to demonstrate the controller performance and robustness.

Reactive distillation (RD), a process-intensified technique, involves the integration of reaction and separation in a single unit. High non-linearities associated with the reactive distillation process constrict the control degrees of freedom and set the key challenge in the design of a robust control system. In this chapter, reactive distillation diphenyl carbonate (RD-DPC) design is optimized, and a decentralized as well as centralized feedback control configuration is applied to carry out the control studies. To execute the control scheme, a dynamic model of RD-DPC process is developed using Aspen Dynamic and interfaced with MATLAB Simulink for online control implementation. A comparative multi-loop feedback controller control performance study is done for different transfer function models obtained by using analytical- and optimization-based process identification techniques. The controller parameters obtained from the simple internal model control (SIMC) tuning relations for decentralized controller and Tanttu & Lieslehto (TL) tuning relations for centralized controller are applied to (i) the linear transfer function model and (ii) non-linear plant model. Set-point tracking, load rejection studies and robust stability analysis are carried out to compare the performance of different models and to investigate the controller performance of the non-linear model.

Reactive distillation (RD), a process intensified technique, involves integrating reaction and separation in a single unit. High non-linearities associated with the RD process constrict the control...

The biggest log modulus tuning (BLT) method is extended to unstable systems. The method is modified to design (i) decentralized Proportional-Integral (PI) controllers and (ii) centralized PI controllers for two-input two-output (TITO) systems. A method is given to specify the value for The internal model controller using Tanttu and Lieslehto method is applied for centralized controller design. The detuning parameter (F) is selected for both the schemes (centralized controller and decentralized controller) to get the value of BLT as +12 dB. Simulation studies are carried out for two TITO systems to evaluate the performance of both the proposed schemes. The centralized controllers produce superior performances and decreased interactions over the decentralized PI controllers. The present method gives robust performances.

In this paper, the simple method of designing decentralized Proportional–Integral-Derivative (PID) controllers by the synthesis method is extended to design centralized PID controllers. The centralized controllers give improved responses and reduced interactions when applied to systems with λij

The simple method of designing decentralised PID controllers for stable systems by the synthesis method is extended to unstable systems. The effectiveness of the proposed method is compared with that of the available decentralised controllers. The robustness of these controllers is evaluated by the inverse maximum singular value versus frequency plot for both the input multiplicative uncertainty and the output multiplicative uncertainty. Simulation results for two input - two output (TITO) systems demonstrate that the proposed method guarantees robust stability and it provides better servo and regulatory responses.

The design of decentralized proportional integral (PI) controller based on biggest log modulus tuning (BLT) tuning method is extended to design centralized PI controllers for two-input–two-output (TITO) systems. The multivariable PI control structure proposed by Tanttu and Lieslehto (1991) is considered. The single detuning parameter (F) is selected in order to get the biggest log modulus as 4 dB. Decentralized PI controllers are also designed using the IMC to get the biggest log modulus as 4 dB. The centralized PI controllers give improved main responses and decreased interactions. This improvement is shown particularly for TITO systems having the relative gain element, λij

In this work, the design and evaluation of a fuzzy logic control of liquid flow process is analyzed experimentally using MATLAB package. MATLAB is a widely used software environment for research and teaching applications on control and automation. The interface is a collection of hardware and software modules used to flexibly connect a plant, process or instrument (etc.) to a digital computer. The experimental performance of proposed fuzzy logic control is carried out on existing computer control of flow process. The program of Real-time data acquisition and control has been developed using modules called, “To Instrument” and “Query Instrument” of MATLAB for experimental work. Thus, The present implementation of intelligent fuzzy logic control on real-time basis is a pioneering work at laboratory scale. It is considered to be a great contribution in area of advanced process control systems. The simulation and experimental results clearly shows that the Intelligent Fuzzy Logic Controller gives a better control without overshoots of liquid flow rate in comparison with conventional PID controller.

In the present work, the matrix notation is used to derive the IMC decentralized and centralized PI controllers. Maclaurin series is applied to the resulting equation to get the controller parameters. For design of the controllers, the diagonal and full elements of the process are used. Whereas for evaluating the performance of the controllers, the full process transfer function matrix is used. To show the performance of the proposed decentralized control system two examples are considered and one example is considered for evaluating the performance of the proposed centralized controller. The performance of the present method is compared with the reported methods.

Higher order transfer function models are approximated by a three parameters models such as critical damped SOPTD and FOPTD models. A design method for centralized PID controllers using Tanttu and Lieslekto method for the identified critical damped Second order plus time delay (SOPTD) is proposed. Centralized PI controllers are designed by the Tanttu and Lieslekto method from the identified First order plus time delay (FOPTD) model. The Centralized SOPTD-PID control system gives enhanced main responses and lesser interactions. This improvement is shown for TITO systems having high interactions (λ11 > 1). The robustness study for the controllers is carried out by using the Inverse Maximum Singular Value versus Frequency plot for the input and output multiplicative uncertainties. Simulation results are given for one TITO system having λ11 > 1. The centralized SOPTD-PID controllers give improved results in comparison with the centralized FOPTD-PID/PI controllers.

Established equivalent transfer function (ETF) matrix method for stable MIMO systems is extended to unstable systems to design multivariable proportional and integral (PI) controllers. The simplified decoupler decomposes the unstable multi-loop systems into independent loops with ETFs as the resultant decoupled process model having unstable poles. Single loop PI controllers are designed by the synthesis method based on the unstable ETFs. Since the overshoot is higher for the unstable systems, a double-loop structure is used to reduce the overshoot. To stabilize the unstable system, inner loop P controllers are designed for the diagonal elements of ETFs by the synthesis method. Further, for the stabilized inner-loop system, diagonal PI controllers are designed based on the identified simple First order plus time-delay (FOPTD) model. Simulation results show that the designed control system gives a better performance than that reported in literature.

In this paper, a new multi centralized control system method proposed for unstable systems using gain and phase-margin specifications. Effective relative gain array based loop interactions are considered to design of off-diagonal controllers. Unstable first order plus time delay models are changed to second order plus time delay model without losing model identity to design a two degree of freedom PID diagonal controllers. Equivalent transfer function method Xiong et al. (J Process Control 17(8):665–673, 2007) is extended to unstable system. Simulation results show that; designed robust control system gives good response and control action. Performance evaluation is done by integral absolute error criteria.