Coupled Tank System Research Articles

Improved centralised control system for rejection of loop interaction in coupled tank system

ABSTRACTIn practice, majority of the processes are multivariable in nature and control of these processes is very intricate, due to the presence of non-zero diagonal elements in the system. This problem is addressed in the paper with the proposal of a centralised PI controller for controlling the interactive Two Input and Two Output processes. The proposed controller includes a diagonal PI controller and a decoupler element in off diagonal. To design PI controller, a well-known SISO tuning technique SIMC is considered and decoupler elements of off diagonal are designed using coefficient matching principle. The main diagonal controller improves the system performance, while the decoupler rejects the interaction; this improves the overall system. The designed controller performance is evaluated practically on a coupled tank system. The designed control system performance for both servo and regulatory operation is studied. The robustness analysis of the proposed method was analysed using inverse maximum singular value versus frequency plot by incorporating the multiplicative uncertainty in both input and output of the system.

System Identification Under Relay and PI Control

This brief presents a symmetrical relay-based identification scheme for a class of linear time-invariant systems with time delay. During off-line identification, the adverse effect of static load disturbance may lead to erroneous system model parameters. Therefore, on-line identification scheme is proposed where the system characteristics is extracted with respect to proportional-integral (PI) controller dynamics in terms of sustained oscillatory responses broadly known as limit cycle at the system output. Utilizing the relay settings (amplitude and hysteresis width), controller parameters and limit cycle information, an explicit set of mathematical expressions for on-line parameter estimation of system dynamics in terms of a stable first order plus time delay (FOPTD) model is deduced from frequency domain and state space analyses. As compared to recent relay-based identification methods, the proposed set of explicit expressions does not require any prior guess of initial values of the system model parameters for the simultaneous solution of a nonlinear set of mathematical equations. Simulation of a benchmark example from literature and experimental results from the coupled tanks system are included for validation of the proposed identification algorithms using the deduced set of mathematical expressions.

A multi-threaded communication architecture for networked control systems

Advancement in communication technology has paved the way for geographically dislocating controllers from the plants they are controlling. Establishing a secure and reliable communication is an essential component to achieve robust control performance. Myriad network control schemes have been proposed but they are incapacitated due to a lack of reliable software paradigm. This highlights the need of a distributed system, which provides platform for smooth communication between a plant and its controller. In this work, we propose CASAPAC, which is a multi-threaded communication architecture designed to ensure reliable and in-order delivery of information between different modules of a network control system. Any control algorithm can be tested and employed over any network using CASAPAC. An adaptive fuzzy controller and a network based gain scheduled PI (Proportional Integral) controller have been tested on different networks using CASAPAC. In both cases, tests were carried out on a real plant of a coupled tank system. CASAPAC was able to handle all the communication efficiently in different scenarios and good control performance was achieved in both cases.

LabVIEW Based Level Control of Coupled Tank System

This paper utilizes Variable Structure Control (VSC) to control the level of a two tank system. By using Sliding Mode Technique in VSC, the levels of the tanks are maintained at a desired setpoint. The system is subjected to the conventional PID controller and the results are brought out. To track the robustness of the system, an external disturbance is intentionally introduced. The ability of disturbance rejection is checked in both VSC and PID controllers. It is found that VSC offers quick settling time, low peak overshoot and low rise time, and as compared to PID control. LabVIEW(Laboratory Virtual Instrument Workbench) is the software used for the control of the whole process. This is very user friendly software. It uses Graphical programming technique. As an extension the control can be implemented by hardware using DAQ cards.

Design of a robust optimal decentralized PI controller based on nonlinear constraint optimization for level regulation: an experimental study

This paper presents the development of a new robust optimal decentralized PI controller based on nonlinear optimization for liquid level control in a coupled tank system. The proposed controller maximizes the closed-loop bandwidth for specified gain and phase margins, with constraints on the overshoot ratio to achieve both closed-loop performance and robustness. In the proposed work, a frequency response fitting model reduction technique is initially employed to obtain a first order plus dead time &#x0028 FOPDT &#x0029 model of each higher order subsystem. Furthermore, based on the reduced order model, a proposed controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed optimal robust decentralized control scheme has been compared with that of a decentralized PI controller. The proposed controller is implemented in real-time on a coupled tank system. From the obtained results, it is shown that the proposed optimal decentralized PI controller exhibits superior control performance to maintain the desired level, for both the nominal as well as the perturbed case as compared to a decentralized PI controller.

Multi-agent distributed model predictive control with fuzzy negotiation

In this work, a multi-agent distributed model predictive control (DMPC) including fuzzy negotiation has been developed. A novel fuzzy inference system is introduced as a negotiation technique between agents in a cooperative game algorithm, allowing for the consideration of economic criteria and process constraints within the negotiation process, providing an easier interpretation of the available knowledge. The fuzzy negotiation produces smoother control actions than where the negotiation is based only on costs evaluation, because both agents provide their best to generate the final control action. The results show good tracking and disturbance rejection in the case study proposed. The methodology has been implemented in a JAVA based platform with a friendly user interface to deploy the multi-agent system (MAS), and it has been validated in the water level control in a four coupled tanks system.

Design of FOPI Controller for Time Delay Systems and Its Experimental Validation

In this paper, we report on the identification and modeling of unknown and higher order processes into first order plus dead time (FOPDT) plants based on the limit cycle information obtained from a single relay feedback test with an online fractional order proportional integral (FOPI) controller. The parameters of the test processes are accurately determined by the state space method while the FOPI controller settings are re-tuned to achieve enhanced performance based on the identified model parameters based on the balanced-tuning method. A new performance index, integral time fractional order absolute error (ITFIAE) is introduced in this paper for balanced tuning of fractional order (FO) controllers. It requires minimum design specifications without a-priori knowledge of gain and phase crossover frequencies and is done non-iteratively without disrupting the closed loop. Four test processes and experimental analysis on a coupled tank system (CTS) validate the theory proposed.

An Expanded Optimal Control Policy for a Coupled Tanks System with Random Disturbance

In this paper, an expanded optimal control policy is proposed to study the coupled tanks system, where the random disturbance is added into the system. Since the dynamics of the coupled tanks system can be formulated as a nonlinear system, determination of the optimal water level in the tanks is useful for the operation decision. On this point of view, the coupled tanks system dynamics is usually linearized to give the steady state operating height. In our approach, a model-based optimal control problem, which is adding with adjusted parameters, is considered to obtain the true operating height of the real coupled tanks system. During the computation procedure, the differences between the real plant and the model used are measured repeatedly, where the optimal solution of the model used is updated. On this basis, system optimization and parameter estimation are integrated. At the end of the iteration, the iterative solution approximates to the correct optimal solution of the original optimal control problem, in spite of model-reality differences. In conclusion, the efficiency of the approach proposed is shown.

Design and experimental realization of a robust decentralized PI controller for a coupled tank system

This paper presents design and realization of a robust decentralized PI controller for regulating the level of a coupled tank system. The proposed controller is designed based on a predefined reference transfer function model in which we adopt a frequency matching of actual and reference models. Realization of control algorithms for a multivariable system is often complicated owing to uncertainties in the process dynamics. In this paper, initially a frequency response fitting model reduction technique is adopted to obtain a First Order Plus Dead Time (FOPDT) model of each higher order decoupled subsystem. Further, using the obtained reduced order model, the proposed robust decentralized PI controller is designed. The stability and performance of the proposed controller are verified by considering multiplicative input and output uncertainties. The performance of the proposed robust decentralized controller has been compared with that of a decentralized PI controller. To validate the performance of the proposed control approach, real-time experimentation is pursed on a Feedback Instrument manufactured coupled tank system.

An FO–[PI]λ controller for inverted decoupled two-input two-output coupled tank system

ABSTRACTIn this paper, a new structured fractional order-[proportional integral] () controller design method is demonstrated. The designed controller is implemented in decoupled Two-Input Two-Output (TITO) Coupled Tank System (CTS) for liquid level control. An inverted decoupling technique is used to decouple the TITO process into two independent SISO (single-input single-output) processes. The designed controller is implemented for each SISO process. A frequency domain approach is used to tune the parameters of the controller. While designing, to approximate the fractional integral terms of the controller, Oustaloup's Recursive Approximation (ORA) method is used in the stable frequency bands. To validate the proposed approach, the performance of the controller is compared with the existing controllers designed based on the same specifications. From the simulation and experimental studies, it is shown that proposed gives better performance than , PI and PID controllers.

Multidimensional membership functions in T–S fuzzy models for modelling and identification of nonlinear multivariable systems using genetic algorithms

In this work, a new method for Takagi–Sugeno (T–S) fuzzy modelling based on multidimensional membership functions (MDMFs) is proposed. It is verified that the fuzzy inference method of one-dimensional membership functions (1DMFs) may place the fuzzy rules in inappropriate locations for modelling of nonlinear multivariable systems, while the application of MDMFs allows a better identification through a smaller number of fuzzy rules. The proposed method uses a genetic algorithm (GA) for the adjustment of the MDMFs and the T–S method for modelling and identification of the nonlinear system. As a validation example, a nonlinear multivariable system, a coupled tanks system, is chosen. The results show that the proposed method presents less identification error than the T–S method, with less number of fuzzy rules.

Real-Time implementation and performance analysis of robust 2-DOF PID controller for Maglev system using pole search technique

In recent times, Magnetic Levitation (Maglev) technology has gained huge popularity in different fields of research. Transportation, nuclear, aerospace, biomedical, civil and electrical engineering are some of the areas where the presence of Maglev technology is prominent. But because of the inherent nonlinear and unstable behaviour, the task of designing a suitable controller becomes very challenging for the control engineers. In this paper, a simple but effective approach has been proposed for the design of 2-DOF Proportional-Integral-Derivative (PID) controller for the control of Maglev system in simulation and real-time for the very first time, to the best of author's knowledge. The controller parameter values have been analytically obtained by optimizing the location of closed loop poles in the s-plane which eventually minimizes the Integral Square Error (ISE) of the closed loop system along with the controller. As the controller parameters are found by searching the best pole location, we name it as pole search technique. The performance of the controller has been compared with those of the 1 & 2-DOF Integer Order and Fractional Order PID and I-PD controllers designed for the same Maglev plant. The result of the comparison reveals that the 2-DOF PID controller, designed in this paper, outperforms other controllers in terms of maximum overshoot, settling time, Integral Absolute Error (IAE), Integral Time Absolute Error (ITAE) and Integral Time Square Error (ITSE). Moreover, to illustrate the loop robustness property, input and output disturbances have been applied in real-time simulation environment and sensitivity and complementary sensitivity analysis have been performed. Additionally, to show the applicability of the proposed technique apart from Maglev, 2-DOF PID controller has been designed for the Ball and Beam and Coupled Tank system and their performance has been compared with the existing results.

Auto-tuning of FOPI Controllers for TITO Processes with Experimental Validation

In this paper, the auto-tuning of a fractional order proportional and integral (FOPI) controller is proposed and experimentally validated for two-input two-output (TITO) processes. The proposed method first identifies an unknown TITO plant into fractional order TITO model with time delay. Furthermore, decoupling the TITO process into two fractional order single-input single-output (SISO) transfer function models makes it easier for designing the decentralized FOPI controllers. The proposed control method is a generalization of both integer order and fractional order TITO systems depending on the value of the order of the model. One advantage of this method is the non-requirement of a-priori information of gain and phase crossover frequencies of the system while tuning the controllers. The proposed algorithm is validated both by simulation of a class of TITO process models as well as by experimental analysis of a coupled tank system (CTS).

A combined control approach for industrial process systems using feed-forward and adaptive action based on second order sliding mode controller design

This paper presents a new method that uses a feed-forward adaptive second order sliding mode control (FF-ASSMC) for a coupled tank process system that is often used in industry. This proposed method is to combine a feedforward action with adaptive feedback for robust performance of the couple tank system for the first time. The reason for using this feedforward action with the feedback sliding mode control (SMC) is to reduce the effect of the measured disturbance on the coupled tank system. In addition to this, an adaptive second-order SMC proposes to track the desired tank’s level trajectories under disturbances and uncertainties. In order to illustrate the efficiency of the proposed FF-ASSMC method, the simulation and real time experimental studies have been realized. The simulation and experimental outcomes strongly verified that the proposed controller gives a quite successful trajectory tracking response and smaller magnitude overshot under external disturbances.

Design and real‐time implementation of an adaptive fuzzy sliding mode controller for a coupled tank system

AbstractIn this paper, an adaptive fuzzy sliding mode controller (AFSMC) is proposed for regulation of liquid level in a coupled tank system (CTS). In this controller design, a fuzzy variable is considered in the sliding surface in order to reduce the chattering effect. The proposed controller exhibits high robustness against external disturbances and also measurement error. To verify the efficacy of the proposed controller, we compared its performances with that of a linear matrix inequality (LMI)–based proportional integral (PI) controller. The efficacy of the proposed controller is verified by implementing this controller in real time on the coupled tank liquid level system. From both the obtained simulation and experimental results, it is observed that the proposed controller exhibits superior control performance to maintain the desired level as compared with the LMI‐based PI controller.

Metamodel-based Optimization of a PID Controller Parameters for a Coupled-tank System

Liquid flow and level control are essential requirements in various industries, such as paper manufacturing, petrochemical industries, waste management, and others. Controlling the liquids flow and levels in such industries is challenging due to the existence of nonlinearity and modeling uncertainties of the plants. This paper presents a method to control the liquid level in a second tank of a coupled-tank plant through variable manipulation of a water pump in the first tank. The optimum controller parameters of this plant are calculated using radial basis function neural network metamodel. A time-varying nonlinear dynamic model is developed and the corresponding linearized perturbation models are derived from the nonlinear model. The performance of the developed optimized controller using metamodeling is compared with the original large space design. In addition, linearized perturbation models are derived from the nonlinear dynamic model with time-varying parameters.

Active Disturbance Rejection Control of a Coupled-Tank System

In process industries, liquid is pumped and stored in interacting coupled tanks. The liquid level in these tanks must be accurately controlled. This study aims to investigate the performance of the active disturbance rejection control method in controlling a coupled-tank system. A mathematical model of the coupled-tank system is derived to facilitate a simulation study. Assuming that the water level in the second tank is the only measured state, an extended observer with time-varying parameters estimates the second state and the total disturbances of the system. The system is then regulated using a time-varying feedback controller. The results show the effectiveness of the method in improving the time domain measures and the disturbance rejection compared to other controllers.

Real-time implementation of self-tuning regulator control technique for coupled tank industrial process system

This article presents the self-tuning regulator control technique for a coupled tank liquid level system that often used in industry. An autoregressive with exogenous model has been used as the liquid process model with the self-tuning control implementation in order to track the desired tank level trajectories with disturbances and uncertainties of the system dynamics. The designed self-tuning controller has been sensitive to parameter variations of the nonlinear coupled tank system. The parameters of the proposed controller are periodically updated themselves during the process by means of online recursive least square method with the forgetting factor algorithm. In this way, the parameter variations and unwanted disturbances of the system are eliminated in real-time application. In order to demonstrate the efficiency of the self-tuning regulator control technique, the real-time studies have been executed. The obtained experimental results demonstrated that the proposed controller gives the better trajectory tracking performance and smaller magnitude in overshot and undershot than the designed classical proportional–integral and sliding mode controllers.

A Comparative Study Between Cascaded FOPI–FOPD and IOPI–IOPD Controllers Applied to a Level Control Problem in a Coupled Tank System

This paper presents a novel liquid level control of a coupled two tank SISO system. Physical system is modeled from the open loop experimental response in two stages. A cascade control strategy is adopted. Fractional Order Proportional Integral (FOPI) and Fractional Order Proportional Derivative (FOPD) controllers are designed for the outer and inner loop, respectively, using frequency domain method. Similarly, conventional Integer Order Proportional Integral and Integer Order Proportional Derivative controllers are also designed to compare the performances. Reference signal tracking performance is tested with multiple step, ramp and sinusoidal reference signals. Ability of disturbance rejection is tested by adding more water into the tanks through a disturbance input channel. Experimental results reveal that the proposed FOPI–FOPD control scheme outperforms its integer order counterparts both in terms of reference signal tracking and disturbance rejection.

An Intelligent Controller Design Approach for MIMO Coupled Tank System

Nowadays, versatilities of controllers have been developed to control the Coupled Tank System (CTS) such as proportional, integral, derivative (PID), fuzzy, fuzzy PID and neuro network. This paper focused on the control of the pump flow rate, in and out of the tank against the cross-sectional area of the CTS’s tank. The main objective of this paper is to design a CTS by using MATLAB since the Fuzzy Logic Controller (FLC) is widely utilized in the control of engineering applications in the industrial. Therefore, the FLC will be utilized to control and improve the performance of the CTS. The conventional PID controller will be applied, which reacts as a benchmark in the performance of the FLC. Parameters such as steady state error, settling time, and maximum overshoot will be part of the simulation results. As a result of the dynamic response executed in the closed-loop environment, it can be concluded that the FLC is capable of performing better than the conventional PID controller.