Liquid Level System Research Articles

Predictive and Backstepping Control of Double Tank Process: A Comparative Study

ABSTRACTThis paper addresses the nonlinear control design problem for a state-coupled two-tank liquid-level system. For this system's dynamics, motivated by a desire to provide precise liquid-level control, two radically different control approaches are presented and compared: the model predictive control and the backstepping control. In the first proposed approach, a model-based predictive controller is designed for the two-tank liquid-level system that ensures exponentially stabilization for a particular class of second-order nonlinear system. Moreover, a robust controller based on a backstepping strategy is designed in order to ensure globally asymptotically stabilization for another particular class of second-order nonlinear systems. To ensure a suitable basis for their comparison, two different control methods are designed and verified with the same test setup. To highlight the efficiency and applicability of the proposed control schemes, theoretical comparisons as well as experimental results are provided and discussed.

Fractional Order PID Controller for Liquid Level System

Fractional Order PID Controller for Liquid Level System

A novel auto-tuning PID control mechanism for nonlinear systems

In this paper, a novel Runge–Kutta (RK) discretization-based model-predictive auto-tuning proportional-integral-derivative controller (RK-PID) is introduced for the control of continuous-time nonlinear systems. The parameters of the PID controller are tuned using RK model of the system through prediction error-square minimization where the predicted information of tracking error provides an enhanced tuning of the parameters. Based on the model-predictive control (MPC) approach, the proposed mechanism provides necessary PID parameter adaptations while generating additive correction terms to assist the initially inadequate PID controller. Efficiency of the proposed mechanism has been tested on two experimental real-time systems: an unstable single-input single-output (SISO) nonlinear magnetic-levitation system and a nonlinear multi-input multi-output (MIMO) liquid-level system. RK-PID has been compared to standard PID, standard nonlinear MPC (NMPC), RK-MPC and conventional sliding-mode control (SMC) methods in terms of control performance, robustness, computational complexity and design issue. The proposed mechanism exhibits acceptable tuning and control performance with very small steady-state tracking errors, and provides very short settling time for parameter convergence.

Modelling and Control of Coupled Tank Liquid Level System using Backstepping Method

Modelling and Control of Coupled Tank Liquid Level System using Backstepping Method

Experimental Validation of a Multi Model PI Controller for a Non Linear Hybrid System in LabVIEW

In this paper a real time Single Spherical Tank Liquid Level System (SSTLLS) has been chosen for investigation. This paper describes the design and development of a Multi Model PI Controller (MMPIC) using classical controller tuning techniques for a single spherical nonlinear tank system. System identification of these different regions of nonlinear process are done using black box modeling, which is identified to be nonlinear and approximated to be a First Order Plus Dead Time (FOPDT) model. A proportional and integral controller is designed using LabVIEW and Chen-Hrones-Reswick (CHR), Zhuang-Atherton (ZA), and Skogestad’s Internal Model Controller (SIMC) tuning methods are implemented in real time. The paper provides the details about the data acquisition unit, shows the implementation of the controller, and comparision of the results of PI tuning methods used for an MMPI Controller.

Observer-Based Backstepping Controller for a State-Coupled Two-Tank System

ABSTRACTThis paper addresses the nonlinear control design problem for a state-coupled two-tank liquid level system. For this system's dynamics, motivated by a desire to provide precise and economic liquid level control, a new output feedback control scheme is developed. In the proposed approach, a robust controller based on backstepping strategy is designed in order to ensure globally asymptotically stabilisation for a particular class of second-order nonlinear systems. Moreover, a model-based backstepping controller combined with a high gain observer is designed for the two-tank, liquid level system. Only one sensor is available to measure the liquid level in the bottom tank and the other process's state is assumed unavailable. The observer converges in a finite time and leads to good estimate of the liquid level in the top tank as well as a good track of the liquid level in the bottom tank with the reference trajectory. To highlight the efficiency and applicability of the proposed control scheme, a comparison with proportional plus integral plus derivative controller as well as a simulation and experimental results are provided.

Repetitive controller: an advanced servomechanism for periodic reference input

The presented work envisaged to explore the possibility of implementing a repetitive control strategy along with a proportional (P) controller for a liquid level system (LLS) in real time to track a periodic reference command. The objective of this paper is to validate the servo mechanism (accurate tracking) and periodic disturbance attenuating property of repetitive control (RC) along with P control system. The whole effort is divided in to two distinct parts. In the first part, the controller and plant are modeled, developed and experimented in software. The tracking performance and stability measure of the plant has been studied with inclusion of repetitive controller (RC) in presence of P controller and compared with conventional P and PI controller in both time and frequency domain subjected to periodic command to establish the usefulness of the RC-P control using simulation. The limitation of the first part is due to the consideration of all ideal condition of experimentation like ideal source, ideal plant etc. In the second part of this work the limitation of the first part of taking all ideal condition is avoided through the development of a real time experimentation setup. In this section, software model of LLS is replaced by its analogous electrical circuit. Emulation of the actual hardware plant is carried out interfaced through DAC NI6221 with PC using LabVIEW for better and flexible experimenting environment. The deployment of RC in Controller In Loop is done to conduct all experiments with actual source of reference and actual hardware plant. The effectiveness of RC with P controller for periodic reference input is shown through simulation and validated through real time experimentation.

PI Controller Design for a Coupled Tank System Using LMI Approach: An Experimental Study

This paper presents a Linear Matrix Inequality (LMI) tuned PI controller for real-time control of a coupled-tank liquid level system. The proposed approach is based on the transformation of the PI controller design problem to a state feedback controller design problem, which is further solved using convex optimization approach. The model of the coupled tank system has been developed based on system identification technique that employs least square error method (LS) for parameter estimation. The proposed controller algorithm has been applied on the identified model. The performance of the proposed control algorithm has been compared with that of a Ziegler-Nichols tuned PI controller. From both the simulation as well as the experimental results, it is observed that the performance of the proposed PI control is more efficient than the widely used Ziegler-Nichols approach.

NN-SANARX model based control of a multi tank liquid-level system

AbstractThis paper is devoted to application of neural network with a specific restricted connectivity structure for identification and control of a real process. Parameters of the identified model are used to design a controller based on dynamic feedback linearization. The designed neural network based controller is verified on mathematical model within MATLAB/Simulink environment and applied to the real-time control of a laboratory plant. Water tank system was chosen as a case study to illustrate applicability of the proposed approach. Several experimental results as well as comparison with some alternative methods are provided.

Servomechanism for periodic reference input: Discrete wavelet transform-based repetitive controller

The presented work explored the possibility of developing a discrete wavelet transform-based repetitive control (DWTRC) strategy along with a proportional controller for a liquid level system (LLS) to track a periodic reference signal. The modified DWTRC with a P control system is a type of servo mechanism, effective for periodic reference input. The entire effort derives from two distinct parts. First, the tracking performance and stability measure of the system with inclusion of a repetitive controller (RC) in presence of P controller that has been studied and compared with conventional P and PI controllers in both time and frequency domains, subjected to periodic command to establish the usefulness of the former. The most obvious disadvantage of the RC with P control is the requirement of large memory for the presence of RC, and the memory requirement linearly increases with both repetition time and sampling frequency. Second, to overcome this difficulty, deployment of the discrete wavelet transform (DWT) in the RC loop is done to reduce the problem of memory requirement, and ensures efficient and high-speed computation due to the filtering and data reduction property of DWT. Finally, the effectiveness of DWTRC is validated through saving memory and optimizing the tracking error with variation of the wavelet order and its decomposition level.

Control of a nonlinear liquid level system using a new artificial neural network based reinforcement learning approach

Most industrial processes exhibit inherent nonlinear characteristics. Hence, classical control strategies which use linearized models are not effective in achieving optimal control. In this paper an Artificial Neural Network (ANN) based reinforcement learning (RL) strategy is proposed for controlling a nonlinear interacting liquid level system. This ANN-RL control strategy takes advantage of the generalization, noise immunity and function approximation capabilities of the ANN and optimal decision making capabilities of the RL approach. Two different ANN-RL approaches for solving a generic nonlinear control problem are proposed and their performances are evaluated by applying them to two benchmark nonlinear liquid level control problems. Comparison of the ANN-RL approach is also made to a discretized state space based pure RL control strategy. Performance comparison on the benchmark nonlinear liquid level control problems indicate that the ANN-RL approach results in better control as evidenced by less oscillations, disturbance rejection and overshoot.

Control Simulation for Three Tank Water Level

Three-tank liquid level system of its vessels belonging to non-linear relationship between the coupling. In this paper, three tank level control experimental system as the research object, the establishment of the level system model, and according to the experimental requirements: upper, middle tank to stabilize the value of the lower tank eventually reaches a given value, forming a typical third-order object of study.

A Laboratory-Level Control Experiment for Introducing Predictive Control to Undergraduates

This paper deals with a simple robust nonlinear control of a liquid-level system. The controller is based on one-step-ahead continuous time minimization of the predicted tracking error. We show different steps for complete engineering design from modeling and identification to real-time implementation of the control algorithm. Simulations are performed to check the tracking performance of the controller. To validate the simulation results, the control algorithm is implemented in real-time to control the liquid-level system. This laboratory experiment is being implemented at King Saud University. During their classes, students learn how to use the nonlinear model of the liquid-level system to design a simple and robust controller that achieves the desired tracking performance both in simulation and in real-time implementation.

Adaptive Fuzzy PI Controller Design for Coupled Tank System:An Experimental Validation

In this paper an adaptive fuzzy PI (AFPI) is proposed for the real- time liquid level control of a coupled tank liquid level system. The parameters, in proposed adaptive fuzzy PI controller are adjusted explicitly by the elected fuzzy rule base. Here the gain of the proposed algorithm is implicitly adapted by the variation of the outputs of FLC. The performance of the proposed controller algorithm has been compared with that of conventional PI controller. From both the simulation as well as experimental results, it is witnessed that the performance of the proposed adaptive fuzzy PI (AFPI) delivers best control action than the widely used conventional PI controller.

An adaptive basis estimation method for compressed sensing with applications to missing data reconstruction

The subject of compressed sensing, especially, the related concept of sparse representation has been growing into an exciting area with a diverse set of applications in the fields of image sensing and analysis, signal compression, network reconstruction, etc. The efficacy of the associated techniques depends on the ability to discover a suitable basis for a sparse representation of the underlying signal. This paper presents a method for discovering this basis adaptively from the data. Specifically, the method estimates the dictionary of basis functions that maps the sub-sampled signal to the sparse representation of the signal. We present an application of this technique to the reconstruction of missing data, which is an important problem in all data-driven methods. Two case studies, namely, the reconstruction of missing data in a liquid level system and missing pixels of a 2-D signal (image) are presented. Results show that the proposed algorithm outperforms the existing KSVD algorithm in terms of both accuracy and speed of the reconstruction.

An observer with controller to detect and reject disturbances

In this paper, a novel states observer is designed. This observer not only estimates the states, but also detects the disturbances by creating estimated signals. Then, both the observed states and detected disturbances are used in a control law to reject the disturbances, avoiding the requirement to know the states and disturbances. The observer is designed by the combination of the poles assignation and geometric techniques. Both the observer and controller work simultaneously. The proposed method is applied in an active suspension system and a liquid-level hydraulic system.

Liquid Level Measurement System Design Based on Laser Displacement Sensor

In order to improve precision, outdated measurement method, complicated structure and weak anti-jam ability in liquid level measurement, a set of liquid level system was designed with the core of high-precision laser displacement sensor. The system adopted non-contact laser trigonometric survey method and powerful virtual instrument techniques. It could conduct online and real-time measurement to infinitesimal displacement on liquid level with high speed and precision. Through measurement experiment, its accuracy and practical applicability is verified.

Energy-shaping and integral control of the three-tank liquid level system

A novel method of energy-shaping and integral control is proposed for the three-tank liquid level system. The mathematical model of the three-tank liquid level system is established based on port-controlled Hamiltonian (PCH) systems and mass balance principle. The three-tank liquid level system PCH controller is designed by means of interconnection assignment and damping injection and energy-shaping. The desired equilibrium point is also determined. The stability of the liquid level system is analyzed based on the passivity-based control theory. The integral control is added to eliminate the steady-state errors of the liquid level system. Moreover, simulation and experiment test are also carried out based on the laboratory experiment platform. The results prove that the proposed control method has good dynamic and steady state performances.

Wavelet based denoising technique for liquid level system

The purpose of this paper is to employ wavelet based noise removal technique to remove measurement noise from differential pressure transmitter (DPT) output indicating the level of a process tank. The liquid level system (LLS) is approximated as a first order plant with time delay. When connected in closed loop, the LLS is ideally associated with a PI controller, an actuator, a final control element and a level sensor (DP transmitter in present system). There are enough chances of contaminating the output of LLS by the high frequency measurement noise. In this work, an attempt has been made to judge the performance of discrete wavelet transform (DWT) and discrete wavelet packet transform (DWPT) based noise removal technique when applied to LLS. The available denoised response using wavelet based filtering is compared with that of conventional Butterworth filtering method. Applying hard thresholding that typically retains a very small number of coefficients, the results are often smoothed at the cost of loosing information. By retaining larger number of coefficients and shrinking them, the soft thresholding methods usually give more useful results to denoise the signal. Threshold value has been calculated by Visu Shrink method and Minimax method in different cases.

OPTIMAL DESIGN METHOD OF PI CONTROLLER FOR MULTIPLE PROCESSES AND COUPLED LIQUID LEVEL SYSTEM

A systematic method is proposed to design optimal proportional-integral (PI) controller for different processes. An augmented integral squared error performance index is used to design optimal PI controller. The optimal control problem can be equivalently transformed into a nonlinear constraint optimization (NLCO) problem through Lyapunov theorems, therefore optimal PI controller can be obtained by solving NLCO problem. The proposed method is used to design optimal PI controllers for multiple processes. System performances of different tuning methods are studied. Control weight factorrs effects on dynamic performances are analyzed. Optimal PI controllers of the proposed method are applied for coupled liquid level system under various set points. Both simulation results and experiment results show effectiveness and usefulness of the proposed method.