Smith Predictor Research Articles

A novel whale optimization smith predictor based on feedforward compensation for controlling wave rotor refrigeration process

AbstractAiming at the difficulty of temperature control and disturbance rejection control in wave rotor refrigeration process (WRRP), a novel whale optimization two‐degree‐of‐freedom (2DOF) Smith predictor based on feedforward compensation method (WO‐2DOFSP‐FC) is proposed. Firstly, the obtained test data of the WRRP are used for system identification and the approximate second‐order model with time‐delay is obtained by using the suboptimal reduction algorithm. This procedure also yields a first‐order model of the disturbance. Then, the whale optimization 2DOF Smith predictor based on feedforward compensation (2DOFSP‐FC) method is proposed. This proposed method improves the 2DOFSP and introduces feedforward compensation control to reduce the influence of the measurable disturbance on the temperature control system. In addition, the Whale Optimization Algorithm (WOA) is proposed to optimally tune the 2DOFSP‐FC controller parameters. Finally, the simulation results show that the proposed WO‐2DOFSP‐FC method can make the controlled system have good characteristics of both set value tracking and disturbance rejection.

Predictive Generalized Active Disturbance Rejection Control for Fractional Order Systems With Time Delay

Abstract In this paper, two different active disturbance rejection control techniques based on notion of Smith Predictor are proposed for control of fractional order stable systems with time delay. In the proposed Smith Predictor-based fractional order linearized active disturbance rejection control (SP-FO-LADRC) technique, fractional order dynamics are treated as a part of generalized disturbance, and the concept of Smith Predictor is used to obtain delay less output, which is fed to an extended state observer (ESO), and an integer order control strategy is developed. To further ameliorate control performance of this technique, complete plant information of commensurate fractional order system is used to formulate another new technique, namely, Smith Predictor-based fractional order generalized active disturbance rejection control (SP-FO-GADRC), which incorporates fractional ESO and leads to formulation of fractional order control law. An extensive simulation study and robustness analysis conducted on three different examples is testimony to efficacy of proposed techniques.

MPC Based Dynamic Voltage Regulation Using Grid-Side BESPS With the Consideration of Communication Delay

Battery energy storage power stations (BESPS) play an important role in the power flow regulation in large-scaled micro-grids. It is proposed that the static Var compensator (SVC) be replaced by BESPS through activation of its dynamic voltage regulation (DVR) function so that the cost of SVC can be saved. An additional controller named energy storage coordination controller (ESCC) is needed to support the control algorithm of DVR and coordinate the individual battery energy storage system units. However, communication delay between the ESCC and the commercial BESS units is compounded by the difficulty of measuring the micro-grid (MG) bus voltage by ESCC. These issues should be considered in the design of the BESPS controller to avoid compromising the micro-grid operation. In this paper, we will be investigating model predictive control (MPC), Smith Predictor and PI based control schemes to deal with the communication delay issue. Kalman Filter based observer is designed to monitor the MG bus voltage as a feedback signal of the ESCC. The stability of the proposed method is further discussed and the results using the control hardware-in-the-loop (CHIL) testing are presented.

Control of time-delay systems through modified Smith predictor using sliding mode controller

Smith-Predictor (SP) is used as a dead-time compensating tool for chemical processes as they are Integrating-Plus-Dead-Time (IPDT), pure integrating-type process, and higher-order-integrating-process. The performances of these processes can be improved by modifying SP. The present work deals with the control of dead-time by integrating the first-order-plus-dead-time (IFOPDT) or first-order-plus-dead-time process (FOPDT), and a modified sliding-mode-controller (SMC) in the proposed modified-Smith-predictor (MSP) structure. Here, a modified novel SMC discontinuous tuning-parameter is derived analytically to satisfy performance criteria such as speed adjustment, reducing overshoot and chattering effects. Furthermore, the MSP-SMC structure is implemented in six different processes. This is done to counteract time-delay and constant load-disturbance for integrating processes and a nonlinear system separately. Also, the proposed work is implemented in the real-time lab setup of a neutralisation process. Furthermore, the robustness and invariance properties of the SMC have been analysed against parametric uncertainty. The optimality of the proposed controller parameters is tested by giving uncertainty in the dead time of the process parameters. The proposed design is also implemented in the non-linear and Multi-Input-Multi-Output processes. The performance metrics, IAEs, of 6 case studies have been obtained using MATLAB and the peak overshoots are compared with similar kinds of works.

Improved control of integrating cascade processes with time delays using fractional-order internal model controller with the Smith predictor

This article proposes an enhanced control of integrating cascade processes. The importance of the scheme shows by controlling a double integrating process with time delay under significant parametric uncertainties and load disturbances. A novel design is proposed based on the Smith predictor principle and uses a fractional-order internal model controller in the outer loop. The required fractional-order tuning parameter follows the desired gain and phase margins. At the same time, another tuning parameter, such as the fractional filter’s time constant, is calculated from the desired performance constraint. Numerical analysis and comparison are performed to showcase the feature of the hybrid structure. The simulation results show that the fractional-order internal model controller–based scheme provides enhanced tracking and faster regulation capabilities and works well under nominal and parameter uncertainty conditions.

Residence Time Distribution-Based Smith Predictor: an Advanced Feedback Control for Dead Time–Dominated Continuous Powder Blending Process

PurposeIn continuous manufacturing (CM), the material traceability and process dynamics can be investigated by residence time distribution (RTD). Many of the unit operations used in the pharma industry were characterized by dead time–dominated RTD. Even though feasible and proper feedback control is one of the many advantages of CM, its application is challenging in these cases. This study aims to develop a feedback control, implementing the RTD in a Smith predictor control structure in a continuous powder blender line.MethodsContinuous powder blending was investigated with near-infrared spectroscopy (NIR), and the blending was controlled through a volumetric feeder. A MATLAB GUI was developed to calculate and control the concentration of the API based on the chemometric evaluation of the spectra. The programmed GUI changed the feeding rate based on the proportional integral derivative (PID) and the Smith predictor, which implemented the RTD of the system. The control structures were compared even on a system with amplified dead time.ResultsIn this work, the control structure of the Smith control was devised by utilizing the RTD of the system. The Smith control was compared to a classic PI control structure on the normal system and on an increased dead time system. The Smith predictor was able to reduce the response time for various disturbances by up to 50%, and the dead time had a lower effect on the control.ConclusionsImplementing the RTD models in the control structure improved the process design and further expanded the wide range of applications of the RTD models. Both control structures were able to reduce the effect of disturbances on the system; however, the Smith predictor presented more reliable and faster control, with a wider space for control tuning.

Design and Analysis of EAST Predictive Control System for Hot Nitrogen Baking Process

To realize the automatic temperature closed-loop control of EAST (Experimental advanced super-conducting tokamak) baking system, the transfer function of EAST baking system is obtained by the step response method after being familiar with the mechanism structure of the baking system. According to the transfer function of the system, two control methods, conventional PI control and PI control based on Smith prediction are novelty proposed. MATLAB simulation analysis shows that PI control based on Smith prediction does not produce an overshoot compared with conventional PI control, and the final error given by tracking slope can be reduced by selecting appropriate PI parameters. Generally, PI control based on Smith prediction has better stability and dynamic performance. The novelty here lies in the introduction of PI control based on Smith prediction to solve the problem of large overshoot in conventional PI control.

Smith predictor PID-based robust adaptive gain-scheduled control for a class of fractional order LPV systems with time delays

Smith predictor PID-based robust adaptive gain-scheduled control for a class of fractional order LPV systems with time delays

Repetitive control design for switched neutral systems with input time‐delay

SummaryThe design of tracking control problem and compensation of disturbance for switched neutral systems with multiple time‐delays and external disturbances are addressed in this paper. In this regard, a modified repetitive control technique based on the Matausek‐Micic modified Smith predictor approach is being implemented, which assures the exact tracking performance and disturbance attenuation with high precision in the considered system. To be specific, the integration of transfer function with modified Smith predictor block not only provides the accurate compensation of input time‐delays but also ensures the exact estimation and attenuation of external disturbances effectually. Furthermore, according to Lyapunov stability approach combined with average‐dwell‐time technique, a group of adequate conditions is derived in the form of matrix inequalities. Simultaneously, by solving the established matrix inequalities using available software the controller gain matrices are calculated. Ultimately, the simulation results of three numerical examples are presented to validate the efficiency and dominance of the suggested control procedure.

Smith Predictor Controller Design Using the Direct Synthesis Method for Unstable Second-Order and Time-Delay Systems

Industrial processes often involve a long time delay, which adversely affects the stability of closed-loop control systems. The traditional Smith Predictor (SP) is a model-based controller used in processes with large time delays. The variation of system parameters and load disturbance situations are disadvantages of the traditional SP, and researchers have, therefore, proposed modified SP structures. In this paper, a design method based on the direct synthesis approach on a modified SP structure is discussed. In the design, an I-PD controller structure is used on the set-point tracking side of the SP, and a cascading PD lead–lag controller is used on the disturbance rejection side. In contrast with other studies in the literature, the use of simpler controllers enables the mathematical expressions that arise in the direct synthesis method to be significantly reduced. The proposed method is examined under the disturbance input effects for normal and parameter-changing conditions on system models with unstable second-order plus time-delay processes. The first plant model has two unstable poles, the second has one stable and one unstable pole, and the third has one unstable and one zero pole. When the results obtained using the proposed method were compared with other methods, significant improvements were achieved in terms of set-point tracking, disturbance rejection, and robustness conditions.

Robust Stability Analysis of Smith Predictor Based Interval Fractional-Order Control Systems: A Case Study in Level Control Process

The robust stability study of the classic Smith predictor-based control system for uncertain fractional-order plants with interval time delays and interval coefficients is the emphasis of this work. Interval uncertainties are a type of parametric uncertainties that cannot be avoided when modeling real-world plants. Also, in the considered Smith predictor control structure it is supposed that the controller is a fractional-order proportional integral derivative (FOPID) controller. To the best of the authors' knowledge, no method has been developed until now to analyze the robust stability of a Smith predictor based fractional-order control system in the presence of the simultaneous uncertainties in gain, time-constants, and time delay. The three primary contributions of this study are as follows: i) a set of necessary and sufficient conditions is constructed using a graphical method to examine the robust stability of a Smith predictor-based fractional-order control system—the proposed method explicitly determines whether or not the FOPID controller can robustly stabilize the Smith predictor-based fractional-order control system; ii) an auxiliary function as a robust stability testing function is presented to reduce the computational complexity of the robust stability analysis; and iii) two auxiliary functions are proposed to achieve the control requirements on the disturbance rejection and the noise reduction. Finally, four numerical examples and an experimental verification are presented in this study to demonstrate the efficacy and significance of the suggested technique.

Smith predictor-based feedforward controller for measurable disturbances

This paper proposes a feedforward extension for the simplified filtered Smith predictor (SFSP) to deal with measurable disturbances. The proposed strategy uses a state-space formulation and can be applied in unified manner to stable, unstable, and integrating linear dead-time processes of any order. The main advantage with using the predictor approach in comparison with other control strategies is the ability to deal with processes with large dead time. The structure improves the disturbance rejection performance by feedforwarding the disturbance while maintaining the good robustness and noise attenuation properties of the SFSP. Simulation results show better performance indices compared with other strategies from the recent literature. In addition, the proposed strategy is applied to control the temperature in a newborn intensive care unit (NICU) to show its effectiveness in a real process.

Memory-Anticipation Strategy to Compensate for Communication and Actuation Delays for Strings-Stable Platooning

Cooperative Adaptive Cruise Control (CACC) has the potential to significantly improve traffic throughput by reducing inter-vehicle following gap. However, communication and actuation delays in CACC systems are detrimental to string stability. A much larger time gap than the lump sum of the two delays is often required for CACC to guarantee string stability, which compromises their benefits on traffic throughput. It remains as a challenge to design string-stable CACC controllers that operate at small time gaps under delays. In this paper, we design a memory-anticipation CACC to explicitly handle communication and actuation delays to fulfill string stability specifications. The proposed controller employs a novel memory-anticipation spacing policy to address communication and actuation delays and is applicable to heterogeneous platoons. Unlike existing CACC controllers, our proposal utilizes past information of the preceding vehicle (i.e. the memory) instead of its current state/control information, which makes the controller robust to communication delay. Furthermore, a Smith predictor (i.e. the anticipation) is designed to compensate for the actuation delay. Both individual vehicle stability and string stability can be guaranteed with the minimum time gap as small as the summation of communication delay and actuation delay. Controller analysis and simulation verify the enhancement of the stability performance with respect to existing studies.

On Smith predictor based controllers for plants with time delay and multiple unstable modes

On Smith predictor based controllers for plants with time delay and multiple unstable modes

Predictive generalised active disturbance rejection for load frequency control with communication delay

This paper formulates a generalised active disturbance rejection control technique based on Smith predictor (SP-GADRC) for power systems with communication delay. The SP-GADRC technique employs essential plant information and uses the notion of Smith predictor to alleviate the deterioration of transient response that arises due to the presence of communication delay in a system. The generalised formulae for computation of controller and observer gains for various single and multi-area power systems are derived. Furthermore, the effect of parametric uncertainty, nonlinearities, model-plant mismatch, load disturbances as well as varying time delay is examined to validate the robustness of the SP-GADRC technique. An elaborate comparative analysis is conducted with various existing approaches to exhibit efficacy of the SP-GADRC technique. The simulation results reveal that SP-GADRC scheme demonstrates an improved disturbance rejection ability, better transient performance and is robust to the presence of nonlinearities and disturbances in system.

Robust tuning of uncertainty and disturbance estimator-based control for stable processes with time delay

To expand the potential of uncertainty and disturbance estimator (UDE)-based control in practical application to most industrial stable processes, this paper proposes a convenient yet robust tuning rule according to the widely used first-order plus time delay (FOPTD) plant. The Smith predictor is first introduced to anticipate the delay-free output, which guarantees signal synchronizations in three control modules and enables remarkable restorations of nominal stability and performance. Then a second-order filter is employed in UDE to decouple the trade-off between disturbance rejection and noise attenuation. Based on this improvement and fixing both tracking speed and feedback gain to suggested patterns, the exhaustive evaluations for robustness against model distortion are executed through scanning the dimensionless filter bandwidth. The boundary demarcation triggered by the plunge of the continuous range of tolerable mismatched delays subsequently facilitates the formulation of an intuitive tuning rule with prescribed robustness. Its inherent model-based scaling property largely enables this rule to be implemented readily in industrial processes just like the proportional-integral-derivative (PID) controller. Several representative simulations are performed to demonstrate the merits of the proposed method over the related control strategies. And the promising prospect of the UDE-based control in the practical application is further illustrated by conducting a water level control experiment.

Smith predictor–based sliding mode control with hyperbolic tangent function for unstable processes

In this work, a modified Smith predictor–based sliding mode control (SP-SMC) method is proposed for unstable plus time-delay processes. Sliding mode control has a discontinuous part in its control law which may cause chattering in the control signal if conventional switching strategy is used. A hyperbolic tangent function is employed as a switching element in the suggested SP-SMC technique to minimize the chattering effect. Optimal values of the controller’s unknown parameters are obtained using whale optimization algorithm which is a meta-heuristic technique. The process model used in the proposed Smith predictor control architecture is identified using measurements of limit cycle output which is obtained from online relay test. The proposed controller is found to be robust towards process parameter uncertainties and load disturbance. Suggested control technique results in fast set-point tracking response and significantly improved disturbance rejection performance compared to some other related methods.

Tip-Tilt Mirror Control Method Using Smith Predictor and Filter-Based Linear Active Disturbance Rejection

Tip-Tilt Mirror Control Method Using Smith Predictor and Filter-Based Linear Active Disturbance Rejection

Hybrid Optimization Based PID Controller Design for Unstable System

PID controllers play an important function in determining tuning parameters in any process sector to deliver optimal and resilient performance for nonlinear, stable and unstable processes. The effectiveness of the presented hybrid metaheuristic algorithms for a class of time-delayed unstable systems is described in this study when applicable to the problems of PID controller and Smith PID controller. The Direct Multi Search (DMS) algorithm is utilised in this research to combine the local search ability of global heuristic algorithms to tune a PID controller for a time-delayed unstable process model. A Metaheuristics Algorithm such as, SA (Simulated Annealing), MBBO (Modified Biogeography Based Optimization), BBO (Biogeography Based Optimization), PBIL (Population Based Incremental Learning), ES (Evolution Strategy), StudGA (Stud Genetic Algorithms), PSO (Particle Swarm Optimization), StudGA (Stud Genetic Algorithms), ES (Evolution Strategy), PSO (Particle Swarm Optimization) and ACO (Ant Colony Optimization) are used to tune the PID controller and Smith predictor design. The effectiveness of the suggested algorithms DMS-SA, DMS-BBO, DMS-MBBO, DMS-PBIL, DMS-StudGA, DMS-ES, DMS-ACO, and DMS-PSO for a class of dead-time structures employing PID controller and Smith predictor design controllers is illustrated using unit step set point response. When compared to other optimizations, the suggested hybrid metaheuristics approach improves the time response analysis when extended to the problem of smith predictor and PID controller designed tuning.

Cooperative Adaptive Cruise Control for Heterogeneous Platoons with Actuator Delay

Cooperative adaptive cruise control (CACC) is a control method that enables close vehicle following with string stable behavior, i.e., disturbances are not amplified through the vehicle string. Consequently, the technique contributes to increased road throughput and safety. General practice in CACC design is to describe the longitudinal vehicle dynamics by a simple first order model. For certain vehicles, however, this model has to be extended by an input delay to better represent the longitudinal behavior. In this paper, we show that the performance of a class of heterogeneous CACC controllers greatly deteriorates when the ego vehicle has a delay in the driveline. The minimum required string stable timegap increases to such a degree, that the controller is no longer suitable for close vehicle following. By implementing a Smith predictor in the control scheme, the delay is compensated, restoring the string stability properties. However, the original vehicle following objective is no longer fulfilled with the inclusion of the Smith predictor. By adopting an alternative timegap, the original control objective is restored for steady state situations, enabling CACC for heterogeneous platoons with actuator delays.