Anti-windup Design in Modified Smith Predictor for Integrating Process with Dead Time

The problem of stability analysis and anti-windup design is investigated for a class of switched linear systems subject to actuator saturation by using the common Lyapunov function method. Suppose that a group of dynamic output controllers have been designed and they can stabilize the closed-loop system in the absence of saturation. Then, the anti-windup compensators are designed, which aims for enlarging the domain of attraction of system with saturation. Finally, the anti-windup compensators are calculated by solving an optimization problem with linear matrix inequalities (LMI) constraints. A numerical example is given to show the effectiveness of proposed method.

Location of poles on the right hand side of s-plane for a process provides unstable behaviour. Obtaining desired output from an unstable process is truly a difficult task especially for processes with considerable dead time. Processes like combustion chamber, distillation column, and chemical reactors are well-known unstable processes with considerable time delay. Smith predictor based control technique is a well-known methodology for controlling such processes with considerable dead time. But, this technique fails to perform satisfactorily during transient as well as steady state operating phases for delay dominated unstable processes. To ensure improved close-loop response for delay dominated processes, Majhi and Atherton proposed modified Smith predictor technique. However, its performance is not found to be adequate, in addition tuning of more than one controller is quite complicated for delay dominated processes with pole located on right half plane. To overcome this limitation, here we propose a unified tuning methodology with simple modified Smith predictor scheme which is capable to provide an overall improved performance in terms of enhanced load recovery. Effectiveness of the proposed scheme is verified through simulation study with the well-known delay dominated unstable process models representing the behavior of chemical reactor and distillation column in comparison with conventional and modified Smith predictor methodologies.

Set point weighted modified Smith predictor for integrating and double integrating processes with time delay

In this paper, a new modified Smith predictor using a rapid load estimator scheme is proposed. The advantage of the design is that the load estimator does not involve the solution of a closed-loop equation that contains dead time, and this can achieve a better load disturbance response. This scheme can be easily extended to the case of double integrators. Robust stability of the proposed method is analyzed, and a simple and effective robust controller design rule is derived. It is demonstrated by simulations that the new controller provides a similar or better setpoint response and a faster load disturbance rejection than the dead-time compensator in other papers.

In this paper, a new modified Smith predictor using a rapid load estimator scheme is proposed. The advantage of the design is that the load estimator does not involve the solution of a closed-loop equation that contains dead time, and this can achieve a better load disturbance response. This scheme can be easily extended to the case of double integrators. Robust stability of the proposed method is analyzed, and a simple and effective robust controller design rule is derived. It is demonstrated by simulations that the new controller provides a similar or better setpoint response and a faster load disturbance rejection than the dead-time compensator in other papers.

This paper presents a two degrees of freedom (2DOF) control scheme for voltage compensation in a dynamic voltage restorer (DVR). It commences with the model of the DVR power circuit, which is the starting point for the control design procedure. The control scheme is based on a 2DOF structure implemented in a stationary reference frame (α-β), with two nested controllers used to obtain a passband behavior of the closed-loop transfer function, and is capable of achieving both a balanced and an unbalanced voltage-sag compensation. The 2DOF control has certain advantages with regard to traditional control methods, such as the possibility of ensuring that all the poles of the closed-loop transfer function are chosen without the need for observers and reducing the number of variables to be measured. The use of the well-known double control-loop schemes that employ feedback current controllers to reduce the resonance of the plant is, therefore, unnecessary. A simple control methodology permits the dynamic behavior of the system to be controlled and completely defines the location of the poles. Furthermore, extensive simulations and experimental results obtained using a 5-kW DVR laboratory prototype show the good performance of the proposed control strategy.

Rapid advancement in medicine and bioscience is causing demand for faster, more accurate and dexterous as well as safer and more reliable micro-manipulators capable of handling biological cells. Current micro-manipulation techniques commonly damage cell walls and membranes due to their stiffness and rigidity. Ionic polymer-metal composite (IPMC) actuators have inherent compliance and with their ability to operate well in fluid and cellular environments they present a unique solution for safe cell manipulation. The reason for the downfall of IPMCs is that their complex behaviour makes them hard to control precisely in unknown environments and in the presence of sizeable external disturbances. This paper presents a novel scheme for adaptively tuning IPMC actuators for precise and robust micro-manipulation of biological cells. A two-degree-of-freedom (2DOF) controller is developed to allow optimal performance for both disturbance rejection (DR) and set point (SP) tracking. These criteria are optimized using a proposed IFT algorithm which adaptively updates the controller parameters, with no model or prior knowledge of the operating conditions, to achieve a compliant manipulation system which can precisely track targets in the presence of large external disturbances, as will be encountered in real biological environments. Experiments are presented showing the performance optimization of an IPMC actuator in the presence of external mechanical disturbances as well as the optimization of the SP tracking. The IFT algorithm successfully tunes the DR and SP to an 85% and 69% improvement, respectively. Results are also presented for a one-degree-of-freedom (1DOF) controller tuned first for DR and then for SP, for a comparison with the 2DOF controller. Validation has been undertaken to verify that the 2DOF controller does indeed outperform both 1DOF controllers over a variety of operating conditions.

An output feedback adaptive tracking scheme is proposed for a class of nonlinear systems with parameter uncertainty and input saturation. The unmeasured states are estimated by constructing filters, then dynamic surface control system is designed, which avoids explosion complexity of backstepping control. The effect of actuator saturation on system performance is compensated by neural network. It is shown that the proposed scheme can guarantee semi-global stability of the closed-loop system and the tracking error can be made arbitrarily small.KeywordsOutput feedback Dynamic surface control Input saturation Neural networks Adaptive control

This paper presents analysis, design and simulation of one degree-of-freedom (1DOF) and two degrees-of-freedom (2DOF) controllers for the indirect field orientation control (1FOC) of induction machine drive system. To achieve zero steady state error, minimum overshoot and minimum settling time, (good dynamic response for disturbance rejection and set point tracking), 1DOF and 2DOF controllers are designed and analyzed. The design of these controllers is developed based on the transfer function of the induction machine in the synchronous reference frame at field orientation control (FOC). The 1DOF controller is an integral plus proportional (IP) configuration while the 2DOF controller consists of proportional plus integral (PI) type in the feedback loop and lead/lag compensator in the feedforward loop. To verify the design of controllers and system performance, the drive system is simulated using SIMULINK for MATLAB. The desired current and speed tracking control performances of the drive can be preserved under wide operating range and good load regulating performance can also be obtained. The dynamic performance of the drive system for different operating conditions is studied with application of IP and 2DOF controllers. Taking into consideration the parameter variations of the induction machine, the dynamic performance have been studied under load changes and set-point variations. The simulation results are provided to demonstrate the effectiveness of the proposed controllers.

This investigation considers stability analysis and control design for nonlinear time-delay systems subject to input saturation. An anti-windup fuzzy control approach, based on fuzzy modeling of nonlinear systems, is developed to deal with the problems of stabilization of the closed-loop system and enlargement of the domain of attraction. To facilitate the designing work, the nonlinearity of saturation is first characterized by sector conditions, which provide a basis for analysis and synthesis of the anti-windup fuzzy control scheme. Then, the Lyapunov–Krasovskii delay-independent and delay-dependent functional approaches are applied to establish sufficient conditions that ensure convergence of all admissible initial states within the domain of attraction. These conditions are formulated as a convex optimization problem with constraints provided by a set of linear matrix inequalities. Finally, numeric examples are given to validate the proposed method.

Three factors that complicate the position and orientation control of unmanned autonomous vehicles are the hardware-induced delays, delays caused by teleoperated modes of operation, and persistent disturbances such as wind. In this article, we study how to overcome these challenges by controlling a twin rotor multi-input, multi-output system. This nonlinear system has two degrees of freedom and significant cross-coupling, making its control particularly challenging. Time delay and external disturbances contribute to system instability and complicate flight control. The effects of time delay can be mitigated using the standard Smith predictor controller. However, this approach performs poorly when persistent disturbances are present. Our contribution is a modified Smith predictor that effectively mitigates disturbances. Additionally, a decoupler is employed to transform the system into two single-input, single-output models, enabling precise control of both the horizontal and vertical planes. The proposed method is implemented on a prototype and compared with the original Smith predictor-based control scheme. Experimental results validate the effectiveness of the proposed approach, showing that our approach reduces the steady-state tracking error to less than 2%, decreases settling time from 30 s to 20 s, and improves disturbance rejection under wind disturbance conditions by 35% compared to the standard Smith predictor. These results demonstrate the superior set-point tracking performance and enhanced disturbance rejection of the proposed approach.

Smith Predictor is very sensitive to uncertain system with variable time-delay. Using dual-locus diagram method, we first analyse the essence of Smith Predictor's sensitivity and present a proposition to illustrate the system stability criteria with relation to system gain and time-delay variation. Then a new modified Smith Predictor is proposed to compensate the variable time-delay system with uncertain model for set-point tracking. After that, we discuss the system internal stability and give two-degree freedom controller self-adaptive to eliminate the impact of system uncertainty with varying time-delay. Examples show the improved performance compared to previous Modified Smith Predictor structures.

A number of tuning rules have been reported in literature for unstable first order plus time delay processes. However, at least to the author knowledge most of the reported methods fail to give robust performance for process models with time delay equal to or greater than the process time constant. In this work, a robust tuning method based on the modified Smith predictor is proposed for unstable first order plus time delay process models. Set point tracking controller is designed using direct synthesis approach. The PD controller which is used for load disturbance rejection is designed so as to satisfy the Routh Hurwitz's stability criterion. Suitable value of the tuning parameter is recommended after studying its effect on the system performance and robustness. This is also an advantage of the present work over the other recently reported strategies where suitable ranges of the tuning parameters' values are provided.

This study proposes the speed control of an asynchronous motor (AM) using the Antiwindup design. First, the conventional vector control based on proportional-integral (PI) controllers is developed for a constant speed set point. Then, a driving cycle is based on measurements on the Safi/Rabat motorway in Morocco using a microcontroller equipped with a GPS device. The collected practical speed is used as a speed reference for conventional vector control. The /Antiwindup controller of the direct rotor flow-oriented control is used to improve the performance of conventional vector control and optimize the energy consumption of the drive train. The effectiveness of the proposed control scheme is verified by numerical simulation. The results of the numerical validation of the proposed scheme showed good performance compared to conventional vector control. The speed control systems are analyzed for different operating conditions. These control strategies are simulated in the MATLAB/SIMULINK environment. The simulation results of the improved vector control of the Asynchronous Machine (AM) are used to validate this optimization approach in the dynamic regime, followed by a comparative analysis to evaluate the performance and effectiveness of the proposed approach. A practical model based on a TMS320F28379D embedded board and its reduced voltage inverter (24V) is used to implement the proposed method and verify the simulation results. Doi: 10.28991/ESJ-2022-06-04-012 Full Text: PDF

The paper addresses the stability analysis of a circular tunnel face driven by a pressurized shield by means of the limit analysis kinematic approach implemented in the context of the Mohr-Coulomb strength condition. Emphasis is given to the assessment of the effects of seismic loading on the value of face support pressure that is required to prevent failure. The approach relies upon the pseudo-static method to model the destabilizing effects induced by the inertial forces associated with the passage of seismic waves in the ground. Rigorous limit analysis solutions for the limit face supporting pressure are derived from the analytical implementation of 3D and 2D failure mechanisms specifically devised for dealing with such a stability analysis problem. Indeed, original analytical expressions are provided and allow the evaluation of the pressure stabilizing the tunnel face. The accuracy of the approach predictions is assessed by comparison with available experimental and analytical results as well as with 2D finite element solutions. The influence of some relevant problem parameters in the context of tunnel face stability analysis is finally investigated, thus providing some preliminary guidelines for practical use in tunnel engineering.