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

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.

This paper presents a new control methodology for a class of integrating systems. A PID controller augmented with a first order lead/lag filter is proposed for improved response. The polynomial approach is employed to derive the controller parameters. The novelty of the proposed method lies in the selection of pole locations. Multiple pole locations are considered where one of the poles is placed for cancelling the zero introduced by controller. The selection of tuning parameter is based on maximum sensitivity (MS). Set point weighting is employed to reduce the overshoot and settling time in the servo response. Various bench marking examples are adopted to evaluate the proposed method in terms of various performance indices. The results are superior to the recently proposed works in terms of both set point tracking and disturbance rejection.

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.

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.

The modified Smith predictor is well known as an effective time-delay compensator for a plant with large time delays, and several papers on the modified Smith predictor have been published. The parametrization of all stabilizing modified Smith predictors for minimum-phase time-delay plants is obtained by Yamada and Matsushima. In addition, Yamada et al. expanded the result by Yamada and Matsushima and proposed the parametrization of all stabilizing modified Smith predictors for non-minimum-phase time delay plants. However, no paper examines the parametrization of all stabilizing 2-degree-of-freedom modified Smith predictors that can specify the input-output characteristic and the feedback characteristic separately. From the practical point of view, it is desirable that the input-output characteristic and the feedback characteristic are specified separately. In this paper, we propose the parametrization of all stabilizing 2-degree-of-freedom modified Smith predictors for time-delay plants that can specify the input-output characteristic and the feedback characteristic separately.

A dead-time compensator for controlling higher-order processes with integral action and long dead-time is proposed. Tuning formulas are derived. If the velocity gain and the dead-time are estimated experimentally, only one parameter, the time constant defining the speed of the closed-loop setpoint response, has to be tuned manually. The same setpoint response is obtained as in the modified Smith predictor, while the load disturbance rejection is considerably faster.

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 smith-predictor-assisted adaptive load disturbance rejection controller for speed variation suppression of PMSM drive

The energy policies of the [Formula: see text] century are increasingly focused on promoting generation solutions with minimal environmental impact. In response to strategic initiatives, the accelerating depletion of fossil fuel reserves has led to integrating renewable sources for power generation. The uncertain nature of solar and wind energy sources, along with fluctuating load demands, leads to frequency instability. This study addresses the challenge of frequency instability by designing a Bayat-tuned fractional-order proportional-integral-derivative (FOPID) controller for a decentralized microgrid [Formula: see text]. The proposed [Formula: see text] model consists of environmentally friendly energy sources such as a biogas turbine generator (BTG), a biodiesel engine generator (BEG), other distributed generation units (DGUs), and energy storage devices (ESDs). The mathematical modeling of [Formula: see text] components is carried out using first-order transfer functions, which are combined to derive the overall transfer function of [Formula: see text] model. This composite model is then approximated as a first-order plus time delay (FOPTD) system to simplify FOPID controller design. The parameters of the FOPID controller are optimized using the Bayat method to achieve robust performance under set-point tracking (SPT) and load disturbance rejection (LDR) scenarios. Based on this approach, three controller variants i.e., FOPID-[Formula: see text], FOPID-[Formula: see text], and FOPID-[Formula: see text], are developed. To validate the effectiveness of the proposed control strategy, various simulation scenarios are considered, including load disturbances and varying levels of solar and wind power penetration. The performance of the controllers is evaluated in terms of frequency deviation, error mitigation, and transient behavior under SPT and LDR conditions. A comparative analysis using error indices, time-domain metrics, control effort, and frequency plots confirms the effectiveness of the Bayat-tuned FOPID designs. Furthermore, real-time validation using the OPAL-RT simulator underscores their practical potential in maintaining frequency stability within [Formula: see text] systems. Owing to the performance analysis, it is justified that discussed FOPID-Bayat controllers consistently ensured controllability with a minimum rise time of [Formula: see text], a nearly constant settling time of [Formula: see text], and reduced control effort down to 0.12. Furthermore, error index evaluation confirmed that FOPID-Bayat[Formula: see text] outperformed other configurations by achieving the lowest IAE (8.737), ITAE (223.0), ITSE (40.39), and ISE (1.706), thereby demonstrating superior efficiency and robustness.

Enhanced IMC-based Load Disturbance Rejection Design for Integrating Processes with Slow Dynamics

A two-degree-of-freedom (2DOF) control scheme is proposed for inverse response processes with time delay. The proposed control structure consists of reference model, feedforward controller and feedback controller. The feedforward controller is designed based on the inverse model of the plant, so that set-point tracking response can follow the one defined by a reference model. The feedback controller, designed using direct synthesis method based on disturbance rejection, can assure the excellent disturbance rejection performance on the premise of guaranteeing stability of the closed-loop system. Compared with existing control method, the proposed control structure can assure system of good set-point tracking performance and disturbance rejection performance simultaneously, and the controller parameters can be adjusted conveniently.Keywordsinverse response processestime delaytwo-degree-of-freedom

A nonlinear PID controller with applications

In this paper a discrete-time domain 2DOF design method is proposed for industrial stable processes with input time delay, based on a recently developed two-degree-of-freedom (2DOF) control structure. The setpoint tracking controller is analytically designed based on the H2 optimal control principle, and another controller for load disturbance rejection is derived by proposing the desired closed-loop complementary sensitivity function. Both controllers can be tuned independently to realize control optimization. Analytical expression of the setpoint response is given for quantitatively tuning the single adjustable parameter in the setpoint tracking controller. At the meantime, the tuning constraints of another adjustable parameter in the controller for disturbance rejection are derived by establishing the sufficient and necessary conditions for holding robust stability of the closed-loop system. Illustrative examples from the literature are used to show the effectiveness and merit of the proposed control method.

Leveling operation is a very important step in the installation process of offshore jacket platform and it is performed by leveling tool. In this paper, the hydraulic lifting subsystem model of leveling tool is established, and a modified Smith predictor is used to address the time delay problem caused by long pipeline. A composite control strategy combining identical and master slave control mode is adopted to solve synchronization control problem of the multi-cylinder hydraulic lifting system. A fuzzy self-tuning PI controller between the master and slave cylinder is designed to compensate the synchronization error. The simulation results show that the modified Smith predictor has better control effect than conventional Smith predictor for the hydraulic system with long pipelines. The synchronous approach has high precision and can meet the leveling requirements.

The compensation of process with time delays has been of interest to academics and pratitioners for several decades. Additionally, proportional integral derivative (PID) controllers are widely used in the process industries. The simplicity and the ability of these controllers to solve most practical control problems have greatly contributed to this wide acceptance. However, they may not provide satisfactory closed loop responses when the process considered is either a high-order plant or a plant with a long dead time. In these cases a powerful technique, the Smith predictor, can be used. However, these regulators cannot reject load disturbance for processes with integration. A review of the literature for compensation methods of process with time delay and Smith predictor (and its modifications) is presented. The focus of the thesis is subsenquently broadened with the consideration of compensation methods for integrating process and the proposition of a new approach. The proposed method for PID (or its variations) controllers is based on the specification of the desired closed loop transfer function for disturbances. Although the approach is designed for disturbance rejection, the set-point responses are usually satisfactory and can be independently tuned. Simulation examples show the simplicity and better robustness of the proposed method over previously published approaches both for the set-point response and for the load disturbance rejection.