Set point weighted modified Smith predictor with PID filter controllers for non-minimum-phase (NMP) integrating processes

A unified design approach for control integrating processes with time delay

The article presents a unified control system designing scheme to obtain enhanced performance for processes including integrator and dead time. A simple control structure including two controllers is proposed. Servo performance and disturbance rejection performance can be adjusted independently by introducing a desired transfer function model in the control structure. Servo controller is designed according to the direct synthesis principle and disturbance rejection controller is derived adopting the internal model control (IMC) theory. Simulations have been conducted on four kinds of integrating plants with dead time. The simulation results exhibit that noteworthy enhancement can be achieved by the presented scheme in comparation with the other methods even though there are perturbed dynamics.

IMC based modified Smith predictor for second order delay dominated processes with RHP

A modified Smith predictor (MSP) with IMC based tuning is proposed for second order delay dominated processes. These processes often exhibit unstable behaviour due to right half poles (RHP) with positive or negative zeros. The control scheme incorporates forward path PI/PID controller with a lead-lag filter and a PD controller in the feedback path. IMC technique having single tuning parameter is utilized to design the forward path controller, while the feedback path controller is tuned by Routh stability criterion. The proposed scheme ascertains quick set point following without overshoot and smooth disturbance rejection, resulting superior closed-loop performance compared to recent MSP schemes. Validation is made based on performance indices and stability margins.

Enhanced PID Controller for Non-Minimum Phase Second Order Plus Time Delay System

A tuning method is developed for the stabilization of the non-minimum phase second order plus time delay systems. It is well known that the presence of positive zeros pose fundamental limitations on the achievable control performance. In the present method, the coefficients of corresponding powers of s, s2 and s3 in the numerator are equated to α, β and γ times those of the denominator of the closed-loop system. The method gives three simple linear equations to get the PID parameter. The optimal tuning parameters α, β and γ are estimated by minimizing the Integral Time weighted Absolute Error (ITAE) for servo problem using fminsearch MATLAB solver aimed at providing lower maximum sensitivity function and keeping in check with the stability. The performance under model uncertainty is also analysed considering perturbation in one model parameter at a time using Kharitonov’s theorem. The closed loop performance of the proposed method is compared with the methods reported in the literature. It is observed that the proposed method successfully stabilizes and improves the performance of the uncertain system under consideration. The simulation results of three case studies show that the proposed method provides enhanced performance for the set-point tracking and disturbance rejection with improved time domain specifications.

A New Control Scheme for Integrating Processes with Inverse Response and Time Delay

This paper presents a novel technique in designing controller for integrating process with inverse response and time delay. Using Pade’s approximation, the positive zero is approximated to a negative zero by modifying the time delay of process. The polynomial approach is employed for the rearranged process to derive the controller parameters. The tuning parameter is selected based on the value of maximum sensitivity. Set point filtering is employed to reduce the overshoot in servo response. Various bench marking examples are considered to evaluate the proposed method. The evaluation is carried out in terms of various performances.

A generalized smith predictor for unstable time-delay SISO systems

In this work, a generalization of the Smith Predictor (SP) is proposed to control linear time-invariant (LTI) time-delay single-input single-output (SISO) systems. Similarly to the SP, the combination of any stabilizing output-feedback controller for the delay-free system with the proposed predictor leads to a stabilizing controller for the delayed system. Furthermore, the tracking performance and the steady-state disturbance rejection capabilities of the equivalent delay-free loop are preserved. In order to place this contribution in context, some modifications of the SP are revisited and recast under the same structure. The features of the proposed scheme are illustrated through simulations, showing a comparison with respect to the corresponding delay-free loop, which is here considered to be the ideal scenario. In order to emphasize the feasibility of this approach, a successful experimental implementation in a laboratory platform is also reported.

Enhanced IMC based PID controller design for non-minimum phase (NMP) integrating processes with time delays

Internal model control (IMC) with optimal H₂ minimization framework is proposed in this paper for design of proportional-integral-derivative (PID) controllers. The controller design is addressed for integrating and double integrating time delay processes with right half plane (RHP) zeros. Blaschke product is used to derive the optimal controller. There is a single adjustable closed loop tuning parameter for controller design. Systematic guidelines are provided for selection of this tuning parameter based on maximum sensitivity. Simulation studies have been carried out on various integrating time delay processes to show the advantages of the proposed method. The proposed controller provides enhanced closed loop performances when compared to recently reported methods in the literature. Quantitative comparative analysis has been carried out using the performance indices, Integral Absolute Error (IAE) and Total Variation (TV).