A general controller evaluation method based on three performance and robustness criteria is presented. It can be used to compare controllers of different structures, but also as a design method to find the optimal parameter setting for a controller of given structure. In this way optimal PI and PID controllers have been designed for a set of different plants. Clear regularities have then been noticed and utilised to formulate sets of tuning rules for non-oscillating stable plants and for plants with integral action. The rules demand very little plant knowledge but the resulting controllers are close to optimum. Furthermore, the user may adjust one or two of the tuning parameters and still get very good results. This means that the user has some freedom to manage the important trade-off between performance, robustness and control activity.

Robust and optimal tuning of PI and PID Controllers

In this paper, a new robust control strategy based on a predictor and the uncertainty and disturbance estimator is developed for a class of uncertain nonlinear systems with input/output delays. The closed-loop system is analyzed and sufficient stability conditions are derived based on Lyapunov analysis. The proposed strategy is applied to the particular case of quadrotor systems and validated through extensive simulations to evaluate performance and robustness. The controller is also implemented in a quadrotor prototype and validated in flight tests.

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Predictor-Based Control of a Class of Time-Delay Systems and Its Application to Quadrotors

The current study endeavors to put together evolution, developments, and future prospects of internal model control strategy. Due efforts have been made to include all the techniques and philosophies used to that end. The brief account of the most recent techniques for near optimal and robust control has been provided along with a summary of conventional control schemes. At the same time, more emphasis is given on the issues in IMC design for single-input, single-output systems, like quantitative filter selection and tuning guidelines, modified structures, and related aspects of contemporary research developments. A set of references of all concerned papers, and a brief summary in them is provided. This paper also presents the results of these techniques as provided in the respective references. Illustrative example is given to show the effectiveness and the merits of the IMC based various forms.

Advances in Internal Model Control Technique: A Review and Future Prospects

Analytical IMC-PID design in terms of performance/robustness tradeoff for integrating processes: From 2-Dof to 1-Dof

In this paper, a decentralized PI/PID controller design method based on gain and phase margin specifications for two-input-two-output (TITO) interactive processes is proposed. The decouplers are designed for systems to minimize the interaction between the loops, and the first order plus dead time (FOPDT) model is achieved for each decoupled subsystem based on the frequency response fitting. An independent PI/PID controller is designed for each reduced order decoupled subsystem to obtain the desired gain and phase margins, and the performance is verified on the original interactive system to show the effectiveness of the proposed design method for the general class of TITO systems. Simulation examples are incorporated to validate the usefulness of the presented algorithm. An experimentation is performed on the Level-Temperature reactor process to show the practical applicability of the proposed method for the interactive system.

Decentralized PI/PID controllers based on gain and phase margin specifications for TITO processes.

Minimizing the integral squared error (ISE) criterion to get the optimal controller parameters results in a PD controller for integrating processes. The PD controller gives good servo response but fails to reject the load disturbances. In this paper, it is shown that satisfactory closed loop performances for a class of integrating processes are obtained if the ISE criterion is minimized with the constraint that the slope of the Nyquist curve has a specified value at the gain crossover frequency. Guidelines are provided for selecting the gain crossover frequency and the slope of the Nyquist curve. The proposed method is compared with some of the existing methods to control integrating plant transfer functions and in the examples taken it always gave better results for the load disturbance rejection whilst maintaining satisfactory setpoint response. For ease of use, analytical expressions correlating the controller parameters to plant model parameters are also given.

PID controller tuning for integrating processes.

In this work, the normalized Internal Model Control (IMC) filter time constant is designed to achieve a specified value of the maximum sensitivity for stable first and second order plus time delay process models, respectively. Since a particular value of the maximum sensitivity results in an almost constant percentage overshoot to controller setpoint change, an empirical relationship between the normalized IMC filter time constant and percentage overshoot is presented. The main advantage of the proposed method is that only a user-defined overshoot is required to design a PI/PID controller. Simulation examples are given to demonstrate the value of the proposed method.

PI/PID controller design based on IMC and percentage overshoot specification to controller setpoint change.

Industrial processes of unstable/integrating nature having a dead time and inverse response characteristics are challenging to control. For controlling such processes, double-loop control structures have proven to be more efficient than conventional PID controllers in a unity feedback configuration. Therefore, a new design method to obtain PI-PD controller settings is proposed for a set of unstable/integrating plant models with dead time and inverse response. The stabilizing proportional–derivative (PD) controller is designed using maximum sensitivity considerations and Routh–Hurwitz stability criteria. The PI controller settings are obtained by comparing the first and second derivatives of expected and actual closed-loop transfer functions about the origin of the s-plane. Adjustable parameters of the inner and outer loops are selected such that the desired value of maximum sensitivity is achieved. Simulation studies are conducted on some benchmark linear and nonlinear plant models used in literature. Robustness of the proposed design is analyzed with perturbed plant models, and quantitative performance measures are computed. It is found that the proposed design yields enhanced and robust closed-loop response than some contemporary works.

New PI-PD Controller Design Strategy for Industrial Unstable and Integrating Processes with Dead Time and Inverse Response

In this work, a recently reported two degree of freedom control structure namely the Parallel Control Structure (PCS) is modified to achieve improved control performance for unstable processes. New tuning rules are proposed using a direct synthesis approach for unstable first order plus time delay (UFOPTD), unstable second order plus time delay (USOPTD) and integrating and unstable plus time delay (IUPTD) process models. The proposed method has two tuning parameters whose suitable values are recommended after studying their effect on the system performance and robustness. This is an advantage of the present work over the other reported control schemes where the authors provide suitable ranges of the tuning parameters values. Simulation examples show that the present scheme results in improved nominal and perturbed responses as compared to the recently reported methods. Also it is observed that satisfactory performance is achieved when the proposed tuning rules are applied on an isothermal chemical reactor which exhibits multiple steady state solutions.

Two degree of freedom control scheme for unstable processes with small time delay.

This study provides a comprehensive review of existing active disturbance rejection control (ADRC) techniques for the control of non-minimum phase (NMP) DC-DC boost converter (DBC). A boost converter presents a challenging control task due to its non-linear and NMP dynamics while operating in continuous conduction mode. ADRC schemes, specifically those that claim improved performance for NMP systems, have been experimentally evaluated for voltage control of DBC. Additionally, a new way of incorporating known system dynamics into the control structure is proposed through a modified scheme. An averaged non-linear model of DBC is used in the simulation to analyse the effectiveness of control schemes and the results are experimentally validated on hardware. It is shown that the proposed method outperforms the reported model-assisted ADRC techniques while utilising only the system pole information.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2018.5767

Ahmad Ali

Papers

PID controller tuning for integrating processes.

PI/PID controller design based on IMC and percentage overshoot specification to controller setpoint change.

New PI-PD Controller Design Strategy for Industrial Unstable and Integrating Processes with Dead Time and Inverse Response

Two degree of freedom control scheme for unstable processes with small time delay.

Active disturbance rejection control of DC–DC boost converter: a review with modifications for improved performance