Improving the control energy use for first order plus time delay plants with fractional proportional integral controllers: a preliminary analysis

Abstract Actuator rate limit deteriorates control performance with amplitude attenuation and phase delay, and may lead to system instability in process control. In this paper, great challenges for first-order plus time delay (FOPTD) systems are concerned. Based on the preliminary knowledge of the definition of rate limiter, the concept of closed-loop onset frequency with rate limiter and classic proportional-integral (PI) tuning rules, the rate limit effects on PI controller are analyzed by simulations. The results show that the rate limiter has significant influence on the stability regions of PI parameters which can be reduced greatly. Besides, PI tuning rules with the same robustness constraint can be obviously effected where Skogestad internal model (SIMC) tuning rule is more robust to the rate limit variation than that of maximize the integral gain (Åström) and robustness constrained optimization (DRO) tuning rule. These results can offer a guideline to tune PI parameters when actuators have non-ignorable rate limit for industrial applications.

Download Full-text

Interactive Tuning Tool of Proportional-Integral Controllers for First Order Plus Time Delay Processes

Symmetry ◽

10.3390/sym10110569 ◽

2018 ◽

Vol 10 (11) ◽

pp. 569 ◽

Cited By ~ 6

Author(s):

Mario Ruz ◽

Juan Garrido ◽

Francisco Vazquez ◽

Fernando Morilla

Keyword(s):

Time Delay ◽

Controller Design ◽

Industrial Process ◽

Implementation Process ◽

Open Loop ◽

Practical Case ◽

Control Loops ◽

Proportional Integral ◽

First Order ◽

Tuning Rules

Engineering education and, particularly, control engineering, has shown growth in research and development activities during last years. Currently, proportional–integral (PI) and proportional–integral–derivative (PID) controllers are the most commonly used in industrial process applications. Nonetheless, it is reported that many of them are badly tuned. From an educational perspective, it is crucial for the student to understand the importance of tuning a control loop correctly. This paper presents an interactive tool focused on the study of PI controllers. The tool provides a set of tuning rules for both open-loop stable and unstable first order plus time delay processes. The different tuning rules can be compared interactively by the user, allowing a critical analysis of basic concepts about stability, robustness, and performance in PI control loops. In addition to educational purposes, the tool has been developed, taking into account practical considerations, such as simulation with a controller discrete implementation, process input saturations, and windup effect. We evaluated students’ achievement in the final examination in the Automatic Control course of the Electronics Engineering degree. Students showed significant improvement in their understanding of PI controller design. A survey and a practical case study were performed to evaluate the effectiveness of the proposed tool.

Download Full-text