Tore Hägglund

Paper: Automatic tuning of simple regulators with specifications on phase and amplitude margins

The paper describes procedures for automatic tuning of regulators of the PID type to specifications on phase and amplitude margins. The key idea is a simple method for estimating the critical gain and the critical frequency. The procedure will automatically generate the appropriate test signal. The method is not sensitive to modelling errors and disturbances. It may be used for automatic tuning of simple regulators as well as initialization of more complicated adaptive regulators.

The future of PID control

Abstract This paper presents the state of the art of PID control and reflects on its future. Particular issues discussed include specifications, stability, design, applications, and performance of PID control. The paper ends with a discussion of alternatives to PID and its future.

Automatic Tuning and Adaptation for PID Controllers—A Survey

Adaptive techniques such as gain scheduling, automatic tuning and continuous adaptation have been used in industrial single-loop controllers for about ten years. This paper gives a survey of the different adaptive techniques, the underlying process models and control designs. The paper ends with an overview of industrial adaptive single-loop controllers.

Design of PI controllers based on non-convex optimization

This paper presents an efficient numerical method for designing PI controllers. The design is based on optimization of load disturbance rejection with constraints on sensitivity and weighting of set point response. Thus, the formulation of the design problem captures three essential aspects of industrial control problems, leading to a non-convex optimization problem. Efficient ways to solve the problem are presented.

A Control-Loop Performance Monitor

A procedure for automatic monitoring of control-loop performance is presented. The control loop performance monitor (CLPM) detects oscillations in the control loop. These oscillations are normally caused by too-high friction in the control valve, but there are other reasons as well. The CLPM is primarily intended to be connected to PID controllers, but it can also be connected to other controllers. The procedure is automatic in the sense that no additional parameters except the normal controller parameters have to be specified. The paper contains both a derivation of the CLPM and results from industrial experiments.

Industrial adaptive controllers based on frequency response techniques

This paper describes several adaptive techniques based on frequency response analysis, which are used in industrial controllers. Automatic tuning is used to obtain PID controller parameters, to build up gain schedules, and to initialize adaptive algorithms. A simple adaptive feedback algorithm which is based on the idea of tracking a point on the Nyquist curve is presented as well as an adaptive feedforward procedure. The adaptive techniques have been implemented in various industrial products. Industrial experiences from using the controllers are summarized in the paper.

Detection and diagnosis of oscillation in control loops

Abstract Previous work presented a real-time algorithm for the detection of oscillations in PI and PID feedback control loops. This paper examines further opportunities for oscillation detection in the off-line analysis of ensembles of data from control loops. Its use with measurements from routine operations is emphasised. The paper presents operational signatures that indicate the cause of an oscillation. Typically, a full diagnosis requires a special test for which the loop is taken out of routine operation. The signatures lead to recommendations about which special test is most appropriate. They therefore reduce the time spent in trouble-shooting by guiding the choice of test.

Automatic Tuning of Simple Regulators

This paper proposes methods for automatic tuning of slmple regulators. The methods are robust and they require little apriori knowledge about the process. The paper presents the Ideas behind the methods and analysis. Apart from being useful In themselves, the methods will also give a solution to the longstanding problem of safe Initialization of more sophisticated adaptive controllers.

Benchmark Systems for PID Control

Abstract This paper describes a collection of systems that are suitable for testing PID controllers. The systems are collected from a wide range of sources.

A friction compensator for pneumatic control valves

A procedure that compensates for staticfriction (stiction) in pneumatic control valves is presented.The compensation is obtained by adding pulses tothe control signal. The characteristics of the pulses are determinedfrom the control action. The compensator is implemented inindustrial controllers and control systems, and the industrialexperiences show that the procedurereduces the control error during stick-slip motionsignificantly compared to standard control without stiction compensation.