User's Manual

Automation and Drives - SCE

T I A Training Document Page 25 of 64 Module

2.7.3.3 PI Controllers

In practice, the PI controller is a controller type that is used very often. It consists of the parallel

connection of a P-controller and an I-controller. When laid out correctly, it combines the advantages

of both controller types (stable and fast, no lasting system deviation), so that their disadvantages are

compensated for at the same time.

Block Diagram

The trend is indicated with the proportional coefficient Kp and the reset time Tn. Based on the

proportional component, the controller output responds immediately to each system deviation e,

while the integral component has an effect only in the course of time. Tn represents the time that

passes until the I-component generates the same margin of the manipulated variable as it is

generated immediately because of the P-component (Kp). As for the I-controller, the reset time Tn

has to be reduced if you want to increase the integral component.

Controller Layout:

Depending on the Kp and Tn dimensioning, the overshoot of the controlled variable can be reduced

at the expense of control system dynamics.

Applications for the PI controller: fast control loops that don’t permit lasting system deviations.

Examples: pressure, temperature, ratio control.

Preface Fundamentals Discontinuous Action Controller Controller Block (S)FB41 Setting the System Appendix

Issued: 02/2008 Control Engineering with STEP 7