Siemens Module B3 manual PI Controllers, Controller Layout

Automation and Drives - SCE

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
	T I A Training Document		Page 25 of 64	Module
				B3
Issued: 02/2008				Control Engineering with STEP 7