**3.1. Tuning methods**

8 MATLAB – A Fundamental Tool for Scientific Computing and Engineering Applications – Volume 1

objective of the control system.

So, the FODT representation is:

So, the FODT representation is:

fermented mash applied at the column A:

Time Delay).

valve actuation:

These variables depend respectively on the steam flow at the basis of the column A and on the flow of fermented mash applied at the column A. The minimization of the variability of the alcoholic content according the brazilian standard NBR 5992-80 is the main design

The distillation process is characterized by a high coupling through the system variables and by a non-linear relationship between them. According (Santos, 2010) the models that represent the relationship between the main process variables is FOTD (First Order with

> ( ) <sup>1</sup> *<sup>s</sup> Ke G s s*

In this work the modeling procedure was developed and the following equation was obtained from the relationship of the pressure variation at the A column and the steam flow

 

*PV <sup>K</sup> MV K C tt s tt s*

´ 85 ´ 174

´ 0,133% / %

 

*tt s tt s*

*PV <sup>K</sup> MV*

Where MP is the Manipulated Variable e PV is the Process Variable.

0,26% / % 3 23

*K bar opennig*

<sup>3</sup> 0,26 ( ) 23 1 *<sup>s</sup> <sup>e</sup> G s s*

The same modeling procedure was developed to obtain the relationship among the variation of the temperature at the distillation tray A20 and the variation of the flow of

<sup>150</sup> ´ 23% 33%

<sup>85</sup> 0,133 ( ) 174 1 *<sup>s</sup> <sup>e</sup> G s s* 

*o*

(97,8 95,8).110%

*opennig*

(0,36 0,44).110% 55 85,91

(7)

(9)

(11)

(8)

(10)

  The above systems were described in (Santos, 2010) and at that work there also were described and applied four tuning methods of the PI control: Ziegler-Nichols (First Method), CHR, Cohen-Coon and IMC (Internal Model Control).

Each method was analyzed through the use of Integral Absolute Error (IAE) and the best results are described at Table 1.


**Table 1.** PI Tuning parameters

The simulation results presented (Santos, 2010) were used at the real process and another manual calibration was made. The new tuning parameters are presented at Table 2.


**Table 2.** Manual PI Tuning parameters adjusted at the process.

The process where the temperature and pressure loops were modelled is described at figure 4 (Santos, 2010).
