**3. Different control strategies**

114 Introduction to PID Controllers – Theory, Tuning and Application to Frontier Areas

Step 3: From the output and input data Henkel matrix are formed and LQ decomposition

Step 4: Then Singular value decomposition method is used to estimate A, B, C and D

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> <sup>0</sup>

identified model actual model

Time in Sec

Fig. 3. Comparison of responses between actual (solid) and identified (Sequential

Mostly, the purpose of identification of transfer functions is to design controller for the system in order to achieve desired performance. Three methods of identifications (two in openloop mode and the other in closed-loop mode) are used to identify the two-input-twooutput process, WB column. Least square and subspace methods have been used to identify the process in openloop and sequential identification technique is used to estimate the

Step 5: From estimated matrices the transfer function were found.

1

identification, dashed line) models of WB column

process in closedloop.

2

3

O utput R esponse

4

5

6

7

8

method is used to spilt the matrix

matrices.

MIMO systems came into use in chemical industries as the processes were redesigned to improve efficiency. Multivariable control involves the objective of maintaining several controlled variables at independent set points. Interaction between inputs and output cause a manipulated variable to affect more than one controlled variable. The various control schemes studied here are the decentralized, centralized and decoupled systems. In decentralized structure, diagonal controllers are used. Hence they result in systems having n controllers. The centralized control systems have n x n controllers. In decoupled systems the process interactions are decoupled before they can actually reach and affect the processes.
