07-12-2012, 03:02 PM
A Dissertation on EMPIRICAL MODELING AND PI/PID CONTROL FOR LEVEL – TEMPERATURE PROCESS
[attachment=42952]
Introduction
Most of the chemical processes are basically multiple input/ multiple output (MIMO) systems [1].
However, compared with single-input single-output counterparts, MIMO systems are more difficult to control due to the existence of interactions between input and output variables.
Applying the tuning methods for a SISO system to multi-loop systems often leads to poor performance and stability.
Many methods have been proposed, how to efficiently take loop interactions into account in the multi-loop controller design [3].
Detuning method or Biggest log modulus tuning(BLT) method.
Sequential loop control(SLC) method.
Relay auto-tuning method.
Independent loop method.
Lee et al’s Method
The literature is to design multi-loop controller for interfacing multi-variable process [1].
The concept of Effective open loop transfer function(EOTF) is used.
Using model order reduction, the EOTF is further approximated to reduced form.
The individual controller of each single loop is then independently designed by IMC method.
Reduced EOTF
A model reduction technique [1] is applied to approximate the EOTF to a reduced-order model.
Such as the first-order plus dead time (FOPDT) and the second-order plus dead time (SOPDT) models.
For a 2×2 system, the general stable square transfer function matrix is represented as
Multi-Loop PID controller design
The IMC-PID design [1] is used for the PID controller tuning in the process industry.
The reduced EOTF ( ), is decomposed to
where and are the non-minimum portion and the minimum phase portion respectively.
The conventional IMC filter, f , is , in which λi is design parameter and mi is filter order.
Liu et al’s Method
In this method, the desired closed loop diagonal transfer functions and the dynamic detuning factors are proposed to reduce the interactions between individual loops [2].
After that, the desired multi-loop controllers are inversely derived.
The mathematical Maclaurin series expansion is utilized to reproduce them in the form of a conventional PI/PID controller for implementation.
Conclusion
In this study both the methods given similar results and performed well.
When compare the method - 1 and the method - 2, first method given slightly better performance results than second method.
So, these two methods can be used for achieving better results in various MIMO process in industry.
[attachment=42952]
Introduction
Most of the chemical processes are basically multiple input/ multiple output (MIMO) systems [1].
However, compared with single-input single-output counterparts, MIMO systems are more difficult to control due to the existence of interactions between input and output variables.
Applying the tuning methods for a SISO system to multi-loop systems often leads to poor performance and stability.
Many methods have been proposed, how to efficiently take loop interactions into account in the multi-loop controller design [3].
Detuning method or Biggest log modulus tuning(BLT) method.
Sequential loop control(SLC) method.
Relay auto-tuning method.
Independent loop method.
Lee et al’s Method
The literature is to design multi-loop controller for interfacing multi-variable process [1].
The concept of Effective open loop transfer function(EOTF) is used.
Using model order reduction, the EOTF is further approximated to reduced form.
The individual controller of each single loop is then independently designed by IMC method.
Reduced EOTF
A model reduction technique [1] is applied to approximate the EOTF to a reduced-order model.
Such as the first-order plus dead time (FOPDT) and the second-order plus dead time (SOPDT) models.
For a 2×2 system, the general stable square transfer function matrix is represented as
Multi-Loop PID controller design
The IMC-PID design [1] is used for the PID controller tuning in the process industry.
The reduced EOTF ( ), is decomposed to
where and are the non-minimum portion and the minimum phase portion respectively.
The conventional IMC filter, f , is , in which λi is design parameter and mi is filter order.
Liu et al’s Method
In this method, the desired closed loop diagonal transfer functions and the dynamic detuning factors are proposed to reduce the interactions between individual loops [2].
After that, the desired multi-loop controllers are inversely derived.
The mathematical Maclaurin series expansion is utilized to reproduce them in the form of a conventional PI/PID controller for implementation.
Conclusion
In this study both the methods given similar results and performed well.
When compare the method - 1 and the method - 2, first method given slightly better performance results than second method.
So, these two methods can be used for achieving better results in various MIMO process in industry.