Slide 1

Future Perspectives of PID Controllers

(industrial process control)

Future Perspectives of PID Controllers

(industrial process control)

Willy Wojsznis

IFAC - PID’12 – Brescia Italy

IFAC Conference on Advances in PID Control

Brescia, 28-30 March 2012

Slide 2

Thoughts Thoughts • Where PID is?

• Why PID ?

• Direction for evolution

• Examples of PID evolution

• Conclusion

IFAC - PID’12 – Brescia Italy

Slide 3

Where PID is? Where PID is?

PID proved it can compete in many applications with new promising techniques, like

Fuzzy Logic

Model based controllers

MPC

Slogans “replace all PID” is not used as10-20 years ago

IFAC - PID’12 – Brescia Italy

Slide 4

Where PID is ? Where PID is ?

IFAC - PID’12 – Brescia Italy

• PID “found” its favorite spot, where it is doing the

better than other techniques

This is the low and intermediate level control in process industry where PID is absolutely dominant control

MPC reign in multivariable control and optimization. PID provide good control at the lower level

Instead of competition – good cooperation

Slide 5

Why PID ? Why PID ?

IFAC - PID’12 – Brescia Italy

• Feedback is universal control

• Intuitive for the human, appreciated by operators

• P I D - the most natural rules

• PID like control used

in nature on various levels

and time scale

(molecular level

- seconds,

species – thousand

of years)

Slide 6

PID – direction for evolution PID – direction for evolution

IFAC - PID’12 – Brescia Italy

Enhanced PID for dealing with special conditions or applications with added logic and calculations

Examples: saturated conditions, wireless, event driven, non-linear ….

Robust adaptive tuning and control

Performance monitoring and reporting

Valve diagnostics – mechanical failure can nullify all gains achieved from improved tuning or control strategy

Slide 7

PID at saturated conditions PID at saturated conditions

IFAC - PID’12 – Brescia Italy

• A better response to major upsets can be achieved through the

use of a dynamic pre-load and reducing the filtering that is

applied in the positive feedback path when the output limited

Slide 8

PID – model based adaptive tuning PID – model based adaptive tuning

IFAC - PID’12 – Brescia Italy

Why model based adaptation?

Model validation for model switching

adaptation with parameter interpolation is performed in parallel with parameter

evaluation

Ratio of maximum to minimum errors

signifies how fast is conversion

If the model with the middle parameter value

has smallest error it indicates the optimum is

within adaptation range

Statistical validation – recent model quality,

parameters standard deviation, number

of adaptations

Well established, intuitive tuning rules – Lambda, IMC, SIMC

Model can be used for other purposes – loop diagnostics, performance monitoring….

Slide 9

PID – model free adaptation PID – model free adaptation

IFAC - PID’12 – Brescia Italy

There are number of smart techniques model free techniques

Fictitious set point

Controller switching

Balancing controller terms

+ SPi(t)

+ PVi(t

)

OUTi(t

)

; and ; k k

k k

PP P I I

I

1( ) ( ) 1i iT k T k

Slide 10

PID – loop diagnostics PID – loop diagnostics

IFAC - PID’12 – Brescia Italy

Valve diagnostics features – mechanical failure can nullify all gains achieved from improved tuning or control strategy

Slide 11

PID – loop diagnostics PID – loop diagnostics

IFAC - PID’12 – Brescia Italy

Simple valve diagnostics can detect valve dead band and hysteresis

2 ( )h A out 2 ( )Ampl PV Kr

2 ( )Ampl PVr

K b h r

Slide 12

PID future - conclusion PID future - conclusion

IFAC - PID’12 – Brescia Italy

PID will continue to be main control on the basic level in the process industry

PID evolution as discussed will enhance PID competitiveness

Model free adaptive tuning can be useful in special applications