CONTROLLER STRUCTURES1. Mini module: Introduction to control structures

Strategic design of control systems. Control objectives Tom Pedersen

2. Mini module: Proces control of basic functionsand common unit processes.Relative Gain Array.Tom Pedersen

3. Mini module: Control of large scale process(sugar production)Kirsten Mølgaard Nielsen

4. Mini module: Control Structure DesignSelf-Optimizing Control Structure.Tom Pedersen

5. Mini module: Planning Kirsten Mølgaard Nielsen

CONTROLLER STRUCTURES

• Unbalanced view of control• Control Theory:

The problems are designed for control (Balancing wedge etc.)It's easy to model the process.There is a good correlation between theory and practice.

• Control in practice:The objective of the control may be difficult to describe.It is difficult to understand the function of the process.Problems with instrumentation (sensors etc)Modelling is difficult.Tuning of controllers

Large scale systems• In this course: Control of large scale systems:

Sugar productionDairyCement productionPaper productionPower stationsBreweriesetc

These are characterised by:

LargeMultiple input/outputNon-linearDifficult to understand the functions and to model.

Goals

Main control objectives (main goals):EconomyProduct qualityEnvironment (Laws)Standards

Sometimes it is possible to derive sub goals (strategic goals) from the main goals and the result is that it is necessary to keep a number of variables at constant set points

For a proper solution static optimization may bee needed as we will se in MM 4.

Strategic design

Strategic design = how to keep certain process variables at constant set points

Building blocks used in the strategic design

PID Controller - - The Archtype:Proportional part provides the controlDerivative part provides anticipation and dynamic

compensationIntegral part gives the steady state regulation

Bottom Up Design

• A way to view systems• A number of building blocks• Ideas to combine them• What are the building blocks of control?• What principles can be used to select and

combine them?• The danger: Can it be done better?• Commissioning: Close loops one by one

Bottom up design of control systemsBuilding blocks:

Feedback

Feedforward

Cascade

Large loop

Repetitive

Mid-range

Split-range

Ratio control

Decoupling

Limiters

Min/Max (selector)

Signal multiplication

Gain scheduling

Variable structur

Top down design of control systems

• Model complete system• Design an integrated system• System concepts

- State feedback- Observers- Model predictive control

• Commissioning:needs careful considerations

BUILDING BLOCKS

1. FEEDBACK

2. FEEDFORWARD

3. CASCADE

3. CASCADE

4. LARGE LOOP

5. REPETITIVE CONTROL

5. REPETITIVE CONTROL

6. MID-RANGE CONTROL

6. MID-RANGE CONTROL

7.SPLIT-RANGE CONTROL

8. RATIO CONTROL

8. RATIO CONTROL

8. RATIO CONTROL

9. DECOUPLING

10. LIMITERS

10. LIMITERS

11. SELECTORS

11. SELECTORS

12. STATIC NONLINEARITY

13. SIGNAL MULTIPLICATION

13. SIGNAL MULTIPLICATION

14. Gain Scheduling

May be a signal multiplication, so that the controller’s proportional gain is multiplied with a measured value.

In normal operation this multiplication factor is 1.

The multiplication may be inserted after the controller.

15. VARIABLE STRUCTUR

EXAMPLE