Copyright Siemens AG 2010 All rights reserved
Introduction
Figure 2-1 Step response of a control loop with compensation (blue) and without compensation (red), i.e. with integral behaviour.
Step Response
3whithout compensation,
| i.e. with |
|
2.5 | ohne |
|
integral |
| |
| Ausgleich | with |
| behaviour | |
| mit | |
2 |
| compensation |
| Ausgleich |
Amplitude | 1.5 |
| |
| 1 |
| 0.5 |
00 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
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|
|
|
| Time (sec) |
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|
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Unstable control loops cannot be stabilized without a controller. Therefore, switch- ing a controller in such a loop to manual mode is not allowed for a longer time.
Hence, the recording of measurement data for the process identification (e.g. for the PID tuner or the MPC configurator) via step experiments in open control loop is not possible. The model type and the control algorithm of the MPC function block are also inappropriate for unstable control loops. Therefore, the unstable part trans- fer functions have to be stabilized by subordinated slave controllers before the ap- plication of the MPC.
8 | MPC Level |
V 1.0, |