The existing control system for the fluid flow control consists of a cascaded PI controller with inner (faster) PI controller for controlling valve position change and outer (slower) PI controller for volume flow rate control. In case of extreme set point changes, for example in case of emergency shut down, it produces pressure surges. To avoid this from happening the approaches considered so far -
1) To add optimal feedforward controller in parallel to volume flow rate controller(outer loop) which will optimize the trajectory to be followed by valve for a given set point change with the pressure inside pipe maintained below given value(boundary constraint), using transient pipe flow model.
2) To add optimizer or a clever signal processor before sending the reference input to the control system
Can you suggest which can be the better approach to handle such scenario? Any other suggestions are also welcome.
Thank you!
Hello
In my opinion, second option should be taken which is same like a setpoint weighting. Take same as 2DOF setpoint input filter as it passes through the proportional action channel and the derivative action channel. This will moderate the impact of sudden setpoint changes on control inputs.
Utkal
The emergency shut down of your valve will produce a pressure surge because your fluid has inertia. It is the same situation that occurs when one switches off a current that was flowing through a circuit with an inductance using a transistor. To protect the transistor (switch) from the overvoltage (sometimes called 'inductive kickback') various classical strategies exist in electronics. These include having a Zener diode across the transistor (switch), a diode in counter-parallel to the inductor, or having a snubber (a combination of capacitor and resistor). for a mechanical equivalent the capacitor+resistor of the snubber would not be difficult to implement. :-)
hi
It seems comparing with classical speed/current loop in dc motors for example that the reference to inner loop be limited to acceptable values.The Power Electronics Fabrik of AEG (Berlin) had a nice practical device to set the control parameters(RC values) using "Optimator Box" which enabled easy commissioning of motor control systems.
Cheers
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