1 / 28

Anti-Slug Control Experiments Using Nonlinear Observers

This research explores the effectiveness of nonlinear observer designs for anti-slug control in multiphase systems. Various observer strategies are examined, including Unscented Kalman Filter and High-Gain Observer, to tackle challenges like nonlinear dynamics and unstable zero dynamics. Experimental results highlight the limitations and benefits of different observer approaches in stabilizing control in pressure-based systems.

chrismoore
Download Presentation

Anti-Slug Control Experiments Using Nonlinear Observers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Anti-Slug Control Experiments Using Nonlinear Observers Esmaeil Jahanshahi, Sigurd Skogestad, Esten I. Grøtli Norwegian University of Science & Technology (NTNU) American Control Conference - June 17th 2013, Washington, DC

  2. Outline • Introduction • Motivation • Modeling • Observer design • Unscented Kalman Filter (UKF) • High-Gain observe • Fast UKF • State-feedback • Experimental results • Controllability limitation

  3. Introduction * figure from Statoil

  4. Slug cycle (stable limit cycle) Experiments performed by the Multiphase Laboratory, NTNU

  5. Introduction • Anti-slug solutions • Conventional Solutions: • Choking (reduces the production) • Design change (costly) : Full separation, Slug catcher • Automatic control: The aim is non-oscillatory flow regime together with the maximum possible choke opening to have the maximum production

  6. Pt,s PC uz PT Motivation Objective: using topside pressure for control Problem 1: Nonlinearity Additional Problem 2: Unstable zero dynamics (RHP-zero) MS=5.87, MT=6.46

  7. Nonlinear observer K State variables PT Solution?! uc uc Pt Questions: • Is this solution applicable for anti-slug control? • Can observer bypass fundamental limitations? • Which kind of observer is suitable? • Experiments

  8. Modeling

  9. Modeling: Simplified 4-state model Choke valve with opening Z x3, P2,VG2, ρG2 , HLT P0 wmix,out L3 x1, P1,VG1, ρG1, HL1 x4 L2 h>hc wG,lp=0 wL,in wG,in w x2 wL,lp h L1 hc θ State equations (mass conservations law):

  10. Experiments 3m

  11. Bifurcation diagrams Experiment Top pressure Subsea pressure Gain = slope

  12. Observer Design

  13. 1. Unscented Kalman Filter Nonlinear plant: (1) Prediction step:

  14. 1. Unscented Kalman Filter (UKF) (2) Update step: (3) Correction step:

  15. 2. High-Gain Observer

  16. 2. High-Gain Observer where

  17. 3. Fast UKF Nonlinear model with transformed states: This is the high-gain observer without the observer term, therefore we do not need to specify the observer gain manually. High-gain Strategy: • Large Qk and small Rk increase the UKF gain • UKF gain: • - Scalingofstates and measurement in themodel

  18. State Feedback Kc : a linear optimal controller calculated by solving Riccati equation Ki : a small integral gain (e.g. Ki = 10−3)

  19. Experimental Results

  20. Experiment High-gain observer – top pressure measurement: topside pressurevalve opening: 20 %

  21. Experiment Fast UKF – top pressure measurement: topside pressurevalve opening: 20 %

  22. Experiment High-gain observer – subsea pressure measurement: topside pressurevalve opening: 20 %

  23. Experiment PI Controller – subsea pressure measurement: subsea pressurevalve opening: 40 %

  24. Experiment Linear observer (KF) – subsea pressure measurement: subsea pressurevalve opening: 40 %

  25. Experiment Summary of experiments Stabilizing Control * Estimation works (open-loop), but slow * Estimation also not working

  26. Chain of Integrators • Fast nonlinear observer using subsea pressure: Not Working??! • Fast nonlinear observer (High-gain) acts like a differentiator • Pipeline-riser system is a chain of integrator • Measuring top pressure and estimating subsea pressure is differentiating • Measuring subsea pressure and estimating top pressure is integrating

  27. Controllability limitation – top pressure Measuring topside pressure we can stabilize the system only in a limited range RHP-zero dynamics of top pressure

  28. Conclusions • Nonlinear observers work only when measuring topside pressure • This works in a limited range (valve opening) • A fast observer is needed for stabilizing control • Fast nonlinear observers fail when measuring subsea pressure • Observer can counteract nonlinearity • But cannot bypass fundamental limitation (non-minimum-phase system) Thank you!

More Related