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1. WO2006109035 - CONCEPTION DE SYSTEME DE COMMANDE POUR SYSTEME DE MELANGE AVEC DE MULTIPLES ENTREES

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

What is claimed is:
1. A control system for mixing at least two materials in a physical system having two or more tanks, comprising:
at least two actuators, each actuator being operable to introduce a material into a first tank to form a first mixture, the first mixture flowing into a second tank to form a second mixture; and
a controller operable, based on a commanded input, to control the at least two actuators to obtain a density of either the first mixture or the second mixture and a volume flow rate of the second mixture out of the second tank;
wherein the density is controlled independently from the volume flow rate.
2. The control system of Claim 1, wherein the actuators are selected from the group consisting of valves, screw feeders, augurs, and elevators.
3. The control system of Claim 1 , wherein the materials are selected from the group consisting of water, carrier fluid, dry cement material, sand, and proppants.
4. The control system of Claim 1 wherein the commanded input comprises:
a commanded combined volume flow rate of the materials passing through the actuators into the first tank [commanded dv/dt]; and
a commanded combined mass flow rate of the materials passing through the actuators into the first tank [commanded drriin/dt].
5. The control system of Claim 4, wherein a first actuator is controlled by a first signal based on a function fi where:
U - [commanded dmin/dt - (commanded dv-m/dt) x pm2] / (ρmi- Pm2)
wherein: pmi = density of a first material; and
pm2= density of a second material.
6. The control system of Claim 4, wherein a second actuator is controlled by a second signal based on a function f2 where:
f2 = [(commanded dvin/dt) x pm1 - commanded dm^/dt] / (pmi- Pm2)
wherein: pmi = density of a first material; and
pm2 = density of a second material.
7. The control system of Claim 4, wherein the commanded dvjdt is based, at least in part, on a volumetric flow rate command feed forward input [dVg/dt input] and the commanded dnrVdt is based, at least in part, on a first indication of density of the first mixture and a first commanded density of the first mixture or the second mixture.
8. The control system of Claim 7, wherein the commanded dvin/dt is further based, at least in part, on an indication of height of the second mixture in the second tank and an operator input height of the second mixture.
9. The control system of Claim 7, wherein the commanded dvjn/dt is further based, at least in part, on the quantity:
F(h)(1-Kv) + Kv(commanded dvi2/dt)
wherein: Kv = a first constant of proportionality;
F(h) = a non-linear function of a height of the first mixture in the first tank; and
commanded dvi2/dt = a commanded volume flow rate of the first mixture
flowing from the first tank into the second tank.
10. The control system of Claim 10, wherein the commanded dvi2/dt is based on:
a first error term determined by subtracting an indication of a height of the second mixture in the second tank from an operator input desired height of the second mixture in the second tank [h2 input]; and
an operator input desired volume flow rate of the second mixture out of the second tank [dvg/dt input].
11. The control system of Claim 10, wherein the first error term is processed by either a first proportional integral controller component or a first proportional controller component.
12. The control system of Claim 7, wherein the commanded dVjn/dt is further based, at least in part, on a volumetric disturbance estimate.
13. The control system of Claim 7, wherein the commanded drrijn/dt is further based, at least in part, on the quantity:
F(h)(pi2)(1 -Km) + ^(commanded dm12/dt);
wherein: Kn, = a second constant of proportionality;
F(h) = a non-linear function of a height of the first mixture in the first tank;
commanded dπWdt = a commanded mass flow rate of the first mixture
flowing from the first tank into the second tank; and
Pi2 = an indication of the density of the first mixture in the first tank.

14. The control system of Claim 13, wherein the commanded dm^/dt is based on a second error term determined by subtracting the first indication of density from the first commanded density.
15. The control system of Claim 13, wherein the commanded dm-i2/dt is based on a second error term determined by subtracting a second indication of density of the second mixture from the first commanded density of the second mixture.
16. The control system of Claim 15, wherein the second error term is processed by either a second proportional integral controller component or a second proportional controller component.
17. The control system of Claim 15, wherein the commanded dmi2/dt is further based on a parameter selected from the group consisting of:
an operator input desired volume flow rate of the second mixture out of the second tank [dVs/dt input]; and
an indication of a height rate of change of the second mixture in the second tank.
18. The control system of Claim 7, wherein the commanded dnWdt is further based, at least in part, on a mass disturbance estimate.
19. The control system of Claim 7, wherein the commanded dVjn/dt is further based, at least in part, on an indication of height of the first mixture in the first tank and a commanded height of the first mixture in the first tank.
20. The control system of Claim 19, further comprising:
a first height sensor operable to produce a first sensed height output of the first mixture in the first tank; and
a first height observer operable to provide the indication of height of the first mixture in the first tank based on the first sensed height output, the commanded height, and a commanded volumetric flow rate.
21. The control system of Claim 20, wherein the first height observer is further operable to provide a first disturbance estimate.
22. The control system of Claim 20, further comprising:
a second height sensor operable to produce a second sensed height output of the second mixture in the second tank; and a second height observer operable to provide an indication of height of the second mixture in the second tank based on the second sensed height output and on the indication of height of the first mixture in the first tank.

23. The control system of Claim 22, wherein the second height observer is further operable to provide the first disturbance estimate.
24. The control system of Claim 7, further comprising:
a first density sensor operable to produce a first sensed density output of the first mixture in the first tank; and
a first density observer operable to provide the indication of density of the first mixture in the first tank based on the first sensed density output, the first commanded density of the first mixture, and a mass flow rate.
25. The control system of Claim 24, wherein the first density observer comprises:
a third proportional integral controller responsive to a third error term determined as the sensed density output minus the first indication of density of the first mixture in the first tank; and
a tank model having an integrating component and a gain component, the gain component inversely proportional to the area of the first tank and to the height of the first mixture in the first tank, the tank model responsive to the output of the third proportional integral controller.
26. The control system of Claim 25, wherein the first indication of density is delayed before determining the third error term.
27. The control system of Claim 24, wherein the first density observer is further operable to provide a second disturbance estimate.
28. The control system of Claim 24, further comprising:
a second density sensor operable to produce a second sensed density output of the second mixture in the second tank; and
a second density observer operable to provide an indication of the density of the second mixture in the second tank based on the second sensed density output and the indication of density of the first mixture in the first tank.
29. The control system of Claim 28, wherein the second density observer is further operable to provide the second disturbance estimate.

30. A control system for mixing at least two materials in a tank, comprising:
at least two actuators, each actuator being operable to introduce a material into the tank to form a mixture; and
a controller operable, based on a commanded input, to control the at least two actuators to obtain a density of the mixture and a volume flow rate of the mixture out of the tank;
wherein the density is controlled independently from the volume flow rate.
31. The control system of Claim 30, wherein the commanded input comprises:
a commanded combined volume flow rate of the materials passing through the actuators into the tank [commanded dvin/dt]; and
a commanded combined mass flow rate of the materials passing through the actuators into the tank [commanded drrijn/dt].
32. The control system of Claim 31, wherein a first actuator is controlled by a first signal based on a function fi, where:
fi = [commanded dnVdt - (commanded dvjr/dt) x pm2] / (pmi- pm2)
wherein: pmi = density of a first material; and
pm2= density of a second material.
and wherein a second actuator is controlled by a second signal based on a function f2, where:
f2 = [(commanded dvin/dt) x pmi - commanded dmin/dt] / (ρmi- Pm2).
33. The control system of Claim 31, wherein the commanded dvin/dt is based, at least in part, on a volumetric flow rate command feed forward input [dVg/dt input] and the commanded dm/dt is based, at least in part, on an indication of density of the mixture and a first commanded density of the mixture.
34. The control system of Claim 33, wherein the indication of density is provided by a density observer and the commanded drrWdt is further based, at least in part, on a mass flow rate disturbance estimate output by the density observer.
35. The control system of Claim 33, wherein the commanded dvjn/dt is further based, at least in part, on an indication of height of the mixture in the tank and a commanded height of the mixture in the tank.

36. The control system of Claim 35, wherein the indication of height is provided by a height observer and the commanded dvjn/dt is further based, at least in part, on a volumetric disturbance estimate output by the height observer.
37. A control system for mixing at least two materials, comprising:
a controller operable to control a physical system comprising a plurality of actuators, each actuator being operable to introduce a material into a first tank to form a first mixture;
wherein the controller operates the actuators to control a desired characteristic of the first mixture.
38. The control system of Claim 37, wherein the actuators are selected from the group consisting of valves, screw feeders, augurs, and elevators.
39. The control system of Claim 37, wherein the materials are selected from the group consisting of water, carrier fluid, dry cement material, sand, and proppants.
40. The control system of Claim 37, wherein the controller further operates the actuators to control a desired operating parameter of the physical system.
41. The control system of Claim 37, wherein the controller further operates the actuators based on a combination of sensors, the sensors selected from the group consisting of: a density sensor measuring the density of the first mixture, a flow rate sensor, and a mixture height sensor measuring the height of the first mixture.
42. The control system of Claim 41, wherein the mixture height sensor comprises a height observer.
43. The control system of Claim 41, wherein the density sensor comprises a density observer.
44. The control system of Claim 41 , wherein the first mixture overflows the first tank into a second tank to form a second mixture, and wherein the controller further operates the actuators to control a desired characteristic of the second mixture.
45. The control system of Claim 44, wherein the controller employs feed forward based on an input selected from the group consisting of. a combined inflow volume of the materials introduced by the actuators, a volume of the first mixture flowing into the second tank, a volume of the second mixture flowing out of the second tank, a density of the first mixture, and a density of the second mixture.

46. The control system of Claim 44, wherein the sensors are further selected from the group consisting of: a density sensor measuring the density of the second mixture and a mixture height sensor measuring the height of the second mixture.
47. The control system of Claim 46, wherein the mixture height sensor measuring the height of the second mixture comprises a height observer.
48. The control system of Claim 46, wherein the density sensor measuring the density of the second mixture comprises a density observer.
49. A method for mixing at least two materials, comprising:
introducing the at least two materials into a physical system;
combining the at least two materials to form a mixture thereof;
independently controlling a desired characteristic of the mixture of the at least two materials and a desired parameter of the physical system.
50. The method of Claim 49, wherein the controlling involves decoupling a volumetric flow rate disturbance parameter.
51. The method of Claim 49, wherein the controlling involves decoupling a mass flow rate disturbance parameter.
52. A method for mixing at least two materials, comprising:
determining a commanded combined mass flow rate of the at least two materials into a first tank [commanded drrWdty
determining a commanded combined volume flow rate of the at least two materials into the first tank [commanded dvjn/dfj; and
independently controlling, based on the commanded dπWdt and the commanded dvjn/dt, a density of a mixture of the at least two materials in the first tank

[Poland a volume flow rate of the mixture out of the first tank [dv^/dt].
53. The method of Claim 52, wherein the controlling includes regulating at least two actuators, each actuator being operable to dispense one of the at least two materials, respectively, into the first tank.
54. The method of Claim 52, further including:
determining a commanded mass flow rate of the mixture from the first tank into a second tank [commanded dm-^/dt]; and wherein determining the commanded drrWdt is based on an indication of the density of the mixture in the first tank and the commanded dmi2/dt; and determining a commanded volume flow rate of the mixture from the first tank into the second tank [commanded dv^/dt]; and wherein determining the commanded dvin/dt is based on an indication of a height of the mixture in the first tank and the commanded dvi2/dt.
55. The method of Claim 54, further comprising:
determining a desired height of the mixture in the second tank [input h2];
determining a desired volume flow rate of the mixture out of the second tank [input dvg/dt], wherein determining the commanded dvi2/dt is based on the input h2, the input dVs/dt, and an indication of a height of the mixture in the second tank; and
determining a desired density of the mixture in the second tank [input ps], wherein determining the commanded drrWdt is based on the input ps and an indication of a density of the mixture in the second tank.
56. The method of Claim 55, further comprising:
sensing the density of the mixture in the first tank [pi2 sensor];
determining an estimated density of the mixture in the first tank [estimated pi2] based on the pi2 sensor and on the commanded dmi2/dt;
providing the estimated pi2 as the indication of the density of the mixture in the first tank;
sensing the density of the mixture in the second tank [ps sensor];
determining an estimated density of the mixture in the second tank [estimated ps] based on ps sensor and on the indication of the density of the mixture in the first tank; and
providing the estimated ps as the indication of the density of the mixture in the second tank.
57. The method of Claim 55, further comprising:
sensing the height of the mixture in the first tank [hi sensor];
determining an estimated height of the mixture in the first tank [hi estimated] based on hi sensor and on the commanded dvi2/dt;
providing the estimated hi as the indication of the height of the mixture in the first tank;
sensing the height of the mixture in the second tank [h2 sensor];

determining an estimated height of the mixture in the second tank [h2 estimated] based on h2 sensor and on the indication of the height of the mixture in the first tank; and
providing the estimated h2 as the indication of the height of the second mixture in the second tank.