Method for detecting the flow rate value of a centrifugal pump

Patent metadata

Field	Value
Publication number	US-10041824-B2
Application number	US-201314419785-A
Country	US
Kind code	B2
Filing date	Aug 1, 2013
Priority date	Aug 7, 2012
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

A method serves for detecting the flow rate of a centrifugal pump, wherein the rotation speed of the pump or of the motor driving the pump, a hydraulic variable of the pump, typically the delivery pressure and an electrical variable of the drive motor, for example the electrical power are determined, and the flow rate is evaluated by way of these variables. For this, variables dependent on the flow rate are determined by way of a mathematic linking of terms of equations describing physical relations of the pump and drive motor, wherein one term contains the rotation speed of the pump and a hydraulic variable of the pump and another term contains an electric or mechanical variable of the drive motor of the pump and the rotation speed of the pump. The flow rate is determined by way of the functional relation between the flow rate and the dependent variable.

First claim

The invention claimed is:

1. A method for controlling a flow rate of a centrifugal pump, the method comprising:
providing a centrifugal pump comprising an inlet and an outlet;
measuring a pressure at at least one of the inlet and the outlet;
determining a hydraulic variable of the pump based on the pressure measured at at least one of the inlet and the outlet;
determining the flow rate of the centrifugal pump by way of a rotation speed of the pump and the hydraulic variable of the pump and an electrical variable of a drive motor of the pump, wherein:
a variable which is dependent on the flow rate is determined by way of a mathematic linking of terms of equations describing physical relations of the centrifugal pump and the drive motor, the terms comprising one term that contains the rotation speed of the pump and the hydraulic variable of the pump and another term that contains an electrical or mechanical variable of the drive motor of the centrifugal pump and the rotation speed of the pump; and
the flow rate is determined by way of a functional relation between the flow rate and the dependent variable;
comparing the dependent variable (y) determined to a corresponding dependent variable (y est ) determined by way of model computation, and repeating the comparison by way of variation of an assumed flow rate (Q est ), until an error variable (y−y est ) is small such that the assumed flow rate (Q est ) corresponds to the flow rate (Q);
controlling the flow rate of the centrifugal pump by an electronic closed-loop control based on the assumed flow rate.

2. A method according to claim 1 , wherein the dependent variable is a variable (Y) which is determined by way of the following equation

Y
=

-
a

*

H
n

+

b
*

P

n
2

in which
a and b are constants to be determined,
H the delivery head,
P the electrical power of the drive motor and
n the rotation speed.

3. A method according to claim 1 , wherein the hydraulic variable is a pressure variable, which corresponds to the pressure at the outlet of the pump or a differential pressure between the inlet and the outlet of the pump.

4. A method according to claim 1 , wherein the electrical variable is a power-dependent variable, a taken-up power (P) of the drive motor.

5. A method according to claim 1 , wherein the mechanical variable is a torque of the motor.

6. A method according to claim 1 , wherein the mathematical linking is an addition or subtraction of at least two terms.

7. A method according to claim 1 , wherein the mathematic linking contains one or more further terms which are constant or dependent on the rotation speed.

8. A method according to claim 1 , wherein the terms, the number of terms and the linking of terms are selected such that a monotonous function of the flow rate is formed over a working range of the pump.

9. A method according to claim 1 , wherein the flow rate is determined by way of a dependent variable (Y), wherein

Y
=

-
a

*

H
n

+

b
*

P

n
2

-

c
*
n

where a and b are constants to be determined, c is a constant to be determined,
H the delivery head,
P the electrical power of the drive motor and
n the rotation speed.

10. A method according to claim 1 , wherein a signal representing the flow rate is filtered with a low-pass filter.

11. A method according to claim 1 , further comprising:
providing a pressure sensor;
sensing a hydraulic pressure of the pump with the pressure sensor, the hydraulic variable comprising the hydraulic pressure.

12. A method according to claim 1 , wherein the rotation speed forms an input variable in the model computation.

13. A method according to claim 1 , wherein the error variable (y−y est ) is summed over time or integrated, and the summed or integrated value represents the flow rate (Q).

14. A centrifugal pump comprising:
an electric drive motor;
a pressure sensor or differential pressure sensor detecting a pressure at one or more of an inlet and an outlet of the centrifugal pump; and
an electronic control, wherein the electronic control is configured for determining a hydraulic variable based on the pressure measured at one or more of the inlet and the outlet of the centrifugal pump, the electronic control being further configured for determining a flow rate of the centrifugal pump by way of a rotation speed of the pump and the hydraulic variable of the pump and an electrical variable of the electric drive motor of the pump, wherein the electronic control:
determines a variable which is dependent on the flow rate by way of a mathematic linking of terms of equations describing physical relations of the centrifugal pump and the drive motor, the terms comprising one term that contains the rotation speed of the pump and the hydraulic variable of the pump and another term that contains an electrical or mechanical variable of the drive motor of the centrifugal pump and the rotation speed of the pump;
determines the flow rate by way of a functional relation between the flow rate and the dependent variable;
compares the dependent variable (y) determined to a corresponding dependent variable (y est ) determined by way of model computation, and repeating the comparison by way of variation of an assumed flow rate (Q est ), until an error variable (y−y est ) is small such that the assumed flow rate (Q est ) corresponds to the flow rate (Q);
controls the flow rate of the centrifugal pump by an electronic closed-loop control based on the assumed flow rate.

15. A centrifugal pump according to claim 14 , wherein the electronic control has an observer-based closed-loop control.

16. A centrifugal pump according to claim 14 , wherein the dependent variable is a variable (Y) which is determined by way of the following equation:

Y
=

-
a

*

H
n

+

b
*

P

Assignees

• Grundfos Holding As

Inventors

• Skovmose Kallesøe Carsten

Classifications

• G01F1/34

  by measuring pressure or differential pressure · CPC title

• G01F1/88

  with differential-pressure measurement to determine the volume flow · CPC title

• G01F1/86

  Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure · CPC title

• G01F1/80 Primary

  operating by measuring pressure, force, momentum, or frequency of a fluid flow to which a rotational movement has been imparted · CPC title

• F04D15/0088

  Testing machines · CPC title