U.S. patent application number 11/993787 was filed with the patent office on 2010-02-11 for control system for a pump.
Invention is credited to Jurgen Mokander, Zhiyong Zhong.
Application Number | 20100034665 11/993787 |
Document ID | / |
Family ID | 35789074 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100034665 |
Kind Code |
A1 |
Zhong; Zhiyong ; et
al. |
February 11, 2010 |
CONTROL SYSTEM FOR A PUMP
Abstract
The present invention relates to pumps comprising variable
frequency drive means and methods for operating such pumps. The
inventive method for operating a pump (1) comprises the steps of
obtaining values of operating parameters of the pump (1) indicating
pump conditions, communicating said values of operating parameters
from variable frequency drive means (2) to a control device (11),
determining if a predetermined condition is fulfilled,
communicating instructions from the control device (11) to the
variable frequency drive means (2), based on the fulfillment of
said predetermined condition. Furthermore, a computer program
product loadable into a memory of a digital computer device,
including software code portions for performing the inventive
method, a pump (1), a pump system and a control device (11) for a
pump are described.
Inventors: |
Zhong; Zhiyong; (Hagersten,
SE) ; Mokander; Jurgen; (Sollentuna, SE) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.;624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Family ID: |
35789074 |
Appl. No.: |
11/993787 |
Filed: |
June 15, 2006 |
PCT Filed: |
June 15, 2006 |
PCT NO: |
PCT/SE06/00710 |
371 Date: |
December 21, 2007 |
Current U.S.
Class: |
417/42 ;
417/44.1 |
Current CPC
Class: |
F04D 15/0077 20130101;
F04D 15/0218 20130101; F04D 15/0066 20130101 |
Class at
Publication: |
417/42 ;
417/44.1 |
International
Class: |
F04D 15/02 20060101
F04D015/02; F04B 49/06 20060101 F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2005 |
EP |
PCT/EP05/52878 |
Claims
1. A method for operating a pump (1) comprising a motor (9) and
variable frequency drive means (2), the latter being arranged to
control the operation of the motor (9) by being connected to said
motor (9) and to a feeder cable of the pump (1), the variable
frequency drive means (2) comprising a rectifier (5), an inverter
(7) and a DC link (10) extending therebetween, furthermore the pump
(1) is operatively connected to a control device (11), the method
being characterized by the steps of: obtaining values of operating
parameters of the pump (1) indicating pump conditions, by means of
sensing means (16), which is comprised as a part of said variable
frequency drive means (2) and which is operatively connected to
said DC link (10), communicating said values of operating
parameters from the variable frequency drive means (2) to the
control device (11), determining (44, 64, 84) by means of the
control device (1) if a predetermined condition is fulfilled based
on said obtained values of operating parameters, and communicating
instructions from the control device (11) to the variable frequency
drive means (2), based on the fulfillment of said predetermined
condition, in order to control the operation of the motor (9) in
accordance with said pump conditions.
2. The method according to claim 1, wherein the step of obtaining
values of operating parameters of the pump (1) comprises the step
of: obtaining values of at least one of the following operating
parameters: the DC link voltage level, the DC link current level,
the torque of the motor (9), or the power of the motor (9).
3. The method according to claim 1, further comprising the step of:
detecting (44, 64, 84) a certain pump condition by using said at
least one operating parameter.
4. The method according to claim 3, wherein said pump condition
concerns the presence of liquid at an inlet of the pump (1).
5. The method according to claim 4, wherein the step of determining
if a predetermined condition is fulfilled comprises the steps of:
running (42) the pump (1) at a first speed level for a
predetermined period of time, running (42) the pump (1) at a second
speed level for a predetermined period of time, and determining
(44) if the power of the motor (9) is proportional to the cube of
the speed of the motor (9), based on the values of operating
parameters obtained by the sensing means (16) for the first speed
level and the second speed level, respectively.
6. The method according to claim 4, wherein the communicated
instructions from the control device (11) to the variable frequency
drive means (2), are run (48) the pump (1) at a desired speed
level, if it is determined that the predetermined condition is
fulfilled, or stop (46) the operation of the pump (1) a
predetermined period of time, if it is determined that the
predetermined condition is not fulfilled.
7. The method according to claim 6, further comprising the steps
of, if the pump (1) is ran at the desired speed level: checking
(50) the presence of liquid at an inlet of the pump (1) by,
obtaining values of operating parameters of the pump (1), by means
of the sensing means (16), communicating said values of operating
parameters from the variable frequency drive means (2) to the
control device (11), determining by means of the control device
(11) if a second predetermined condition is fulfilled based on said
obtained values of operating parameters, and communicating
instructions from the control device (11) to the variable frequency
drive means (2), based on the fulfillment of said second
predetermined condition, in order to control the operation of the
motor (9).
8. The method according to claim 7, wherein the step of determining
if a second predetermined condition is fulfilled comprises the step
of: comparing (50) the obtained values of operating parameters with
a predetermined reference level.
9. The method according to claim 7, wherein the communicated
instructions from the control device (11) to the variable frequency
drive means (2), are run (48) the pump (1) at the desired speed
level, if it is determined that the second predetermined condition
is fulfilled, and stop (52) the operation of the pump (1) a
predetermined period of time, if it is determined that the second
predetermined condition is not fulfilled.
10. The method according to claim 2, further comprising the step
of: maintaining the value of the at least one operating parameter
at a substantially constant level.
11. The method according to claim 10, wherein the step of
determining if a predetermined condition is fulfilled comprises the
steps of: running (62) the pump (1) at a desired speed level,
determining (64) if the power of the motor (9) is lower than a
predetermined reference level of the power of the motor (9), based
on the values of the power of the motor (9) obtained by the sensing
means (16) for the desired speed level.
12. The method according to claim 10, wherein the communicated
instructions from the control device (11) to the variable frequency
drive means (2), are run (62) the pump (1) at the desired speed
level, if it is determined that the predetermined condition is not
fulfilled, or calculate (66) the speed of the motor (9) required to
reach a predetermined reference level of the power of the motor
(9), if it is determined that the predetermined condition is
fulfilled, and run the pump (1) at said calculated speed.
13. The method according to claim 12, further comprising the steps
of, if the pump (1) is ran at the calculated speed: comparing (68)
the calculated speed of the pump (1) with a preset maximum speed of
the pump (1), and run (70) the pump (1) at said calculated speed,
if the calculated speed is lower than the preset maximum speed, or
run (72) the pump (1) at said preset maximum speed, if the
calculated speed is higher than the preset maximum speed.
14. The method according to claim 3, wherein said pump condition
concerns clogging of the pump (1).
15. The method according to claim 14, wherein the step of
determining if a predetermined condition is fulfilled comprises the
steps of: running (82) the pump (1) at a desired speed level,
determining (84) if the power of the motor (9) is higher than a
predetermined reference level of the power of the motor (9), based
on the values of the power of the motor (9) obtained by the sensing
means (16) for the desired speed level.
16. The method according to claim 14, wherein the communicated
instructions from the control device (11) to the variable frequency
drive means (2), are run (82) the pump (1) at the desired speed
level, if it is determined that the predetermined condition is not
fulfilled, or run (86) the pump (1) reversely at a predetermined
speed for a predetermined period of time, and run the pump (1) in
its normal operation direction at the desired speed level after
said predetermined period of time of reverse operation, if it is
determined that the predetermined condition is fulfilled.
17. The method according to claim 16, further comprising the steps
of: repeating (88) said step of determining if the power of the
motor (9) is higher than a predetermined reference level of the
power of the motor (9), and repeating the steps according to claim
16.
18. The method according to claim 14, wherein the following steps
are performed at regular intervals during the operation of the pump
(1): running the pump (1) reversely at a predetermined speed for a
predetermined period of time, and running the pump (1) in its
normal operation direction at a desired speed level after said
predetermined period of time of reverse operation.
19. Computer program product (14) loadable into a memory (13) of a
digital computer device, including software code portions for
performing the method of claim 1 when said computer program product
(14) is ran on said digital computer device.
20. A pump comprising a motor (9) and variable frequency drive
means (2), the latter being arranged to control the operation of
the motor (9) by being connected to said motor (9) and to a feeder
cable of the pump (1), the variable frequency drive means (2)
comprising a rectifier (5), an inverter (7) and a DC link (10)
extending therebetween, furthermore the pump (1) is operatively
connected to a control device (11), characterized in that sensing
means (16) is comprised as a part of said variable frequency drive
means (2), which sensing means (16) is operatively connected to
said DC link (10) and which is arranged to obtain values of
operating parameters of the pump (1) indicating pump conditions,
the variable frequency drive means (2) being arranged to
communicate to the control device (11) said values of operating
parameters, furthermore the control device (11) is arranged to
determine if a predetermined condition is fulfilled based on said
obtained values of operating parameters and to communicate
instructions to the variable frequency drive means (2), based on
the fulfillment of said predetermined condition, in order to
control the operation of the motor (9) in accordance with said pump
conditions.
21. The pump according to claim 20, wherein said control device
(11) is adapted to obtain values of at least one of the following
operating parameters: the DC link voltage level, the DC link
current level, the torque of the motor (9), or the power of the
motor (9).
22. The pump according to claim 21, wherein said control device
(11) is adapted to: run the pump (1) at a first speed level for a
predetermined period of time, run the pump (1) at a second speed
level for a predetermined period of time, and determine if the
power of the motor (9) is proportional to the cube of the speed of
the motor (9), based on the values of the at least one operating
parameter obtained by the sensing means (16) for the first speed
level and the second speed level, respectively.
23. The pump according to claim 22, wherein said control device
(11) is adapted to: run the pump (1) at a desired speed level, if
it is determined that the predetermined condition is fulfilled, or
stop the operation of the pump (1) a predetermined period of time,
if it is determined that the predetermined condition is not
fulfilled.
24. The pump according to claim 21, wherein the control device (11)
is adapted to: maintain the value of the at least one operating
parameter at a substantially constant level.
25. The pump according to claim 24, wherein the control device (11)
is adapted to: run the pump (1) at a desired speed level, determine
if the power of the motor (9) is lower than a predetermined
reference level of the power of the motor (9), based on the values
of the power of the motor (9) obtained by the sensing means (16)
for the desired speed level.
26. The pump according to claim 24, wherein the control device (11)
is adapted to: run the pump (1) at the desired speed level, if it
is determined that the predetermined condition is not fulfilled, or
calculate (66) the speed of the motor (9) required to reach a
predetermined reference level of the power of the motor (9), if it
is determined that the predetermined condition is fulfilled, and
run the pump (1) at said calculated speed.
27. The pump according to claim 26, wherein the control device (11)
is adapted to: compare (68) the calculated speed of the pump (1)
with a preset maximum speed of the pump (1), and run (70) the pump
(1) at said calculated speed, if the calculated speed is lower than
the preset maximum speed, or run (72) the pump (1) at said preset
maximum speed, if the calculated speed is higher than the preset
maximum speed.
28. The pump according to claim 21, wherein the control device (11)
is adapted to: run (82) the pump (1) at a desired speed level,
determine (84) if the power of the motor (9) is higher than a
predetermined reference level of the power of the motor (9), based
on the values of the power of the motor (9) obtained by the sensing
means (16) for the desired speed level.
29. The pump according to claim 28, wherein the control device (11)
is adapted to: run the pump (1) at the desired speed level, if it
is determined that the predetermined condition is not fulfilled, or
run (86) the pump (1) reverse at a predetermined speed for a
predetermined period of time, and--run the pump (1) in its normal
operation direction at the desired speed level after said
predetermined period of time of reverse operation, if it is
determined that the predetermined condition is fulfilled.
30. The pump according to claim 21, wherein the control device
(11), at regular intervals during the operation of the pump (1), is
adapted to: run the pump (1) reversely at a predetermined speed for
a predetermined period of time, and run the pump (1) in its normal
operation direction at a desired speed level after said
predetermined period of time of reverse operation.
31. A pump station comprising a pump (1) according to claim 20, and
further comprises an operator unit (22) comprising input means (24)
and display means (26), which is adapted to present information
related to the operation of the pump (1).
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
pumps, and more specifically the present invention relates to pumps
comprising variable frequency drive means. Furthermore, the present
invention also relates to a method for operating such pumps.
BACKGROUND OF THE INVENTION AND PRIOR ART
[0002] Pumps comprising variable frequency drive means, such as
sewage pumps, drainage pumps and de-watering pumps as well as
submersible pumps, for example, are commonly used for pumping
fluids in mining applications such as in mining shafts, wells, at
construction sites, or at other applications. Normally, submersible
pumps are submersed, wholly or partly, during long periods of time
both when they are in operation and when in an off-state.
[0003] A problem often encountered with pumps in general and with
submersible pumps in particular, is so called snoring operation,
which means that the pumps sucks partly liquid and partly air. This
is due to the fact that the liquid level has fallen below the
required level of the pump causing the pump to start sucking partly
air. From this moment the pump is no longer productive and uses
energy unnecessarily. Water silt remains in the mining shaft or in
the well and particles will begin to settle and accumulate in the
hydraulics of the pump. As long as the pump is in this snoring
state, those particles remain at the hydraulics and cause extra
wear on the impeller, the suction cover, the seals, etc. This
ineffective pumping contributes in a significant way to the
increase of the overall operating costs of the pump. In addition,
this snoring operation may damage the pump motor due to
overheating. In certain applications, in order to overcome this
snoring problem, sensors, such as level switches, are used to sense
the fluid level within the well. However, these level sensors may,
for example, be blocked or be subjected to a level shift due to a
collision with subjects in the fluid such as a tree branch, and
will thus in such a case deliver an erroneous signal.
[0004] U.S. Pat. No. 6,481,973 to Struthers, present a pump system
addressing a part of the abovementioned problem. Even though this
pump system comprises variable frequency drive means it makes use
of another control method to detect if the liquid level falls below
a preset level, as a complement to level switches. More precisely,
this pump system detects if there is a sudden increase in the speed
of the motor or a sudden drop of the motor torque. Said operation
of the motor is monitored by a sensor connected to the AC output
link extending from the variable frequency drive means to the
motor. However, this pump system embraces great disadvantages. In
the case when the increase of the speed of the motor is slow, the
system might not recognize the change as an indication of dry
running of the pump. In another case, the pump system is not able
to detect if the water level is high enough for pump operation upon
start of the pump, since in this state there cannot be a sudden
increase of the speed of the motor or a sudden drop of the motor
torque. Thereby, the pump will run for a considerable time until it
is switched off due to overheating, and the pump runs the risk of
getting seriously damaged.
[0005] In many applications, such as the above-mentioned, the pump
operates in a dynamic environment and thus the pump should be able
to operate in an efficient way in large range of head/pressure. The
pump head corresponds to the height the pump, using a given power,
is able to lift a given amount of liquid, for example, water, see
FIG. 3 where a typical pump curve is indicated by the line 30. The
degree of utilization of the power of the pump may be reduced at
low flows (Q). Thus, it would be an advantage to have a pump being
able to pump at a high (or increased) degree of utilization of the
power of the pump also at lower flows.
[0006] Another problem of frequent occurrence, especially when the
pump has been in an off-state for quite a long period of time, is
clogging of the intake and/or the impeller, which is caused mainly
by particles in the fluid that sediment at the intake and in the
impeller and build silt having a relatively thick or solid
consistency. This, in turn, entails that a large starting torque of
the pump motor is required in order to initiate the rotating of the
pump impeller. Often a maximum starting torque is even required in
order to start the rotation and the motor has to be operated at a
maximum torque during a significant period of time. This consumes
large amounts of energy and also wears the pump impeller and the
motor. When the pump has been in an off-state for a long period
even a maximum starting torque may not be enough and in such cases
the pump has to be manually cleaned. In addition, a pump may also
be clogged during running, for example, by particles sucked into
the impeller. Thus, the reliability of pumps operated in such
environments is low.
[0007] Abovementioned pump system according to U.S. Pat. No.
6,481,973 to Struthers, is addressed to this problem as well.
However, this method is erroneously directed to keep the motor
running even if it is determined that the pump is clogged. More
precisely, if an unacceptably high motor torque is detected for a
given speed of the motor, the pump system will lower the speed of
the motor and at the same time increase the level of acceptable
motor torque. The aim is to get a stronger pump which is able to
overcome the strength of the solid matter, but a stronger motor
combined with a hard pollutant may lead to damages of the impeller,
the impeller seat, the pump housing, etc.
[0008] Another known problem with pumps comprising conventional
variable frequency drive means, is that the latter is usually
mounted distant from the pump at a dry location above ground. More
precisely, this necessitates a long power cable leading from the
variable frequency drive means to the motor of the pump, which for
conventional variable frequency drive means can result in severe
problems with electromagnetic interference. In abovementioned U.S.
Pat. No. 6,481,973 to Struthers, the variable frequency drive means
is mounted within the pump casing, more precisely on a plate
connected to the motor. However, the operation of the variable
frequency drive means in this case is adversely affected by the
heat emitted from the motor, which may lead to erroneous operation
of the variable frequency drive means.
[0009] Thus, there is a need of an improved pump and an improved
control method for controlling such a pump in an efficient way with
respect to energy consumption and the durability of the pump.
BRIEF DESCRIPTION OF THE INVENTION
[0010] Thus, one object of the present invention is to provide an
improved pump, a pump system including such a pump, a computer
program, a control device for such a pump and methods for
controlling such a pump and pump systems in an efficient way with
respect to pump capacity at varying pump head.
[0011] Another object of the present invention is to provide an
improved pump, a pump system including such a pump, a computer
program, a control device for such a pump and methods for
controlling such a pump and pump systems in an efficient way with
respect to energy consumption.
[0012] Another object of the present invention is to provide an
improved pump, a pump system including such a pump, a computer
program, a control device for such a pump and methods for
controlling such a pump and pump systems in an efficient way with
respect to durability of the pump.
[0013] It is a further object of the present invention to provide
an improved pump, pump system including such a pump, a computer
program, a control device for such a pump and a method for
controlling such a pump and pump systems in a manner that reduces
the wear of the pump and extends the pump life.
[0014] It is still another object of the present invention to
provide an improved pump, pump system including such a pump, a
computer program, a control device for such a pump and a method for
controlling such a pump and pump systems in an environmental
efficient way.
[0015] It is yet another object of the present invention to provide
an improved pump, pump system including such a pump, a computer
program, a control device for such a pump and a method for
controlling such a pump and pump systems in an efficient way with
respect to start reliability as well as reliability during
operation.
[0016] These and other object are achieved according to the present
invention by providing an improved pump, pump system including such
a pump, a computer program, and methods for controlling such a pump
and pump systems having the features defined in the independent
claims. Preferred embodiments are defined in the dependent
claims.
[0017] In the context of the present invention, the term "pump
speed" is defined as the numbers of revolutions per time unit of
the pump.
[0018] According to a first aspect of the present invention, there
is provided a method for operating a pump comprising a motor and
variable frequency drive means, the latter being arranged to
control the operation of the motor by being connected to said motor
and to a feeder cable of the pump, the variable frequency drive
means comprising a rectifier, an inverter and a DC link extending
therebetween, furthermore the pump is operatively connected to a
control device. The method comprises the steps of:
[0019] obtaining values of operating parameters of the pump
indicating pump conditions, by means of sensing means, which is
comprised in said variable frequency drive means and which is
operatively connected to said DC link,
[0020] communicating said values of operating parameters from the
variable frequency drive means to the control device,
[0021] determining by means of the control device if a
predetermined condition is fulfilled based on said obtained values
of operating parameters, and
[0022] communicating instructions from the control device to the
variable frequency drive means, based on the fulfillment of said
predetermined condition, in order to control the operation of the
motor in accordance with said pump conditions.
[0023] According to a second aspect of the present invention there
is provided a pump arranged to be operated in accordance with the
abovementioned method.
[0024] According to a third aspect of the present invention, there
is provided a computer program product loadable into a memory of a
digital computer device, including software code portions for
performing the method of according to the first aspect of the
present invention when the computer program product is run on the
computer device.
[0025] According to a fourth aspect of the present invention, there
is provided a pump system comprising a pump according to the second
aspect of the invention.
[0026] According to a further aspect of the present invention,
there is provided a control device for a pump according to the
second aspect of the invention.
[0027] Thus, the present invention is based on the idea of
obtaining values of operating parameters of the pump substantially
continuously from the variable frequency drive means, which
operating parameters indicate pump conditions and which are
measured in an easy and inexpensive way and at the same time with
high accuracy; and controlling the variable frequency drive means
based on the obtained values of operating parameters, wherein the
operation of the motor is adjusted in accordance with said pump
conditions. Thereby, the pump is operated in an efficient way with
respect to output capacity at varying flows, energy consumption and
durability of the pump. Moreover, since the wear of the pump parts
such as the impeller and the seals is reduced, the pump life can be
extended. Due to the fact that all information required for the
control of the pump and pump motor and variable frequency drive
means is obtained from the variable frequency means, no external
sensors are required.
[0028] According to a preferred embodiment of the present
invention, the operating parameters may be: the DC link voltage of
the variable frequency drive means, the DC link current of the
variable frequency drive means, the speed of the motor, or the
like. By means of these operating parameters the power of the
motor, the torque of the motor, or other suitable quantities may be
determined.
[0029] In a preferred embodiment of the present invention, the
event of dry running of the pump is determined based of the
obtained values of operating parameters, e.g. the power of the
motor at different motor speeds are compared with a predetermined
reference value. If it is determined that the power of the motor is
lower than the predetermined reference level, the operation of the
pump motor is stopped during a period of time having a
predetermined length. Moreover, the motor is restarted when the
predetermined period of time has expired and the same check is
performed once again until the predetermined condition is
fulfilled. Thus, the snoring operation problem, which, as discussed
above, causes extra wear of the pump, and in particular of the
impeller, may cause the pump motor to overheat and also leads to
unnecessary energy consumption, is dealt with and an efficient way
of operating a pump comprising variable frequency drive means in
respect of energy consumption and durability can thereby be
obtained. Furthermore, the pump life can be extended owing to the
fact that the wear of pump parts such as the impeller, seals and
suction cover is significantly reduced.
[0030] In an alternative embodiment of the present invention, the
power of the motor is maintained at a substantially constant level.
The obtained operating parameter value is compared with a
predetermined reference level of the operating parameter; if the
operating parameter value is lower than the predetermined reference
level, the speed of the motor required to obtain the predetermined
power level is calculated; and the pump is ran at the calculated
speed. Preferably, the calculated speed is compared with a preset
maximum allowed speed of the pump; and if the calculated speed is
higher than the preset maximum speed of the pump, the pump is ran
at the preset maximum speed. Thus, the problem of maintaining a
high degree of utilization of the power of the pump over a large
range of flows is dealt with. As is shown in FIG. 3 by line 32, the
pump head/pressure can be increased by 20% to 30% by means of the
method according to said second aspect. Thus, by increasing the
speed of the motor the pump will reach a higher pump head at lower
flows than a conventional pump. Hence, an efficient way of
operating a pump comprising variable frequency drive means in
respect of pump capacity at varying pump head is obtained.
[0031] According to an another embodiment of the present invention,
a detection whether the pump is clogged is performed; and if it is
detected that the pump is clogged, the pump is ran reversely at a
predetermined speed during a period of time having a predetermined
length. Thereafter the pump is stopped and started in the normal
direction. Moreover, the step of running the pump impeller
reversely, stopping it and change the operating direction is
repeated until it is detected that the clogging condition has
ceased. Thus, the problem of clogging or jam of the intake and/or
pumping house, which may be caused by particles in the fluid that
sediment at the intake and at the impeller and build silt having a
relatively thick or solid consistency, is dealt with. Owing to the
fact that pump runs backwards and forward again in a repeated
manner, the clogging can be removed in an efficient way. Thereby
the starting reliability can be increased. In addition, this
embodiment provides for an efficient way of operating a pump
comprising variable frequency drive means in respect of energy
consumption and durability since the wear of, especially, the pump
impeller is reduced. Moreover, since the clogging condition can be
removed in an efficient way the energy consumption of the pump can
also be reduced.
[0032] As realized by the person skilled in the art, the method
according to the present invention, as well as preferred
embodiments thereof, are suitable to realize or implement as a
computer program or a computer readable medium, preferably within
the contents of a control device or a processing means of a pump or
a pump system.
[0033] The features that characterize the invention, both as to
structure and to method of operation, together with further objects
and advantages thereof, will be better understood from the
following description read in conjunction with the accompanying
drawings. It is to be expressly understood that the drawings is for
the purpose of illustration and description and is not intended as
a definition of the limits of the invention. These and other
objects attained, and advantages offered, by the present invention
will become more fully apparent as the description that now follows
is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Above-mentioned and other features and advantages of the
present invention will be apparent from the following detailed
description of preferred embodiments, merely exemplifying, in
conjunction with the attached drawing, wherein:
[0035] FIG. 1 schematically shows an embodiment of a pump according
to the present invention;
[0036] FIG. 2 schematically shows an embodiment of a pump system
according to the present invention;
[0037] FIG. 3 shows a pump curves for a conventional pump and a
pump operated in accordance with the present invention;
[0038] FIG. 4 shows the principles of a method of an embodiment
according to the present invention;
[0039] FIG. 5 shows the principles of a method of another
embodiment according to the present invention;
[0040] FIG. 6 shows the principles of a method of yet another
embodiment according to the present invention;
[0041] FIG. 7 schematically shows a further embodiment of a pump
and a control device for such a pump according to the present
invention;
[0042] FIG. 8 schematically shows another embodiment of a pump and
a control device for such a pump according to the present
invention; and
[0043] FIG. 9 schematically shows yet another embodiment of a pump
and pump system according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0044] In the following, there will be disclosed preferred
embodiments of a method for operating a pump and a pump system.
[0045] With reference first to FIG. 1, a first embodiment of a pump
according to the present invention will be described. For purpose
of illustration, the embodiments of the present invention described
hereinafter are utilized in present submersible pumps comprising
variable frequency drive means. But, as the skilled man within the
art easily realizes, the present invention can also be utilized in
other types of pumps, such as sewage pumps, drainage pumps,
de-watering pumps, etc.
[0046] The submersible pump 1 of FIG. 1 comprises a variable-speed
unit 2, preferably variable frequency drive means (VFD unit)
connected via a connection cable 3 to a power source (not shown)
delivering, for example, a single phase voltage or a three phase
voltage. Unlike prior art pumps comprising a VFD unit, which are
only designed to receive a power supply within the range from
approximately 200 V to approximately 250 V, the pump 1 according to
the present invention is able to receive a power supply within the
range from approximately 90 V to approximately 250 V. Thereby, the
inventive pump 1 may be used both in countries/regions having a
standard power supply of approximately 110 V and in
countries/regions having a standard power supply of approximately
230 V. Thereto, prior art pumps are designed to be supplied with
electricity having a frequency of 50 Hz or 60 Hz, which are known
standards for different countries and/or different regions in a
country. However, the inventive pump is designed to be used in many
different countries, i.e. the input frequency may be at least
within the range of 50-60 Hz, but in reality the inventive pump may
cope with which ever frequency available. Thus, a given pump may be
used connected to many different power mains, i.e. a given pump is
a globally usable pump ready to be put into operation.
[0047] The VFD unit 2 comprises an electromagnet interference
filter 4 (EMI filter) arranged at the connection cable 3 in order
to filter out electromagnet interference at the input. The
connection cable 3 is connected to a feeder cable of the pump 1.
The EMI filter 4 is connected to a rectifier 5, which in turn is
connected via a DC link 10, including a capacitor 6, to a
transducer or inverter 7. The inverter 7 converts the DC current to
a three-phase current, which is supplied to a pump motor 9 via a
connection 8. The function and components and parts of a VFD unit 2
is well-known for the man skilled within the art and hence they
will not be described in further detail herein.
[0048] It is important that the VFD unit 2 is mounted thermally
shielded from the motor 9 and at the same time mounted in a
thermally conductive arrangement with the pumped fluid, such that
the temperature of the VFD unit 2 is kept at a low level during
operation, which eliminates a source of error.
[0049] A control device 11 is arranged operatively connected to the
pump 1 and in communication with the VFD unit 2 via a communication
bus (not shown) and controls or drives the pump 1, e.g. to increase
or decrease the speed of the motor 9 in order to pump a larger or a
smaller amount of liquid, for example, water. Further, the VFD unit
2 comprises sensing means 16, which is operatively connected to
said DC link 10 and which is arranged to obtain values of operating
parameters of the pump 1 indicating pump conditions.
[0050] The VFD unit 2 is arranged to communicate to the control
device 11 said values of operating parameters, which, according to
a preferred embodiment of the present invention, may be: the DC
link voltage, the DC link current, the speed of the motor, or the
like. By means of these operating parameters the power of the pump
1 or of the motor 9, the torque of the motor 9, or other suitable
quantities may be determined. The control device 11 is arranged to
determine if a predetermined condition is fulfilled based on said
obtained values of operating parameters and to communicate
instructions to the VFD unit 2, based on the fulfillment of said
predetermined condition, in order to control the operation of the
motor 9 in accordance with said pump conditions.
[0051] The control device 11 is, in turn, controlled by processing
means 12, which includes storing means 13. The storing means 13 may
include a random access memory (RAM) and/or a non-volatile memory
such as read-only memory (ROM). In this embodiment, the storing
means 13 comprises a computer program 14 comprising instructions
for bringing a computer or a microprocessor, such as the
processsing means 12, to cause method steps in accordance with the
present invention. As will be appreciated by one of ordinary skill
in the art, storing means may include various types of physical
devices for temporary and/or persistent storage of data which
includes solid state, magnetic, optical and combination devices.
For example, the storing means may be implemented using one or more
physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash
memory, and the like.
[0052] With reference now to FIG. 2, an alternative embodiment of
the present invention will be described. In this embodiment, the
control device 11 is arranged in communication via an interface
unit (not shown) with an operator unit 22 including input means in
the form of a keyboard 24, which allows the operator to input, for
example, control commands, and a display means or screen 26 for
presenting information related operation of the pump, for example,
time history of the operating parameters, or status information of
the pump. In one embodiment, the operator unit 22 is a personal
computer. The communication link between the pump 1 and the
operator unit 22 can be a wireless link or a hard wired link.
Furthermore, the operator unit 22 can, in turn, be connected to a
communications network, such as the Internet. By means of the
operator unit 22, the operator is capable of monitoring the
operation of the pump as well as different operating parameters
associated to the operation thereof via the display 26. According
to another embodiment, the display is a touch sensitive screen and
in this case a number of soft-keys can be arranged on the screen in
order to present different commands at different presented
interfaces on the display 26. Furthermore, the operator unit may
comprise storing means (not shown), which, in turn, may include a
random access memory (RAM) and/or a non-volatile memory such as
read-only memory (ROM). As will be appreciated by one of ordinary
skill in the art, storing means may include various types of
physical devices for temporary and/or persistent storage of data
which includes solid state, magnetic, optical and combination
devices. For example, the storing means may be implemented using
one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS,
flash memory, and the like.
[0053] Running data of the pump 1, such as operating parameters
like running time, number of starts, energy consumption, and alarm
data, as well as service record can be obtained and stored in a
logging file in the storing means 13. The logging file can be
presented for an operator by means of the operator unit 22.
Moreover, the logging file can be downloaded to the operator unit
22 for, e.g. storage.
[0054] Of course, there are a number of conceivable designs of the
control device 11, for example, the control device can be realized
by means of a processor including, inter alia, programmable
instructions for executing the methods according to the present
invention. According to another embodiment, the control device is
implemented in the form of a micro-chip or the like data carrier
comprising software adapted to execute the functions described
above and hereinafter. Furthermore, in FIGS. 7-9 alternative
embodiments of the present invention are shown. Like or similar
parts and/or devices in FIGS. 1, 2 and 7-9 are being denoted with
the same reference numerals. In FIG. 7, the control device 11,
which may be encapsulated in a hermetically sealed housing, is
arranged on an outer surface of the pump housing. The control
device 11 can be attached or fixed at the housing in a number of
ways. For example, the device 11 can be fixed by means of screws.
In FIG. 8, the control device 11 is in form of a plug-in unit
adapted to be inserted in a control device receiving recess 15. In
FIG. 9, the control device 11 is arranged in the control panel
22.
[0055] With reference now to FIG. 4, the general principles of the
method for operating a pump according to a first aspect of the
present invention will be described. This first aspect of the
method according to invention deals with the snoring operation
problem or the dry running operation problem, which, as discussed
above, entails increased wear of pump part such as the impeller and
the seals, may cause the pump motor to overheat and also leads to
that unnecessary energy is consumed. In addition, pump motors are
designed to provide optimum performance when they are pumping and
operating in liquid, so prolonged dry running operation can damage
the pump motor. Thus, the first aspect of the invention provides
for a an efficient way of operating a pump 1 comprising a VFD unit
2, as described with reference to any one of FIGS. 1-2 and 7-9 in
respect of energy consumption, pump life, and durability.
[0056] First, at step 40, the operation of the pump is initiated,
i.e. the pump is started. Then at steps 42 and 44 it is determined
if a predetermined condition is fulfilled. For example, at step 42,
the pump is operated at a first speed level for a predetermined
period of time and at a second speed level for a predetermined
period of time. Preferably, said first speed level and said second
speed level are low speed levels. For each speed level, the power
of the motor 9 is determined and thereafter, at step 44, it is
checked whether the relation between the speed of the motor 9 and
the power of the motor is approximately a cubic function (if the
power of the motor is proportional to the cube of the speed of the
motor) using the two speed levels and the resulting power from each
one of them. If the relation is a cubic function, the pump can be
ran in normal operation and if the relation is not a cubic function
it is an indication that the pump 1 pumps air and it is determined
that the liquid level is too low and the pump cannot be ran at the
desired speed level. This determination is performed in the control
device 11, e.g. in the processing means 12. It shall be pointed out
that the relationship between the speed level and the resulting
power not necessarily has to be cubic, other exponents may be
appropriate for other mixtures of fluids, i.e. liquids and
gases.
[0057] If, in step 44, it is determined that the liquid level is
not sufficient, the algorithm proceeds to step 46, where the
control device 11 sends instructions to the VFD unit 2 to
stop/pause the operation of the pump during a predetermined time
period, e.g. a number of minutes, maybe about 2 minutes. When this
period of time has expired, the algorithm returns to step 42.
[0058] On the other hand, if, at step 44, it is determined that the
liquid level is sufficient, the algorithm proceeds to step 48,
where the speed of the pump 1 is increased to a desired speed.
Thus, the pump 1 is now operated in a normal manner.
[0059] In order to avoid the snoring operation it is checked
substantially continuously that the pump 1 does not pump air during
operation. Therefore, at step 50, it is checked whether the liquid
level still is sufficient, i.e. whether the pump 1 sucks air partly
or mainly or if it is pumping liquid, by determining if a second
predetermined condition is fulfilled. This is performed on a
substantially continuous basis. In order to perform this check, a
value of a suitable operating parameter is obtained by the sensing
means 16 of the VFD unit 2, which value is communicated to the
control device 11. For example, the DC link voltage, the DC link
current, or the like can be used directly or can be used to
determine, for example, the torque of the motor 9 or preferably the
power of the motor 9. A sudden drop of the power of the motor 9
during operation indicates that the pump 1 pumps air instead of
liquid.
[0060] For example, the second condition is a comparison between
the power of the motor 9, for example, and a predetermined
reference level, which may be stored in the storing means 13, and
if the power of the motor is lower than the predetermined reference
level, it is determined that the liquid level is too low.
Preferably, the predetermined level may be about 70% of the maximum
power of the motor for the present speed of the motor 9.
Alternatively, a step comparable to step 42 may be performed at a
regular basis between step 48 and step 50, in order to determine if
liquid is present at the inlet of the pump 1'.
[0061] If it is determined that the liquid level at the inlet of
the pump is sufficient, i.e. the power of the motor 9 is higher
than the predetermined level, the algorithm returns to step 48. On
the other hand, if it is determined that the fluid level at the
inlet of the pump is too low, i.e. the power of the motor is lower
than the predetermined level, the algorithm instead proceeds to
step 52, where the operation of the pump is stopped. Subsequently,
the algorithm proceeds to step 46, where the operation of the pump
is kept stopped during a predetermined period of time. When this
pause period has expired, the algorithm proceeds to step 42.
[0062] With reference now to FIG. 5, the general principles of the
method for operating a pump according to a second aspect of the
present invention will be described. This second aspect of the
method according to invention deals with the problem of maintaining
the power of the pump at a substantially constant level over a
large range of flows. As is shown in FIG. 3 by line 32, the pump
head/pressure can be increased by 20% to 30% by means of the method
according to the second aspect. The power of the pump is kept at a
substantially constant level at varying pump head by adjusting the
speed of the motor. Due to the fact that the pump is operated more
efficient at low flows a smaller pump can be used to pump a given
amount of liquid, and the wear of the pump can also be reduced. The
inventive pump is an universally usable pump which is designed to
be used in many different applications having varying demands. A
high pump capacity may be achieved for a given pump for varying
pump head by adjusting the speed of the motor. Thus, the second
aspect of the invention provides for a an efficient way of
operating a pump comprising a VFD unit 2 as described with
reference to any one of FIGS. 1-2 and 7-9 in respect of energy
consumption and durability.
[0063] First, at step 60, the operation of the pump 1 is initiated,
i.e. the pump 1 is started. Then, at step 62, the pump is ran at a
desired speed level. An operating parameter of the pump is
monitored substantially continuously and values corresponding to
the operating parameter are obtained by the sensing means 16 of the
VFD unit 2, which value is communicated to the control device 11.
For example, the DC link voltage, the DC link current, or the like
can be used directly or can be used to determine, for example, the
torque of the motor 9 or preferably the power of the motor 9. At
the control device 11 the power of the motor 9, for example, is
compared with a predetermined reference level at step 64, e.g. the
rated power of the motor 9, which may be stored in the storing
means 13, in, for example the processing means 12. If, at step 64,
it is determined that the power level of the motor is higher than
the predetermined reference level, the algorithm returns to step
62, and the operation of the pump is maintained at said desired
speed level. On the other hand, if it is determined that the power
level of the motor is lower than the predetermined level, the
algorithm proceeds to step 66, where the speed required to reach
the predetermined power level of the motor is calculated in the
processing means 12.
[0064] Thereafter, at step 68, the calculated speed is compared
with a preset maximum speed. If the calculated speed is found to be
higher than the preset maximum speed, the algorithm proceeds to
step 70, where the control device 11 communicates instructions to
the VFD unit 2 to run the motor 9 at the preset maximum speed, and
the algorithm returns to step 64. If it is found that the
calculated speed is lower than the preset maximum speed, the
algorithm proceeds to step 72 and the control device 11
communicates instructions to the VFD unit 2 to run the motor 9 at
the calculated speed. Thereafter, the algorithm proceeds to step 64
where the procedure is continued. By maintaining the power of the
motor at a substantially constant level, the head/pressure can be
increased at low flows as indicated by means of line 32 in FIG.
3.
[0065] Turning now to FIG. 6, the general principles of the method
for operating a pump according to a third aspect of the present
invention will be described. This third aspect of the method
according to invention deals with the problem of clogging or jam of
the intake and/or the impeller of the pump 1, which may be caused
by particles in the fluid that sediment at the intake and in the
impeller and build silt having a relatively thick or solid
consistency. Thus, a large starting torque of the pump motor is
required in order to initiate the rotating of the pump impeller.
This consumes large amounts of energy and also wears the pump
impeller and the motor. When the pump has been in an off-state for
long period even a maximum starting torque may not be enough and in
such cases the pump has to be manually cleaned, and, consequently,
the starting reliability of pumps operated in such environments
will be low. Thus, the third aspect of the invention provides for a
an efficient way of operating a pump comprising a VFD unit 2 as
described with reference to any one of FIGS. 1-2 and 7-9 in respect
of energy consumption, durability and starting reliability.
[0066] First, at step 80, the operation of the pump 1 is initiated,
i.e. the pump 1 is started. Then, at step 82, the pump is ran at a
desired speed level. Thereafter, at step 84, a check is performed
whether the pump is clogged/jammed. This can as an example be
performed in the following two ways. One way is to measure an
operating parameter of the pump and compare it with a predetermined
reference level, for example, determine the power of the motor 9
and comparing it with a predetermined reference level of the power
of the motor 9, for example, the rated power of the motor 9. If the
measured power of the motor is higher than this predetermined
reference level, it is an indication of a clogged/jammed condition.
The second way is to monitor an alarm function of the variable
frequency drive means 2 and an alarm indicating DC link
over-current is used as an indication of a clogged/jammed
condition.
[0067] If it, in step 84, is determined that the pump 1 is not
clogged, the algorithm returns to step 82, where the operation of
the pump 1 is maintained. On the other hand, if it is determined
that the pump 1 is clogged, the algorithm proceeds to step 86,
where the control device 11 communicates instructions to the VFD
unit 2 to drive the impeller reversely at a first speed during a
predetermined period of time. After the predetermined period of
time the pump 1 is stopped and then ran in a forward rotating
direction again. Preferably, such a cycle lasts about 1-10 seconds.
Then, at step 88, it is checked whether the clogging state has
ceased, as is performed at step 84 above. If not, the procedure
returns to step 86. This cycle is repeated until the clogging
condition has been removed. If the clogging state has ceased, the
algorithm returns to step 82.
[0068] In order to prevent clogging during normal operation of the
pump 1, the following procedure can be performed at regular
intervals: running the pump 1 reversely at a predetermined speed
during a period of time having a predetermined length, stopping the
pump 1 after said period and running the pump 1 at its normal
rotation direction. Thereby, the operational reliability of the
pump can be improved still more.
[0069] Reference is now made to FIG. 3. The lines shown at
reference numbers 30 and 32 are examples of liquid flow and head
ratio for a certain pump 1, which is supplied with a 3 phase
voltage having a frequency of 60 Hz from the VFD unit 2. 60 Hz is
the standard frequency in some countries in the power mains, but by
means of the VFD unit 2, this level may be increased considerably,
e.g. up to 150 Hz, and by doing so said lines 30, 32 will be more
or less offset in an direction upwards in the chart of FIG. 3, and
a certain pump may be used for very fluctuating applications and
conditions.
Feasible Modifications of the Present Invention
[0070] Although specific embodiments have been shown and described
herein for purposes of illustration and exemplification, it is
understood by those of ordinary skill in the art that the specific
embodiments shown and described may be substituted for a wide
variety of alternative and/or equivalent implementations without
departing from the scope of the invention. Those of ordinary skill
in the art will readily appreciate that the present invention could
be implemented in a wide variety of embodiments, including hardware
and software implementations, or combinations thereof. As an
example, many of the functions described above may be obtained and
carried out by suitable software comprised in a micro-chip or the
like data carrier. This application is intended to cover any
adaptations or variations of the preferred embodiments discussed
herein. Consequently, the present invention is defined by the
wording of the appended claims and equivalents thereof.
* * * * *