Note: Descriptions are shown in the official language in which they were submitted.
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CONTROL SYSTEM FOR A PUMP
Technical field of the Invention
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
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.
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 part-
icles remain at the hydraulics and cause extra wear on
the impeller, the suction cover, the seals, etc. This
ineffective pumping contributes in aµsignificant 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,
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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.
US 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.
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. =
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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 consis-
tency. 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
, 15 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.
Abovementioned pump system according to US 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 over-
come 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.
Another known problem with pumps comprising conven-
tional variable frequency drive means, is that the latter
is usually mounted distant from the pump at a dry loca-
tion above ground. More precisely, this necessitates a
long power cable leading from the variable frequency
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drive means to the motor of the pump, which for conven-
tional variable frequency drive means can result in
severe problems with electromagnetic interference. In
abovementioned US 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. How-
ever, 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.
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
Thus, one object of the present invention is to pro-
vide 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.
Another object of the present invention is to pro-
vide 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 con-
sumption.
Another object of the present invention is to pro-
vide 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.
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
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systems in a manner that reduces the wear of the pump and
extends the pump life.
It is still another object of the present invention
to provide an improved pump, pump system including such a pump,
5 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.
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.
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.
In the context of the present invention, the term
"pump speed" is defined as the numbers of revolutions per time
unit of the pump.
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 variable
frequency drive means 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
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comprising a rectifier, an inverter, a DC link extending
therebetween, and sensing means connected directly on said DC
link between the rectifier and the inverter, furthermore the
pump is operatively connected to a control device, the method
comprising: obtaining values of operating parameters of the
pump indicating pump conditions from said sensing means by
sensing conditions on said DC link, communicating said values
of operating parameters from the variable frequency drive means
to the control device, determining by means of the control
device if a predetermined condition is fulfilled based on said
obtained values of operating parameters, and communicating
instructions from the control device to the variable frequency
drive means, based on the fulfilment of said predetermined
condition, in order to control the operation of the motor in
accordance with said pump conditions.
According to a second aspect of the present invention
there is provided a computer-readable medium having computer
executable instructions stored thereon for execution by one or
more computers, that when executed implement the method as
described above.
According to a third aspect of the present invention,
there is provided a pump comprising a motor and variable
frequency drive means, the variable frequency drive means 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, wherein the
variable frequency drive means comprises sensing means, said
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sensing means being connected directly on said DC link between
the rectifier and the inverter to obtain values of operating
parameters of the pump indicating pump conditions by sensing
conditions on said DC link, the variable frequency drive means
being arranged to communicate to the control device said values
of operating parameters, furthermore the control device 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,
based on the fulfilment of said predetermined condition, in
order to control the operation of the motor in accordance with
said pump conditions.
According to a fourth aspect of the present
invention, there is provided a pump system comprising a pump
according to the third aspect of the invention.
According to a further aspect of the present
invention, there is provided a control device for a pump
according to the third aspect of the invention.
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.
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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 fre-
quency means, no external sensors are required.
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 ope-
rating parameters the power of the motor, the torque of
the motor, or other suitable quantities may be deter-
mined.
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 predeter-
mined 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 prede-
termined 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 consump-
tion, 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 ob-
tained. Furthermore, the pump life can be extended owing
to the fact that the wear of pump parts such as the im-
peller, seals and suction cover is significantly reduced.
In an alternative embodiment of the present inven-
tion, the power of the motor is maintained at a substan-
tially constant level. The obtained operating parameter
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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.
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 clog-
ged, 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 impel-
ler reversely, stopping it and change the operating
direction is repeated until it is detected that the clog-
ging 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 rela-
tively 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
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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 con-
dition can be removed in an efficient way the energy
consumption of the pump can also be reduced.
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 procesbing means of a pump or a pump system.
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 con-
junction 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
Above-mentioned and other features and advantages
of the present invention will be apparent from the follo-
wing detailed description of preferred embodiments, mere-
ly exemplifying, in conjunction with the attached draw-
ing, wherein:
Fig. 1 schematically shows an embodiment of a pump
according to the present invention;
Fig. 2 schematically shows an embodiment of a pump sys-
tem according to the present invention;
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Fig. 3 shows a pump curves for a conventional pump and a
pump operated in accordance with the present
invention;
Fig. 4 shows the principles of a method of an embodiment
5 according to the present invention;
Fig. 5 shows the principles of a method of another embo-
diment according to the present invention;
-Fig. 6 shows the principles of a method of yet another
embodiment according to the present invention;
10 Fig. 7 schematically shows a further embodiment of a
pump and a control device for such a pump accor-
ding to the present invention;
Fig. 8 schematically shows another embodiment of a pump
and a control device for such a pump according to
the present invention; and
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
In the following, there will be disclosed preferred
embodiments of a method for operating a pump and a pump
system.
, 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 uti-
lized in present submersible pumps comprising variable
-30 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.
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
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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 I 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 diffe-
rent 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 ope-
ration.
The VFD unit 2 comprises an electromagnet inter-
ference 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.
It is important that the VFD unit 2 is mounted ther-
mally 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
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is kept at a low level during operation, which eliminates
a source of error.
A control device 11 is arranged operatively connec-
ted 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 indi-
cating pump conditions.
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 cur-
rent, 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.
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 bring-
ing a computer or a microprocessor, such as the process-
sing 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,
=
=
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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. '
With reference now to fig. 2, an alternative embo-
diment of the present irivention 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 parame-
ters, or status information of the pump. In one embodi-
ment, 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 con-
nected 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 opera-
tion 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 diffe-
rent 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)
= 30 and/oaf 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.
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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.
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.
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
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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
5 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 con-
sumption, pump life, and durability.
First, at step 40, the operation of the pump is ii-
10 tiated, i.e. the pump is started. Then at steps 42 and 44
it is determined if a predetermined condition is ful-
filled. 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
15 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 rela-
tion 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.
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,
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maybe about 2 minutes. When this period of time has
expired, the algorithm returns to step 42.
On the other hand, if, at step 44, it is determined
that the liquid level is sufficient, the algorithm pro-
ceeds 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.
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 prede-
termined 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.
For example, the second condition is a comparison
between the power of the motor 9, for example, and a pre-
determined 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 prede-
termined level may be about 70% of the maximum power of
the motor for the present speed of the. motor 9. Alterna-
tively, 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
2.
If it is determined that the liquid level at the
inlet of the pump is sufficient, i.e. the power of the
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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 pre-
determined period of time. When this pause period has
expired, the algorithm proceeds to step 42.
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 com-
prising 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.
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 continu-
ously and values corresponding to the operating parameter
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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 predeter-
mined 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 algo-
rithm 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 algo-
rithm proceeds to step 66, where the speed required to
reach the predetermined power level of the motor is cal-
culated in the processing means 12.
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 andthe 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.
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
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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 relia-
bility.
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 opera-
ting parameter of the pump and compare it with a prede-
termined reference level, for example, determine the
power of the motor 9 and comparing it with a predeter-
mined 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.
If it, in step 84, is determined that the pump 1 is
not clogged, the algorithm returns to step 82, where the
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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
5 the impeller reversely at a first speed during a prede-
termined 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
10 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 algo-
rithm returns to step 82.
15 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 pre-
determined length, stopping the pump 1 after said period
20 and running the pump 1 at its normal rotation direction.
Thereby, the operational reliability of the pump can be
improved still more.
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 fluctu-
ating applications and conditions.
Feasible modifications of the present Invention
Although specific embodiments have been shown and
described herein for purposes of illustration and exemp-
lification, it is understood by those of ordinary skill
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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.
