WO2006136202A1

WO2006136202A1 - Control system for a pump

Info

Publication number: WO2006136202A1
Application number: PCT/EP2005/052878
Authority: WO
Inventors: Zhiyong Zhong; Jürgen MÖKANDER
Original assignee: Itt Manufacturing Enterprises Inc.
Priority date: 2005-06-21
Filing date: 2005-06-21
Publication date: 2006-12-28
Also published as: AP2007004184A0; AR054792A1; CN101203678A; JP5017665B2; MY148008A; CA2606556A1; EP1893874A1; MX2007014262A; NZ562227A; IL186295A0; AP2193A; BRPI0612493A2; EA200800095A1; IL186295A; CN101203678B; AU2006259944B2; WO2006137777A1; US20100034665A1; KR20080015403A; NO20080379L

Abstract

The present invention relates to variable frequency drive pumps and methods for operating such pumps. The inventive method for operating a pump (1) having an inlet and an outlet, which pump (1) comprises variable frequency drive means (2) adapted to drive a motor (9) of said pump (1), comprises the steps of obtaining (50; 64; 84) operating parameters of said pump (1) substantially continuously, said operating parameters indicating pump conditions; and controlling (52; 66; 86) said variable frequency drive means (2) based on said obtained operating parameters, wherein the operation of said motor (9) is adjusted to said pump conditions. Furthermore, a pump, a computer program product loadable into a memory of a digital computer device, including software code portions for performing the inventive method, a control device (11) for a pump and a pump system are described.

Description

Control system for a pump

Technical field

The present invention relates generally to the field of pumps, and, more specifically, the present invention relates to variable frequency drive pumps and methods for operating such pumps.

State of the art

Variable frequency drive pumps (VFD pumps), such as sewage pumps, drainage pumps and de-watering pumps as well as submersible pumps, for example, for pumping fluids in mining applications such as in mining shafts, wells or at construction sites. 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, in particular, submersible pumps is so called snoring operation, which means that the pumps sucks party liquid and partly air. This is due to the fact that the water 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 still remains in the mining shaft or in the well and particles begin to settle and start to 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, suction cover and the seals. This ineffective pumping contributes in a significant way to the overall running 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 a level switch, are used to sense the fluid level. 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, thus, delivering an error signal.

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 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 efficiency of a pump may, as indicated in Fig. 3, 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) efficiency also at lower flows.

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.

Thus, there is a need of an improved pump and improved control methods for controlling such a pump in an efficient way with respect to energy consumption, durability of the pump, and pump life.

Brief description of the invention

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 energy consumption

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. 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.

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.

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 having an inlet and an outlet, the pump comprising variable frequency drive means adapted to drive a motor of the pump. The method comprises the steps of obtaining operating parameters of the pump substantially continuously from the variable frequency means, the operating parameters indicating pump conditions; and controlling the variable frequency drive means based on the obtained operating parameters, wherein the operation of the motor is adjusted to the pump conditions. According to a second aspect of the present invention there is provided a pump comprising variable frequency drive means adapted to drive a motor of the pump; and control device communicating with the variable frequency drive means, the control device comprising processing means and being adapted to obtain values corresponding to operating parameters of the pump, the operating parameters indicating pump conditions, from the variable frequency means and to send control instructions to the variable frequency drive means based on the obtained operating parameters for controlling the variable frequency drive means, wherein the operation of the motor is adjusted to the pump conditions.

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.

According to a fourth aspect of the present invention, there is provided a pump system including a pump comprising variable frequency drive means adapted to drive a motor of the pump; and control device communicating with the variable frequency drive means, the control device comprising processing means and being adapted to obtain values corresponding to operating parameters of the pump from the variable frequency means, the operating parameters indicating pump conditions, and to send control instructions to the variable frequency drive means based on the operating parameters for controlling the variable frequency drive means, wherein the operation of the motor is adjusted to the pump conditions.

According to a further aspect of the present invention, there is provided a control device for a pump. The control device is characterized in that it is adapted to communicate with the variable frequency drive means, the control device comprising processing means and being adapted to obtain values corresponding to operating parameters of the pump from the variable frequency means, the operating parameters indicating pump conditions, and to send control instructions to the variable frequency drive means based on the operating parameters for controlling the variable frequency drive means, wherein the operation of the motor is adjusted to the pump conditions.

Thus, the present invention is based on the idea of obtaining operating parameters of the pump substantially continuously from the variable frequency means, which operating parameters indicate pump conditions; and controlling the variable frequency drive means based on the obtained operating parameters, wherein the operation of the motor is adjusted to the pump conditions. Thereby, the pump is operated in an efficient way with respect to 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 means is obtained from the variable frequency means and/ or the motor itself, no external sensors are required.

According to embodiment of the present invention, the operating parameters in any one of: the DC link power of the variable frequency unit, the current of the variable frequency unit, or the torque of the motor.

In a preferred embodiment of the present invention, the obtained operating parameter value of the variable frequency unit is compared with a predetermined parameter level substantially continuously; and if it is determined that the parameter value is lower than the predetermined level, the operation of the pump motor is stopped during a period of time having a predetermined length. Moreover, the motor is restarted at a first speed level when the predetermined period of time has expired; the presence of fluid at the inlet is checked by comparing the parameter value with the predetermined parameter level; and the speed of the motor is increased from the first level if it is determined that the parameter value is higher than the predetermined parameter level. 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 that unnecessary power is consumed is dealt with, and an efficient way of operating a VFD pump in respect of power 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.

In an alternative embodiment of the present invention, maintaining the output power of the pump at a substantially constant level. Furthermore, the operating parameter value is compared with a predetermined parameter level substantially continuously; if the parameter value is lower than the predetermined power 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 the maximum allowed speed of the pump; and if the calculated speed is higher than the maximum allowed speed of the pump, the pump is ran at the maximum speed. Thus, the problem of maintaining the efficiency 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 the second aspect. Due to the fact that the pump is operated more efficient at low flows the wear of the pump can be reduced. Hence, an efficient way of operating a VFD pump in respect of power consumption and durability 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 clogged, the pump is ran reversely at a predetermined speed during a period of time having a predetermined length, it is then stopped and ran at 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 a an efficient way of operating a VFD pump in respect of power 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 power 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 processing means of a pump or a pump system.

The features that characterize the invention, both as to organization and to method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawings. It is to be expressely 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 following detailed description of preferred embodiments, merely exemplifying, in conjunction with the attached drawing, wherein:

Fig. 1 schematically shows an embodiment of a pump according to the present invention;

Fig. 2 schematically shows an embodiment of a pump system according to the present invention; 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 according to the present invention;

Fig. 5 shows the principles of a method of another embodiment according to the present invention;

Fig. 6 shows the principles of a method of yet another embodiment according to the present invention;

Fig. 7 schematically shows a further embodiment of a pump and a control device for such a pump according 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

■ i • i system according to the present invention.

Description of preferred embodiments

In the following, there will be disclosed preferred embodiments of a methods 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 utilized in submersible VFD-pumps. 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, and de-watering pumps.

The submersible pump 1 of Fig. 1 comprises a variable-speed unit 2, preferably a variable frequency drive unit (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. The VFD unit 2 comprises an electro-magnet interference filter 4 (EMI filter) arranged at the connection cable 3 in order to filter out electro-magnet interference at the input. A rectifier 5 is connected to the EMI filter 4 connected via a DC link 10, in turn, including a capacitor 6 a transducer 7. The transducer 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 is well- known for the man skilled within the art and hence they will not be described in further detail herein.

Control device 11 is arranged in communication with the VFD unit 2 via a communication bus (not shown) and controls or drives the pump 1 to, for example, increase or decrease the speed in order to pump a larger or a smaller amount of fluid, for example, water. Furthermore, the control device 11 is capable of obtaining signals corresponding to the measurements of operating parameters, for example the DC power of the DC link 10 or the torque of the motor. 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 processing 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.

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.

Running data of the pump 1, such as operating parameters like running time, number of starts, power 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 axe 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 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-run 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 power is consumed. In addition, pump motors are designed to provide optimum performance when they are pumping and operating in fluid, so ~.Λ prolonged dry-run operation can damage the pump motor. Thus, the first aspect of the invention provides for a an efficient way of operating a VFD pump as described with reference to any one of Figs. 1-2 and 7-9 in respect of power consumption, pump life, and durability.

First, at step 40, the operation of the pump is initiated, i.e. the pump is started. Then, at step 42, the pump is ran at a first low speed level and at a second low speed level. Thereafter, at step 44, it is checked whether the relation between the speed of the pump and the power is a cubic function (the power of the pump is a cubic function of the speed) using the two speed levels and the resulting power from each 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 determined that the fluid level is too low and the pump cannot be ran at full speed. This check is performed in the control device 11, for example, in the processing means 12. If, in step 44, it is determined that the fluid level is not sufficient, the algorithm proceeds to step 46, where the control device 11 sends an instruction to the VFD unit 2 to pause the operation of the pump is during a predetermined period of time, for example, a number of minutes, 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 fluid level is sufficient, the algorithm proceeds to step 48, where the speed of the pump is increased to full speed. Thus, the pump is now operated in a normal manner.

In order to avoid the snoring operation it is checked substantially continuously that the pump not pumps air during the operation of the pump. Therefore, at step 50, it is checked whether the fluid level still is sufficient, i.e. whether the pump sucks air partly or mainly of if it is pumping fluid. This is performed on a substantially continuous basis. In order to perform this check, an operating parameter is obtained by the control device 11. For example, the DC link power, the current or the torque of the motor can be used. Preferably, the DC link power is used.

The DC link power is compared with a predetermined power level, which may be stored in the storing means 13, and if the DC link power level is lower than the predetermined level, it is determined that the fluid level is too low. Preferably, the predetermined level may be about 70 % of the maximum DC power.

If it is determined that the fluid level at the inlet of the pump is sufficient, i.e. the DC link power 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 DC link power 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 stopped during a predetermined period of time. When this pause period has expired, the algorithm proceeds to further on 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 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. 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. Thus, the second aspect of the invention provides for a an efficient way of operating a VFD pump as described with reference to any one of Figs. 1-2 and 7-9 in respect of power consumption and durability.

First, at step 60, the operation of the pump is initiated, i.e. the pump is started. Then, at step 62, the pump is ran at full speed. A operating parameter of the pump is monitored substantially continuously and values corresponding to the parameter is obtained by the control device 11 and compared with a predetermined parameter level at step 64. For example, the DC link power, the current or the torque of the motor can be used. Preferably, at step 64, the DC link power is used and compared with the rated power of the pump motor, 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 DC link power level is higher than the predetermined level, the algorithm returns to step 62, and the operation of the pump is maintained at full speed. On the other hand, if it is determined that the DC link power level is lower than the predetermined level, the algorithm proceeds to step 66, where the speed required to reach the predetermined power level is calculated in the processing means 12.

Thereafter, at step 68, the calculated speed is compared with the maximum speed. If the calculated speed is found to be higher than the maximum speed, the algorithm proceeds to step 70, where the control device 11 sends an instruction to the VFD unit 2 to run the motor at maximum speed, and the algorithm returns to step 64. If it is found that the calculated speed is lower than the maximum speed, the algorithm proceeds to step 72 and the control device 11 sends an instruction to the VFD unit 2 to run the motor at the calculated speed. Thereafter, the algorithm proceeds to step 64 where the procedure is continued. By maintaining the power 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 aspect of the method according to invention deals with the problem of clogging or jam of the intake and/ or impeller, 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 VFD pump as described with reference to any one of Figs. 1-2 and 7-9 in respect of power consumption, durability and starting reliability.

First, at step 80, the operation of the pump is initiated, i.e. the pump is started. Then, at step 82, the pump is ran at full speed. Thereafter, at step 84, a check is performed whether the pump is clogged/jammed. This can be performed in two ways. One way is to measure an operating parameter of the pump and compare it with a predetermined level, for example, measure the

DC power of the motor and comparing it with a predetermined DC power level, for example, the rated power of the pump motor. If the measured power is higher that this predetermined level, it is an indication of a clogged/jammed condition. The second way is to monitor the alarm function of the variable frequency unit 2 and an alarm indicating over-current is used as an indication of a clogged/jammed condition.

If it, in step 84, is determined that the pump is not clogged, the algorithm returns to step 82, where the operation of the pump is maintained. On the other hand, if it is determined that the pump is clogged, the algorithm proceeds to step 86, where the control device 11 sends an instruction to the VFD unit 2 to drive the impeller reversely at full speed during a predetermined period of time, it 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. 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.

In order to prevent clogging during running of the pump, 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 operation reliability of the pump can be improved.

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.

Claims

1. A method for operating a pump (1) having a an inlet and an outlet, said pump (1) comprising variable frequency drive means (2) adapted to drive a motor (9) of said pump (1), c h a r a c t e r i z e d by the steps of: obtaining (50; 64; 84) operating parameters of said pump (1) substantially continuously from said variable frequency means (2), said operating parameters indicating pump conditions; controlling (52; 66; 86) said variable frequency drive means (2) based on said obtained operating parameters, wherein the operation of said motor (9) is adjusted to said pump conditions.

2. The method according to claim 1, wherein the step of obtaining operating parameters of said pump (1) comprises the step of obtaining at least one of said parameters: the DC link power level, the current level of said variable frequency drive means (2) or the torque of said motor (9).

3. The method according to claim 1 or 2, further comprising the step of detecting (50; 64; 84) a certain pump condition by using said at least one parameter.

4 The method according to claim 3, wherein said pump condition includes the presence of fluid at said inlet.

5. The method according to claim 2-4, further comprising the steps of: running said pump (1) at low speed; checking (42) whether said pump (1) can operated at full speed; and if it is determined that said pump (1) not can be operated at full speed, stopping (46) the operation of said pump motor (9) during a period of time having a predetermined length.

6. The method according to claim 5, further comprising the steps of: if it is determined that said pump (1) can be operated at full speed, running (48) said pump (1) at full speed; checking (50) the presence of fluid at said inlet by comparing said operating parameter with a predetermined parameter level; and if it is determined that the fluid level is too low, stopping (52) the operation of the pump (1).

7. The method according to claim 2, further comprising the step of maintaining (70, 72) the operating parameter at a substantially constant level.

8. The method according to claim 7, further comprising the steps of: comparing (64) the operating parameter with a predetermined parameter level substantially continuously; if said operating parameter is lower than said predetermined parameter level, calculating (66) the speed of the motor (9) required to obtain said predetermined parameter level; and running (72) said pump (1) at said calculated speed.

9. The method according to claim 8, further comprising the steps of: comparing (68) the calculated speed with the maximum allowed speed of said pump (1); and if said calculated speed is higher than the maximum allowed speed of said pump (1), running (70) said pump (1) at said maximum speed.

10. The method according to claim 3, wherein said pump condition includes a clogging condition of said pump (1).

11. The method according to claim 10, performing the following procedure at regular intervals during operation of said pump: running said pump (1) reversely at a predetermined speed during a period of time having a predetermined length, stopping said pump (1) after said period and running said pump (1) at its normal rotation direction.

12. The method according to claim 10, further comprising the steps of: detecting (84) whether said pump (1) is clogged; and if it is detected that said pump (1) is clogged, running (86) said pump (1) reversely at a predetermined speed during a period of time having a predetermined length, stopping said pump (1) after said period and running said pump (1) at its normal rotation direction.

13. The method according to claim 12, further comprising the steps of: repeating (86, 88) said step of running said pump impeller reversely at a predetermined speed during a period of time having a predetermined length, stopping said pump (1) after said period and running said pump (1) at its normal rotation direction until it is detected that said clogging condition has ceased.

14. The method according to any one of preceding claims, wherein said predetermined parameter level is a predetermined power level.

15. The method according to any one of preceding claims, wherein said pump is a submersible pump.

16. Computer program product (14) loadable into a memory (13) of a digital computer device, including software code portions for performing the method of one of claim 1-12 when said computer program product (14) is run on said computer device.

17. A pump (1) having a an inlet and an outlet, said pump (1) comprising variable frequency drive means (2) adapted to drive a motor (9) of said pump (1), c h a r a c t e r i z e d by control device (11) communicating with said variable frequency drive means (2), said control device (11) comprising processing means (12) and being adapted to obtain values corresponding to operating parameters of said pump (1) indicating pump conditions from said variable frequency means (2), and to send control instructions to said variable frequency drive means (2) based on said operating parameters for controlling said variable frequency drive means (2), wherein the operation of said motor (9) is adjusted to said pump conditions.

18. The pump according to claim 17, wherein said control device (11) is adapted to obtain a value corresponding to at least one of the operating parameters: the DC link power level, the current level of said variable frequency drive means (2) or the torque of said motor (9).

19. The pump according to claim 17 or 18, wherein said control device (11) is adapted to compare the value corresponding to said at least one parameter with a predetermined parameter value; and if it is determined that said value corresponding to said at least one parameter is lower than said predetermined parameter level value, send an instruction to said variable frequency drive means (2) to stop the operation of said motor (9) during a period of time having a predetermined length.

20. The pump according to claim 18, wherein the control device (11) is adapted to send an instruction to the variable frequency drive means (2) to restart the motor (9) at a first speed level when said predetermined period of time has expired; check the presence of fluid at said inlet by comparing a value corresponding to said at least one parameter with said predetermined parameter level; and send an instruction to the variable frequency drive means (2) to increase the speed of the motor (9) from said first level if it is determined that said value corresponding to said at least one parameter is higher than said predetermined parameter level.

21. The pump according to claim 18, wherein the control device (11) is adapted to maintain said at least one parameter at a substantially constant level.

22. The pump according to claim 20, wherein the control device (11) is adapted to compare the value corresponding to said at least one parameter with a predetermined parameter level value; if said value corresponding to said at least one parameter is lower than said predetermined parameter level value, calculate the speed of the motor (9) required to obtain said predetermined parameter level value; and send an instruction to the variable frequency drive means (2) to run said pump (1) at said calculated speed.

23. The pump according to claim 22, wherein the control device (11) is adapted to compare the calculated speed with the maximum allowed speed of said pump (1); and if said calculated speed is higher than the maximum allowed speed of said pump (1), send an instruction to the variable frequency drive means (2) to run said pump (1) at said maximum speed.

24. The pump according to claim 17 or 18, wherein said control device (11) is adapted to perform the following procedure at regular intervals during operation of said pump: send an instruction to the variable frequency drive means (2) to run said pump (1) reversely at a predetermined speed during a period of time having a predetermined length, stop said pump (1) after said period and running said pump (1) at its normal rotation direction.

25. The pump according to claim 17 or 18, wherein said control device (11) is adapted to detect whether said pump (1) is clogged; and if it is detected that said pump (1) is clogged, send an instruction to the variable frequency drive means (2) to run said pump impeller reversely at a predetermined speed during a period of time having a predetermined length, stopping said pump (1) after said period and running said pump (1) at its normal rotation direction.

26. The pump according to claim 25, wherein said control device (11) is adapted to repeat the step of running said pump impeller reversely at a predetermined speed during a period of time having a predetermined length, stopping said pump (1) after said period and running said pump (1) at its normal rotation direction until it is detected that said clogging condition has ceased.

27. The pump according to any one of preceding claims, wherein said predetermined parameter level is a predetermined power level.

28. The pump according to any one of preceding claims, wherein said pump is a submersible pump.

29. A pump system including a pump (1) having a an inlet and an outlet, said pump (1) comprising a variable frequency drive means (2) adapted to drive a motor (9) of said pump (1), c h a r a c t e r i z e d by control device (11) communicating with said variable frequency drive means (2), said control device (11) comprising processing means (12) and being adapted to obtain values corresponding to operating parameters of said pump (1) from said variable frequency means (2), said operating parameters, indicating pump conditions, and to send control instructions to said variable frequency drive means (2) based on said operating parameters for controlling said variable frequency drive means (2), wherein the operation of said motor (9) is adjusted to said pump conditions.

30. The system according to claim 29, comprising a submersible pump (1) according to any one of preceding claims 14-22.

31. The system according to claim 29 or 30, further comprising an operator unit (22) including input means (24) and display means (26) adapted to present information related to the operation of the pump (1).

32. A control device (11) for a pump (1) having a an inlet and an outlet, said pump (1) comprising variable frequency drive means (2) adapted to drive a motor (9) of said pump (1), c h a r a c t e r i z e d in that said control device is adapted to communicate with said variable frequency drive means (2), said control device (11) comprising processing means (12) and being adapted to obtain values corresponding to operating parameters of said pump (1) from said variable frequency means (2) said operating parameters, indicating pump conditions, and to send control instructions to said variable frequency drive means (2) based on said operating parameters for controlling said variable frequency drive means (2), wherein the operation of said motor (9) is adjusted to said pump conditions.

33. The control device according to claim 32, wherein said control device is adapted in accordance with any one of the preceding claims 18-28.