WO2013068016A1 - Correction de la vitesse de pompes - Google Patents

Correction de la vitesse de pompes Download PDF

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Publication number
WO2013068016A1
WO2013068016A1 PCT/DK2012/050411 DK2012050411W WO2013068016A1 WO 2013068016 A1 WO2013068016 A1 WO 2013068016A1 DK 2012050411 W DK2012050411 W DK 2012050411W WO 2013068016 A1 WO2013068016 A1 WO 2013068016A1
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WO
WIPO (PCT)
Prior art keywords
speed
corrected
cor
impeller
corrected speed
Prior art date
Application number
PCT/DK2012/050411
Other languages
English (en)
Inventor
Lau Halkjaer
Original Assignee
Wärtsilä Svanehøj A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Wärtsilä Svanehøj A/S filed Critical Wärtsilä Svanehøj A/S
Publication of WO2013068016A1 publication Critical patent/WO2013068016A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
    • F04D15/0066—Control, e.g. regulation, of pumps, pumping installations or systems by changing the speed, e.g. of the driving engine

Definitions

  • the present invention relates to a method of controlling the rotating speed of an impeller of a pump.
  • the impeller driven by an electrical motor having an adjustable rotating speed, and the method determines a correction to an actual rotating speed to avoid instabilities.
  • EP 0 584 713 discloses a method of controlling an electric motor driving a centrifugal pump. According to the disclosure therein, an electrical measuring signal is produced, being proportional to the current drawn by the motor or by a power-control device, and based on the known characteristics of the motor and the pump, the electrical measuring signal is processed to produce a control signal being used as input signal to the power control device. The electrical measuring signal is processed in such a manner, that the control signal causes the discharge pressure of the pump to be substantially constant over a large variation interval for the flow.
  • the invention disclosed in EP 0 584 713 aims at keeping the pressure constant and does not contain any teaching as to how ensure stability (stable pump curves).
  • EP 1936250 discloses and operating process for a centrifugal pump, the revs of which can be regulated, with an unstable pump characteristic. The effective pump characteristic at a low throughput rate is raised sufficiently to ensure that there is only one intersection point between it and the actual pipeline network
  • an improved controlling method would be advantageous, and in particular a more efficient and/or reliable controlling method would be advantageous. It is a further object of the present invention to provide an alternative to the prior art. In particular, it may be seen as an object of the present invention to provide a controlling method that solves the problems of the prior art.
  • the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method of controlling the rotating speed of the impeller of a pump by determining a corrected rotating speed of the impeller, the impeller is being driven by an electrical motor having an adjustable rotating speed, the method comprises: determining based on actual power consumption or actual torque, a temporary corrected speed, - assigning the corrected speed to be the temporary corrected speed if the temporary corrected speed is within corrected speed limits, or - the corrected speed limit being exceeded of the corrected speed limits by the temporary corrected speed if outside the corrected speed limits, i.e. e.g. the corrected speed limit being exceeded by the temporary corrected speed if the temporary corrected speed is outside the corrected speed limits
  • Corrected speed is preferably used to indicate that an operator chooses a reference speed for the pump and that the speed determined by the invention is a correction to this speed in the sense that instabilities are avoided which otherwise would - or could - occur (if the speed was maintained at the reference speed).
  • Duty point means preferably corresponding values of delivery head H produced by and volume flow Q through a pump; the duty point is typically referenced to an operating curve for a pump.
  • Speed of pump means preferably the rotating speed of the one or more impellers of a centrifugal pump.
  • Temporary corrected speed means a speed that has been calculated and may be assigned to be a corrected speed in case the temporary corrected speed is within certain limits.
  • Figure 1 illustrates a pump curve and indicates inter alia an instability that might be presented by pumps having a pump curve as shown
  • Figure 2 shows schematically a fluid mechanical set-up in which instabilities have been avoided by the present invention
  • Figure 3 shows schematically a diagram for correction of the frequency in dependency of the power consumption.
  • Figure 1 illustrates schematically an instability that might be presented by pumps.
  • Figure 1 shows in a conventional manner a pump curve, that is corresponding values of volume flow Q (m 3 /h) and delivery head H (mlc) for a constant rotating speed n of the impeller.
  • the head increases constantly from maximum flow towards a point D where maximum delivery head is obtained, this point D is located in between the two points A and B on the pump curve.
  • HA HB resulting in that the flow through the pump jumps - or might jump - between Q A and QB often in a violent and unpredictable manner, which is considered as instability of the pump which is highly undesirable.
  • the pump curve of figure 1 may for some pumps or fluid mechanics set-ups in general be considered as somehow excessive disclosing the evolution of the curve from point B to zero flow. In many cases, the evolution of the pump curve from point C or D to zero flow is more horizontal, which however still may result in instabilities avoided by the present invention.
  • FIG. 2 shows schematically a situation where instabilities of a pump have been removed by the present invention.
  • Figure 2 shows schematically, a cross sectional view of a tank 1 in a ship.
  • the tank 1 contains a liquid 2 which is to be pumped out of the tank 1 by a pump 3 submerged in the tank 1.
  • the pump 3 is a centrifugal pump with one or more impellers and having a motor (not shown), typically being an electrical motor, driving the impeller(s) of the pump 3.
  • the outlet of the pump 3 is connected by pipes 4 to a controllable closing valve 5 arranged typically on the deck 6 of the ship.
  • the pump 3 with its motor and the valve 5 are connected to a control unit 7 adapted to control the speed of the impellers (via the motor) and the opening state of the valve 5.
  • the speed of the impeller(s) is set by a frequency converter 8 powering the motor driving the impeller(s) in response to received signals from the control unit 7.
  • the control unit and the frequency controller 8 are shown as being two separate units, this represents a division as to functionality and in many preferred embodiments the frequency converter 8 and the control unit 7 are integrated into a single, physical unit.
  • the example figure 2 is related to a ship, but the invention is not related to ships alone, but can be used in several other cases.
  • the flow Q through the pump 3 (and the valve 5) is inter alia controlled by the opening state of the valve 5 at least when the pump 3 operates at a constant rotating speed n.
  • the control unit 7 operates the opening state of the valve 5 to control the volume flow Q through the valve.
  • the control unit 7 also receives a power signal being indicative of the duty point at which the pump operates.
  • the power signal is preferably the power consumption of the motor, although torque of the motor or the flow through the pump may also be used as power signal.
  • the various power signals are correlated e.g. as torque / power / rotating speed and correlations between flow and e.g. power exist for pumps.
  • the rotating speed of the motor is coupled to the speed of the impellers and that the flow through the pump is determinable by the law of continuity by determining flow e.g. through the valve 5.
  • control unit 7 determines a rotating speed of the pump 3 in response to a received power signal and the frequency converter 8 sets the speed to the pump to the determined rotating speed.
  • the control unit 7 comprises in a conventional manner a central processing unit with memory and instructions for the central processing unit 7 enabling it to carry out the control method disclosed herein.
  • the memory stores inter alia the instructions as well as pre-set parameters.
  • the control unit 7 being adapted to co-operate with a frequency controller 8 controlling the rotating speed of a motor driving impeller(s) of the pump 3 to set the rotating speed of the impeller to a value determined by the control unit 7.
  • the valve 5 is typically controlled in manner where the flow gradually decreases as the liquid level in the tank 1 decreases. This results in that the flow Q in the beginning of the emptying process is high and the discharge head H is low (with reference to figure 1).
  • the rotating speed n of the pump is increased when the volume flow Q becomes smaller than a preselected value.
  • the preselected value is typically chosen as the maximum delivery head D in figure 1.
  • the controlling is preferably implemented in the following manner.
  • the controlling determines a rotating speed preferably at fixed regular time intervals.
  • a rotating speed is to be determined, the output torque from motor is determined and input to the control unit 7 as a signal.
  • the rotational speed may either be provided by a direct measurement or provided as the rotating speed set by the control unit 7 at a previous determination of a rotating speed.
  • the rotating speed of the pump 3 is governed by the frequency of the electrical power applied to the electrical motor driving the impeller(s) of the pump 3 and the algorithm adapted to determine the rotating speed of the pump 3 is designed to co-operate with the frequency converter in dependency of the output torque.
  • a diagram for correction of the frequency in dependency of the output torque is disclosed in figure 3.
  • n re f is the non-corrected speed of the pump 3.
  • Q se t is preferably a point between C and D in figure 1. If n re f is equal to the nominal speed n n0 m the torque at Q se t is M h (with reference to figure 1). In this case the speed of the pump is n re f for duty points higher than Q set During operation, the output torque of the motor 9 in figure 3 driving the pump 3 is determined. If the value is higher than M h; n cor is set to n re f.
  • the calculator determines a n cor being different from n re f.
  • n cor n ref * (l+ a S peed * (M h - M curve )/( M h - M,))
  • M act M curve * (ricor / flriom)
  • f: n ref * (a S peed * Mact)/(M h - M
  • Equation (1) contains a cubic equation (eq. la) with two conditions (eq. lb and lc) to be satisfied by n cor as found by equation 1.
  • the corrected speed is determined by solving equation la for n cor and checking this value against the condition equations lb and lc.
  • the result obtained by solving equation la for n cor may or may not be the corrected speed for the pump depending on whether that value fulfills the conditions (equation lb and lb)
  • the result obtained by solving equation la is termed temporary corrected speed and labelled ⁇ ⁇ - .
  • n cor : n ref
  • n cor : n re f
  • the method according to the invention utilizes equation 1 to provide a value for the speed which could be used as a rotational speed for the pump, and this value is - to avoid confusion with the corrected speed - termed temporary corrected speed as the value may be changed due to condition equations lb and lc.
  • the preferred embodiment is even further disclosed.
  • nnom nominal speed the speed at which the power limits are determined n r ef Reference speed (operators choice of speed)
  • Mhigh M h * (n re f / n n0 m) 2 The maximum torque that can be measured under normal conditions.
  • the actual torque M ac t is determined. If the value of M ac t is in the interval between M mi n and M hi g h the equation eq. (la) above is solved for n cor , that is eq. (la') above is used to provide the temporary corrected speed ⁇ ⁇ ⁇ . The determination is done by utilizing an iterative method, e.g. Newton's iteration method. This result in a temporary corrected speed ⁇ ⁇ - being checked for validity before being assigned to be n cor in the following manner:
  • n cor : n re f * (1+Ospeed) if ⁇ ⁇ - > n re f * (l+a S peed)
  • n cor : n re f if ⁇ ⁇ - ⁇ n re f
  • n cor : n re f * (l+a S peed) if ⁇ ⁇ - ⁇ n re f * (l+a S peed)
  • n cor : n re f if ⁇ ⁇ - > n re f
  • n cor is made regularly, typically with 2-5 seconds intervals.
  • Ct is one or more constants
  • F is a function including algebraic calculus as well as logical
  • the corrected speed is assigned to be the corrected speed limit being exceeded by the temporary corrected speed.
  • the corrected speed limits limits the corrected speed to an interval between the reference rotational speed, n re f and n re f (1+ cispeed) being a deviation from the reference rotational speed, the deviation being determined by the size of correction on speed (a spe ed) -
  • the corrected speed limits are n re f and n re f (1+ a spe ed) -
  • the dotted line from zero flow to point D represents the correction (rotational speed increased) made.
  • the correction may be seen as indicated in figure 1 to move point A vertically upwardly.
  • the torque curve has also been drawn.
  • the rotating speed of the impeller(s) of the pump 3 in figure 3 is controlled by a frequency converter 8 controlling the electrical motor 9.
  • setting the rotating speed of the impeller(s) to the corrected speed is carried out by operating the frequency converter to control the electrical motor so as to operate at a rotating speed resulting in the corrected speed for the impeller(s).
  • controlling according to the present invention is applicable for system of pumps, valves or other components (coupled in parallel and/or serial).

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Non-Positive-Displacement Pumps (AREA)

Abstract

La présente invention concerne un procédé de commande de la vitesse de rotation d'une turbine de pompe. La turbine est entraînée par un moteur électrique présentant une vitesse de rotation réglable et le procédé détermine une correction devant être apportée à une vitesse de rotation réelle pour éviter les instabilités.
PCT/DK2012/050411 2011-11-08 2012-11-08 Correction de la vitesse de pompes WO2013068016A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP11188259 2011-11-08
EP11188259.3 2011-11-08

Publications (1)

Publication Number Publication Date
WO2013068016A1 true WO2013068016A1 (fr) 2013-05-16

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ID=47191463

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DK2012/050411 WO2013068016A1 (fr) 2011-11-08 2012-11-08 Correction de la vitesse de pompes

Country Status (1)

Country Link
WO (1) WO2013068016A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4678404A (en) * 1983-10-28 1987-07-07 Hughes Tool Company Low volume variable rpm submersible well pump
EP0584713A1 (fr) 1992-08-21 1994-03-02 T. Smedegaard A/S Méthode de contrôle d'un moteur éléctrique actionnant une pompe centrifuge
EP1936250A1 (fr) 2004-08-10 2008-06-25 VOSS Fluid GmbH Bague coupante métallique
EP1936205A1 (fr) * 2006-12-22 2008-06-25 Grundfos Management A/S Procédé destiné au fonctionnement d'un agrégat de pompe centrifuge à vitesse de rotation réglable

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4678404A (en) * 1983-10-28 1987-07-07 Hughes Tool Company Low volume variable rpm submersible well pump
EP0584713A1 (fr) 1992-08-21 1994-03-02 T. Smedegaard A/S Méthode de contrôle d'un moteur éléctrique actionnant une pompe centrifuge
EP1936250A1 (fr) 2004-08-10 2008-06-25 VOSS Fluid GmbH Bague coupante métallique
EP1936205A1 (fr) * 2006-12-22 2008-06-25 Grundfos Management A/S Procédé destiné au fonctionnement d'un agrégat de pompe centrifuge à vitesse de rotation réglable

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