EP2657529A1 - Method and system for identifying and controlling a centrifugal pump - Google Patents

Abstract

The method involves selecting a speed, and controlling a variable speed drive (3) to apply the speed to an electric motor (2). A solenoid valve (6) is controlled over the whole of its operating range at the selected speed. The pressure and the flow rate of a fluid flowing in a pumping circuit are measured, and an electric power supplied to the motor for each operating point of the solenoid valve is measured. A pressure curve is determined, for the selected speed, as a function of the flow rate and the curve of the power supplied as a function of the flow rate. An independent claim is also included for a control system for controlling a centrifugal pump included in a pumping circuit.

Description

Technical field of the invention

The present invention relates to a method and system for identifying and controlling a centrifugal pump.

State of the art

A pumping circuit in which a centrifugal pump is included is controlled by a control system.

$$\mathrm{Pression}=\mathrm{Pression\_VitesseNominale\; x}{\left(\mathrm{Vitesse}/\mathrm{VitesseNominale}\right)}^2$$

$$\mathrm{Puissance}=\mathrm{Puissance\_VitesseNominale\; x}{\left(\mathrm{Vitesse}/\mathrm{VitesseNominale}\right)}^3$$

This control system comprises an electric motor operating the centrifugal pump and controlled by a variable speed drive. The system also includes a valve or a valve to control flow in the pumping circuit. In normal operation, the control of the centrifugal pump is carried out from pump curves. These pump curves are defined for a single speed called the nominal speed, and represent the pressure as a function of flow, the mechanical power as a function of flow. For a speed other than the nominal speed, there are extrapolation laws known as rake law to create the link between the quantities of the pumping circuit (Pressure, Flow) and the mechanical quantities (Power, Speed): $$\mathrm{Debit}=\mathrm{Speed\_SpeedNominale\; x}\left(\mathrm{Speed}/\mathrm{VitesseNominale}\right)$$

$$\mathrm{Pressure}=\mathrm{Pressure\_ValueNominale\; x}{\left(\mathrm{Speed}/\mathrm{VitesseNominale}\right)}^2$$

$$\mathrm{Power}=\mathrm{Power\_ValueNominal\; x}{\left(\mathrm{Speed}/\mathrm{VitesseNominale}\right)}^3$$

• La captation des différentes grandeurs se fait sans la garantie de synchronisation précise entre ces quatre mesures. Il est connu que l'action d'une vanne ou d'un robinet génère des variations dans le système de pompage. En fonction de la configuration du système de pompage, ces variations peuvent être oscillantes et il est alors difficile de capturer un quadruplet de grandeurs cohérentes entre elles.
• Les courbes de pompe sont établies à vitesse nominale en respect d'une norme ISO 9906 annexe A qui requiert une précision de 8%, pouvant se révéler insuffisante pour les activités de contrôle demandées.
• En pratique, l'extrapolation réalisée selon des lois théoriques ne permet pas toujours d'obtenir la précision souhaitée.
• L'utilisation d'un variateur de vitesse pour contrôler le moteur électrique et ainsi supprimer les mesures mécaniques externes introduit un biais de corrélation entre les données disponibles dans le système de contrôle et d'estimation, i.e. les courbes de pompe, et les données de mesure ou d'estimation disponibles (vitesse estimée, puissance mécanique estimée). Il est en effet connu que, sans capteur de grandeurs mécaniques (position, vitesse, couple ou puissance) et selon le type d'algorithme de contrôle employé, un variateur de vitesse peut s'avérer imprécis dans l'estimation de vitesse et de puissance.

The pump curves and the extrapolation laws can already be stored in the system or reconstructed during an identification phase. In this identification phase, a pressure sensor and a flow sensor are used to measure the flow rate and the pressure of the fluid flowing in the pumping circuit at each speed of the electric motor corresponding to a mechanical power supplied to the pump. So far, the identification phase, carried out at a nominal speed, allows a correlation between measurement data of the system, whether it is the data related to the pumping circuit (pressure, flow) or the data. mechanical (speed, power). The known drawbacks to the use of these data are of several orders:

• Capturing the various quantities is done without the guarantee of precise synchronization between these four measurements. It is known that the action of a valve or a tap generates variations in the pumping system. Depending on the configuration of the pumping system, these variations can be oscillating and it is difficult to capture a quadruplet of sizes consistent with each other.
• Pump curves are established at nominal speed in accordance with ISO 9906 Annex A, which requires an accuracy of 8%, which may be insufficient for the requested control activities.
• In practice, the extrapolation carried out according to theoretical laws does not always make it possible to obtain the desired precision.
• The use of a variable speed drive to control the electric motor and thus to suppress the external mechanical measurements introduces a correlation bias between the data available in the control and estimation system, ie the pump curves, and the data of the controller. measurement or estimation available (estimated speed, estimated mechanical power). It is indeed known that, without a sensor of mechanical quantities (position, speed, torque or power) and according to the type of control algorithm used, a variable speed drive may be inaccurate in the estimation of speed and power .

The aim of the invention is to propose a method and a control and identification system making it possible, during a dedicated phase, to ensure the synchronized correlation between the mechanical data applied to the electric motor available in the drive. speed and pump circuit data collected by external sensors. This correlation will make it possible to estimate with very great precision the quantities of the pumping circuit (pressure, flow rate), without using sensors in the pumping circuit, independently of the manufacturer data, that is to say nominal pump curves. .

The purpose of estimating pressure and flow quantities can be either to diagnose the measuring elements or to control or monitor the pumping circuit, without pressure and flow sensors.

Presentation of the invention

• un variateur de vitesse et un moteur électrique commandé par le variateur de vitesse de manière à actionner la pompe centrifuge,
• une mesure ou une estimation par le variateur de vitesse de la puissance mécanique fournie au moteur électrique,
• une électrovanne destinée à commander le circuit de pompage,
• un capteur de pression destiné à mesurer la pression du fluide circulant dans le circuit de pompage,
• un capteur de débit destiné à mesurer le débit du fluide circulant dans le circuit de pompage,
• une unité de commande et de traitement,

ledit procédé comportant une phase d'identification de la pompe centrifuge, mise en oeuvre par l'unité de commande et de traitement, préalablement au fonctionnement normal de ladite pompe centrifuge, ladite phase d'identification comportant :

• une première étape de sélection d'une vitesse et de commande du variateur de vitesse pour appliquer ladite vitesse au moteur électrique,
• une deuxième étape de commande de l'électrovanne sur toute sa plage de fonctionnement à ladite vitesse sélectionnée,
• une troisième étape de mesure de la pression et du débit du fluide circulant dans le circuit de pompage ainsi que de la puissance électrique fournie au moteur pour chaque point de fonctionnement de l'électrovanne,
• une quatrième étape de détermination, pour ladite vitesse sélectionnée, de la courbe de pression en fonction du débit et de la courbe de la puissance fournie en fonction du débit.

This object is achieved by a method of controlling a centrifugal pump included in a pumping circuit controlled by a control system, said control system comprising:

• a variable speed drive and an electric motor controlled by the variable speed drive so as to actuate the centrifugal pump,
• a measurement or estimation by the variable speed drive of the mechanical power supplied to the electric motor,
• a solenoid valve for controlling the pumping circuit,
• a pressure sensor for measuring the pressure of the fluid flowing in the pumping circuit,
• a flow sensor for measuring the flow rate of the fluid flowing in the pumping circuit,
• a control and processing unit,

said method comprising a phase of identification of the centrifugal pump, implemented by the control and processing unit, prior to the normal operation of said centrifugal pump, said identification phase comprising:

• a first step of selecting a speed and controlling the speed variator to apply said speed to the electric motor,
• a second step of controlling the solenoid valve over its entire operating range at said selected speed,
• a third step of measuring the pressure and the flow rate of the fluid flowing in the pumping circuit as well as the electrical power supplied to the motor for each operating point of the solenoid valve,
• a fourth step of determining, for said selected speed, the pressure curve as a function of the flow rate and the curve of the power supplied as a function of the flow rate.

According to a feature, the second step, the third step and the fourth step are implemented for several speeds applied to the electric motor.

According to another feature of the invention, for a selected speed, the third step and the fourth step are implemented for each operating point of the solenoid valve.

• un variateur de vitesse et un moteur électrique commandé par le variateur de vitesse de manière à actionner la pompe centrifuge,
• une mesure ou une estimation par le variateur de vitesse de la puissance mécanique fournie au moteur électrique,
• une électrovanne destinée à commander le circuit de pompage,
• un capteur de pression destiné à mesurer la pression du fluide circulant dans le circuit de pompage,
• un capteur de débit destiné à mesurer le débit du fluide circulant dans le circuit de pompage,
• une unité de commande et de traitement comportant un module d'identification de la pompe centrifuge, activé préalablement au fonctionnement normal de ladite pompe centrifuge,

ledit module d'identification comportant :

• des moyens de sélection d'une vitesse et des moyens de commande du variateur de vitesse pour appliquer ladite vitesse au moteur électrique,
• des moyens de détermination de la puissance fournie au moteur électrique pour ladite vitesse sélectionnée,
• des moyens de commande de l'électrovanne sur toute sa plage de fonctionnement à ladite vitesse sélectionnée,
• des moyens de récupération des mesures de la pression et du débit du fluide circulant dans le circuit de pompage pour chaque point de fonctionnement de l'électrovanne,
• des moyens de détermination, pour ladite vitesse sélectionnée, de la courbe de pression en fonction du débit et de la courbe de la puissance fournie en fonction du débit.

The invention also relates to a control system for a centrifugal pump included in a pumping circuit, said control system comprising:

• a variable speed drive and an electric motor controlled by the variable speed drive so as to actuate the centrifugal pump,
• a measurement or estimation by the variable speed drive of the mechanical power supplied to the electric motor,
• a solenoid valve for controlling the pumping circuit,
• a pressure sensor for measuring the pressure of the fluid flowing in the pumping circuit,
• a flow sensor for measuring the flow rate of the fluid flowing in the pumping circuit,
• a control and processing unit comprising an identification module for the centrifugal pump, activated prior to the normal operation of said centrifugal pump,

said identification module comprising:

• means for selecting a speed and means for controlling the speed variator to apply said speed to the electric motor,
• means for determining the power supplied to the electric motor for said selected speed,
• means for controlling the solenoid valve over its entire operating range at said selected speed,
• means for recovering measurements of the pressure and the flow rate of the fluid flowing in the pumping circuit for each operating point of the solenoid valve,
• means for determining, for said selected speed, the pressure curve as a function of the flow rate and the curve of the power supplied as a function of the flow rate.

According to a particularity, the control and processing unit is included in the variable speed drive.

Brief description of the figures

• la figure 1 représente le circuit de pompage et le système de commande de l'invention,
• la figure 2 représente la séquence appliquée lors de la phase d'identification de la pompe centrifuge,
• les figures 3A et 3B représentent respectivement les courbes de pompe pression/débit et les courbes de pompe puissance moteur/débit caractérisées par la séquence de la figure 2. En gras sont notées les courbes de pompe à la vitesse nominale.

Other features and advantages will appear in the following detailed description with reference to the accompanying drawings in which:

• the figure 1 represents the pumping circuit and the control system of the invention,
• the figure 2 represents the sequence applied during the identification phase of the centrifugal pump,
• the Figures 3A and 3B respectively represent the pressure / flow pump curves and the engine power / flow pump curves characterized by the sequence of the figure 2 . In bold are noted the pump curves at nominal speed.

Detailed description of at least one embodiment

A pumping circuit comprises a centrifugal pump 1 controlled by a control system. Such a control system comprises an electric motor 2 for operating the centrifugal pump and a speed variator 3 for controlling said electric motor.

The architecture of a variable speed drive is well known, it will not be described in this application.

The characterization of the centrifugal pump 1 consists in implementing an identification phase, carried out prior to the normal operation of the pump in the pumping circuit. This identification phase is performed at least once, for example before the first start of the pumping circuit.

The identification phase of the centrifugal pump 1 consists in reconstructing the pump curves for the nominal speed but also at other operating speeds to cover the full operating range. As represented on Figures 3A and 3B , pump curves define, for each speed of the electric motor, the pressure (Pf) of the fluid flowing in the pumping circuit as a function of the flow rate (Df) of the fluid flowing in the pumping circuit ( figure 3A ) and the motor power (Pmot) as a function of the flow rate (Df) of the fluid flowing in the pumping circuit ( figure 3B ).

To reconstruct the pump curves, the control system must also comprise a pressure sensor 4 for measuring the pressure (Pf) of the fluid flowing in the pumping circuit and a flow sensor 5 for measuring the flow (Df). fluid flowing in the pumping circuit. Once the identification phase is over, these sensors are no longer useful and can be removed. Alternatively, the pumping actuator composed of a variable speed drive and a centrifugal pump identified according to the proposed method, can be inserted into another pumping circuit that does not have sensors for pressure and flow quantities, and thus provide a sensorless control of the pumping circuit.

Moreover, to ensure the correlation between the input data and the data collected during the identification phase, the control system comprises a control and processing unit 30 for centralizing the control and the control. treatment. This control and processing unit 30 may for example be a programmable controller or be that which is already present in the variable speed drive 3. In the remainder of the description, it will be considered that the control and processing unit 30 is included. in the drive controller. The control and processing unit 30 comprises a module for identifying the characteristics of the centrifugal pump 1, activated by the operator or activated automatically, for example during the first power-up of the system.

The control system of the invention is represented on the figure 1 . On this figure 1 , the variable speed drive 3 is connected to the electric motor 2 and the electric motor 2 controls the centrifugal pump 1. A solenoid valve 6, placed on the pumping circuit, is controlled directly by the control and processing unit 30. The flow sensor 5 and the pressure sensor 4 are connected directly to the control and processing unit 30 to send their measurement data.

As shown on the figure 2 when the identification module is activated, the identification phase of the centrifugal pump 1 starts. In a first step (E1), the control and processing unit 30 activates control means of the variable speed drive 3 to apply a first speed to the electric motor 2. The speed is for example chosen in a range of 30% at 120% of the nominal speed. In a second step (E2), for said selected speed, the control and processing unit 30 activates control means of the solenoid valve 6 for an operating point. Then, in a third step (E3), for each operating point of the solenoid valve 6, the control and processing unit 30 records the values provided by the pressure sensor 4 (Pf) of the fluid flowing in the pumping circuit and by the flow sensor 5 (Df) of the fluid circulating in the pumping circuit and determines, by measurement or by estimation, the power (PMot) supplied by the variable speed drive 3. All these measurement data are sent to the control and processing unit 30, which records them in storage means (step E4). The control and processing unit 30 repeats the same operations for a new speed to be applied to the electric motor 2, this until sweeping all the speeds. From the data collected, the control and processing unit 30 activates means for determining the pump curves.

• Les courbes de pompe, à différentes vitesses, peuvent être employées lors du fonctionnement normal du circuit de pompage. Un principe d'interpolation peut être utilisé pour estimer le débit et la pression pour une vitesse intermédiaire à deux courbes.
• Le même principe peut aussi être appliqué si uniquement deux courbes sont acquises pour la valeur de vitesse nominale et une valeur de vitesse minimale.
• Un autre principe peut être de stocker uniquement la courbe correspondant à la vitesse nominale et de calculer des coefficients d'ajustement des lois d'affinité à partir des autres courbes de pompe mesurées pour des vitesses inférieures.

Once all the data has been collected, the control and processing unit 30 establishes each pump curve to cover several possible use cases:

• The pump curves, at different speeds, can be used during normal operation of the pumping circuit. An interpolation principle can be used to estimate flow and pressure for an intermediate two-curve velocity.
• The same principle can also be applied if only two curves are acquired for the nominal speed value and a minimum speed value.
• Another principle may be to store only the curve corresponding to the nominal speed and to calculate affinity law adjustment coefficients from the other pump curves measured for lower speeds.

Whatever the principle of use of the pump curves, it is possible to use these curves to estimate the pressure and the flow rate during normal operation of the pumping circuit when the pressure and flow sensors are not present.

Claims (5)

A method of controlling a centrifugal pump (1) included in a pumping circuit controlled by a control system, said control system comprising: - a variable speed drive (3) and an electric motor (2) controlled by the variable speed drive so as to actuate the centrifugal pump, a measurement or an estimation by the variable speed drive of the mechanical power supplied to the electric motor, a solenoid valve (6) intended to control the pumping circuit, a pressure sensor (4) for measuring the pressure of the fluid flowing in the pumping circuit, a flow sensor (5) intended to measure the flow rate of the fluid flowing in the pumping circuit, a unit (30) for controlling and processing, said method being characterized in that it comprises a phase of identification of the centrifugal pump (1), implemented by the control and processing unit (30), prior to the normal operation of said centrifugal pump, said phase identification comprising: a first step of selecting a speed and controlling the speed controller (3) to apply said speed to the electric motor (2), a second step of controlling the solenoid valve (6) over its entire operating range at said selected speed, a third step of measuring the pressure and the flow rate of the fluid flowing in the pumping circuit as well as the electrical power supplied to the motor for each operating point of the solenoid valve (6), a fourth step of determining, for said selected speed, the pressure curve as a function of the flow rate and the curve of the power supplied as a function of the flow rate. Control method according to claim 1, characterized in that the second step, the third step and the fourth step are implemented for several speeds applied to the electric motor (2). Control method according to claim 1 or 2, characterized in that , for a selected speed, the third step and the fourth step are implemented for each operating point of the solenoid valve (6). Control system for a centrifugal pump (1) included in a pumping circuit, said control system comprising: - a variable speed drive (3) and an electric motor (2) controlled by the variable speed drive so as to actuate the centrifugal pump (1), a measurement or an estimation by the variable speed drive of the mechanical power supplied to the electric motor, a solenoid valve (6) intended to control the pumping circuit, a pressure sensor (4) for measuring the pressure of the fluid flowing in the pumping circuit, a flow sensor (5) intended to measure the flow rate of the fluid flowing in the pumping circuit, a unit (30) for controlling and processing, said system being characterized in that the control and processing unit (30) comprises an identification module of the centrifugal pump, activated prior to the normal operation of said centrifugal pump, and in that said identification module comprises: means for selecting a speed and means for controlling the speed variator (3) to apply said speed to the electric motor (2), means for determining the power supplied to the electric motor (2) for said selected speed, means for controlling the solenoid valve (6) over its entire operating range at said selected speed, means for recovering the measurements of the pressure and the flow rate of the fluid flowing in the pumping circuit for each operating point of the solenoid valve (6), means for determining, for said selected speed, the pressure curve as a function of the flow rate and the curve of the power supplied as a function of the flow rate. Control system according to claim 4, characterized in that the control and processing unit (30) is included in the variable speed drive (3).

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