Method and control device for variable rotational speed control of a displacement pump unit and displacement pump arrangement

Abstract

A displacement pump arrangement, method for operating the displacement pump arrangement and a control device for controlling the displacement pump arrangement provide rotational-speed-variable control of an expeller pump unit for feeding a fluid. The arrangement includes an expeller pump and a drive, the drive being composed of an electric drive motor and a frequency converter, and a control device. The control device controls a state value such as a final pressure of the expeller pump a setpoint value. The control device detects state values of a control variable are supplied by the drive, in particular relating to the position, rotational speed and torque of the drive motor, and adjusts the displacement pump output to reach the setpoint value without using sensors.

Claims

1. A method for the variable rotational speed control of a displacement pump unit for delivering a fluid, the displacement pump unit including a displacement pump, a drive including an electric drive motor having a stator and a frequency converter, and a control device, comprising the acts of: determining, using the control device, at least one state value of the drive based on drive motor electrical parameters, wherein the at least one state value includes the position of the drive motor and one or both of rotational speed and torque of the drive motor, the drive motor being a sensorless synchronous reluctance motor having a rotor with flux barriers; determining, using the control device, from the at least one state value of the drive a value of a parameter of the displacement pump; and controlling, using the control device, the drive motor using the value of the parameter to control the displacement pump to reach a predetermined pump operation set point value, wherein the drive motor electrical parameters of the sensorless synchronous reluctance motor are obtained by the control device without drive motor rotational speed or position sensors, and the control device is configured to determine when the predetermined set point value is reached based on a relationship between a change in the position of the drive motor and an amount of change of the parameter per unit of position change.

2. The method as claimed in claim 1, wherein the parameter is a delivered fluid volume, the predetermined set point value is a final delivered fluid volume value, and the act of controlling the drive motor to reach the predetermined set point value includes operating the drive motor and comparing using the control device the delivered fluid volume with the final delivered fluid volume value and stopping operation of the displacement pump unit when the delivered fluid volume reaches the final delivered fluid volume value.

3. A control device for controlling a displacement pump and a drive including an electric drive motor provided with stator and rotor and a frequency converter, comprising: a processing device; and a memory device, the control device being configured to use the processing device to determine at least one state value of the drive based on drive motor electrical parameters, wherein the at least one state value includes the position of the drive motor and one or both of rotational speed and torque of the drive motor, determine from the at least one state value a value of a parameter of the displacement pump, and control the drive motor using the value of the parameter to control the displacement pump to reach a predetermined pump operation set point value, wherein the drive motor is controlled with electrical parameters of the drive motor obtained by the control device without drive motor rotational speed or position sensors, and the control device is configured to determine when the predetermined set point value is reached based on a relationship between a change in the position of the drive motor and an amount of change of the parameter per unit of position change stored in the memory device.

4. A displacement pump arrangement, comprising: a displacement pump for delivering a fluid, a variable rotational speed drive, the variable rotational speed drive including an electric drive motor provided with stator and rotor and a frequency converter, a control device, the control device including a processing device; and a memory device, the control device being configured to use the processing device to determine at least one state value of the drive based on drive motor electrical parameters, wherein the at least one state value includes the position of the drive motor and one or both of rotational speed and torque of the drive motor, determine from the at least one state value a value of a parameter of the displacement pump, and control the drive motor using the value of the parameter to control the displacement pump to reach a predetermined pump operation set point value, wherein the drive motor is controlled with electrical parameters of the drive motor obtained by the control device without drive motor rotational speed or position sensors, and the control device is configured to determine when the predetermined set point value is reached based on a relationship between a change in the position of the drive motor and an amount of change of the parameter per unit of position change stored in the memory device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a displacement pump arrangement according to the prior art,

(2) FIG. 2 shows a displacement pump arrangement according to an embodiment of the invention,

(3) FIG. 3 shows a control engineering representation of a pressure control according to an embodiment of the invention,

(4) FIG. 4a shows a control engineering representation of a method sequence according to an embodiment of the invention with regard to initializing the fluid volume determination and valve opening, and

(5) FIG. 4b shows a control engineering representation of a method according to an embodiment of the invention with regard to fluid volume determination and valve closure.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) FIG. 1 shows a displacement pump arrangement 1 according to the prior art in a schematic illustration. A displacement pump 2 is connected on its pressure side 3 and on its suction side 4 to a pipeline system of a plant, not specifically illustrated, and is driven by a shaft 5 by an electric motor 6 comprising rotor and stator, here a conventional asynchronous motor. The electric motor 6 can be operated with a variable rotational speed and is supplied via a frequency converter 7 in a multi-phase manner, three-phase here, with a multi-phase, three-phase here, electric alternating voltage network 9. By a predefined frequency set point f.sub.sp, the frequency converter 7 operates the electric motor 6 at a specific but variable rotational speed. Electric motor 6 and frequency converter 7 form the drive for the displacement pump 2. On the pressure side 3 of the displacement pump 2, by a pressure sensor 10, a signal in accordance with the final pressure p.sub.act of the arrangement 1 is registered and forwarded to a control device 11. The control device 11 is used to control the final pressure p.sub.act of the displacement pump 2 to a predefined final pressure set point p.sub.sp by a frequency set point f.sub.sp. In order to avoid overpressures and to dissipate pressure quickly in such a displacement pump arrangement 1, separate pressure relief valves, not illustrated here, are necessary on the pressure side. Maintaining the required pressure at a delivery rate equal to zero, what is known as the zero delivery rate, is not possible in this arrangement. The time for adjusting the pressure when opening a slide valve arranged on the pressure side, not illustrated here, is prolonged.

(7) FIG. 2 shows a schematic illustration of a displacement pump arrangement 1 according to an embodiment of the invention having a displacement pump unit for delivering a fluid, which comprises a displacement pump 2 and a variable rotational speed drive. The drive is formed by an electric drive motor 6 provided with stator and rotor and a frequency converter 7. The electric motor 6 is connected via the frequency converter 7 in a multi-phase manner, three-phase here, to a multi-phase, three-phase here, electric alternating voltage network 9. A control device 11 controls the displacement pump 2 to a predefined final pressure set point. On the pressure side 3 of the displacement pump 2 there is arranged a valve 13, configured as a shut-off valve, for closing the pipeline on the pressure side. The control device 11 registers the motor state values comprising angular position .sub.act, rotational speed .sub.act and torque M.sub.act of the drive motor 6. The control device 11 has a memory device for the storage of parameters, dependencies and/or characteristic curves. The control device 11 determines the final pressure p.sub.act from the torque M.sub.act in order to control the displacement pump unit to the predefined final pressure p.sub.sp without using sensors. To this end, the control device 11 has the pressure controller 15 shown in FIG. 3 and explained in more detail, which generates a required frequency set point f.sub.sp. According to the invention, as opposed to the prior art, neither a sensor signal of a pressure of the displacement pump nor another sensor is needed. According to the invention, the control device instead uses a motor torque-final pressure dependency of the displacement pump unit stored in the memory device of the control device 11, in order to control the final pressure p.sub.act of the displacement pump by the motor torque-final pressure dependency of the displacement pump unit. Furthermore, the control device 11 is able to determine the fluid volume delivered from the position information .sub.act from the drive motor 6 and a value of the sealed displacement pump volume, the stroke volume and/or to control a predefined fluid delivery rate. Via the actuating signal r, the control device 11 can actuate the shut-off valve 13 and open or close the same. In addition, with the aid of the rotational speed information .sub.act, the accuracy of the pressure determination is improved by the dynamic torque component being taken into account in the starting state.

(8) FIG. 3 shows a control engineering representation of the mode of action of the pressure controller 15 according to the invention. The actual value of the displacement pump final pressure p.sub.act is given by M.sub.act, according to a motor torque-final pressure dependency 17 stored in the memory device of the control device 11. In this exemplary embodiment, this dependency is approximated by a linear model and is given by the following formula together with the constant k.sub.1:
p.sub.act=k.sub.1.Math.M.sub.act(Equation 1)

(9) According to the invention, further models 17 are provided, for example a pressure model which depicts the dynamic starting behavior according to the above equation 2. A control difference e between set point p.sub.sp and calculated controlled variable p.sub.act is fed to a controller 16, here a proportional-integral controller (PI controller), which calculates the required frequency set point f.sub.sp therefrom.

(10) FIG. 4a shows a control engineering representation of a method sequence according to the invention for determining a delivered fluid volume in relation to the initialization and valve opening. FIG. 4b shows, in a corresponding way, the method sequence in relation to the actual volume determination and final valve closure. With a given starting condition (start=1) and in the case of a control difference e lying below a threshold s, by an actuating signal r a valve 13 arranged on the pressure side 3 of the displacement pump 2 is opened and kept open for the start of a delivery with a defined fluid delivery volume V.sub.sp. The condition, according to which the control difference e is to be below a specific threshold, ensures that the desired pressure level is built up before the delivery. In addition, by taking this starting condition into account, the determination of the volume is carried out under the assumption that the displacement pump is completely filled. For the purpose of initializing the determination of quantity, the initial angular position .sub.act,0 is set to the actual value of the motor angular position .sub.act. According to FIG. 4b, the delivered volume V.sub.act, with k.sub.2 as a factor, is given in accordance with the closed delivery volume of the displacement pump (stroke volume) as:
V.sub.act,k=k.sub.2.Math..sub.k(Equation 3)

(11) The determination of volume is carried out cyclically in successive iteration steps identified by index k, where .sub.k represents the value of the entire angular distance swept over by the rotor. In the event that a predefined fluid delivery rate V.sub.sp has been reached (V.sub.act,k>V.sub.sp), the delivery operation is stopped (start=0) and the shut-off valve 13 is closed (r:=0). By such a method, the control device according to the invention determines the fluid volume delivered from the position information .sub.act of the drive motor and the value of the sealed displacement pump volume, and is able to control to a predefined fluid delivery rate V.sub.sp at a predefined pressure.

(12) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.