Electrically operated displacement pump control system and method

Abstract

An electrically operated displacement pump includes an electric motor having a stator and a rotor. The rotor is connected to the fluid displacement member to drive axial reciprocation of the fluid displacement member. A drive mechanism is disposed between and connected to each of the rotor and the fluid displacement member. The drive mechanism receives a rotational output from the rotor and provides a linear input to the fluid displacement member. A controller controls operation of the motor based on an operating state of the motor to control pumping by the displacement pump.

1 . A displacement pump for pumping a fluid, the pump comprising:
 an electric motor including a stator and a rotor configured to rotate about a pump axis;   a diaphragm configured to pump fluid and disposed coaxially with the rotor;   a drive connected to the rotor and the diaphragm, the drive configured to convert a rotational output from the rotor into a linear input to the diaphragm; and   a controller configured to operate the pump in a start-up mode and a pumping mode, wherein during the start-up mode the controller is configured to:
 cause the motor to drive the diaphragm in a first axial direction along the pump axis; and 
 determine an axial location of the diaphragm based on the controller detecting a first current spike when the diaphragm encounters a first stop. 
   
     
     
         2 . The displacement pump of  claim 1 , wherein the controller is further configured to determine whether the first stop is a mechanical stop. 
     
     
         3 . The displacement pump of  claim 2 , wherein the mechanical stop corresponds with a travel limit of the diaphragm. 
     
     
         4 . The displacement pump of  claim 2 , wherein the controller is configured to:
 cause the motor drive the diaphragm in a second axial direction opposite the first axial direction;   detect a second stop;   measure a stroke length between the first stop and the second stop; and   compare the measured stroke length to a reference stroke length to determine a stop type of the first stop.   
     
     
         5 . The displacement pump of  claim 4 , wherein the controller is configured to classify at least one of the first stop and the second stop as a fluid stop based on the measured stroke length being less than the reference stroke length. 
     
     
         6 . The displacement pump of  claim 2 , wherein the controller is configured to determine a stop type of the first stop based on a comparison of a plurality of stop locations. 
     
     
         7 . The displacement pump of  claim 6 , wherein the controller is configured to determine that the first stop is a mechanical stop based on the comparison indicating that differences between the plurality of stop locations are less than a threshold difference. 
     
     
         8 . The displacement pump of  claim 6 , wherein the controller is configured to determine that the first stop is a fluid stop based on the comparison indicating at least one difference between the plurality of stop locations exceeds a threshold difference. 
     
     
         9 . The displacement pump of  claim 8 , wherein the fluid stop is due to downstream fluid pressure acting on the diaphragm. 
     
     
         10 . The displacement pump of  claim 1 , wherein the controller is configured to determine a stop type of the first stop based on a slope of a current profile of the first current spike. 
     
     
         11 . The displacement pump of  claim 1 , wherein the axial location is determined based on rotations of the rotor. 
     
     
         12 . A displacement pump for pumping a fluid, the pump comprising:
 an electric motor including a stator and a rotor configured to rotate about a pump axis;   a first fluid displacer configured to pump fluid and disposed coaxially with the rotor;   a second fluid displacer configured to pump fluid and disposed coaxially with the rotor;   a drive connected to the rotor and the first and second fluid displacers, the drive configured to convert a rotational output from the rotor into a linear input to the first and second fluid displacers; and   a controller configured to operate the pump in a start-up mode and a pumping mode, wherein during the start-up mode the controller is configured to:
 cause the motor to drive the first and second fluid displacers in a first axial direction; and 
 determine an axial location of at least one of the first and second fluid displacers based on the controller detecting a first current spike when the at least one of the first and second fluid displacers encounters a first stop; 
   wherein moving the first and second fluid displacers in the first axial direction moves one of the first and second fluid displacers through a pumping stroke and moves the other of the first and second fluid displacers through a suction stroke; and   wherein moving the first and second fluid displacers in a second axial direction opposite the first axial direction moves the one of the first and second fluid displacers through a suction stroke and moves the other of the first and second fluid displacers through a pumping stroke.   
     
     
         13 . A method of operating a reciprocating pump, the method comprising:
 driving, by an electric motor, a first fluid displacer in a first axial direction on a pump axis, the first fluid displacer disposed coaxially with a rotor of the electric motor; and   determining, by a controller, an axial location of the first fluid displacer based on the controller detecting a first current spike due to the first fluid displacer encountering a first stop and the rotor stopping rotation.   
     
     
         14 . The method of  claim 13 , further comprising:
 driving the first fluid displacer in the first axial direction a plurality of times to generate a plurality of stop locations; and   determining, by the controller, a stop type of the first stop based on axial locations of each of the plurality of stop locations.   
     
     
         15 . The method of  claim 14 , further comprising:
 comparing the plurality of stop locations to determine the stop type;   classifying the first stop as a mechanical stop based on differences between the stop locations being less than a threshold difference; and   determining that the first stop is a fluid stop based on the comparison indicating differences between any two of the plurality of stop locations exceeding the threshold difference.   
     
     
         16 . The method of  claim 13 , further comprising:
 driving, by the electric motor, a second fluid displacer in a second axial direction opposite the first axial direction along the pump axis, the second fluid displacer disposed coaxially with the rotor;   detecting a second current spike due to the second fluid displacer encountering a second stop and the rotor stopping rotation; and   determining, by a controller, a measured stroke length based on an axial location of the first current spike and an axial location of the second current spike.   
     
     
         17 . The method of  claim 16 , further comprising:
 comparing the measured stroke length to a reference stroke length; and   classifying at least one of the first stop and the second stop as one of a mechanical stop and a fluid stop based on the comparison of the measured stroke length and the reference stroke length.   
     
     
         18 . The method of  claim 13 , further comprising:
 classifying the first stop as one of a mechanical stop and a fluid stop based on a current profile generated by the first current spike.   
     
     
         19 . The method of  claim 13 , further comprising:
 driving, by the electric motor, a second fluid displacer in a second axial direction opposite the first axial direction along the pump axis, the second fluid displacer disposed coaxially with the rotor; and   determining, by the controller, an axial location of the second fluid displacer based on the controller detecting a second current spike due to the second fluid displacer encountering a second stop and the rotor stopping rotation.   
     
     
         20 . The method of  claim 19 , further comprising:
 recording the locations of the first stop and the second stop as travel limits for the first fluid displacer and the second fluid displacer, such that a distance between the first stop and the second stop defines a maximum stroke length.