Systems and methods for determining proper phase rotation in downhole linear motors

Abstract

Systems and methods for determining proper phase rotation in a linear motor where the phase rotations associated with power and return strokes are initially unknown. Power having an initial phase rotation is provided to a linear motor until the motor's mover reaches the end of the stroke, and then power to the motor is discontinued. While power is discontinued, the mover is monitored to detect its movement. if the mover moves without power, the mover was at the top of the stroke, so the initial phase rotation is associated with an upward stroke of the mover, and a second phase rotation which is opposite the initial phase rotation is associated with a downward stroke of the mover. Otherwise, the initial phase rotation is associated with the downward stroke of the mover and the second, opposite phase rotation is associated with the upward stroke of the mover.

What is claimed is: 
     
         1 . A method for determining proper phase rotation in a linear electric motor, wherein phase rotations associated with power and return strokes are initially unknown, the method comprising:
 providing power having an initial phase rotation to a linear electric motor;   monitoring a position sensor signals from position sensors in the linear electric motor;   determining from the position sensor signals when a mover of the linear electric motor has reached the end of a stroke driven by the power having the initial phase rotation;   in response to determining that the mover of the linear electric motor has reached the end of the stroke, discontinuing providing power to the linear electric motor;   monitoring the position sensor signals from the position sensors in the linear electric motor;   determining from the position sensor signals whether the mover moves while the power to the linear electric motor is discontinued;   in response to determining that the mover moves while the power to the linear electric motor is discontinued, associating the initial phase rotation with an upward stroke and associating a second phase rotation which is opposite the initial phase rotation with a downward stroke; and   in response to determining that the mover does not move while the power to the linear electric motor is discontinued, associating the initial phase rotation with a downward stroke and associating a second phase rotation which is opposite the initial phase rotation with an upward stroke.   
     
     
         2 . The method of  claim 1 , wherein the linear electric motor comprises a motor of an electric submersible pump (ESP) system and wherein the ESP system is installed in a well; wherein the downward stroke comprises a power stroke of the ESP system and the upward stroke comprises a return stroke of the ESP system; and further comprising, after associating the initial and opposite phase rotations with respective ones of the upward and downward strokes, operating the ESP system, wherein power is provided to the ESP system according to a power stroke profile during the power stroke of the ESP system and according to a return stroke profile during the return stroke of the ESP system. 
     
     
         3 . The method of  claim 1 , wherein determining when the mover of the linear electric motor has reached the end of the stroke driven by the initial phase rotation comprises monitoring position sensor signals from position sensors in the linear electric motor, counting signal transitions sensor signals, and determining that a threshold number of signal transitions have been counted. 
     
     
         4 . The method of  claim 1 , wherein determining when the mover of the linear electric motor has reached the end of the stroke driven by the initial phase rotation comprises determining that the mover of the linear electric motor has reached a hard stop in the motor. 
     
     
         5 . The method of  claim 1 , wherein determining from the position sensor signals whether the mover moves while the power to the linear electric motor is discontinued comprises determining whether any signal transitions are detected in the position sensor signals. 
     
     
         6 . The method of  claim 1 , wherein prior to providing the power having the initial phase rotation to the linear electric motor, the linear electric motor is stopped. 
     
     
         7 . The method of  claim 6 , further comprising, prior to providing the power having the initial phase rotation to the linear electric motor, coupling a multiphase power cable between an electric drive system and the linear electric motor, wherein the electric drive system provides the power the linear electric motor, and wherein prior to providing the power having the initial phase rotation to the linear electric motor, a correspondence of phases at the electric drive system to phases at the linear electric motor is unknown. 
     
     
         8 . An apparatus comprising:
 a controller of an electric drive system for a linear motor, wherein in a startup phase, the controller is configured to
 generate output power for the linear motor, wherein the output power has an initial phase rotation, 
 monitor position sensor signals received from the linear motor, 
 determine from the position sensor signals when a mover of the linear motor has reached the end of a stroke driven by the generated output power having the initial phase rotation, 
 discontinue generating the output power, and 
 monitor the position sensor signals and determine from the position sensor signals whether the mover moves while the output power is discontinued; 
   wherein if the mover moves while the power to the linear motor is discontinued, the controller is configured to associate the initial phase rotation with an upward stroke and associate a second phase rotation which is opposite the initial phase rotation with a downward stroke; and   wherein if the mover does not move while the power to the linear motor is discontinued, the controller is configured to associate the initial phase rotation with the downward stroke and associating the second phase rotation which is opposite the initial phase rotation with the upward stroke.   
     
     
         9 . The apparatus of  claim 8 , wherein the controller is further configured to, after associating the initial and opposite phase rotations with respective ones of the upward and downward strokes, generate output power for the linear motor, wherein the output power is generated according to a first stroke profile during the upward stroke of the linear motor and according to a second stroke profile during the downward stroke of the linear motor. 
     
     
         10 . The apparatus of  claim 8 , wherein the controller is configured to determine when the mover of the linear motor has reached the end of the stroke by counting signal transitions in the received sensor signals and determining that a threshold number of signal transitions have been counted. 
     
     
         11 . The apparatus of  claim 8 , wherein determining from the position sensor signals whether the mover moves while the power to the linear motor is discontinued comprises determining whether any signal transitions are detected in the position sensor signals. 
     
     
         12 . A system comprising:
 an electric submersible pump (ESP) system installed in a well;   an electric drive system positioned at the surface of the well; and   one or more electrical cables coupled between the an electric drive system and the ESP system, wherein the one or more electrical cables carry power from the electric drive system to the ESP system and carry position sensor signals from the ESP system to the electric drive system;   wherein the electric drive system includes a controller for a linear motor of the ESP system;   wherein in a startup phase, the controller is configured to
 generate output power for the linear motor, wherein the output power has an initial phase rotation, 
 monitor the position sensor signals received from the linear motor, 
 determine from the position sensor signals when a mover of the linear motor has reached the end of a stroke driven by the generated output power having the initial phase rotation, 
 discontinue generating the output power, and 
 monitor the position sensor signals and determine from the position sensor signals whether the mover moves while the output power is discontinued; 
   wherein if the mover moves while the power to the linear motor is discontinued, the controller is configured to associate the initial phase rotation with an upward stroke and associate a second phase rotation which is opposite the initial phase rotation with a downward stroke; and   wherein if the mover does not move while the power to the linear motor is discontinued, the controller is configured to associate the initial phase rotation with the downward stroke and associating the second phase rotation which is opposite the initial phase rotation with the upward stroke.   
     
     
         13 . The system of  claim 12 , wherein the electric drive system is configured to, after the initial and opposite phase rotations are associated with respective ones of the upward and downward strokes, provide power to the linear motor, wherein the power is generated by the electric drive system according to a first stroke profile during the upward stroke of the linear motor and according to a second stroke profile during the downward stroke of the linear motor. 
     
     
         14 . The system of  claim 12 , wherein the controller is configured to determine when the mover of the linear motor has reached the end of the stroke by counting signal transitions in the received sensor signals and determining that a threshold number of signal transitions have been counted. 
     
     
         15 . The system of  claim 12 , wherein determining from the position sensor signals whether the mover moves while the power to the linear motor is discontinued comprises determining whether any signal transitions are detected in the position sensor signals. 
     
     
         16 . The system of  claim 12 , wherein the linear motor includes a plurality of Hall-effect position sensors and circuitry that combines a plurality of outputs generated by the Hall-effect position sensors into a composite signal that is communicated to the controller, wherein the position sensor signals comprise the composite signal.