Abstract: Systems and methods for determining the existence of a pump-off condition in an ESP system and controlling the motor to prevent fluid pound that would otherwise result from the pump-off condition. The current drawn by the ESP motor during a power stroke is monitored and the instantaneous force generated by the motor is determined from the instantaneous current. Pump-off conditions may be indicated by sudden, large decreases in the generated force, smaller decreases in force that occur over a longer period, or forces below those seen during a dwell time. In response to detecting a pump-off condition, the motor may be stepped through the rest of the stroke, temporarily halted and re-initialized, thereby preventing potentially damaging fluid pound that would otherwise result from the pump-off condition.

Abstract: Systems and methods for operating linear motors, and for determining whether a linear motor has reached the end of its power and return strokes. In one embodiment, an electric drive controller of an ESP system monitors position signals received from the system's linear motor and determines transition time differentials, transition counts from the beginning of a stroke, elapsed stroke times and related parameters. If predetermined conditions relating to these parameters are met, the controller determines that the linear motor's mover has reached the end of its stroke. The controller therefore reverses the phase order of the drive's output power and thereby reverses the direction of the mover.

Abstract: Systems and methods for determining the existence of a pump-off condition in an ESP system and controlling the motor to prevent fluid pound that would otherwise result from the pump-off condition. The current drawn by the ESP motor during a power stroke is monitored and the instantaneous force generated by the motor is determined from the instantaneous current. Pump-off conditions may be indicated by sudden, large decreases in the generated force, smaller decreases in force that occur over a longer period, or forces below those seen during a dwell time. In response to detecting a pump-off condition, the motor may be stepped through the rest of the stroke, temporarily halted and re-initialized, thereby preventing potentially damaging fluid pound that would otherwise result from the pump-off condition.

Abstract: Systems and methods for operating linear motors, and for determining whether a linear motor has reached the end of its power and return strokes. In one embodiment, an electric drive controller of an ESP system monitors position signals received from the system's linear motor and determines transition time differentials, transition counts from the beginning of a stroke, elapsed stroke times and related parameters. If predetermined conditions relating to these parameters are met, the controller determines that the linear motor's mover has reached the end of its stroke. The controller therefore reverses the phase order of the drive's output power and thereby reverses the direction of the mover.

Abstract: Systems and methods for determining the instantaneous force generated by a motor. In one embodiment, AC power (e.g., three-phase power) is provided to a linear motor of an ESP. An instantaneous current for each of the phases is measured at a particular point in time. These instantaneous current vectors are used to determine an instantaneous force by, for example, computing a root-mean-square of the instantaneous current vectors and multiplying the root-mean-square by a power factor. The instantaneous force computation may be performed successively for multiple, distinct points in time, and these computed force values may be used to form a graphical representation of the force generated by the linear motor over the stroke of the motor. The computed force values may also be used as the basis for controlling the motor.