Positive displacement pump controller and method of operation

1. A pumping system comprising:

an electric motor;

a piston disposed within a piston cylinder;

a drive shaft configured to be rotatably driven by the electric motor;

a connecting arm;

an eccentric connected between the drive shaft and the connecting arm, wherein the eccentric and the connecting arm convert rotation of the drive shaft into linear reciprocation of the piston within the piston cylinder; and

a controller communicatively coupled to the electric motor;

wherein the controller is configured to operate the electric motor in a first mode and a second mode;

wherein in the first mode the controller causes the electric motor to rotate the drive shaft through a series of full rotations in which the drive shaft rotates continuously in a first rotational direction to cause a first series of stroke cycles of the piston, each stroke cycle of the first series of stroke cycles comprising one upstroke and one downstroke of the piston; and

wherein in the second mode the controller causes the electric motor to oscillate the drive shaft in a series of arc cycles corresponding to a second series of stroke cycles of the piston, each arc cycle of the series of arc cycles comprises the drive shaft rotating through a first arc in the first rotational direction less than one full rotation and through a second arc in a second rotational direction less than one full rotation, each stroke cycle of the second series of stroke cycles comprising one upstroke and one downstroke of the piston, and

wherein each stroke cycle of the first series of stroke cycles causes greater displacement of the piston than each stroke cycle of the second series of stroke cycles.

2. The pumping system of claim 1 , wherein in the second mode the controller causes the drive shaft to oscillate back and forth within a region, causing the piston to complete a partial upstroke and a partial downstroke within the piston cylinder.

3. The pumping system of claim 2 , wherein the region is one of a first high pressure region, a second high pressure region, a first high flow region, and a second high flow region.

4. The pumping system of claim 3 , wherein:

the first high pressure region corresponds to an oscillation of the eccentric about a 12 o'clock position;

the second high pressure region corresponds to the oscillation of the eccentric about a 6 o'clock position;

the first high flow region corresponds to the oscillation of the eccentric about a 3 o'clock position; and

the second high flow region corresponds to the oscillation of the eccentric about a 9 o'clock position.

5. The pumping system of claim 2 , wherein in the second mode the controller causes the drive shaft rotate through a first pre-determined angular rotation in the first rotational direction and rotate through a second pre-determined angular rotation in the second rotational direction.

6. The pumping system of claim 1 , wherein the controller is configured to cause the electric motor to switch the electric motor from the first mode to the second mode; and wherein the controller is configured to cause the electric motor to switch the electric motor from the second mode to the first mode.

7. The pumping system of claim 1 , wherein oscillating the drive shaft comprises:

increasing a speed of the drive shaft in the first rotational direction until the speed reaches a first speed;

decreasing the speed of the drive shaft in the first rotational direction until the drive shaft stops rotation in the first rotational direction; and

increasing the speed of the drive shaft in the second rotational direction until the speed reaches the first speed.

8. The pumping system of claim 7 , wherein in the second mode the controller is configured to:

increase a torque of the drive shaft in the first rotational direction until the torque reaches a peak value;

decrease the torque of the drive shaft in the first rotational direction until the drive shaft stops rotation in the first rotational direction; and

increase the torque of the drive shaft in the second rotational direction until the torque reaches the peak value, wherein the peak value of the torque is less than a maximum torque threshold.

9. The pumping system of claim 1 , wherein the controller operates the electric motor in the first mode or the second mode based on a fluid pressure set-point or a fluid flow set-point.

10. The pumping system of claim 1 , wherein the controller operates the electric motor in the first mode or the second mode based on one or more of a speed of the electric motor, a torque of the electric motor, electric current supplied to the electric motor, and a position of the drive shaft.

11. The pumping system of claim 1 and further comprising an intermediate drive, wherein the intermediate drive is positioned between the electric motor and the drive shaft, and wherein the intermediate drive is coupled to both the electric motor and the drive shaft such that the intermediate drive receives input rotation from the electric motor and the intermediate drive outputs rotation to the drive shaft.

12. A method of operating a pumping system including a piston disposed within a piston cylinder, a drive shaft rotatably driven by an electric motor, an eccentric connected between the drive shaft and a connecting arm, the eccentric and the connecting arm configured to convert rotation of the drive shaft into linear reciprocation of the piston within the piston cylinder, and a controller communicatively coupled to the electric motor, the method comprising:

causing, by the controller, the electric motor to operate in a first mode in which the electric motor rotates the drive shaft through a series of full rotations in which the drive shaft rotates continuously in a first rotational direction to cause a first series of stroke cycles of the piston, each stroke cycle of the first series of stroke cycles comprising one upstroke and one downstroke of the piston; and

causing, by the controller, the electric motor to operate in a second mode in which the electric motor oscillates the drive shaft in a series of arc cycles corresponding to a second series of stroke cycles of the piston, each arc cycle of the series of arc cycles comprises the drive shaft rotating through a first arc in the first rotational direction less than one full rotation and through a second arc in a second rotational direction less than one full rotation, each stroke cycle of the second series of stroke cycles comprising one upstroke and one downstroke of the piston;

wherein each stroke cycle of the first series of stroke cycles causes greater displacement of the piston than each stroke cycle of the second series of stroke cycles.