# Patent

## Title
Energy saving system and method for devices with rotating or reciprocating masses

## Abstract

A system and method are provided for reducing the energy consumed by a pump jack electric motor by reducing the supply voltage to the motor when the motor would be generating energy in open loop mode. By substantially eliminating the energy generation mode, the braking action of the utility grid in limiting the acceleration of the motor and system that would otherwise occur is substantially removed. The motor and system will speed up, allowing the natural kinetic energy of the cyclic motion to perform part of the pumping action. In particular, when the energy consumption for the electric motor connected with the device having a rotating or reciprocating mass goes to zero, the line voltage to the motor is switched off, causing the frequency of the voltage across the motor terminals to increase. When the period of the voltage across the motor terminals returns to substantially the same as the period of the line voltage, the line voltage is switched on or reapplied to the motor.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 13/451,041 filed Apr. 19, 2012 which is a continuation-in-part of co-pending U.S. application Ser. No. 12/873,510 filed Sep. 1, 2010, which claims the benefit of U.S. Provisional Application No. 61/240,399 filed Sep. 8, 2009, and which application is a continuation-in-part of U.S. application Ser. No. 12/207,913 filed Sep. 10, 2008, which claims the benefit of both U.S. Provisional Application 61/135,402 filed Jul. 21, 2008 and U.S. Provisional Application 60/993,706 filed Sep. 14, 2007, all of which applications are hereby incorporated by reference for all purposes in their entirety.
This application also claims the benefit of U.S. Provisional Application No. 61/485,721 filed May 13, 2011, which application is hereby incorporated by reference for all purposes in its entirety.
This application is a continuation-in-part of co-pending U.S. application Ser. No. 12/207,913 filed Sep. 10, 2008, which claims the benefit of both U.S. Provisional Application 61/135,402 filed Jul. 21, 2008 and U.S. Provisional Application 60/993,706 filed Sep. 14, 2007, all of which applications are hereby incorporated by reference for all purposes in their entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electric motors used to operate pump jacks and other devices with rotating or reciprocating masses.
2. Description of the Related Art
A pump jack is an above ground driving device for a reciprocating piston pump installed downhole in an oil well. The pump jack mechanically lifts liquid out of the well when there is not enough bottom hole pressure for the liquid to flow by itself to the surface. The pump jack is often powered by an electric motor that receives electrical power from an electric utility grid. A pump jack converts the rotary mechanism of the electric motor to a vertical reciprocating motion to drive the downhole pump. There are many different designs of pump jacks, including, but not limited to, conventional, the Lufkin Mark II, beam-balanced, air-balanced, slant hole and conventional portable. Pump jacks are available from many different suppliers, including Lufkin Industries, Inc. of Lufkin, Tex. and Cook Pump Company of Coffeyville, Kans.
The pump jack electric motor usually rotates a set of pulleys to a gear system or transmission, which in turn drives a pair of cranks or crank arms. For a typical conventional pump jack design, the cranks raise and lower an end of a lever or beam, known as a “walking beam,” that is pivoted on a sampson post or A-frame. A curved metal box known as a “horse head” is on the other end of the walking beam from where the crank arms are connected with the beam. A counterweight or reciprocating mass is typically attached to one end of the cranks. A pitman arm usually spans between the counterweight and the end of the walking beam opposite the horse head. A cable connects the horse head to a vertical polished rod, which is connected to the vertical string of tubulars or sucker rods running to the downhole pump.
The counterweight assists the motor in lifting the string of sucker rods or tubular string. When the motor lifts the counterweight upward, the horse head moves downward, pushing the sucker rods or tubular string downward. After the counterweight reaches the top of its rotation, it swings around and assists the electric motor to rotate the walking beam in the opposite direction using the counterweight's momentum and mass (kinetic energy). When the counterweight is free-falling downward from its uppermost position, the horse head moves upward, lifting the string of sucker rods upward. U.S. Pat. No. 4,051,736 proposes an improved pump jack for reciprocating an oil well pump.
Although there are different downhole pump designs, downhole pumps have traditionally comprised a plunger or piston reciprocating within a pump barrel located at or near the end of the production tubing. Two independent valves typically accomplish the pumping action. A standing check valve may be secured in the pump barrel beneath the piston, and the piston may include a traveling check valve. The upstroke of the piston opens the standing valve, and draws fluid into the pump barrel as the traveling valve remains closed. The downstroke of the piston opens the traveling valve and forces upward the fluid from the pump barrel as the standing barrel remains closed. U.S. Pat. Nos. 3,578,886; 4,173,451; and 6,904,973 propose downhole pumps.
It is well known that electric motors can enter an energy generation mode of operation. For an electric motor used with a pump jack, an energy generation mode can occur at any time during the rotation of the counterweight, depending on the condition of the balance between the counterweight and the tubular or rod string. The condition of the balance may fluctuate from pumping stroke to stroke, depending on the amount and composition of fluid being lifted by the rod string in each stroke. The polished rod and attached sucker rod or tubular string may be moving upwards or downwards in the energy generation mode.
A well owner must pay his electrical bill based upon the amount of power the pump jack motor consumes. The amount of energy consumed is measured by an energy meter. In the past, the amount of power consumed was measured by an analog electricity meter. Many digital electricity meters are now used. The energy meter, whether of analog or digital design, may be configured, at the discretion of the utility company, to allow or prevent crediting the customer for generated energy that is supplied back to the power grid. A pump jack system is such an inefficient generator that the quantity of consumed energy required to produce any generation significantly exceeds the generated energy. Therefore, regardless of whether the utility company credits generated energy, it is always beneficial to the customer to avoid energy generation.
During periods of generation, an electric motor will attempt to attain a voltage that exceeds the utility's line voltage, thereby causing current to flow in the opposite direction. The load provided by the utility grid serves as a brake, limiting the acceleration of the electric motor that would have otherwise occurred. This braking action of the electric motor prevents the falling weights of the pump jack from developing additional kinetic energy that might have assisted the pumping action. This converted kinetic energy could have served as an alternative to electrical energy from the utility grid.
In the past, engineers have tried unsuccessfully to save significant amounts of energy by turning off the pump jack electric motor during a portion of the pump jack cycle that may have included a period of generation. This has been attempted with various mechanical switches and relays. However, the parameters of the downhole pumps and wells vary over time, so these mechanical solutions have not worked.
Fluid flow in the well may vary as the well fills, and then “pumps off.” In some cases the volume of fluid pumped may change from one stroke to the next. The changing volumes, densities, viscosities, weights, and other properties of materials and/or fluids pumped, such as gas, oil, water, and slurry, may greatly alter the combined weight of the rod string and the column of fluid, thereby affecting the balance of the system and the demand on the electric motor. In some wells the tubular strings may be thousands of feet in length. The influx of different fluids into the well over time will significantly impact the operation of the motor.
With the introduction of the microprocessor, it became possible to turn off the electric motor by observing the current and voltage. However, the problem was knowing when to turn the electric motor back on. Various open-loop time delays were unsuccessfully attempted in the past. The microprocessor solutions also failed since the parameters of the downhole pumps and wells vary over time.
U.S. Pat. No. 6,489,742 proposes a motor controller that includes power conveyance to an induction motor with a digital signal processor that calculates and optimizes supply of current for existent motor loading from a power supply and main voltage through a control element.
U.S. Pat. No. 8,085,009 proposes an IGBT/FET-based energy savings device, system and method wherein a predetermined amount of voltage below a nominal line voltage and/or below a nominal appliance voltage is saved. U.S. Pat. No. 8,085,010 proposes a TRIAC/SCR-based energy savings device, system and method wherein a predetermined amount of voltage below a nominal line voltage and/or below a nominal appliance voltage is saved. U.S. Pat. No. 8,120,307 proposes a system and method for providing constant loading in AC power applications wherein at least one turn-on point of at least one half cycle of a modulating sine wave is determined, at least one turn-off point of the at least one half cycle of the modulating sine wave is determined, and at least one slice located between the at least one turn-on point and the at least one turn-off point in removed. U.S. Pat. No. 8,004,255 proposes a power supply for IGBT/FET drivers that provides separated, isolated power to each IGBT/FET driver.
Proportional-integral-derivative (“PID”) control is a widely used technique applied to control algorithms and feedback mechanisms. A PID controller, as it is generally referred to, calculates a value based upon an “error.” Typically, the “error” is calculated as the difference between a measured process variable and a desired set point or target value. The PID controller attempts to minimize the error by adjusting the process control variables. In essence, the PID controller is a digital filter that has proportional, integral, and derivative parameters. The proportional value determines the reaction to the current error, the integral value determines the reaction based on the sum of the recent errors, and the derivative value determines the reaction based on the rate at which the error has been changing.
The above discussed U.S. Pat. Nos. 3,578,886; 4,051,736; 4,173,451; 6,489,742; 6,904,973; 8,004,255; 8,085,009; 8,085,010; and 8,120,307 are incorporated herein by reference for all purposes in their entirety.
A need exists to efficiently manage the energy usage of a pump jack electric motor, particularly during the energy generation mode.
Energy generated from electrical motors is needlessly wasted in oil wells and other applications where energy generation can occur. The energy generation from the electric motor happens when the balance of the well is imperfect. The balance of the well may be imperfect for a number of reasons, including, but not limited to: (1) varying compositions of oil, water and gas; (2) improper set-up of the well balance at installation; and (3) improper set-up of the well balance after maintenance. There are many additional factors affecting well balance.
In most cases, due to the well imbalance the electric motor is driven to a degree by the heavy portion of the well cycle. The energy generated by the electric motor under such circumstances is passed through the electricity meter in the opposite direction and may result in a credit. However, the trend with modern electricity meters is to disallow this credit. Even if the credit is given, the returned energy must originate from consumption of electrical power. While the motor is an efficient provider of mechanical energy to operate the well, it is a very inefficient generator in conjunction with the well mechanism and pump-rod string.
A need exists for a novel way to eliminate the energy generation from the motor that is fully adaptive to any well and requires no special set up procedures.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of one or more embodiments of the present invention, a closed loop motor controller system reduces the supply voltage to a pump jack electric motor when the motor would be generating energy in open loop mode, when the phase angle between the voltage and current would be greater than 90 degrees. By reducing the supply voltage to the motor, the observed phase angle between voltage and current may be reduced to a value below 90 degrees. Under these conditions, the motor is still not consuming energy. Through pulse width modulation (“PWM”) techniques, the real power component may be reduced virtually to zero, leaving a reactive component greater than zero. By allowing some current flow, primarily of a reactive nature, an observable feedback parameter may be used in the closed loop control system as an indication of the motor load condition, to which the motor controller may react, allowing power to be supplied when needed. Similarly, the closed loop motor controller system may achieve further energy savings by reducing the supply voltage to the motor when the motor is lightly loaded and consuming energy. By minimizing or eliminating energy that would otherwise be consumed by the system, energy savings may result both from reduction of the supply voltage to the motor and from the minimization or elimination of the braking action from the utility grid on the motor. The motor and system will speed up, allowing the natural kinetic energy of the cyclic motion to perform part of the pumping action.
A target phase angle may be supplied either as a constant for all motor loads, or as a variable function of the motor load at any instant. The target phase angle may be equal to or less than 90 degrees, although a target phase angle greater than 90 degrees is also contemplated. When the motor is generating or consuming energy, and the observed phase angle in open loop mode would be greater than the target phase angle, the system may reduce the supply voltage until the observed phase angle is substantially the target phase angle. Any further reduction in the observed phase angle below the target phase angle may be interpreted as an increase in motor load, such as during the energy consumption mode, to which the system may respond by increasing the supply voltage until the target phase angle is once again reached. The necessary information may be computed from the observed phase angle between the voltage and current consumed by the motor.
According to one aspect of one or more embodiments of the present invention, the line (or grid) voltage and the voltage across the electric motor terminals are monitored. During a first time segment, the electric motor is consuming energy while driving the rotating or reciprocating mass. When the energy consumption of the electric motor goes to zero during the pumping cycle, the supply voltage to the electric motor is switched off, and the electric motor enters a second time segment. An increase in frequency of the voltage across the electric motor terminals will occur during this second time segment. The cyclic period of the electric motor voltage during this second time segment will be shorter than the period of the line (or grid) voltage. When the period of the electric motor voltage returns to substantially the same as the period of the line (or grid) voltage, the grid power is switched back on to the electric motor, ending the second time segment and reentering the first time segment again. The switching back on of the power may occur at a zero crossing point and when the transitions from positive to negative, or negative to positive, between the line (or grid) voltage and the electric motor voltage are the same. The first and second time segments may be repeated. A microprocessor in conjunction with memory identifies the point at which power may be reapplied to the electric motor.
Other aspects of the present invention will be apparent from the following description and the appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
A better and further understanding of the present invention can be obtained with the following detailed descriptions of the various disclosed embodiments in the drawings in which like parts are given like reference numerals, and wherein:
FIG. 1 is a block diagram of a digital signal processor (DSP) with hardware inputs and outputs in accordance with one or more embodiments of the present invention.
FIG. 2 is a block diagram of a DSP-based motor controller in accordance with one or more embodiments of the present invention.
FIG. 3 is a diagram showing a phase rotation detection method in accordance with one or more embodiments of the present invention.
FIG. 4 is a flow chart showing a phase rotation detection method in accordance with one or more embodiments of the present invention.
FIG. 5 is a graph showing power control device outputs for positive phase rotation in accordance with one or more embodiments of the present invention.
FIG. 6 is a graph showing power control device outputs for negative phase rotation in accordance with one or more embodiments of the present invention.
FIG. 7 is a block diagram of a window comparator in accordance with one or more embodiments of the present invention.
FIG. 8 is a schematic of the window comparator in accordance with one or more embodiments of the present invention.
FIG. 9 is a graph of a current waveform and zero-cross signals in accordance with one or more embodiments of the present invention.
FIG. 10 is a schematic of a virtual neutral circuit in accordance with one or more embodiments of the present invention.
FIG. 11 is a graph showing power control device outputs for single phase applications in accordance with one or more embodiments of the present invention.
FIG. 12 is a three-dimensional graph showing a three-dimensional control line in accordance with one or more embodiments of the present invention.
FIG. 13 is a three-dimensional graph showing a control line projected onto one plane in accordance with one or more embodiments of the present invention.
FIG. 14 is a graph showing a two-dimensional plotted control line in accordance with one or more embodiments of the present invention.
FIG. 15 is a graph showing a sweeping firing angle/duty cycle in a semi-automatic calibration in accordance with one or more embodiments of the present invention.
FIG. 16 is a graph showing a directed sweep of a firing angle/duty cycle in accordance with one or more embodiments of the present invention.
FIG. 17 is a graph showing plotted semi-automatic calibration data in accordance with one or more embodiments of the present invention.
FIG. 18 is a graph showing plotted semi-automatic calibration data in accordance with one or more embodiments of the present invention.
FIG. 19 is a graph showing plotted semi-automatic calibration data in accordance with one or more embodiments of the present invention.
FIG. 20 is a flow chart of a semi-automatic high level calibration in accordance with one or more embodiments of the present invention.
FIG. 21 is a flow chart of a semi-automatic high level calibration in accordance with one or more embodiments of the present invention.
FIG. 22 is a flow chart of a manual calibration in accordance with one or more embodiments of the present invention.
FIG. 23 is a flow chart of a fixed voltage clamp in accordance with one or more embodiments of the present invention.
FIG. 24 is a graph showing a RMS motor voltage clamp in accordance with one or more embodiments of the present invention.
FIG. 25 is a graph showing a RMS motor voltage clamp in accordance with one or more embodiments of the present invention.
FIG. 26 is a flow chart of a stall mitigation technique in accordance with one or more embodiments of the present invention.
FIG. 27 is a graph showing the stall mitigation technique in accordance with one or more embodiments of the present invention.
FIG. 28 is an elevational view of one embodiment of a pump jack positioned with a tubular string in a well in accordance with one or more embodiments of the present invention.
FIG. 29 is a plot of observed phase angle versus time for a pump jack motor in an open loop mode in accordance with one or more embodiments of the present invention.
FIG. 30 is the system block diagram connected to the motor in accordance with one or more embodiments of the present invention.
FIG. 31 is a plot of observed phase angle versus time for a pump jack motor in a closed loop control mode with a reduction of motor voltage to achieve a target phase angle within one complete pumping cycle in accordance with one or more embodiments of the present invention.
FIG. 32 is a single phase waveform plot of incoming line voltage in accordance with one or more embodiments of the present invention.
FIG. 32A is a heavily chopped single phase waveform plot of the voltage supplied to the motor after the application of PWM techniques in accordance with one or more embodiments of the present invention.
FIG. 32B is a lightly chopped single phase waveform plot of the voltage supplied to the motor after the application of PWM techniques in accordance with one or more embodiments of the present invention.
FIG. 32C is a variably chopped single phase waveform plot of the voltage supplied to the motor after the application of PWM techniques in accordance with one or more embodiments of the present invention.
FIG. 32D is the plot of FIG. 31 illustrating the periods when heavy chopping, light chopping, and no chopping may occur in accordance with one or more embodiments of the present invention.
FIG. 33 is a block diagram of a motor controller disposed between an existing control panel and a pump jack electric motor in accordance with one or more embodiments of the present invention.
FIG. 34 is a schematic oscillogram showing an increase in frequency of voltage across a motor in accordance with one or more embodiments of the present invention.
FIG. 35 is a flow diagram showing a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention.
FIG. 36 is a flow diagram showing a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention.
FIG. 37 is a flow diagram showing a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Specific embodiments of the present invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. Further, in the following detailed description of embodiments of the present invention, numerous specific details are set forth to provide a more thorough understanding of the present invention. In other instances, well-known features have not been described in detail to avoid obscuring the description of embodiments of the present invention.
With reference to FIG. 1, a block diagram of a digital signal processor (“DSP”) 1 and hardware inputs and outputs is shown. The DSP 1 can observe the operational characteristics of a motor and make corrections to root mean square (“RMS”) voltage for the motor that is running and under closed loop control. Hardware inputs 2 capture phase zero crossing inputs 36, phase line voltage 37, phase motor voltage 38 and current 9 and passed through the DSP 1 for processing and then onto power control devices through the power control device outputs 14.
Referring now to FIG. 2, a block diagram of a system and method of the DSP-based motor controller 4 is shown. First, the motor controller 4 reads the voltages 37 of each phase A, B and C and current 9 to capture the zero-crossing inputs 36. At this point voltage 13 and current 9 may be converted from analog to digital using converters 62. Next, computations 63 of motor phase angle for each phase are calculated to yield an observed phase angle 5. Next, a target phase angle 10 which has been derived from a preprogrammed control line 6 is compared to the observed phase angle 5. The difference between the target phase angle 10 and observed phase angle 5 yields a resulting phase error signal (11, 28) which is processed by a PID controller 12 which has proportional, integral and differential components. The output from the PID controller 12 is the new control voltage (13, 29) to the motor 3, which can be obtained through the use of power control devices 33, such as TRIACs, SCRs, IGBTs or MOSFETS, to yield power control device outputs 14 of RMS motor voltage 13 supplied with line voltages 50 for each phase for maximum energy savings.
In this closed loop system, the voltage 13 of each phase of the motor 3 and the current are continually monitored. The motor controller 4 will drive the observed phase angle 5 to the point on the calibrated control line 6 corresponding to the load that is on the motor. At this point, maximum energy savings will be realized because the control line 6 is based on known calibration data from the motor 3. The motor controller 4 can control the motor 3 just as if a technician set the voltage 13 by hand. The difference is that the DSP 1 can dynamically respond to changes in the load in real-time and make these adjustments on a cycle by cycle basis.
Referring now to FIG. 3, in a three-phase system, the motor controller 4 is used to automatically determine the phase rotation. Zero-crossing detectors on the line voltages provide an accurate measurement of the angle between the phase A line voltage zero crossings 15 and the phase B line voltage zero crossings 16. For positive phase rotation 18, the angle is nominally 120° and for negative phase rotation 19, the angle is nominally 60°.
Referring to FIG. 4, a flow chart for phase rotation detection is shown. After a power-on-reset (“POR”) 20, it is easy for the motor controller 4 to determine positive phase rotation 18 and the negative phase rotation 19. First, the time is measured from phase A line voltage zero crossings to phase B line voltage zero crossings 39. Next it is determined if the time is greater than or less than 90 degrees 40. If it greater than 90 degrees, then it is an ACB rotation 42. If the time is less than 90 degrees, then it is an ABC rotation 41. The motor controller 4 can control three-phase or single-phase motors with the same basic software and hardware architecture. For the three-phase case, depending on the phase rotation, the motor controller 4 can drive power control device outputs 14.
Referring now to FIG. 5 which shows power control device outputs for positive drive rotation, the motor controller drives phase A power control device outputs 14 and phase B power control device outputs 14 together during the phase A line voltage zero crossings 15 turn-on time as indicated by the oval 22a. Similarly, the motor controller drives power control devices which drive phase B 16 and phase C power control device outputs 14 together during the phase B turn-on time as indicated by the oval 22b. Finally, the motor controller 4 drives phase C 17 and phase A power control device outputs 14 together during the phase C power control device outputs 14 turn-on time as indicated by the oval 22c. Note that the example shown in FIGS. 5 and 6 depicts a firing angle/duty cycle 23 of 90°.
Referring now to FIG. 6 which shows the TRIAC drive outputs for negative phase rotation, the motor controller 4 drives phase A power control device outputs 14 and phase C power control device outputs 14 together during the phase A line voltage zero crossings 15 turn-on time as indicated by the oval 22c. Similarly, the motor controller 4 drives phase B 16 and phase A power control device outputs 14 together during the phase B line voltage zero crossings 16 turn-on time, as indicated by oval 22a. Finally, the motor controller drives phase C power control device outputs 14 and phase B power control device outputs 14 together during the phase C line voltage zero crossings 17 turn-on time, as indicated by oval 22b. 
Now referring to FIG. 7, a block diagram of a window comparator is shown. The DSP based motor controller uses the window comparator 88 to detect zero-crossings of both positive and negative halves of a current wave form. When RMS motor voltage is reduced by the motor controller, it is difficult to detect zero crossings of current waveform because the current is zero for a significant portion of both half cycles. First, motor current is provided 89, a positive voltage is provided 90 as a reference for a positive half cycle and a negative voltage is provided 91 as a reference. Next, the current, positive voltage and negative voltage are presented to two comparators 92 and are then passed through an OR gate 93 to create a composite zero-cross digital signal 94.
As further illustrated in FIG. 8, a schematic of the window comparator 88 is shown. The motor current is provided 89, a positive voltage is provided 90 as a reference for a positive half cycle and a negative voltage is provided 91 as a reference. Next, the current, represented as a positive voltage and negative voltage, is processed by two comparators 92 and are then passed to an OR gate 93 to create a composite zero-cross digital signal 94.
Further, FIG. 9 shows graphs of a current waveform 95, a positive voltage half cycle 96, a negative voltage half cycle 97 and an OR function 98.
Now referring to FIG. 10, a schematic of a virtual neutral circuit is shown. A virtual neutral circuit may be used as a reference in situations where three phase power is available only in delta mode and there is no neutral present for use as a reference. The virtual neutral circuit comprises three differential-to-single-ended amplifiers 77. Because phase to phase voltages are high, input resistors 78 are used to form a suitable attenuator 79 together with feedback resistors 80 and ground reference resistors 81. Because the danger exists of a loss of phase, protection diodes 82 are used to protect the differential-to-single-ended amplifiers 77. The differential-to-single-ended amplifiers 77 are coupled to a summing amplifier 83 through DC blocking capacitors 84 and summing resistors 85 together with the feedback resistor 80. The output of the summing amplifier 83 is boosted by amplifier 27 thereby providing a low impedance output which is at neutral potential. Additional resistors divide a supply rail thereby allowing the summing amplifier 83 to handle alternating positive and negative signals. An alternate connection is available in the event that a neutral 86 is available along with a jumper block for alternate neutral connection 87.
Referring now to FIG. 11 showing a power control device output 14 for a single-phase application, the output 14 for phase A is turned on each half-cycle based on a power control device output 14 derived from the voltage zero-crossing input 15. The power control device output 14 for phase B line voltage zero crossings and phase C line voltage zero crossings are disabled in the DSP 1 and the hardware may not be present. The power control device outputs 14 are not paired as they were in the three-phase case.
Referring now to FIG. 12 which illustrates a three-dimensional control line for the motor operating space of a motor bounded by an observed phase angle 5 on the y-axis. A controlled firing angle/duty cycle 23 showing the decrease in voltage is shown on the x-axis and the percent load 24 on a motor is shown on the z-axis.
Every motor operates along a parametrical control line 25 within its operating space. For example, when a given motor is 50% loaded and the firing angle/duty cycle 23 is set to 100°, a phase angle 5 of approximately 55° is observed.
The parametrical control line 25 shown in FIG. 12 is defined by five parametric operating points 26 ranging from a loaded case 44 in the upper left corner, to an unloaded case 45 in the lower right corner. Furthermore, the parametrical control line 25 has special meaning because it is the line where a motor is using the least energy possible. If the firing angle/duty cycle 23 is increased and the motor voltage 13 decreased then a motor would slow down and possibly stall. Similar results would be seen if the load on the motor 3 is increased.
As illustrated in FIG. 13, the parametric control line 25 may be parameterized and projected onto one plane described by phase angle 5 in the vertical direction and the firing angle/duty cycle 23 in the horizontal direction.
Further, as shown in FIG. 14, the parametrical control line 25 may be displayed on a two-dimensional graph. On the x-axis, increasing firing angle/duty cycle 23 may be equated with a decreasing motor voltage. This is because small firing angle/duty cycles result in high voltage and large firing angle/duty cycles result in low voltage. The motor controller will drive the observed phase angle 5 to the point on the control line 25 that corresponds to the load presently on a motor. To accomplish this, a DSP computes the phase angle 5 between the voltage and current.
Referring back to the block diagram of FIG. 2, the DSP 1 then computes the next target phase angle 5 based on the present value of the RMS voltage 13, or equivalently the present value of the firing angle/duty cycle. The difference between the observed phase angle and the target phase angle 10 results in a phase angle error, which is processed through a PID controller 12 or similar device to generate a new control target. This control target changes the voltage in such a way as to minimize the phase angle error. The target phase angle 10 is dynamic and it changes as a function of the firing angle/duty cycle.
As stated above, the motor controller 4 will drive the observed phase angle 5 to the point on the control line 25 that corresponds to the load presently on the motor 3. This operating point 26 provides the maximum energy savings possible because the control line 25 is calibrated directly from the motor 3 that is being controlled.
This method for calibration is called semi-automatic calibration. The semi-automatic calibration is based on the DSP 1 sweeping the control space of the motor. As shown in FIG. 15, sweeping the control space means that the DSP increases the firing angle/duty cycle 23 and records the current 9 and firing angle/duty cycle 23 of each phase at discrete points along the way. Thus, in this manner it is possible to see the beginning of the stall point 21 of the motor. A well-defined linear portion of observed calibration data curve obtained from sweeping the control space 7, which is used to determine points on the control line 6, has a constant negative slope at lower firing angle/duty cycles 23. Then, as the firing angle/duty cycle 23 continues to increase, the current 9 begins to flatten out and actually begins to increase as the motor 3 begins to slip and starts to stall, called the “knee” 31.
As shown in FIG. 16, subsequent sweeps can be directed at smaller ranges of motor voltages to “zoom in” on the knee. The motor controller 4 requires multiple sweeps in order to get data that is statistically accurate. There is a tradeoff between the number of sweeps and the time required to calibrate the control line 25. A measure of the quality of the calibration can be maintained by the DSP 1 using well known statistical processes and additional sweeps can be made if necessary. This is true because the DSP 1 has learned the approximate location of knee 31 from the first sweep.
There is little danger of stalling during the semi-automatic sweep because of the controlled environment of the setup. A technician or operator helps to insure that no sudden loads are applied to the motor 3 under test while a semi-automatic calibration is in progress.
The process of sweeping the control space can be performed at any fixed load. For example, it can be performed once with the motor 3 fully loaded and once with the motor 3 unloaded. These two points become the two points that define the control line 25. It is not necessary to perform the calibration at exactly these two points. The DSP 1 will extend the control line 25 beyond both these two points if required.
There are many numerical methods that can be applied to find the stall point 21 in the plot of the current motor voltage 23. As shown in FIG. 17, a method is to use the “least squares” method to calculate a straight line that best fits the accumulated data tabulated from the first five motor voltages 23.
The continuation of this method is shown in FIG. 18. Using the previous data points the value of the current 9 may be predicted. Graphically, the DSP 1 is checking for one or more points that deviate in the positive direction from the predicted straight line.
As shown in FIG. 19, the DSP 1 is looking for the beginning of the knee in the curve. The first point that deviates from the predicted control line may or may not be the beginning of the knee 31. The first point with a positive error may simply be a noisy data point. The only way to verify that the observed calibration data curve obtained from sweeping the control space 7 is turning is to observe data obtained from additional sweeps.
Semi-automatic calibration may be performed in the field. Referring now to FIG. 20, a flow chart showing how semi-automatic calibration is performed is shown. First the motor 3 is placed in a heavily loaded configuration 44. Ideally this configuration is greater than 50% of the fully rated load. Next a calibration button 32 on the motor controller 4 is pressed to tell the DSP 1 to perform a fully-loaded measurement. The DSP 1 runs a calibration 46 which requires several seconds to explore the operating space of the motor 3 to determine the fully-loaded point. The motor controller 4 indicates that it has finished this step by turning on an LED.
Next the motor 3 is placed in an unloaded configuration 45. Ideally this configuration is less than 25% of the rated load. Then a calibration button 32 on the motor controller 4 is pressed 47 to tell the DSP 1 to perform an unloaded measurement. The DSP 1 runs the calibration 46 to determine the unloaded point. The motor controller 4 indicates that it has finished calibrating both ends 47 of the control line 25 by turning on a light emitting diode (“LED”). The DSP 1 then determines the control line 48 using the two measurements and applies this control line when it is managing the motor 3. The values of the control line 25 are stored in non-volatile memory 49.
FIG. 21 shows a more detailed flow chart of the semi-automatic calibration. First a first calibration sweep is run 46 with the motor voltage set at a certain degree 51, depending on if it is a first sweep or previous sweeps have been run 106, in which the motor controller measures the motor 52 until the motor controller detects a knee 53. If a knee 53 is detected the firing angle/duty cycle is decreased by two degrees 54 and the phase angle and the motor voltage are recorded to the memory 55. This process is repeated to obtain at least four sweeps 56 to get a computed average value 57 of the phase angle and the firing angle/duty cycle. If during any step along the calibration sweep, the knee is not detected, then the firing angle/duty cycle is increased by at least one degree 58 and the nest step is measured 59.
An alternative method for calibration is called manual calibration. FIG. 22 shows a flow chart of manual calibration. First a motor is placed on a dynamometer 70. Next the motor is connected to a computer for manual control 71 which allows the motor to be run in a open-loop mode and the firing angle/duty cycle of the AC induction motor to be manually set to any operating point. Then the motor is placed in a fully unloaded configuration 45. Next the firing angle/duty cycle is increased and the RMS motor voltage is reduced 72 until the motor is just about to stall. The firing angle/duty cycle and phase angle are recorded and this becomes a calibrated point which is recorded 73. Then the motor is started with drive elements fully on 74. Then the motor is placed in a fully loaded configuration 44. Next the firing angle/duty cycle is increased or decreased until the RMS motor voltage is chopped by the motor controller 75 until the motor is just about to stall. The firing angle/duty cycle are recorded and this becomes another calibrated point which is recorded 73. Finally the two calibrated points are used to form a control line 76.
When the RMS line voltage is greater than a programmed fixed-voltage, the DSP controller clamps the RMS motor voltage at that fixed voltage so energy savings are possible even at full load. For example, if the mains voltage is above the motor nameplate voltage of 115V in the case of a single phase motor then the motor voltage is clamped at 115V. This operation of clamping the motor voltage, allows the motor controller to save energy even when the motor is fully loaded in single-phase or three-phase applications.
FIG. 23 shows a flow chart of the fixed voltage clamp. First a phase error is computed 64. Next a voltage error is computed 65. Then the RMS motor voltage of the AC induction motor is determined and compared to a fixed voltage threshold 66. If the RMS motor voltage is greater than the fixed voltage threshold then it is determined whether or not control target is positive 67. If the control target is positive then a voltage control loop is run 68. If the RMS motor voltage of the AC induction motor is less than a fixed-voltage threshold, then the a control line closed loop is run 69 and the entire process is repeated. If the control target is determined not to be positive then a control line loop is run 69 and the entire process is repeated again.
In some cases, it may not be possible to fully load the motor 3 during the calibration process. Perhaps 50% is the greatest load that can be achieved while the motor is installed in the field. Conversely, it may not be possible to fully unload the motor; it may be that only 40% is the lightest load that can be achieved.
FIG. 24 shows an example of both load points being near the middle of the operating range. On the unloaded end 45 at the right of the control line 25, the DSP 1 will set the fixed voltage clamp 60 of the voltage at minimum voltage 35. When the load on the motor increases, the DSP 1 will follow the control line moving to the left and up the control segment 61. This implementation is a conservative approach and protects the motor 3 from running in un-calibrated space.
As further shown in FIG. 25, on the fully loaded end 44 at the left, the DSP 1 will synthesize a control segment 61 with a large negative slope. This implementation is a conservative approach and drives the voltage to full-on.
Referring now to FIG. 26, the DSP-based motor controller uses a special technique to protect a motor from stalling. First, the DSP actively monitors for a significant increase in current 99 which indicates that load on the motor has increased. Next, if a significant increase is observed 100 then the DSP turns motor voltage to full on 101. Next, the DSP will attempt to reduce motor voltage to return to the control 102 and the DSP returns to actively monitoring for a significant increase in current 99. This technique is a conservative and safe alternative to the DSP attempting to track power requirements that are unknown at that time.
As further shown in FIG. 27, a graph of the stall mitigation technique, the load on the motor is represented on an x-axis and time is represented on a y-axis. The bottom line represents the load on the motor 103 and the top line represents the power applied to the motor by the DSP 104. Prior to point a 105, the DSP is dynamically controlling the motor at a fixed load. In between point a 105 and point b 30, the load on the motor is suddenly increased and the DSP turns the motor voltage to full on. At point c 34, the DSP reduces the motor voltage to point d 43.
In FIG. 28, a pump jack 30′ is positioned on the ground adjacent well W. Prime mover or motor 6′ drives gear system or transmission 8′ with drive belt 18′. Motor 6′ may be connected with a electric utility grid for the supply of power. One end of counterweight arm or crank arm 10′ is disposed with gear system 8′, and the other end of counterweight arm 10′ is disposed with counterweight or rotating mass 12′. There are preferably two counterweight arms 10′, with counterweight 12′ disposed between them. Lever or walking beam 2′ pivots on sampson post or A-frame 14′. One end of pitman arm or beam arm 16′ is rotationally attached with one end of beam 2′, and the other end of beam arm 16′ is rotationally attached with rotating mass 12′ and an end of counterweight arm 10′. Beam protrusion or head 4′ is disposed on the end of beam 2′ adjacent to well W. As can now be understood, pump jack 30′ has a conventional design.
One end of cable 20′ is attached with beam head 4′, and the other end of cable 20′ is attached with polished rod or rod 22′. Rod 22′ is disposed with the substantially vertical tubular string or sucker rods 26′ extending in the well W through the production tubing to the downhole pump 28′. Tubular string may comprise sucker rods, pipe, tubulars, or other components used with a pump jack or other similar device to assist in pumping or lifting fluids from a well. The motor 6′ may drive the pump jack 30′ by rotating an end of the counterweight arm 10′ about a horizontal axis. As the counterweight 12′ moves upward, beam 2′ pivots about a horizontal axis on A-frame 14′ and moves the beam head 4′ downward. As the counterweight 12′ moves past its uppermost position, it free-falls downward due to gravity and its momentum, and beam 2′ pivots about A-frame 14′ and moves beam head 4′ upward. The pushing and pulling of the string of tubulars 26′ by the beam head 4′ operates the piston in the downhole pump 28′. The tubular string 26′ moves and reciprocates substantially vertically in the well W.
The motor 6′ is normally in energy consumption mode. However, the motor 6′ may be in the energy generation mode when the falling masses (either the counterweight 12′ or the rod or tubular string 26′) are free-falling, thereby accelerating the motor 6′ beyond its synchronous speed, where the speed is limited by the generated current. Although an exemplary conventional pump jack 30′ is shown in FIG. 28, it is contemplated that all pump jack designs, including, but not limited to, different conventional designs, the Lufkin Mark II design, beam-balanced design, and conventional portable design may be used with the embodiments of the invention. Although the embodiments are shown with pump jacks, it is also contemplated that all of the embodiments may be used with any device having a rotating or reciprocating mass.
Turning to FIG. 29, plot 36′ with observed phase angle on the vertical axis 32′ and time on the horizontal axis 34′ is shown for an electric motor attached to a pump jack, such as motor 6′ and pump jack 30′ in FIG. 28, in open loop mode. The embodiments of the invention described below with FIGS. 30-32D have not been attached to the electric motor; therefore, the motor is in the open loop mode. Second horizontal line 40′ is drawn at an observed phase angle of 90 degrees on the vertical axis 32′. When the plot 36′ exceeds an observed phase angle of 90 degrees, which it does in plot first segment 42′ above second horizontal line 40′, then the motor is in the energy generation mode. At those times when the motor is generating, rather than consuming energy, the current lags the voltage by a phase angle in excess of 90 degrees. The greater the phase angle during generation, the greater the power being generated. The motor is in the heavy energy consumption mode in plot second segment 44′ below first horizontal line 38′. First horizontal line 38′ is drawn at a target phase angle less than 90 degrees on the vertical axis 32′. The target phase angle is discussed in detail below with FIGS. 30 and 31.
In FIG. 30, closed loop motor controller 50′ is schematically shown connected to an electric motor 62′, such as motor 6′ in FIG. 28, which may be connected with a pump jack, such as pump jack 30′ in FIG. 28. Other pump jack designs are also contemplated for use with FIG. 30. Motor controller 50′ may be a PID controller. However, other closed loop motor controllers are also contemplated. A DSP based motor controller is contemplated, such as the DSP based motor controller in FIGS. 1 and 2, although other types of DSP based motor controllers are also contemplated. Closed loop motor controller 50′ may be connected with motor (6′, 62′) in the same manner as shown in FIGS. 1 and 2. A microprocessor based controller is also contemplated. In one embodiment, the closed loop controller system may have a PID controller as a component. In the closed loop control system or servo system 48′, controller 50′ may compute 52′ the observed phase angles from the voltage and current supplied to the motor 62′.
Advantageously, no sensors need to be positioned with the motor (6′, 62′), the pump jack 30′ or the downhole pump 28′. Further, the closed loop system 48′ may be adaptive to each individual downhole pump and to changing parameters and requirements of the pump and well over time, including, but not limited to, changing volumes, densities, viscosities, weights, and other properties of materials and/or fluids pumped, such as gas, oil, water, and slurry. Voltage and current monitored by the system 48′ serve as an indicator of the well condition, allowing the system to be adaptive to the changing well parameters. Monitoring the voltage and current on a substantially continuous basis allows for a substantially continuous reading of well conditions. The closed loop system 48′ also adapts when the existing components of the pump jack system are replaced with other components having different characteristics, such as for example replacing the tubular string with a different tubular string having a different weight, or replacing the counterweight with a different sized counterweight, provided that the mechanical system is rebalanced after the components are substituted. After rebalancing of the mechanical system, the embodiments of the invention allow the energy savings to resume.
A target phase angle 58′ input into the controller 50′ may be compared with the computed observed phase angle 52′, and the error 60′ or difference between the two values determined by the controller 50′. It is contemplated that the target phase angle 58′ may be substantially 90 degrees, or the target phase angle 58′ may be greater or less than 90 degrees. At the time of installation, a target phase angle 58′ may be selected that produces optimum results for the motor in use. The target phase angle 58′ may be constant for all motor loads, such as 65 degrees, although other constant target phase angles 58′ are also contemplated. The target phase angle 58′ may also be a variable function of the motor load at any instant. The setting for the target phase angle 58′ may be the lowest possible target phase angle that maintains a sufficiently observable current flow at all times while still supplying sufficient power to meet the motor's requirements at all loads.
The motor controller 50′ may control the supply motor voltage 54′ applied to motor 62′ based upon the error 60′. When the error 60′ is significant because the observed phase angle is too large, such as during the period of open loop energy generation mode, controller 50′ may reduce the supply motor voltage to the motor 62′ to a lower value, such as to reduce the observed phase angle 52′ to the target phase angle 58′. When the error 60′ is significant because the observed phase angle 52′ is too small, such as during the heavy energy consumption mode, controller 50′ may increase the supply voltage 54′ to the motor 62′ to a higher value to move the observed phase angle 52′ to the target phase angle 58′. In this closed loop system 48′, the voltage and current may be continuously monitored and controlled by the motor controller 50′. It is also contemplated that the supply voltage 54′ may be controlled through the use of power control devices, such as TRIACs, SCRs, IGBTs, or MOSFETs, as shown in FIG. 2. Also, controller 50′ uses timers and pulse width modulation (“PWM”) techniques to control the supply voltage, which are discussed in detail below with FIGS. 32-32D. Other techniques are also contemplated.
Returning to FIG. 30, the controller 50′ reads the voltages of each phase and current in the motor 62′ to capture the zero-crossing points. FIGS. 5 and 6 of U.S. Pat. No. 8,085,009 B2 propose an oscillogram and circuitry diagram, respectively, of a volts zero crossing point determining means that is contemplated. Other types of volts zero crossing point determining means are also contemplated. Voltage and current may be converted from analog to digital using one or more analog to digital converters for monitoring and/or control purposes, as shown in FIG. 2. Controller 50′ may perform computations 52′ of motor phase angle to yield an observed phase angle. Controller 50′ may compare the observed phase angle 52′ with the target phase angle 58′ and control the supply motor voltage 54′ in response. The phase angle may be monitored in one or more phases. Controller 50′ may be used to automatically determine the phase rotation. A circuit diagram of a phase support means and phase rotation determination means that is contemplated is proposed in FIG. 7 of U.S. Pat. No. 8,085,009, where multiple phase operations are employed.
Further, it is contemplated that the voltages may be monitored from phase-to-phase or from phase-to-neutral. A schematic of a contemplated virtual neutral circuit is in FIG. 10. Other virtual neutral circuits are also contemplated. A virtual neutral circuit may be used as a reference in situations where three phase power is available only in delta mode and there is no neutral present for use as a reference. It is also contemplated that a window comparator may be used to detect zero-crossings of both positive and negative halves of a current wave form. A window comparator is illustrated in FIGS. 7 and 8. Other window comparators are also contemplated. FIGS. 8, 9 and 10 of U.S. Pat. No. 8,085,009 propose a circuit diagram and then two oscillograms, respectively, of a half cycle indentifying means that is contemplated.
Turning to FIG. 31, plot 64′ with observed phase angle on the vertical axis 32′ and time on the horizontal axis 34′ is shown for an electric motor attached with a pump jack, such as motor 6′ and pump jack 30′ in FIG. 28, in closed loop mode. As in FIG. 29, there is a target phase angle of less than 90 degrees at first horizontal line 38′. Unlike in FIG. 29, the electric motor output represented in FIG. 31 is from a closed loop system 48′ disposed with the motor as shown in FIG. 30. Plot first segment 70′ in FIG. 31 is where the observed phase angle would exceed the target phase angle in open loop mode. However, in closed loop mode in plot first segment 70′ the error signal 60′ creates a control effort by the controller 50′ to reduce the supply voltage 54′ to the motor to maintain the target phase angle 38′. When the observed phase angle would exceed 90 degrees in open loop mode, the large values of observed phase angle create large values of the error signal 60′ in FIG. 30.
During plot first segment 70′, the motor is effectively turned off using PWM techniques, but without actually cutting the power to the motor. There is still current flowing in the motor during this time, which allows the controller 50′ to know when to increase the supply voltage to the motor needed during the energy consumption mode. The real component of the current may be reduced virtually to zero, leaving a reactive component greater than zero. By allowing some current flow when it is reducing voltage, mostly of a reactive nature, an observable feedback parameter is provided that is used in the closed loop control system 48′ as an indication of the load condition, to which the controller 50′ may react, supplying power when needed in the energy consumption phase.
Since the current is of reactive nature, the only power remaining is of an apparent nature. The current flow allows the controller to continuously observe the phase angle between the current and the voltage. The maximum motor voltage reduction occurs approximately at plot first location 66′ in FIG. 31 when the observed phase angle in open loop mode as shown in FIG. 29 would otherwise be at its maximum value greater than 90 degrees.
When the observed phase angle exceeds the target phase angle in closed loop mode, the supply voltage may be reduced with PWM techniques until the observed phase angle reaches the target phase angle. At the beginning of plot first segment 70′ in FIG. 31, the motor controller 50′ reduces the observed phase angle from open loop mode down to the target phase angle. The controller 50′ thereafter maintains the observed phase angle substantially at the target phase angle. Any further reduction in observed phase angle below the target phase angle may be interpreted as an increase in load, to which the controller 50′ may respond by increasing the supply voltage 54′ until the target phase angle is once again reached. The maximum increase of supply voltage to the motor occurs at plot second location 68′ when the observed phase angle drops below the target phase angle. When the counterweight or reciprocating mass is driven by the motor, the values of the observed phase angle will typically be smaller than the target phase angle, which will create an error signal that creates a control effort by the controller 50′ to increase the supply voltage to the motor. The motor is in the heavy energy consumption mode in plot second segment 44′ below first horizontal line 38′.
Turning to FIG. 32, waveform plot 200 of incoming line voltage is illustrated in single phase, although three-phase voltage is also contemplated. In FIG. 32A, PWM techniques have been used to chop out or remove voltage waveform plot segments 204 while leaving voltage waveform plot segments 202. FIG. 32A illustrates heavy chopping of the supply voltage in which large segments 204 of the voltage waveform are chopped out. FIG. 32B illustrates light chopping of the voltage waveform with PWM techniques, wherein the voltage waveform plot segments 206 that are chopped out are smaller than the chopped out segments 204 shown in FIG. 32A. In FIG. 32B, the waveform plot segments 208 that are left are larger than the waveform plot segments 202 that are left in FIG. 32A.
The heavy chopping in FIG. 32A occurs during the period that open loop energy generation mode would be occurring, such as in FIG. 31 at plot first location 66′. In FIG. 32D, the period of heavy chopping is illustrated at plot segment 210. The reduction of voltage shown in FIG. 32A reduces the real component of the current virtually to zero, while leaving a reactive component greater than zero. This is the period when the motor is effectively turned off, while still leaving sufficient current to observe the phase angle.
When the motor is in heavy energy consumption mode, such as occurs in FIG. 31 at plot second segment 44′, then substantially no voltage waveform segments are eliminated, and the motor supply voltage is substantially as shown in FIG. 32. In FIG. 32D, the period of substantially no chopping occurs at plot segment 212.
In FIG. 32D, the DSP controller is in control mode at plot locations 226 and 228. During those periods, the motor is not in heavy energy consumption mode and not in the period when open loop energy generation mode would be occurring. In control mode, light chopping as shown in FIG. 32B may occur or variable chopping as shown in FIG. 32C may occur to control the motor voltage. This may happen when the motor is lightly loaded, saving energy while the motor is still consuming energy. Variable chopping in FIG. 32C uses PWM to chop waveform plot segments (214, 216, 218, 220, 222, 224) of varying sizes to control the motor voltage. The size of the voltage waveform plot segments (214, 216, 218, 220, 222, 224) chopped in FIG. 32C may all be different, leaving voltage waveform plot segments that are also all different sizes.
It should be understood that the motor controller may use any combination or permutation of light chopping, heavy chopping, variable chopping or no chopping to control the observed phase angle of the motor supply voltage to the target phase angle. The DSP or motor controller attempts to maintain a substantially constant observed phase angle and will chop the amount required to do so. The DSP controls the motor voltage based on observing the phase angle. The amount of the chopping of the supply voltage may vary.
When the electric motor running open loop is in energy generation mode, the load presented by the utility grid effectively acts as a brake on the motor, thereby limiting its speed. This occurs due to the generated voltage attempting to exceed the voltage presented by the utility, thereby causing the current presented to flow in the opposite direction. When the closed loop controller system and method is applied as shown in FIGS. 30-32D, this braking action may be effectively minimized or removed, and the motor and system will typically speed up during this time. This additional kinetic energy stored in the system will be used to perform a portion of the pumping action without consuming energy in the motor. Minimizing or substantially preventing energy generation eliminates the need to consume energy in other parts of the pumping cycle, thereby saving energy.
As can now be understood, the electric power supplied to the motor is “effectively” turned off during the energy generation mode that would occur in open loop, while maintaining the feedback signals of voltage and current to determine when to turn the electric motor back on when the observed phase angle is diminishing. This system and method will constantly adapt to changing parameters in the well, which could not be done in the past. For one example, the motor and system are adaptive to pumping two or more fluids at different times having different densities or weights. Voltage and current monitored by the system serve as an indicator of the well condition, allowing the system to be adaptive to the changing well parameters. By not entering the energy generation mode, the braking action that is created by the open loop energy generation mode may be minimized or eliminated, so the benefit of speed up in the system is obtained. By minimizing or eliminating energy that would otherwise be consumed by the system, energy savings may result both from reduction of the supply voltage to the motor and from the minimization or elimination of the braking action of the motor when in generation mode.
All types and designs of electric motors are contemplated for use with the different embodiments of the invention described above, including, but not limited to, AC induction motors and AC synchronous motors. All types and designs of pump jacks are contemplated for use with the different embodiments of the invention described above, including, but not limited to, all conventional designs, the Lufkin Mark II design, beam-balanced design, and conventional portable design. Although the embodiments have been shown with pump jacks, it is also contemplated that all of the embodiments described above may be used with any device having a rotating or reciprocating mass. Although some of the embodiments have been shown with single phase voltage and current, all of the embodiments of the invention are contemplated with single or multiple phase voltage and current.
In one or more embodiments of the present invention, power provided by an electric utility grid or other line source to power an electric motor that is itself configured to power a pump jack may be selectively removed and then reapplied to the electric motor such that the electric motor does not consume nor provide power from or to the electric utility grid or other line source during a period of generation by the electric motor.
The point at which the power to the motor is removed is the point where the consumption of the motor substantially goes to zero. This may be achieved by monitoring the observed phase angle and comparing it with a target phase angle, such as 90 degrees. At that point, the switch off point may be activated. At the time of switch off there is no power applied to the motor. The motor may be disconnected from the power controller. Under such circumstances, without the motor generated power being returned to the electric utility grid, the potential electrical energy exists as kinetic energy in the overall rotating and reciprocating mechanism. This energy causes the well cyclic times to increase. Since the motor is still mechanically connected to the accelerating rotating or reciprocating mass or machine, the motor's rotational speed increases. Under these circumstances, the potential energy of the motor, in generation, will exhibit an increase in frequency of the voltage across its terminals. The cyclic period of the motor voltage will be shorter than the period of the grid voltage.
To ascertain the point at which the power should be reapplied to the motor, the period of the line voltage is compared to the period of the generated voltage. When the period of the generated voltage returns to substantially the same as the period of the line voltage, the power can be reapplied to the motor. It is contemplated that when the cyclic period of the generated voltage is substantially the same as the line voltage, the power may be turned back on at a zero crossing point when the transitions are identical. Turning power back on at a zero crossing assures that there will be no current spikes. Also, matching the transitions from positive to negative, or visa versa, of the line voltage and the generated voltage allows for smooth transitions. Measuring the periods can be achieved through use of zero crossing techniques applied to both the line and motor volts. A microprocessor in conjunction with memory can identify the point at which power can be re-applied. Other systems are also contemplated.
Returning to FIG. 30, an exemplary installation of a closed loop motor controller 50′ implementing the method is schematically shown connected to an electric motor 62′, which may be connected with a pump jack. Motor controller 50′ may be a PID controller. However, other closed loop motor controllers are also contemplated. A DSP based motor controller is contemplated, such as the DSP based motor controllers in FIGS. 1 and 2, although other types of DSP based motor controllers are also contemplated.
Closed loop motor controller 50′ may be connected with motor 62′ in the same manner as shown in FIGS. 1 and 2. A microprocessor based controller is also contemplated. In one embodiment, the closed loop controller system may have a PID controller as a component. In the closed loop control system or servo system 48′, controller 50′ may compute 52′ the observed phase angles from the voltage and current supplied to the motor 62′.
Turning to FIG. 33, another exemplary installation of a motor controller 410 implementing the method is shown. Motor controller 410 may be the same as motor controller 50′. Motor controller 410 may be inserted in electrical connection between the existing electrical control panel 405 and the electric motor 415 that drives the pump jack 420. The electric power supply may run through a utility meter 400 to the control panel 405.
In FIG. 34, first plot 500 is the exemplary line or grid voltage, shown with a frequency of 60 Hz and first plot half period 505. The zero intersect-to-intersect 505 forms one half cycle of one of the 60 Hz periods. The zero crossing is used rather than the peak as the zero crossing is easier to more accurately determine the exact start and exact finish point. The peak of the sign wave first plot 500 is difficult to determine since the rate of change at the peak is the slowest transition and the zero cross is the fastest point. The motor (62′, 415) is supplied with the line voltage during the first time segment when the motor (62′, 415) is consuming power to drive the rotating or reciprocating mass. The motor (62′, 415) ceases to consume energy during the well pumping cycle when the observed phase angle exceeds a target phase angle, such as 90 degrees. At that time, the supply voltage to the motor (62′, 415) is switched off, and the second time segment is entered.
As discussed above, the motor's rotational speed increases during the second time segment when the motor (62′, 415) is removed from the electric grid as the reciprocating or rotating mass accelerates. The potential energy of the motor (62′, 415) exhibits an increase in frequency of the voltage across the motor's terminals. Second plot 510, third plot 520, and fourth plot 530 are exemplary voltages across the motor at different times during the second time segment when the motor (62′, 415) has been disconnected from the line voltage. The reciprocating or rotating mass accelerates and causes the motor (62′, 415) to rotate faster. Second plot 510 is at a frequency of 63 Hz, third plot 520 is at a frequency of 66 Hz, and fourth plot 530 is at a frequency of 69 Hz. Other frequencies are also contemplated.
Second plot cyclic half period 515, third plot cyclic half period 525, and fourth plot cyclic half period 535 are all shorter than the first plot cyclic half period 505 of the grid voltage or first plot 500. The zero intersect-to-intersect 515 forms one half cycle of one of the 63 Hz periods. The zero intersect-to-intersect 525 forms one half cycle of one of the 66 Hz periods. The zero intersect-to-intersect 535 forms one half cycle of one of the 69 Hz periods. When the cyclic period of the voltage across the motor (62′, 415) returns to substantially equal the cyclic period of the grid voltage or first plot 500, then the power is switched back on to the motor (62′, 415), and it reenters the first time segment. It is also contemplated that when the cyclic period of the generated voltage is substantially the same as the line voltage, the power may be turned back on at the zero crossing point when the transitions are identical. The first time segment and second time segment are thereafter repeated as described above.
With regard to FIG. 34, it can be seen that the higher rate or frequency is accompanied by a shorter period in time. The pump and/or rotating or reciprocating mass accelerates when the power supply to the motor is removed, and the period between the zero crossings shortens. This will continue to a maximum deviation, and then reduce back to the period of the line power. During the second time segment, the microprocessor will continually monitor and compare the periods. When the period is substantially equal to the period of the line power, the line power will be turned back on to fulfill the work requirement of the pumping cycle.
In FIG. 35, a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention is shown. In Step S1, a utility grid or line voltage and current is full on to an electric motor during a first time segment where the electric motor is connected with the pump jack. In Step S2, the pump jack counterweight is in a consumption mode while being rotated by the electric motor during the first time segment. In Step S3, a phase angle between the utility grid or line voltage and current supplied to the electric motor during the first time segment is observed and measured. In Step S4, the observed phase angle is compared with a target phase angle during the first time segment. If the observed phase angle is not greater than the target phase angle, then Step S3 is repeated. In Step S5, the line voltage and current to the electric motor is switched or turned off when the observed phase angle is greater than the target phase angle. In Step S6, a generated motor voltage of the electric motor is observed during a second time segment initiated by the switching off of the line voltage and current to the electric motor in Step S5. In Step S7, a period of the generated motor voltage of the electric motor is determined or measured during the second time segment. In Step S8, a period of the line voltage is determined during the second time segment. In Step S9, the period of motor voltage is compared to the period of the line voltage. If the period of the motor voltage is not substantially equal to the period of the line voltage then the Step S7 and Step S8 measurements are taken again and compared at Step S9. When the period of the generated motor voltage becomes substantially equal to the period of the line voltage, then the motor line voltage and current are switched or turned on and reapplied to the electric motor in Step S10.
In FIG. 36, a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention is shown. In Step T1, electric utility grid or line voltage and current are supplied to an electric motor connected with the pump jack during a first time segment. In Step T2, the pump jack counterweight is in a consumption mode while being rotated by the electric motor during the first time segment. In Step T3, the phase angle between the electric utility grid or line voltage and current supplied to the motor during the first time segment is observed and measured. In Step T4, the observed phase angle is compared with a target phase angle during the first time segment. In Step T5, the electric utility grid or line voltage and current are switched or turned off to the electric motor when the observed electric motor phase angle is greater than the target phase angle. If not, Step T3 is repeated. In Step T6, an electric motor voltage across the electric motor during a second time segment after the step of switching off in Step T5 is monitored or observed. In Step T7, the pump jack counterweight is rotated during the second time segment with the motor speeding up initially causing a cyclic period of the electric motor voltage across the electric motor to be shorter than a cyclic period of the electric utility grid or line voltage. In Step T7, the motor speeds up initially during the generation mode, then the motor slows down. The period of the motor voltage is measured during Step T7. In Step T8, a period of the line voltage is determined or measured during the second time segment. In Step T9, the cyclic period of the electric motor voltage across the electric motor is compared with the cyclic period of the electric utility grid or line voltage during the second time segment. In Step T10, the electric utility grid or line voltage and current are switched full on to the electric motor when the cyclic period of the electric motor voltage returns to substantially equal to the cyclic period of the electric utility grid or line voltage. If the period of motor voltage is not substantially equal to the period of the line voltage, then the Step T7 and Step T8 measurements are taken again and compared at Step T9.
In FIG. 37, a method of saving energy for a pump jack with a counterweight disposed with a well in accordance with one or more embodiments of the present invention is shown. In Step L1, electric utility grid or line voltage and current are supplied to an electric motor connected with the pump jack during a first time segment. In Step L2, the pump jack counterweight is in a consumption mode while being rotated by the electric motor during the first time segment. In Step L3, the phase angle between the electric utility grid or line voltage and current supplied to the electric motor during the first time segment is observed and measured. In Step L4, the observed phase angle is compared with a target phase angle during the first time segment. In Step L5, the electric utility grid or line voltage and current are switched or turned off to the electric motor when the observed electric motor phase angle is greater than the target phase angle. If the observed phase angle is not greater than the target phase angle, then Step L3 is repeated. In Step L6, an electric motor voltage across the electric motor is monitored or observed during a second time segment after the Step L5 of switching off. In Step L7, the pump jack counterweight is rotated during the second time segment, with the motor speeding up initially, causing a cyclic period of the electric motor voltage across the electric motor to be shorter than a cyclic period of the electric utility grid voltage. The electric motor period is measured in Step L7. In Step L8, a period of the line voltage is determined or measured during the second time segment. In Step L9, the cyclic period of the electric motor voltage across the electric motor is compared with the cyclic period of the electric utility grid or line voltage during the second time segment. If the period of motor voltage is not substantially equal to the period of line voltage, then Step L7 and Step L8 are repeated. If the voltages are equal, then Step L10 is run. In Step L10, the electric utility grid or line voltage and current are checked as to whether the electric motor is at a zero crossing point when the cyclic period of the electric motor voltage returns to substantially equal to the cyclic period of the electric utility grid or line voltage. If a transition from positive to negative of the electric motor voltage occurs at substantially the same time as a transition from positive to negative of the electric utility grid or line voltage, then in Step L11 the motor voltage is turned full on. If not, Step L10 is repeated or run again.
Advantageously, in one or more embodiments of the present invention, the method of saving energy for a pump jack with a counterweight disposed with a well selectively removes power to the motor when the consumption of the motor substantially goes to zero, thereby saving energy.
Advantageously, in one or more embodiments of the present invention, the method of saving energy for a pump jack with a counterweight disposed with a well is fully adaptive to any well and requires no special setup procedures.
Advantageously, in one or more embodiments of the present invention, the method of saving energy for a pump jack with a counterweight disposed with a well can utilize existing electric motors and pump jacks.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

## Claims

1. A method of saving energy for an electric motor coupled to a rotating mass, the method comprising:
detecting a line voltage and a current supplied to the electric motor;
observing a phase angle between the line voltage and the current;
comparing the observed phase angle with a target phase angle;
switching-off the line voltage to the electric motor when the observed phase angle is greater than the target phase angle;
monitoring a motor voltage generated at the electric motor while the line voltage is switched off;
determining a period of the voltage generated at the electric motor;
determining a period of the line voltage;
determining a line zero crossing point corresponding to the line voltage;
determining a motor zero crossing point corresponding to the voltage generated at the electric motor; and
switching-on the line voltage to the electric motor when:
the period of the voltage generated at the electric motor is substantially equal to the period of the line voltage; and
the line zero crossing point substantially matches the motor zero crossing point.

2. The method of claim 1, wherein monitoring the motor voltage generated at the electric motor is performed continuously while the line voltage is switched off.

3. The method of claim 1, wherein said target phase angle is 90 degrees.

4. The method of claim 1, wherein monitoring the motor voltage is performed with a microprocessor.

5. The method of claim 1, wherein switching-on the line voltage is performed when the voltage generated at the electric motor transitions from positive to negative at substantially a same time as when the line voltage transitions from positive to negative.

6. A system for saving energy for an electric motor coupled to a rotating or reciprocating mass, the system comprising:
a processor; and
a non-transitory computer-readable storage medium that stores instructions for controlling the processor to perform steps comprising:
detecting a line voltage and a current supplied to the electric motor;
observing a phase angle between the line voltage and the current;
comparing the observed phase angle with a target phase angle;
switching-off the line voltage to the electric motor when the observed phase angle is greater than the target phase angle;
monitoring a motor voltage generated at the electric motor while the line voltage is switched off;
determining a period of the voltage generated at the electric motor;
determining a period of the line voltage; and
switching-on the line voltage to the electric motor when the period of the voltage generated at the electric motor is substantially equal to the period of the line voltage.

7. The system of claim 6, wherein the non-transitory computer readable storage medium further stores instructions for controlling the processor to perform steps comprising:
determining a line zero crossing point corresponding to the line voltage;
determining a motor zero crossing point corresponding to the voltage generated at the electric motor; and
switching-on the line voltage to the electric motor when the line zero crossing point substantially matches the motor zero crossing point.

8. The system of claim 7, wherein the non-transitory computer readable storage medium further stores instructions for controlling the processor to switch-on the line voltage when the voltage generated at the electric motor transitions from positive to negative at substantially a same time as when the line voltage transitions from positive to negative.

9. The system of claim 6, wherein the non-transitory computer readable storage medium further stores instructions for controlling the processor to continuously monitor the motor voltage generated at the electric motor while the line voltage is switched off.

10. The system of claim 6, wherein the target phase angle is 90 degrees.

11. The system of claim 6, wherein the non-transitory computer readable storage medium further stores instructions for controlling the processor to continuously determine the period of the voltage generated at the electric motor while the line voltage is switched off.

12. The system of claim 6, wherein the non-transitory computer readable storage medium further stores instructions for controlling the processor to continuously determine the period of the line voltage while the line voltage is switched off from the electric motor.

13. The system of claim 6, wherein the rotating mass includes a counterweight provided on a pump jack.

14. A non-transitory computer-readable storage medium storing instructions which, when executed by a device having an electric motor and a processor, cause the processor to perform steps comprising:
detecting a line voltage and a current supplied to the electric motor;
observing a phase angle between the line voltage and the current;
comparing the observed phase angle with a target phase angle;
switching-off the line voltage to the electric motor when the observed phase angle is greater than the target phase angle;
monitoring a motor voltage generated at the electric motor when the line voltage is switched off;
determining a period of the voltage generated at the electric motor;
determining a period of the line voltage; and
switching-on the line voltage to the electric motor when the period of the voltage generated at the electric motor is substantially equal to the period of the line voltage.

15. The non-transitory computer-readable storage medium of claim 14, which further stores instructions that cause the processor to perform steps comprising:
determining a line zero crossing point corresponding to the line voltage;
determining a motor zero crossing point corresponding to the voltage generated at the electric motor; and
switching-on the line voltage to the electric motor when the line zero crossing point substantially matches the motor zero crossing point.

16. The non-transitory computer-readable storage medium of claim 15, which further stores instructions that cause the processor to switch-on the line voltage when the voltage generated at the electric motor transitions from positive to negative at substantially a same time as when the line voltage transitions from positive to negative.

17. The non-transitory computer-readable storage medium of claim 14, which further stores instructions that cause the processor to continuously monitor the motor voltage generated at the electric motor while the line voltage is switched off.

18. The non-transitory computer-readable storage medium of claim 14, which further stores instructions that cause the processor to continuously determine the period of the voltage generated at the electric motor while the line voltage is switched off.

19. The non-transitory computer-readable storage medium of claim 14, which further stores instructions that cause the processor to continuously determine the period of the line voltage while the line voltage is switched off from the electric motor.

20. The non-transitory computer-readable storage medium of claim 14, which further stores instructions that cause the processor to set the target phase angle at 90 degrees.