JPH11132155A - Pump off control method - Google Patents

Abstract

(57) [Problem] To provide a pump-off control method that can detect a pump-off state at low cost and that does not stop the motor when the pump is off. SOLUTION: The average value or the effective value of the instantaneous value of the secondary current of the induction motor is compared with the average reference value or the effective reference value after the end of the downstroke of each cycle, and the instantaneous value is compared with the average reference value or the effective value reference value. When the average value or the effective value is large, the occurrence of pump-off is detected. Also, when the pump-off condition is continuously detected more than once after the end of the downstroke, the pump jack speed is reduced by a preset speed, and a new secondary current average value reference value corresponding to the reduced speed is set. Alternatively, an effective value reference value is set, an average value or an effective value of the instantaneous value of the actual secondary current in the town stroke after that point is calculated, and the calculated value is compared with the set reference value. If the set value is larger than the set reference value, the pump jack speed is further reduced by a preset speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pump-off control method for a beam pump driven by a pump jack.

[0002]

2. Description of the Related Art A sensor used for pump-off control in a beam pump oil well is a conventional type using a sensor such as a fluid level or a pressure detector, a flow sensor, a vibration sensor, and a motor current sensor in an oil well underground hole. Dynagraph cards that can analyze and record rod loads. The recent modern dynagraph card system is said to be the most reliable and accurate pump-off detection system.However, a rod load sensor such as a strain gauge is required for the sucker rod, and the detection signal of that sensor is used. Since the processing is performed in relation to the rotational position of the pump jack, a microcomputer device is required, and it is inevitably complicated and expensive. Further, the conventional method of placing a sensor in a downhole has a problem in that it is difficult to install the sensor several thousand feet underground, and there are problems such as wiring. The vibration sensor of the type installed on the ground has a problem of setting the vibration level of the pump off and the no pump off, and it is difficult to accurately detect the vibration level. The method of detecting the pump jack motor current is based on the fact that the motor current changes due to the rotation of the pump jack even if the sucker rod load is constant, and that the motor current becomes oscillating due to the characteristics of the soccer rod system. , Could not accurately detect pump-off.
In addition, in the conventional method, even if a modern dynagraph card method is used, the pump jack vibrates using an induction motor whose speed cannot be adjusted. However, for this reason, the pump jack is stopped due to a decrease in the suction pressure due to a temporary increase in the floating gas of the downhole pump and a primary fluctuation of the characteristics of the liquid, thereby reducing the productivity of the oil well. In order to avoid this situation, (a) the pump is stopped only when the pump-off is continuously detected 3 to 5 times or more, or (b) the pump jack drive motor is turned on.
A countermeasure for turning off is taken.

[0003]

However, (A)
For example, when the pump casing is partially filled with floating gas at each suction stroke, the opening of the discharge valve is slightly delayed due to the viscosity of the liquid, and the discharge valve is located at a position far away from the maximum position of the down stroke. Opening would cause overpressure, which could cause the rod to bend underneath or even break the pump barrel. The countermeasure (b) has a drawback that excessive mechanical or electrical stress is applied to the pump unit and the motor by repetition of the on-off operation, resulting in quicker wear of the equipment and an increase in maintenance costs. Therefore, an object of the present invention is to provide a pump-off control method that can detect a pump-off state at low cost and that does not stop the motor when the pump is off.

[0004]

According to a first aspect of the present invention, there is provided a pump-off control method, wherein the speed of an induction motor for driving a pump jack is controlled by a variable voltage, variable frequency power supply inverter. In the control method, the speed of the induction motor and the instantaneous value of the secondary current are detected, the downstroke time of each cycle of the pump jack is detected, and the secondary current of the induction motor during the downstroke time of each cycle is detected. Average or instantaneous value of the instantaneous value of the secondary current of the induction motor for comparison with the calculated average or effective value of the instantaneous value of the secondary current of the induction motor. A value reference value is set, and the average value or the effective value of the instantaneous value of the secondary current and the average value reference value or the effective reference value are downstretched in each cycle. Was compared after completion of detecting the pump off occurs when the effective value is greater instantaneous value than the case where the average value of the instantaneous value from the average value reference value is greater or the effective value reference value. The average reference value or the effective value reference value of the secondary current of the induction motor may be set to a value corresponding to the pump speed of the pump jack. This makes it possible to detect pump-off under the condition of constant volumetric efficiency. Further, when the pump-off condition is continuously detected more than once after the end of the downstroke, the pump jack speed is controlled to be reduced by a preset speed, and a new secondary corresponding to the reduced speed is controlled. Set the average value or the effective value reference value of the current, calculate the average value or the effective value of the instantaneous value of the actual secondary current in the downstroke after that time, and calculate the calculated value and the set reference value. If the calculated value is larger than the set reference value, it is detected that the pump-off condition still exists at the reduced speed, and this operation is continuously detected more than once. In such a case, the pump jack speed is controlled so as to be further reduced by a preset speed, and the average value or the effective value reference corresponding to the speed and the actual value at the speed are controlled. While detecting the pump-off by sequentially comparing the calculated average value or the calculated effective value of the current instantaneous value, the pump jack speed is controlled to be gradually decreased in a stepwise manner, so that the pump-off condition is released by speed control. It may be performed. Further, if the pump-off condition is detected, the speed is reduced by a preset speed, and the pump jack is operating at the new speed, and if the pump-off condition is not detected more than once continuously, At this speed, the pump-off condition is released and the pump-off release is detected, and the speed is increased by the speed reduced by the pump-off detection.
Set a new average value or effective value reference of the secondary current corresponding to the increased speed, calculate the average value or effective value of the instantaneous value of the actual secondary current in the downstroke after that time, By comparing the calculated value with the set reference value, if the calculated value is smaller than the set reference value, at the increased speed,
It is detected that the pump-off condition has been released,
If this operation is continuously detected more than once, the pump jack speed is controlled to be further increased by a preset speed, and the average value reference or the effective value reference corresponding to the speed and the actual value at that speed are controlled. By sequentially comparing the calculated average value or the calculated effective value of the secondary current sequential value and gradually increasing the pump jack speed gradually until the pump jack condition is detected, the pump off condition is controlled. The speed reduced by the pump-off operation may be restored to a predetermined pump jack operation speed while confirming the release.

According to the above method, without using a conventional expensive dynagraph card system composed of a rod load sensor and a microcomputer, the pump-off control of the inverter used for controlling the speed of the pump jack is performed. Incorporating software not only reduces the cost but also enables accurate detection of pump-off. In addition, since the speed of the pump jack is controlled, the speed of the pump jack can be reduced to a state where there is no pump off by detecting the pump off. Thereby, continuous production of the oil well can be performed without giving excessive force to the downhole pump and the sucker rod system. That is, as compared with an oil well to which a conventional pump jack driven at a constant speed is applied, it is possible to increase the productivity of the well and improve the safety of the equipment. In addition, the maximum speed of the downhole pump can be set in advance in response to changes in oil well conditions over a relatively long period of time, such as an increase in suspended gas or a decrease in oil well level. It is possible to reduce the possibility of the oil well, thereby contributing to the stable operation of the oil well.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a pump-off control method according to the present invention to which a vector control inverter that can easily take out an instantaneous value of a secondary current is applied, and FIG. 2 is a block diagram showing a configuration of a pump-off control device. is there. In FIG. 1, 1 is an induction motor for driving a pump jack, and 2 is directly connected to the induction motor 1.
Is a speed detector for detecting the speed of the motor, 3 is a vector control inverter having a known current minor loop, and 4 is a pump-off controller. The vector control inverter 3 includes a straight line commander 31, a speed adjuster 32, a current adjuster 33, a PWM
A controller 34, a current transformer 35 and a vector calculator 36 are provided. The straight line commander 31 functions to limit the speed reference Np, which is the output of the pump-off control device 4, to an acceleration rate set inside, and convert the speed reference Np to the speed reference Ns of the induction motor 1. The speed reference Ns is compared with the actual speed Ni detected by the speed detector 2, and the deviation is amplified by the speed adjuster 32 to output the secondary current command I _2g . Motor current is detected by current transformer 35, only the secondary current component by vector calculator 36 is detected as I _2, is compared with the secondary current command I _{2 g.} Then, the deviation is amplified by the current regulator 33, the pulse width of the voltage is adjusted by the PWM controller 34, and the secondary current necessary for driving the load is supplied to the induction motor 1. Thus, the vector control inverter 3 determines that the actual speed Ni is equal to the speed reference Np.
The motor speed is automatically adjusted to be approximately equal to In this figure, a control circuit of the magnetic speed component current of the induction motor 1 necessary for the vector control is known, and is omitted for the sake of simplicity because it is not directly related to the pump-off control of the present invention.

[0007] As shown in FIG. 2, the pump-off control device 4 includes a calculator 41, a secondary current reference generator 42, and a comparator 4.
3, an output relay 44, a sequencer 45, a speed command function generator 46, a pump jack main speed setting device 47, a speed command switching device 48, and a speed command device 49. The arithmetic unit 41 has a function of calculating and storing an effective value and an average value of the instantaneous value of the secondary current with respect to each down stroke time of the pump jack.
Corresponding to the actual speed Ni and I _2RMS of detecting the I _2AV. The secondary current reference generator 42, when there is no pump off,
That is, the average value of the secondary current during normal operation, I _2AV ^*
Alternatively, an effective value reference I 2 _RMS ^* is set, and the set value is adjusted according to the actual speed Ni of the pump jack. The average value I _2AV or the effective value I _2RMS of the instantaneous value of the actually detected secondary current is _compared with the respective set value I _2AV ^* or I _2RMS ^* by the comparator 43. If I _2AV > I _{2A V} ^* or I _2RMS
If> _2RMS ^* , the output relay 44 switches to the DN side. Conversely, if I _2AV ≦ I _2AV ^* or I _2RMS ≦ I _2RMS ^* , the output relay 44 switches to the UP side. I _{2 AV} > I _2AV ^* or I _2RMS > I _2RMS ^* detects the occurrence of pump-off as described later, and I _2AV ≦ I _2AV ^* or I _2RMS ≦ I _2RMS ^* detects the release. . The sequencer 45 has a function of totally controlling the pump-off sequence and a function of issuing a speed command for decreasing and increasing the speed of the pump jack in response to occurrence and release of the pump-off. That is, the DN or UP signal of the output relay 44 is counted, and when the DN signal is detected, for example, twice or more continuously, the pump-off sequence program is started. When the pump-off sequence program is started, the sequencer 45 automatically determines the notch of the pump jack speed during operation and controls the speed command function generator 46 so that the speed becomes one notch lower than that. Conversely, if the UP signal is counted twice consecutively, the pump-off reset (pump-off release) sequence program is started, and the pump jack speed is one notch lower than the operating speed, contrary to the above-described case where the pump-off occurs. The speed command function generator 46 is controlled so that the speed becomes high. The main speed setting device 47 sets the maximum speed corresponding to the state of the oil well at that time, for example, Nps = 100% speed, 80% speed. Therefore, if pump-off is detected during operation at the set speed, the speed is reduced by the speed command function generator 46 by one notch speed. That is, the pump jack speed is ΔN
by pn → △ Np _1, Nps one △ Np ₁ = Np next,
Wait for the pump-off condition to disappear. When the reading pump-off is detected, one more notch is added, for example, △ Np ₂
= 2 × △ Np ₁ . However, Nps-
If Npn ≦ 0, the pump jack stops. In this case, a pump stop / control switching sequence program in the sequencer 45 is started. In this pump stop / control switching sequence program, the pump off program is stopped, and the speed command switch 48 is switched to the speed command device 49 side. The speed command unit 49 generates a very low speed command for searching for the presence or absence of a pump-off condition. When this switching is completed, the no-pump off searching program in the sequencer 45 starts.
This is a control program for forcibly restarting the pump jack that has been stopped due to pump off after a certain period of time, causing it to operate at a very low speed, and checking for pump off conditions during the slow speed operation. And the ON / OFF of the fine speed command of the speed command device 49 and the presence / absence of pump off during the fine speed operation are checked. If the pump-off release is detected twice or more consecutively during the low-speed operation, the no-pump-off searching program switches the speed command switch 48 to the main speed setting Nps side and restarts the pump-off control sequence program. In this way, the pump jack is Nps- △ N
At the speed of pn = Np, it is controlled again, and while confirming the cancellation of the pump-off condition, the speed is automatically increased and restored to the set initial speed Nps. As described above, the pump-off control device 4 calculates and stores the average value or the effective value of the instantaneous value of the secondary current of the induction motor 1 and compares each with the respective reference values, thereby canceling pump-off or pump-off. Is to be detected.

The reason why the pump-off can be detected by detecting the average value or the effective value of the instantaneous value of the secondary current of the induction motor 1 will be described below. FIG. 3 shows a sucker rod torque and a net deceleration when the pump jack is operated at a rated stroke speed of 11.3 strokes / min and a pump unit of APIC114-143-64 at 50% of the rated speed. Machine torque,
The secondary current of the induction motor 1 is obtained by computer simulation. The pump jack stroke position is also shown in the figure. FIG. 3A shows the characteristics when the pump is not turned off, that is, in the case of normal operation. FIG. 3B shows the characteristics when the pump is turned off and the volumetric efficiency is 64%.
This is the characteristic in the case where it is reduced to: These (a) and (b)
By comparing with the above, the point at which the sucker rod torque or the net reduction gear shaft torque at the time of the downstroke or the secondary current of the induction motor 1 decreases is later when the pump-off occurs. I understand. Therefore, if these instantaneous values are detected corresponding to a specific stroke position and compared with a reference value in the case of normal operation without pump-off, pump-off can be detected. For example, in the present embodiment, the crank angle 66d
EG (each position near a crank angle measured by setting the crank angle of the pump jack when the tip position of the pump jack is at the highest position as 0 deg (hereinafter, this angle is referred to as θ 'base angle) is detected. The pump off can be detected by comparing the value of the secondary current of the induction motor 1 at that time with the value of the secondary current in the normal operation.
5%, the volumetric efficiency ηv of the pump is 40%,
Computer simulation analysis was performed on the same pump jack as above for the case of 63.7%,
The obtained secondary current of the induction motor 1 is converted to the crank angle (θ ′
Base). As shown, even if the volumetric efficiency decreases, the occurrence of pump-off can be detected by the method described above. However, in this embodiment, as the speed of the pump jack increases,
The secondary current of the induction motor 1 has a vibration response due to the vibration characteristics of the sucker rod system, and the method of comparing the instantaneous value of the secondary current with respect to the specific crank angle with the reference value as described above ensures reliable pump-off. Difficult to detect. FIG. 5 illustrates this. This figure plots the results of computer simulation analysis of the secondary current of the induction motor 1 with respect to the crank angle in the case where the pump is turned off at the 100% stroke speed and in the case of the normal operation. Crank angle 66d as shown
It can be seen that comparison of the instantaneous value of the secondary current near eg with the reference value makes accurate detection of pump-off difficult. In the present invention, this problem is solved by the method of calculating and detecting the average value or the effective value of the secondary current of the induction motor 1 with respect to the town stroke time (strictly, a reference down stroke time as described later) as described above. did.

Hereinafter, the induction motor 1 for each down cycle will be described.
The fact that pump-off can be detected based on the average value or the effective value of the instantaneous values of the secondary current will be described. FIG. 6 shows the average value and the effective value of the secondary current of the induction motor 1 during the down stroke obtained by computer analysis. The volume efficiency is shown on the X axis, and the secondary currents I _2RMS and I _2AV of the induction motor 1 are shown on the Y axis. And the stroke speed of the pump jack, 1.00 p.
u. (100% speed), 0.5 p. u. (50% speed), 0.25 p. u. (25% speed) is a plot of the result of analysis for the case of (25% speed). During normal operation without pump-off, the volumetric efficiency is almost 100%, and the volumetric efficiency gradually decreases as the pump-off becomes severe. Now, volumetric efficiency is 6
When it is determined that a case where the pressure drops to 3.7% (0.6637 pu) or less is detected as occurrence of pump-off, the secondary current value in normal operation without pump-off and the secondary current value when pump-off occurs are calculated as follows. The values differ greatly as shown in FIG. (Note 1) I _2RMS: effective value calculated from the instantaneous secondary current during downstroke (A) I _2AV: average value calculated from the instantaneous secondary current during downstroke (A) (2) rating of the motor two Next current: 36.9 (A) That is, if this current difference is used, it is clear that accurate detection of pump-off can be made, for example, by digital current difference calculation. Next, a method of calculating the effective value or average value of the instantaneous value of the secondary current at each town stroke will be described. This calculation includes the induction motor 1
, The instantaneous value of the secondary current, the speed at that time, and the measurement start and end time signals are required. In particular, how to detect the signal of the downstroke start at the start of the measurement becomes a problem. Of course, if a mechanical or magnetic sensor for detecting the crank angle zero position for each rotation is provided in the pump jack, this problem can be relatively easily solved. However, in the present invention, without using such a mechanical or magnetic sensor in order to simplify the system configuration, the zero point of the reduction gear shaft net torque is set to a special crank angle determined by the mechanical constant of the pump jack. Since the fixed point is fixed, the zero-cross point of the secondary current of the induction motor 1 is also fixed with respect to the crank angle, and the problem is solved by applying this property.

FIG. 8 is an example in which the secondary current and the rod position of the induction motor 1 when the pump jack is operating normally at 100% speed and the rod position are plotted against the crank angle (θ ′ base). In this figure, in the present invention, point A (0
deg) to the point B (180 deg) with respect to the actual downstroke, the point from the point A '(secondary current zero cross point) to the point B is determined as a reference cycle time, and is obtained by the following equation. T _E = (T _S /2)+(△θ/Vo)=(1/S)｛30+(△θ/6.0)｝ (sec)… (1) where T _E : average value of secondary current Or, the reference down stroke time for calculating the effective value (sec) T _S : Pump jack stroke time = 60 / S (sec) S: Pump jack stroke speed (spm) Vo: Average crank rotation speed = 360 / T _S = 6.0 × S (deg / sec) Δθ: phase difference angle (deg) between the crank angle at the zero cross point of the secondary current and the crank angle at the end of the upstroke: (known by the mechanical design specifications of the pump jack) If point A ′ can be detected for each stroke cycle while the pump jack is operating,
By integrating the instantaneous value of the secondary current or the square value of the instantaneous secondary current at every minute time Δt (sec) of the secondary current for _E seconds, the effective value or the average value can be obtained by the following equation, respectively. It is possible. I _2RMS = ｛Σ (I _2t ² × △ t) / T _E ^1/2 (A) (2) I _2AV = Σ (I _2t × △ t) / T _E (A) (3) I _2t : instantaneous value of secondary current at time t (A) Δt: minute time for integration operation (sec)

Next, a method of detecting the point A 'will be described.
Point A 'is a point at which the rod torque is zero before the end of the upstroke, and must be distinguished from a rod torque zero point near the end of the downstroke. For this purpose, the present invention applies the direction and magnitude of the secondary current and the logical operation of those signals. Now, an example in which the case where the induction motor 1 is generating electric-side torque is designed as a plus of the secondary current will be described. The operation of the pump jack on the down-stroke side causes the induction motor 1 to generate a braking torque, and the secondary current becomes negative, which is stored. Next, in order to detect that the pump jack has shifted to the up stroke side, there is provided means for detecting that the actual secondary current has become 50% or more. The negative memory of the secondary current and the AND logic of the secondary current of 50% or more detect and store that the pump jack has certainly shifted from the down stroke to the up stroke. Therefore, the zero point when the secondary current changes from plus to zero or minus after this point is the above-mentioned point A ', which can be easily detected by a known logical operation. For reference, FIG. 9 shows a flow of calculating the average value and the effective value of the instantaneous values of the secondary current described above. The arithmetic unit 41 in FIG. 2 is an arithmetic unit having the above-described functions of operation, storage, and logic control. Next, the fact that the zero-cross point of the secondary current is determined by the mechanical constant of the pump jack will be described. The instantaneous value of the secondary current is a value that is directly proportional to the net reduction gear shaft torque, and its zero-crossing point is the point at which the next net reduction gear shaft torque gives zero. T _L = W _PR・ TF + L _C・ W _CB・ cos (d-θ) = W _PR・ TF + T _CB (kg-m)… (4) where T _{L is the} net reduction gear shaft torque (kg-m ) W _PR : police load (kg) TF: pump jack torque factor (m) L _C : counterbalance turning radius (m) W _CB : counterbalance weight (kg) d: angle at which counterbalance effect is maximized Required phase angle (deg) T _CB : counterbalance torque (kg-m) The TF in equation (4) is determined by the mechanical constant of the pump jack link mechanism and the crank rotation angle. For example, in the pump unit APIC456-304-120, the TF is zero at 182.1 deg and 366.0 deg. In another example, APIC114-
In 143-64, 184.9 deg and 358.1 d
At eg, the TF is zero. However, the angle at which this TF is given is expressed on a θ ′ basis. Therefore,
If the crank angle is also represented by θ 'instead of θ,
The second term T _{CB in} equation (4) is 180 deg and 360 deg
And becomes zero. That is, the zero point of TF and the zero point of T _CB are very close. Therefore, the point at T _L zero, that is,
The zero point of the secondary current will be fixed at a specific value determined by the mechanical constant of the pump jack. That is,
If the point A 'is detected by the above-described method, a mechanical or magnetic sensor for detecting the crank angle is not required.
As described above, the reference value for detecting pump-off or no-pump-off based on the average value and effective value of the secondary current of the induction motor 1 for each cycle of the pump jack is, for example, 63.7 in FIG. % Can be set by setting the current value corresponding to each speed. The data as shown in FIG. 6 is stored in the secondary current reference generator 42 shown in FIG. 2, and is selected by a speed signal as shown in the figure.

[0012]

As described above, according to the present invention,
Inexpensive by incorporating pump-off control software in the inverter used for pump jack speed control without using a conventional expensive dynagraph card system consisting of a rod load sensor and microcomputer In addition, accurate pump-off detection can be performed. In addition, since the speed of the pump jack is controlled, the detection of pump off causes
The pump jack speed can be reduced to a state where there is no pump off. Thereby, continuous production of the oil well can be performed without giving excessive force to the downhole pump and the sucker rod system. That is, as compared with an oil well to which a conventional pump jack driven at a constant speed is applied, it is possible to increase the productivity of the well and improve the safety of the equipment. In addition, the maximum speed of the downhole pump can be set in advance in response to changes in oil well conditions over a relatively long period of time, such as an increase in suspended gas or a decrease in oil well level. It is possible to reduce the possibility of the oil well, thereby contributing to the stable operation of the oil well.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a pump-off control method according to the present invention.

FIG. 2 is a block diagram illustrating a detailed configuration of a pump-off control device of FIG. 1;

FIG. 3 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of a secondary current of an induction motor for each cycle of a pump jack.

FIG. 4 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of a secondary current of an induction motor in each cycle of a pump jack.

FIG. 5 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of the secondary current of the induction motor for each cycle of the pump jack.

FIG. 6 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of a secondary current of the induction motor for each cycle of the pump jack.

FIG. 7 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of a secondary current of the induction motor for each cycle of the pump jack.

FIG. 8 is a diagram for explaining a method of detecting pump-off based on an average value and an effective value of instantaneous values of the secondary current of the induction motor for each cycle of the pump jack.

FIG. 9 is a flowchart showing a process of calculating the average value and the effective value of the instantaneous values of the secondary current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction motor 2 Speed detector 3 Vector control inverter 4 Pump-off control device 41 Computing unit 42 Secondary current reference generator 43 Comparator 44 Output relay 45 Sequencer 46 Speed command function generator 47 Main speed setting unit 48 Speed command switch 49 Speed commander

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuo Kono 13-20 Kosita-cho, Yawatanishi-ku, Kitakyushu-city, Fukuoka Prefecture (72) Inventor Richard El Prat 45014 Fairfield Harwood Court, Ohio USA 9823 P.O. Box 9039 Electric Motor Systems, Inc. (72) Inventor Brian McKinnon Alberta, Canada T2 Sea 3 Sea 6 Calgary 76 Avenue South East 5115 Warmac Electric (1994) Limited

Claims (4)

[Claims] 1. A pump-off control method for a pump jack drive system in which an induction motor for driving a pump jack is speed-controlled by an inverter of a variable voltage and variable frequency power supply, wherein a speed of the induction motor and an instantaneous value of a secondary current are provided. Detecting the downstroke time of each cycle of the pump jack, calculating the average or effective value of the instantaneous value of the secondary current of the induction motor in the downstroke time of each cycle, and calculating the calculated An average value or an effective value reference value of the secondary current of the induction motor for comparison with an average value or an effective value of the instantaneous value of the secondary current of the induction motor, and an average of the instantaneous value of the secondary current is set. After the downstroke of each cycle is completed, the average value of the instantaneous value is larger than the average value reference value or the effective value. A pump-off control method, wherein a pump-off occurrence is detected when the instantaneous value is greater than the effective value reference value. 2. The pump-off control method according to claim 1, wherein an average value reference value or an effective value reference value of the secondary current of the induction motor is set to a value corresponding to a pump speed of a pump jack. 3. When the pump-off condition is detected more than once consecutively after the downstroke is completed, the pump jack speed is controlled to decrease by a preset speed, and a new pump jack speed corresponding to the reduced speed is controlled. The average value or the effective value reference value of the secondary current is set, and the average value or the effective value of the instantaneous value of the actual secondary current in the town stroke after that point is calculated. When the calculated value is larger than the set reference value, it is detected that the pump-off condition still exists at the reduced speed, and this operation is continuously performed a plurality of times. If the above is detected, control is performed so that the pump jack speed is further reduced by a preset speed, and the average value or effective value reference corresponding to the speed and the speed are used. And controlling the pump jack speed to decrease gradually in steps while the pump-off is detected by sequentially comparing the calculated average value or the calculated effective value of the actual secondary current instantaneous value. Item 3. The pump-off control method according to item 1 or 2. 4. A pump-off condition is detected, the speed is reduced by a preset speed, and no pump-off condition is detected more than once continuously while the pump jack is operating at the new speed. In this case, the pump-off condition is canceled at this speed, the pump-off release is detected, the speed is increased by the speed reduced by the pump-off detection, and the average of the new secondary current corresponding to the increased speed is increased. Setting a value reference or an effective value reference, calculating the average value or the effective value of the instantaneous value of the actual secondary current in the downstroke after that time, and comparing the calculated value with the set reference value. Thus, when the calculated value is smaller than the set reference value, it is detected that the pump-off condition is still released at the increased speed, If this operation is continuously detected more than once, the pump jack speed is controlled to be further increased by a preset speed, and the average value reference or the effective value reference corresponding to the speed and the actual value at that speed are controlled. 2. The control method according to claim 1, wherein the pump average speed is sequentially increased gradually until the pump jack condition is detected by comparing the calculated average value or the calculated effective value of the secondary current sequential values. The pump-off control method according to any one of claims 1 to 3.