Pump-off control method of pump jack

• US 6,599,095 B1
• Filed: 10/29/2001
• Issued: 07/29/2003
• Est. Priority Date: 04/28/1999
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Yaskawa Denki
• Original Assignee: Kabushiki Kaisha Yaskawa Denki
• Inventors: Kawamoto, Koji, Kawano, Tetsuo, Takada, Noriyuki, Pratt, Richard L., Yamakawa, Takayuki, Miyano, Toshio, Mackinnon, Brian, Ryu, Hidetoshi
• Primary Examiner(s): Freay, Charles G.
• Assistant Examiner(s): Solak, Timothy P.
• Application Number:
  US09/959,515
• Time in Patent Office: 638 Days
• Field of Search: 417/44.11, 417/45, 417/42, 417/53
• US Class Current: 417/53
• CPC Class Codes: F04B 2201/0202 Linear speed of the piston
• CPC Class Codes: F04B 2203/0201 Current
• CPC Class Codes: F04B 2203/0204 Frequency of the electric current
• CPC Class Codes: F04B 47/02 the driving mechanisms being situated at ground level F04B47/12 takes precedence
• CPC Class Codes: F04B 49/065 and making use of computers

Abstract

A pump off control method comprises detecting the speed of the induction motor and an instantaneous value of secondary current of the induction motor. Down stroke time in every cycle of the pump jack is detected. An average value of instantaneous values of the secondary current of the induction motor in the down stroke time in said every cycle is calculated. An average value reference of the secondary current of the induction motor to be compared with calculated average value of the instantaneous values of the secondary current of the induction motor is set. The calculated average value of the instantaneous values of the secondary current is compared with the average value reference after the down stroke end in each cycle. An occurence of pump off is detected if the calculated average value of the instantaneous values is greater than the average value reference.

Claims

1. A system for pump off control of a pump jack drive system of induction motor drive comprising:

means for detecting speed of the induction motor and an instantaneous value of secondary current of the induction motor;

means for detecting down stroke time in every cycle of the pump jack;

means for detecting each maximum value of the secondary current instantaneous values in each down stroke time of the secondary current;

means for detecting and storing a time value from each down stroke reference point to said each maximum value of the secondary current instantaneous values; and

means for setting a reference time value to be compared with the detected and stored time value,

wherein the system is capable of comparing the detected and stored time value with the reference time value after the down stroke end every cycle and the system is further capable of detecting an occurrence of a pump off condition as a case where the time at which the instantaneous value of the secondary current reaches the maximum value lags behind the setup reference value.

2. The system as claimed in claim 1 wherein said reference time value represents a lag time from a beginning to the maximum value of the secondary current being set based on a pump jack stroke time ratio so that pump off can be detected without being affected by change in pump jack speed setting.

3. The system as claimed in claim 1 or 2 wherein when a pump off condition is detected once or successively more than once after the down stroke end, control is performed so as to lower pump jack speed by a preset speed amount,

wherein the system is capable of detecting a time value at which the actual secondary current instantaneous value reaches the maximum value from the reference point at the speed and further capable of comparing said time value with the setup reference time,

wherein if the secondary current instantaneous value maximum value time is greater than the setup reference value, the system is determined such that the pump off condition is still existing at the lowered speed,

wherein if the operation is detected once or successively more than once, the system is capable of performing control to further lower the pump jack speed by the preset speed amount, and

wherein the system is capable of performing control to lower the pump jack speed gradually in sequence so long as pump off is detected.

4. The system as claimed in any one of claims 1 or 2 wherein the system is capable of detecting pump off condition and lowering speed by the preset speed amount, wherein if pump off condition is not detected once or successively more than once in a state in which the pump jack operates at the lowered speed, the system is capable of detecting pump off reset,

wherein the speed is raised by the preset speed amount,

wherein the time value at which the actual secondary current instantaneous value reaches the maximum value at the raised speed is detected and the time value is compared with the reference time,

wherein if the time is less than the reference time value the pump off condition being still reset at the raised speed is detected,

wherein if the operation is detected once or successively more than once, control is performed so as to further raise the pump jack speed by the preset speed amount, and

wherein control is performed so as to raise the pump jack speed gradually in sequence to the speed at which pump off condition is detected.

5. A pump off control method of a pump jack drive system adapted to control speed of an induction motor for driving a pump jack, said pump off control method comprising the steps of:

a) detecting the speed of the induction motor and an instantaneous value of secondary current of the induction motor;

b) detecting down stroke time in every cycle of the pump jack;

c) calculating an average value of instantaneous values of the secondary current of the induction motor in the down stroke time in said every cycle;

d) setting an average value reference of the secondary current of the induction motor to be compared with calculated average value of the instantaneous values of the secondary current of the induction motor;

e) comparing the calculated average value of the instantaneous values of the secondary current with the average value reference after the down stroke end in each cycle, and

f) detecting occurrence of pump off if the calculated average value of the instantaneous values is greater than the average value reference.

6. The pump off control method as claimed in claim 5 wherein the reference value is set based on a pump speed of the pump jack.

7. The pump off control method as claimed in claim 5 or 6 wherein when a pump off condition is detected successively more than once after the down stroke end, the method further comprises:

g) performing control to lower pump jack speed to a lowered speed by a preset speed amount;

h) repeating said steps c-e;

i) repeating said steps g-h as long as pump off is detected.

8. The pump off control method as claimed in any one of claims 5 or 6 wherein pump off condition is detected and speed is lowered by a preset speed amount, wherein if pump off condition is not detected successively more than once in a state in which the pump jack operates at the new lowered speed, the method further comprises:

g) performing control to raise pump jack speed amount to a raised speed by the preset speed amount;

h) repeating said steps c-e;

i) repeating said steps g-h as long as pump off is detected.

9. The pump off control method as claimed in claim 5 wherein the average value is one of an arithmetic mean and a root mean square value.