Pump jack pump-off control method and pump jack control apparatus

• US 8,106,615 B2
• Filed: 10/04/2007
• Issued: 01/31/2012
• Est. Priority Date: 10/24/2006
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Yaskawa Denki
• Original Assignee: Kabushiki Kaisha Yaskawa Denki
• Inventors: Yamamoto, Yoichi, Kawamoto, Koji, Kawano, Tetsuo, Tsuruta, Tatsumi
• Primary Examiner(s): DOUGHERTY, THOMAS M
• Application Number:
  US12/446,852
• Publication Number:
  US 20100014989A1
• Time in Patent Office: 1,580 Days
• Field of Search: 318/471, 417/42, 417/44.11, 417/45, 417/53
• US Class Current: 318/471
• CPC Class Codes: F04B 2201/121 Load on the sucker rod
• CPC Class Codes: F04B 2203/0204 Frequency of the electric current
• CPC Class Codes: F04B 2203/0207 Torque
• CPC Class Codes: F04B 2203/0209 Rotational speed
• 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

It is an object of the invention to provide a pump jack pump-off control method and a pump jack control apparatus in which, even when the speed of a pump jack is reduced due to generation of a pump-off condition, the pump jack is not caused to stop due to the motor overload abnormality or the coagulated crude oil and, even when the pump-off condition is generated, the reduction of the production capacity of the pump jack can be prevented as much as possible. On detecting the pump-off condition, while the pump jack is in operation with the speed thereof being reduced, or while the pump jack is in operation at the lowest speed, according to the overload warning signal of an ac electric motor, the pump jack is switched over to its intermittent operation. Also, the pump jack can be operated in such a manner that the stroke speed of the pump jack in the up stroke operation can be switched from a sinusoidal wave form over to a rectangular wave form, or, in the operation of the pump jack by an inverter, the pump jack can be operated such that it can carry out its up stroke operation with a limit imposed on torque.

Claims

1. A pump jack pump-off control method in which a pump jack is driven by an inverter having a power supply of a variable voltage and a variable frequency using an ac electric motor, the ac electric motor is protected against overload, and a pump-off condition of the pump jack is detected according to an average value or effective value of a secondary current of the ac electric motor during a down stroke period in each cycle of the pump jack or according to a delay time from each down stroke reference point to the maximum value of the secondary current of the ac electric motor,

the method comprising the steps of:

on detecting the pump-off condition, reducing a speed of the pump jack by an amount equivalent to a previously set speed;

on detecting the pump-off condition in the reduced speed as well, reducing the pump jack speed sequentially step by step down to a previously set lowest speed; and

during an operation of the pump jack with a speed thereof being reduced or during an operation of the pump jack at the lowest speed, switching the pump jack into an intermittent operation thereof according to an overload warning signal supplied from the ac electric motor.

2. The pump jack pump-off control method as set forth in claim 1, wherein

in the intermittent operation, removal of the overload warning signal of the ac electric motor is a condition of start of re-operation of the pump jack.

3. The pump jack pump-off control method as set forth in claim 1, wherein

in the intermittent operation, a previous pump-off condition of the pump jack is used as a condition of start of re-operation of the pump jack.

7. A pump jack pump-off control method as set forth in claim 1 further comprising:

on detecting the pump-off condition, switching the stroke speed in an up stroke operation of the pump jack from a sinusoidal wave form over to a rectangular wave form or driving the pump jack to execute an up stroke operation thereof during the operation thereof by the inverter with imposing a limit on torque.

8. The pump jack pump-off control method as set forth in claim 7,

wherein on detecting the pump-off condition, the pump jack is operated in such a manner that a down stroke average speed of the pump jack is larger than an up stroke average speed thereof.

4. A pump jack control apparatus, comprising:

an inverter configured to supply a power of a variable voltage and a variable frequency to drive an ac electric motor; and

a pump-off control portion which,

according to an average value or effective value of a secondary current of the ac electric motor during a down stroke period in each cycle of the pump jack or according to a delay time from each down stroke reference point to the maximum value of the secondary current of the ac electric motor, detects a pump-off condition of the pump jack,

on detecting the pump-off condition, reduces a speed of the pump jack by a previously set speed, and

on detecting the pump-off condition in the reduced speed as well, reduces the pump jack speed sequentially step by step down to a previously set lowest speed,

wherein the inverter includes an overload protection portion which, based on size of a current flowing in the ac electric motor, outputs an overload warning signal according to a calculation value obtained using at least adding calculation or according to a detect value of a temperature sensor mounted on the ac electric motor, and

wherein the pump-off control portion includes a pump jack control portion which, during an operation of the pump jack while the pump jack speed is being reduced or during an operation of the pump jack at the lowest speed, switches the pump jack into an intermittent operation thereof according to the overload warning signal of the ac electric motor.

5. The pump jack control apparatus as set forth in claim 4,

wherein the pump-off control portion, on detecting the pump-off condition, outputs a speed instruction to the inverter in such a manner that a stroke speed of the pump jack in an up stroke operation thereof is switched from a sinusoidal wave form over to a rectangular wave form.

6. The pump jack control apparatus as set forth in claim 5,

wherein the pump-off control portion, on detecting the pump-off condition, outputs a speed instruction to the inverter in such a manner that a down stroke average speed of the pump jack is larger than an up stroke average speed thereof.