SYSTEM AND METHOD FOR CONVERTERLESS OPERATION OF MOTOR-DRIVEN PUMPS
A converterless motor-driven pump system includes an off-grid prime mover. The off-grid prime mover has a rotational driveshaft and operates in response to a throttle control command to control a rotation speed of the rotational driveshaft. An electric power generator is driven by the off-grid prime mover to generate AC power. A variable speed induction motor is directly powered by the electric power generator. A pump that may be submersible is driven by the at least one variable speed induction motor. A system controller that may be local or remote is programmed to generate the throttle control command in response to one or more pump operating characteristics such that the off-grid prime mover, the electric power generator, and the variable speed induction motor together operate to regulate a pressure at the inlet of the electric pump.
Latest General Electric Patents:
- Electric machine
- Hybrid modular multilevel converter (HMMC) based on a neutral point pilot (NPP) topology
- Electric machines with air gap control systems, and systems and methods of controlling an air gap in an electric machine
- Rotor with non-through shaft, assembly of rotors, rotor with multiple magnetic masses and associated rotary electrical machine
- Connector and seal used therefor and anesthesia machine using the connector
The subject matter of this disclosure relates generally to motor-driven pumps, and more particularly, to a system and method for converterless operation of motor-driven pumps.
The conventional approach to controlling the speed of motor-driven pumps is through the use of a variable speed drive (VSD) that is fed by a fixed frequency AC supply. The VSD synthesizes voltages and currents of such frequency as is necessary to operate the pump in the desired manner. In the oil and gas industry, the voltage output by the VSD is usually stepped up to a medium voltage using a transformer because high voltage motors are deployed in wells to reduce the size of the power cable needed to supply the motor.
There is a need in the oil and gas industry to provide a system for operating ESPs that is less complex, less costly, and that has a smaller footprint. A system that reduces the capital expense, weight and footprint size will advantageously reduce the time it takes to put a well into production using power generated on-site when compared with the time it takes to put a well into production using utility power because of the delays associated with getting the utility to install necessary power lines.
It is possible to use the natural gas produced by the well to support operation of the generator, thereby reducing the operating expense of the system. Depending on the selection of the generator and the prime mover, it may be necessary to couple the generator and the prime mover through a gearbox. It is generally possible to select a gearbox with a fixed ratio, thereby avoiding the need for changing gear ratios during system operation.
BRIEF DESCRIPTIONAccording to one embodiment, a converterless motor-driven pump system comprises:
at least one off-grid prime mover comprising a rotational driveshaft and operating in response to a throttle control command to control a rotation speed of the rotational driveshaft;
at least one electric power generator driven by the at least one off-grid prime mover to generate AC power;
at least one variable speed motor directly powered by the at least one electric power generator;
at least one electric submersible pump driven by the at least one variable speed motor, wherein one or more operating characteristics associated with the at least one electric submersible pump are monitored by one or more corresponding sensors;
a system controller programmed to generate the throttle control command in response to the one or more pump operating characteristics such that the at least one off-grid prime mover, the at least one electric power generator, and the at least one variable speed motor together operate to regulate a pressure at the inlet of the at least one electric submersible pump; and
monitoring and protection equipment comprising circuit breakers to ensure safety to personnel around the system, and to provide protection to the prime mover, generator, and variable speed motor during system starting, or in response to equipment failure or in response to occurrence of one or more unforeseen events.
According to another embodiment, a method of operating an electric submersible pump comprises:
controlling a driveshaft speed of an off-grid prime mover in response to a throttle control command;
controlling an AC power output of an electric power generator in response to the driveshaft speed of the off-grid prime mover;
controlling a speed of a variable speed motor directly in response to the AC power output of the electric power generator; and
monitoring operating characteristics of the electric submersible pump and generating the throttle control command in response thereto such that together the off-grid prime mover, the electric power generator, and the variable speed motor operate to regulate a pressure at an inlet to the electric submersible pump.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:
While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
DETAILED DESCRIPTIONThe embodiments described herein are directed to control of motor-driven pumps in applications that are operating independently of a utility power grid, and combine the control of a prime mover and an AC generator to provide substantially similar functionality as a variable speed drive (VSD) to reduce system complexity, cost and footprint size. Such embodiments are particularly useful in the oil and gas industry where the usual control objective is to regulate the pressure at the inlet of the motor driven submersible pump, although other control objectives, including without limitation, temperature, speed, or vibration can be applied in like fashion.
A sensor package 28 is attached to the motor-driven pump 26 that may comprise, for example, one or more temperature sensors and one or more pressure sensors to provide an indication of various pump operating temperatures and pressures. An important pressure is the inlet pressure to the pump 26, since this pressure provides a direct indication of whether the well is being operated at the proper loading for maximizing well production. The sensor package 28 may further comprise one or more vibration sensors configured to monitor various pump vibration characteristics and to provide an indication whether a predetermined vibration level is exceeded. At least one speed sensor may be included in the sensor package 28 in order to accurately monitor the rotational speed of the pump. Other types of sensors may be included in the sensor package 28 depending on the particular application requirements.
The converterless ESP system 20 advantageously i) eliminates the need for a variable speed drive and transformer, simplifying the system, resulting in improved system reliability, ii) can use pumped gas via the pump 26 itself as the fuel to run the prime mover 22, resulting in very low fuel costs, and iii) operates independently of a utility power grid.
It can be appreciated that there may be reasons to retain a transformer between the generator 22 and the motor driven pump 26. Such reasons may include, without limitation, minimizing system cost and/or maximizing operational flexibility. According to one aspect, the decision to retain or remove the transformer from the system 20 may be made on the basis of system optimization rather than conceptual operation of the system 20.
The programmable system controller 36 is responsible for monitoring the pump operating conditions, including without limitation input and output pressures, pump temperature(s), pump vibration levels, and pump rotational speed, and commanding the throttle position control 38 of the prime mover 21 that will drive the pump 26 output to the desired pump operating point in response to one or more of the monitored operating conditions. According to one aspect, the system controller 36 also monitors the shaft speed of the prime mover 21 and commands the generator exciter 39 of the synchronous generator 22 accordingly.
The programmable system controller 36 may comprise, without limitation, one or more computers and/or data processors/devices and associated display devices. The data processors/devices may comprise one or more CPUs, DSPs and associated data storage devices, data acquisition devices and corresponding handshaking devices that may be integrated with the system controller 36 and/or distributed throughout the converterless ESP system 30. The system controller 36 may communicate with a remote operations center 37 that is able to monitor system operation and modify system operating objectives without requiring action of a local operator.
According to another aspect, the system controller 36 monitors the voltage, frequency and current being supplied to the motor 34, and generates the prime mover throttle control command in response to the monitored information to modify control of the prime mover 21. The rate of change in prime mover driveshaft speed, for example, might be controlled to maintain the generator current below a specified value by limiting the current being supplied by the generator 22. Such operation can help reduce stress on the system, thereby making the converterless ESP system 30 more reliable.
According to another aspect, the generator 22 may be a permanent magnet generator that does not require excitation. It can be appreciated that use of a permanent magnet generator would further simplify the converterless ESP system 30 without sacrificing performance.
It can be appreciated that the pump motor 34 may be any electric motor that can be line started, including not only induction motors, but also a special class of permanent magnet motors known as line-start permanent magnet motors.
In summary explanation, a converterless ESP system eliminates the variable speed drive and, potentially, its associated transformer from a motor driven submersible pump system, resulting in a simpler system that reduces capital expense, weight and system footprint. The use of power generated on-site advantageously reduces the time it takes to put a well into production resulting from delays in getting the utility to install requisite power lines. Further, the use of natural gas produced by the well itself advantageously reduces the operating expense.
Since the output of the generator 22 is substantially sinusoidal when compared with the output of a variable speed drive, a filter is not required between the generator 22 and the motor 34. The output of a variable VSD, for example, contains significant high frequency content, the result of chopping up DC voltage/current to produce AC voltage/current. This chopping action disadvantageously creates high frequency components called harmonics that are detrimental to the motor driving the pump. A filter is usually installed between the VSD and the motor; however, anecdotal data suggest that even such a filter may not always adequately filter out the harmonics, leading to accelerated aging of the insulation systems in the transformer 19, cable 32, and motor 34. This disadvantageously reduces the life of the ESP system
A VSD also draws nonsinusoidal currents from its supply, unless an active front end is applied to the VSD. These resulting harmonics are detrimental to the generator supplying the VSD. Many system designs oversize the generator so that it can better tolerate the harmonic currents drawn by the VSD. Other system designs will use an active power filter to source the harmonic currents drawn by the VSD, thereby alleviating the generator from having to supply them. Either of such approaches adds to the cost and complexity of the system.
The principles described herein with reference to the various embodiments include reduced capital expense and more timely well production. The off-grid converterless system embodiments advantageously allow putting a well into production sooner since there is frequently a substantial waiting period for the utility to install supply lines to the well site, as stated herein. At such time as utility power is available, the well operator can remove the prime mover and generator, replacing them with a variable speed drive and transformers if desired.
For reasons of safety and system protection, system elements may be included that are responsible for monitoring the operation of the system equipment, with means to instruct the controller 36 to shut down the system 30 if a failure or external event causes an exception to intended operation. Exemplary system elements may include, without limitation, one or more pump pressure sensors, pump speed sensors, pump temperature sensors, pump vibration sensors, pump viscosity sensors, pump gas volume fraction sensors, specific gravity sensors, motor current sensors, motor temperature sensors, motor voltage sensors, and motor frequency sensors. A pump gas volume fraction sensor, for example, may be employed to determine a volumetric ratio of liquid versus gas that is flowing through the pump(s). External events causing a system shutdown may include, for example, i) a volume fraction that gets too large, i.e., too much gas for pump to handle, ii) a motor temperature that gets too high, or iii) a clogged pump, causing pump pressure to get too high. Monitored sensor signals are transmitted to the system controller 36 that ensures that the motor 34 and pump 26 are operating within prescribed design, safety, specification and/or threshold limits
Another embodiment includes monitoring the voltage, frequency, temperature and current being supplied to the motor 34 via the generator 22, and acquiring the monitored information, as represented in block 52. The acquired motor supply voltage, frequency, temperature and current information is used by the system controller 36 to determine whether the prime mover driveshaft should rotate at a different speed. If a different prime mover driveshaft speed is required, the system controller 36 transmits an appropriate throttle command 38 to the prime mover 21, causing a change in the running speed of the prime mover 21, as represented in block 54. This embodiment can be employed in applications where it might be of interest to, for example, limit the current being supplied by the generator 22; so the rate of change in prime mover speed could be controlled to keep the generator current less than a specified value.
Since some applications may employ a permanent magnet generator that does not require excitation, it can be appreciated that a generator exciter will not be required in such applications. The use of a permanent magnet generator further simplifies the converterless ESP system 30 without sacrificing performance, as stated herein.
Although particular embodiments have been described herein with application to electric submersible pumps, the principles described herein can just as easily be applied to other applications including without limitation, geothermal applications. In such applications, gas turbines or reciprocating engines can be employed to rotate the generator.
The principles described herein can be applied to a motor generator set feeding a plurality of ESPs (i.e., when an existing oil field is to be expanded to include, for example, 50% more wells, wherein the wells are in close proximity to each other). The controller 36 in this application is further programmed according to one embodiment to provide for load balancing among the ESP motors, thereby reducing unwanted losses.
The controller 36 may further be configured with synchronization logic and programmed according to yet another embodiment to generate a control signal that activates an auxiliary/spare generator to provide a parallel operation capability.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
Claims
1. A converterless motor-driven pump system comprising:
- at least one off-grid prime mover comprising a rotational driveshaft and operating in response to a throttle control command to control a rotation speed of the rotational driveshaft;
- at least one electric power generator driven directly or indirectly by the at least one off-grid prime mover to generate AC power;
- at least one variable speed motor directly or indirectly powered by the at least one electric power generator;
- at least one electric submersible pump driven by the at least one variable speed motor, wherein one or more operating characteristics associated with the at least one electric submersible pump are monitored by one or more corresponding sensors; and
- a system controller programmed to generate the throttle control command in response to the one or more pump operating characteristics such that the at least one off-grid prime mover, the at least one electric power generator, and the at least one variable speed motor together operate to regulate a pressure at the inlet of the at least one electric submersible pump such that a desired operating point of the at least one electric submersible pump is maintained.
2. The converterless motor-driven pump system according to claim 1, wherein the system controller is integrated with the converterless motor-driven pump system.
3. The converterless motor-driven pump system according to claim 1, wherein the system controller communicates with an operation center remote from the converterless motor-driven pump system.
4. The converterless motor-driven pump system according to claim 1, wherein the prime mover comprises at least one of a reciprocating engine or a turbine.
5. The converterless motor-driven pump system according to claim 1, wherein the electric generator comprises at least one of a permanent magnet generator and a wound-field synchronous generator.
6. The converterless motor-driven pump system according to claim 5, further comprising a generator exciter configured to provide excitation to the wound-field synchronous generator.
7. The converterless motor-driven pump system according to claim 6, further comprising a speed sensor configured to monitor the rotation speed of the rotational driveshaft.
8. The converterless motor-driven pump system according to claim 7, wherein the system controller is further programmed to control the excitation of the generator exciter in response to the rotation speed of the rotational driveshaft.
9. The converterless motor-driven pump system according to claim 1, further comprising an electric submersible pump cable directly or indirectly linking the generated AC power to the variable speed motor.
10. The converterless motor-driven pump system according to claim 1, further comprising a pressure sensor configured to monitor the inlet pressure of the at least one electric submersible pump.
11. The converterless motor-driven pump system according to claim 1, further comprising a transformer between the at least one generator and the at least one electric submersible pump.
12. The converterless motor-driven pump system according to claim 1, wherein the system controller is further programmed to shut down the converterless motor-driven pump system in response to one or more variable speed motor sensor signals that exceed prescribed limits or one or more electric submersible pump signals that exceed prescribed limits.
13. A method of operating a converterless motor-driven pump system, the method comprising:
- controlling an AC power output of an electric power generator in response to an off-grid prime mover driveshaft speed, wherein the driveshaft speed of the off-grid prime mover is controlled via a throttle control command;
- controlling a speed of a variable speed motor directly in response to the AC power output of the electric power generator;
- controlling an electric submersible pump (ESP) in response to the speed of the motor, and
- monitoring operating characteristics of the ESP and generating the throttle control command in response thereto such that together the off-grid prime mover, the electric power generator, and the variable speed motor operate to regulate a pressure at an inlet to the ESP and further to maintain a desired operating point for the ESP.
14. The method of operating a converterless motor-driven pump system according to claim 13, wherein monitoring operating characteristics comprises monitoring operating characteristics via a localized controller.
15. The method of operating a converterless motor-driven pump system according to claim 13, wherein monitoring operating characteristics comprises monitoring operating characteristics via a remote control center.
16. The method of operating a converterless motor-driven pump system according to claim 13, wherein controlling a driveshaft speed of an off-grid prime mover comprises controlling a driveshaft speed of at least one of a reciprocating engine and a turbine engine.
17. The method of operating a converterless motor-driven pump system according to claim 13, wherein controlling an AC power output of an electric power generator comprises controlling an AC power output of at least one of a wound-field synchronous generator and a permanent magnet generator.
18. The method of operating a converterless motor-driven pump system according to claim 17, wherein controlling an AC power output of the wound-field synchronous generator comprises controlling an AC power output of a wound-field exciter.
19. The method of operating a converterless motor-driven pump system according to claim 18, further comprising controlling the AC power output of the wound-field exciter in response to the driveshaft speed of the off-grid prime mover.
20. The method of operating a converterless motor-driven pump system according to claim 17, further comprising controlling the AC power output of the permanent magnet generator in response to the driveshaft speed of the off-grid prime mover.
21. The method of operating a converterless motor-driven pump system according to claim 13, further comprising directly or indirectly linking the generated AC power to the variable speed motor via an electrical submersible pump cable.
22. The method of operating a converterless motor-driven pump system according to claim 13, further comprising linking the generated AC power to the variable speed motor via a transformer and an electrical submersible pump cable.
23. The method of operating a converterless motor-driven pump system according to claim 13, wherein monitoring operating characteristics of the ESP comprises monitoring an inlet pressure to the ESP, and generating the throttle control command in response thereto such that a desired ESP operating point is maintained.
Type: Application
Filed: Sep 19, 2013
Publication Date: Mar 19, 2015
Applicant: GENERAL ELECTRIC COMPANY (Schenectady, NY)
Inventors: David Allan Torrey (Ballston Spa, NY), Deepak Aravind (Bangalore)
Application Number: 14/031,236
International Classification: F04D 15/00 (20060101); F04D 13/08 (20060101);