U.S. patent application number 14/031236 was filed with the patent office on 2015-03-19 for system and method for converterless operation of motor-driven pumps.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Deepak Aravind, David Allan Torrey.
Application Number | 20150078917 14/031236 |
Document ID | / |
Family ID | 51492495 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150078917 |
Kind Code |
A1 |
Torrey; David Allan ; et
al. |
March 19, 2015 |
SYSTEM AND METHOD FOR CONVERTERLESS OPERATION OF MOTOR-DRIVEN
PUMPS
Abstract
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.
Inventors: |
Torrey; David Allan;
(Ballston Spa, NY) ; Aravind; Deepak; (Bangalore,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
51492495 |
Appl. No.: |
14/031236 |
Filed: |
September 19, 2013 |
Current U.S.
Class: |
417/42 ;
417/44.1; 417/44.3 |
Current CPC
Class: |
F04D 13/08 20130101;
F04D 15/0066 20130101; F04B 2203/0209 20130101; F04B 2203/0202
20130101; F04B 49/103 20130101; F04B 47/06 20130101; H02P 9/04
20130101; E21B 43/128 20130101; F04B 49/06 20130101; F04B 2203/0201
20130101 |
Class at
Publication: |
417/42 ;
417/44.1; 417/44.3 |
International
Class: |
F04D 15/00 20060101
F04D015/00; F04D 13/08 20060101 F04D013/08 |
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.
Description
BACKGROUND
[0001] 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.
[0002] 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.
[0003] FIG. 1 illustrates a conventional system 10 that is known in
the oil and gas industry for operating electric submersible pumps
(ESPs) 12 in an off-grid application. One or more prime movers that
are directly coupled to generators 14 produce an AC voltage having
a fixed frequency and amplitude to supply electrical loads 15. The
prime movers may comprise, for example, a reciprocating engine that
is fueled by either natural gas or diesel fuel, or a turbine. The
generated AC power is fed to a VSD 16 that is responsible for
regulating the operation of the ESPs 12 subsequent to stepping up
the AC voltage to a medium voltage level that is supplied to ESP
motor(s) 18 via a suitable transformer 19.
[0004] 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.
[0005] 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 DESCRIPTION
[0006] According to one embodiment, a converterless motor-driven
pump system comprises:
[0007] 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;
[0008] at least one electric power generator driven by the at least
one off-grid prime mover to generate AC power;
[0009] at least one variable speed motor directly powered by the at
least one electric power generator;
[0010] 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;
[0011] 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
[0012] 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.
[0013] According to another embodiment, a method of operating an
electric submersible pump comprises:
[0014] controlling a driveshaft speed of an off-grid prime mover in
response to a throttle control command;
[0015] controlling an AC power output of an electric power
generator in response to the driveshaft speed of the off-grid prime
mover;
[0016] controlling a speed of a variable speed motor directly in
response to the AC power output of the electric power generator;
and
[0017] 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.
DRAWINGS
[0018] 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:
[0019] FIG. 1 illustrates a conventional electrical submersible
pump (ESP) system that is known in the art;
[0020] FIG. 2 illustrates a converterless ESP system according to
one embodiment;
[0021] FIG. 3 is a block diagram illustrating a system controller
interfacing with and controlling a converterless ESP system
according to one embodiment; and
[0022] FIG. 4 is a block diagram illustrating a method of providing
off-grid power to a motor-driven submersible well pump according to
one embodiment.
[0023] 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 DESCRIPTION
[0024] The 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.
[0025] FIG. 2 illustrates a converterless ESP system 20 according
to one embodiment. In this embodiment, the prime mover(s) 21 is/are
directly controlled to regulate the pump inlet pressure. More
specifically, the ESP system 20 comprises one or more prime movers
21 that are coupled to one or more generators 22, means 24 for
electrically connecting the output of the generator(s) 22, and a
motor-driven pump 26. The prime mover 21 is typically a
reciprocating engine that is fueled by either natural gas or diesel
fuel, but is not so limited, as other types of prime movers such
as, without limitation, turbines may also be employed as the prime
mover 21. Depending on the selection of the prime mover 21 and the
generator 22, it may be desirable to use a gearbox to match the
shaft speeds of the prime mover 21 and generator 22. It is
preferable to use a fixed ratio gearbox to keep the system 20 as
simple as possible. The motor-driven pump 26 is typically located
within a well for purposes of artificially lifting a fluid from the
well. The fluid could be, without limitation, water, gas or oil in
a well, or a combination thereof. It is likely some amount of
solids, such as sand or proppant, will be entrained with the
fluid.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] FIG. 3 is a block diagram illustrating the flow of power and
information for a converterless ESP system 30 according to one
embodiment. The power flows from the prime mover 21 through the
generator 22 and cable 32 to the motor 34 and subsequently the pump
26. The power between the prime mover 21 and the generator 22 is
mechanical driveshaft power, as is the power between the induction
motor 34 and the pump 26. A gearbox between the prime mover 21 and
the generator 22 may advantageously be employed for purposes of
system optimization, as stated herein.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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
[0037] 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.
[0038] 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.
[0039] FIG. 4 is a block diagram illustrating a method 40 of
providing off-grid power to a motor-driven submersible well pump 26
according to one embodiment. A prime mover 21 driveshaft is coupled
directly or indirectly to a generator 22; while the generator 22 is
electrically coupled to a motor that may be a line start motor such
as an induction motor or permanent magnet motor 34 via a power
cable 32 that may be, for example, without limitation, an
electrical submersible pump cable; and the motor driveshaft is
directly coupled to the submersible well pump 26, as represented in
block 42. The prime mover 21 is turned-on to rotate its driveshaft,
causing the generator 22 to produce AC power sufficient to power
the motor 34, that subsequently drives the submersible well pump
26, as represented in block 44. A sensor package 28 that may
comprise, without limitation, various pressure sensors, temperature
sensors, vibration sensors, and speed sensors associated with the
submersible well pump 26 function to monitor operating conditions
including without limitation, pump inlet pressure, pump vibration
levels, pump rotational speed, and temperatures at desired points
associated with the submersible well pump 26, as represented in
block 46. The monitored operating data is acquired by a system
controller 36 that determines whether the prime mover driveshaft
should be rotating at a different speed. The system controller 36
then transmits an appropriate throttle control command 38 to the
prime mover 21, causing the prime mover driveshaft to rotate faster
or slower as necessary to ensure the submersible well pump 26 is
operating at the desired operating point, as represented in block
48. According to one embodiment, the system controller 36 also
monitors the rotational speed of the prime mover driveshaft via one
or more speed sensors 25 associated with the driveshaft of the
prime mover 21, and commands the exciter 39 of a generator 22 to
supply an appropriate level of excitation to the generator 22 when
the generator 22 is a synchronous generator, as represented in
block 50.
[0040] 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
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
* * * * *