U.S. patent application number 12/599579 was filed with the patent office on 2010-09-23 for compressor motor control.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100236264 12/599579 |
Document ID | / |
Family ID | 40032177 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100236264 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
September 23, 2010 |
COMPRESSOR MOTOR CONTROL
Abstract
A compressor, which is susceptible to protective shutdowns when
certain operating conditions are sensed, includes a control feature
wherein, when the compressor is restarted after a period of time,
it may be caused to operate in an unloaded mode such that a
reoccurrence of the shutdowns is less likely.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
40032177 |
Appl. No.: |
12/599579 |
Filed: |
May 15, 2007 |
PCT Filed: |
May 15, 2007 |
PCT NO: |
PCT/US07/11627 |
371 Date: |
November 10, 2009 |
Current U.S.
Class: |
62/115 ;
62/228.1 |
Current CPC
Class: |
F25B 49/022 20130101;
F25B 2700/21156 20130101; Y02B 30/70 20130101; F25B 49/005
20130101; F25B 2600/2515 20130101; F25B 41/22 20210101; F25B
2600/2509 20130101; F25B 2400/13 20130101; F25B 2600/026 20130101;
F25B 2700/151 20130101; F25B 2600/0253 20130101; F25B 2500/08
20130101 |
Class at
Publication: |
62/115 ;
62/228.1 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F25B 1/00 20060101 F25B001/00 |
Claims
1. A control for operating a refrigerant system of the type having
a motor-driven compressor which is subject to variable load
conditions, An identification mechanism identifying a condition
indicative of an excessive compressor load when operating the
compressor in a first loaded mode; and an unloading mechanism for
responsively reducing the compressor load to prevent compressor
shutdown.
2. A control as set forth in claim 1 wherein said identification
mechanism comprises at least one sensor.
3. A control as set forth in claim 1 wherein said compressor load
is associated with a compressor motor load.
4. A control as set forth in claim 2 wherein said at least one
sensor includes a compressor motor current sensor.
5. A control as set forth in claim 2 wherein said at least one
sensor includes a sensor for sensing the temperature of the
compressor drive motor.
6. A control as set forth in claim 2 wherein said at least one
sensor includes both a compressor motor current sensor and a
compressor motor temperature sensor.
7. A control as set forth in claim 2 wherein said at least one
sensor includes at least one of a temperature sensor and a pressure
sensor sensing operating conditions within the refrigerant
system.
8. A control as set forth in claim 1 wherein said unloading
mechanism automatically reduces the load on the compressor motor by
switching to one of the following modes of operation:
non-economized and bypass to suction.
9. A control as set forth in claim 1 wherein said unloading
mechanism automatically reduces the load on the compressor motor by
at least one of the following means: a suction modulation valve, a
suction pulse width modulation valve, a variable speed drive for
the compressor motor, a multi-speed drive for the compressor motor,
permanent disengagement of at least some of the compression
elements, engagement-disengagement of compression elements in the
pulse width modulation manner, variable air management system and a
variable number of active heat exchangers in the refrigerant
system.
10. A control as set forth in claim 1 and including a compressor
drive motor overload protection which is adapted to shut down the
operation of the compressor.
11. A control as set forth in claim 10 wherein said motor overload
protection comprises a line break shutdown apparatus.
12. A control as set forth in claim 7 wherein said motor overload
protection comprises an overload sensor.
13. A control as set forth in claim 10 and including a counter for
counting the number of consecutive shutdowns by the compressor
drive motor overload protection and a timer for recording the time
from an initial shutdown of the compressor by the line break
apparatus to the time of a subsequent shutdown of the compressor by
the line break apparatus.
14. A control as set forth in claim 13 and including a tinier for
recording the time from an initial shutdown of the compressor to
the time of a subsequent shutdown of the compressor.
15. A control as set forth in claim 14 wherein said unloading
mechanism reduces the load on the compressor drive motor only when
the counter has recorded a predetermined number of shut offs within
a predetermined period of time.
16. A control as set forth in claim 1 and including a loading
mechanism for selectively and automatically increasing, the load on
the compressor when certain predetermined conditions are met.
17. A control as set forth in claim 16 and including a timer for
recording the time from the last shutdown of the compressor by the
line break apparatus.
18. A control as set forth in claim 17 wherein a loading mechanism
increases load on the compressor drive motor when a predetermined
period of time from the last shutdown has expired.
19. A method of controlling a refrigeration system of the type
having a motor driven compressor which is subject to variable load
conditions comprising the steps of: sensing a condition indicative
of an excessive compressor load when operating the compressor in a
first loaded mode; and responsively reducing the compressor load to
prevent compressor shutdown
20. A method as set forth in claim 19 wherein said sensed condition
indicative of an excessive compressor load is one indicative of an
excessive compressor motor load.
21. A method as set forth in claim 19 wherein said reducing step is
initiated prior to an anticipated overload shutdown.
22. A method as set forth in claim 19 wherein said recovery step is
initiated after the occurrence of an overload shutdown and prior to
restarting the compressor drive motor after a period if time.
23. A method as set forth in claim 19 wherein said sensing step
comprises the step of sensing the compressor motor current.
24. A method as set forth in claim 19 wherein said sensing step is
that of sensing the temperature of the compressor drive motor.
25. A method as set forth in claim 19 wherein said sensing step
involves the sensing of both the compressor motor current and the
compressor motor temperature.
26. A method as set forth in claim 19 wherein said compressor load
reducing step automatically reduces the load on the compressor
motor by switching to one of the following modes of operation: a
non-economized and bypass to suction.
27. A method as set forth in claim 19 wherein said load reducing
step automatically reduces the load on the compressor motor by at
least one of the following means: a suction modulation valve, a
suction pulse width modulation valve, a variable speed drive for
the compressor motor, a multi-speed drive for the compressor motor,
permanent disengagement of at least some of the compression
elements, engagement-disengagement of compression elements in the
pulse width modulation manner, variable air management system and a
variable number of active heat exchangers in the refrigerant
system.
28. A method as set forth in claim 19 and including the step of
counting the number of consecutive shut offs by the line break
apparatus and recording the time from initial shutting off of the
compressor by a line break apparatus to the time for a subsequent
shutting off of the compressor a line break.
29. A method as set forth in claim 28 wherein said load reducing
step involves reducing the load capacity mode of operation only
when the counter has recorded a predetermined number of shut offs
within a predetermined period of time.
30. A method as set forth in claim 19 and including the step of
selectively increasing the load capacity mode of operation under
certain predetermined conditions.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to refrigerant systems and,
more particularly, to selectively unloading the compressor of a
refrigerant system.
[0002] Air conditioning and refrigeration systems typically include
protective mechanisms which sense when a compressor becomes
overloaded. When such condition is sensed the compressor is
typically shut down for a period of time and then typically
restarted again after the shutdown. In some cases, when a
catastrophic failure is detected, the compressor may not be
re-started until the root cause of the failure is identified by an
operator, technician or maintenance personnel. Typically, the
protective mechanism is associated with the measurement of the
electric current in the motor and/or the motor temperature or a
direct effect of these parameters on the protection device such as
an electric motor line break that is tripped in response
thereto.
[0003] This condition will normally occur in high temperature
ambient environments when the cooling is most needed, and the
refrigerant system operates at extremely high loads to satisfy
these cooling demands. That is, during the period in which if the
compressor motor is shut down as a result of protection device
engagement, there will be no cooling for an occupant of the
conditioned space or food refrigeration in the refrigeration
chamber. When the motor is re-started; it will still be subjected
to high load conditions and is likely to be shut down once again in
a relatively short period of time. Therefore, there may be
prolonged periods of higher than desired temperature conditions
when there is little or no cooling being provided, thereto causing
discomfort to an occupant of the climate-controlled environment or
spoilage of the food in the refrigeration container. It is
desirable to obtain some cooling, even if at a reduced rate, during
these periods of time when extreme environmental conditions are
imposed on the refrigerant system.
DISCLOSURE OF THE INVENTION
[0004] Briefly, in accordance with one aspect of the invention, at
or near the time in which the compressor motor is re-started after
a line break shutdown has occurred, the compressor is caused to
operate at a reduced load mode such that it is less likely to
result in another line break shutdown occurrence.
[0005] In accordance with another aspect of the invention, when a
compressor shutdown is anticipated and likely to occur, the
compressor is switched to the next less loaded mode of operation to
avoid or prevent shutdown conditions.
[0006] In accordance with yet another aspect of the invention, the
unloading of the compressor may be accomplished by switching the
refrigerant system from an economized to a non-economized mode,
from a non-economized mode to a bypass mode, throttling the flow
through a suction modulation valve, or operating a suction
modulation valve in the pulse width modulation manner.
[0007] In accordance with another aspect of the invention, the
unloading of the compressor may be accomplished by at least one of
the following means: a variable speed drive for the compressor
motor, a multi-speed drive for the compressor motor, permanent
disengagement of at least some of the compression elements,
engagement-disengagement of the compression elements in the pulse
width modulation manner, a variable air management system and a
variable number of active heat exchangers in the refrigerant
system.
[0008] By still another aspect of the invention, provision may be
made to count the number of line break shutdown occurrences and to
cause a compressor unloading only after a predetermined number of
line break shutdowns occur within a predetermined period of
time.
[0009] By yet another aspect of the invention, provision may be
made to return to a more loaded mode of operation after certain
predetermined conditions had been met.
[0010] In the drawings as hereinafter described, a preferred
embodiment is depicted; however, various other modifications and
alternate constructions can be made thereto without departing from
the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic illustration of the present invention
as incorporated into a refrigerant system.
[0012] FIG. 2 is a flow chart depicting an exemplary method of
control in accordance with the present invention.
[0013] FIG. 3 is a graphic illustration of the results of the
present invention implementation.
DETAILED DESCRIPTION OF THE INVENTION
[0014] There is schematically shown in FIG. 1, a refrigerant
circuit in which a compressor 11, a condenser, 12 an expansion
device 13 and an evaporator 14 are connected in typical serial
refrigerant flow relationship. The condenser 12 is positioned such
that ambient air is passed thereover by a condenser fan 16 for
purposes of de-superheating, condensing and then subcooling the
refrigerant vapor being received from the compressor 11. As known,
the condenser 12 of a sub-critical cycle becomes a gas cooler for
trans-critical applications, where it operates above the
refrigerant critical point. The evaporator 14 is positioned to
receive return air from a conditioned space, which may be mixed
with a portion of fresh air, to be cooled and for delivering the
cooled air to the climate-controlled environment by way of an
evaporator fan 17. The refrigerant is evaporated and typically
superheated in the evaporator 14. Although a basic refrigerant
system arrangement is depicted in FIG. 1, various options and
enhancement features are feasible and known in the art. All these
system configurations are within the scope and can equally benefit
from the invention.
[0015] As will be understood, the refrigerant system compressor 11
is subject to a variable load depending on various factors such as
ambient temperature, thermal (sensible and latent) load demand in
the conditioned space, electrical power supplied to the compressor,
etc. Accordingly, provision is made for operating the compressor 11
in various modes to match cooling or heating demands in the
climate-controlled space.
[0016] In the exemplary refrigerant system schematic shown in FIG.
1, in order to vary the degree of loading or unloading of the
compressor 11, there are provided several unloading features such
as an economizer 18, a bypass valve 19 and a suction modulating
valve 21. Although a discussion below is limited only to these
three unloading features, other options may be provided, that may
include, but are not limited to, variable or multi-speed compressor
motors, variable air management systems, a variable number of
components (such as heat exchangers) operating in parallel, etc.
All these unloading steps are well within the scope of the
invention.
[0017] For economized operation, such as, for example, when an
additional capacity is needed, as during pulldown or at
steady-state operation at high ambient temperatures or deep
refrigeration conditions, the liquid refrigerant in the main
circuit entering the evaporator expansion device 13 is further
cooled by operation of the economizer heat exchanger 18. To
activate the economizer heat exchanger 18, the economizer expansion
device 22 is opened so as to allow a portion of the refrigerant to
flow through the economizer heat exchanger 18 to absorb heat from
the liquid refrigerant flowing to the evaporator expansion device
13. Therefore, thermal cooling potential of the refrigerant
entering the evaporator 14 is increased, enhancing performance
(capacity and efficiency) of the refrigerant system. The resultant
"medium" temperature/pressure economizer refrigerant vapor is
injected into the compressor 11 at a mid-point thereof. This
economizer flow is mixed with the partially compressed suction
refrigerant vapor, and typically cools this suction vapor to a
lower temperature. Since the economizer refrigerant is entering the
compressor 11 at a higher pressure then the refrigerant entering
through a suction port of the compressor 11, less energy (per a
unit of mass) is required to compress this refrigerant vapor from
the economizer pressure to the discharge pressure, as compared to
the compression of the suction vapor from the suction pressure to
the discharge pressure. Regardless, overall compressor power is
increased, due to additional amount of refrigerant that is injected
through the economizer port (or ports) and needed to be compressed
and then circulated throughout the system. Therefore, the
economized mode of operation imposes a higher load on the
compressor 11, in comparison to the conventional (non-economized)
mode of operation. It should be pointed out that if the economizer
expansion device 22 does not have a shutdown capability, an
additional flow control device should be integrated into the
economizer circuit. Also, as known in the art, there are many
variations of the economizer cycle schematic shown in FIG. 1, all
of which are within the scope of the invention.
[0018] The bypass mode of operation is activated by opening a
bypass valve 19 which allows a portion of the partially compressed
refrigerant vapor to pass back to a suction port of the compressor
11 so as to thereby decrease the compressor power (since a reduced
amount of refrigerant is compressed from a mid-stage pressure to a
discharge pressure) and refrigerant system capacity (since a lower
amount of refrigerant is circulated through the evaporator 14).
[0019] To operate the refrigerant system in the suction modulation
mode, the suction modulation valve 21 is selectively moved to a
partially closed position so as to decrease the flow of refrigerant
to the compressor 11. This is intended to further balance the
compressor capacity with the thermal load in the climate-controlled
space. In this mode of operation, a liquid injection solenoid valve
(not shown) may be selectively opened as required to provide a
sufficient amount of expanded liquid refrigerant, flow into the
suction port of the compressor 11 for cooling of the compressor
motor. It should be noted that the suction modulation valve 21 may
be substituted by a pulse width modulation valve or the like to
control refrigerant flow into the suction port of the compressor
11.
[0020] As was mentioned before, any other unloading techniques,
such as, for instance, in addition to examples disclosed above,
disengaging of some pistons of a multi-piston reciprocating
compressor or controlling engagement of the scroll elements of a
scroll compressor in a pulse width modulation manner, are within
the scope of the invention.
[0021] Implementation of the various devices for loading/unloading
the compressor 11 as described hereinabove is accomplished by way
of a controller 23. That is, the controller 23 is connected, to the
economizer expansion device 22 by way of an electrical conduit 24,
to the compressor 11 by way of an electrical conduit 26, to the
bypass valve 19 by way of an electrical conduit 27 and to the
suction modulation valve 21 by way of an electrical conduit 28.
[0022] Also sensors 29 and 31, which are connected to the
controller 23 by electrical conduits 32 and 33, respectively, may
be provided. A sensor 29 is provided to sense the current in the
motor driving the compressor 11, and sensor 31 is provided to sense
the temperature of the drive motor for that compressor 11. One or
both of these sensed conditions may be used to determine that the
compressor 11 is in an overloaded condition (or is approaching an
overloaded condition) and needs to be temporarily shut down. On the
other hand, this temporary shutdown may be accomplished by a line
break, which could be, for instance, a bi-metal plate contactor,
installed on the compressor motor and which automatically reacts to
excessive current and/or temperature. Other sensors can also be
installed to determine if the compressor operation is approaching
the overloaded condition. Such sensors may, for example, include
pressure sensors installed either on the high or low pressure side
of the refrigerant system, as well as temperature sensors
associated with the refrigerant system condenser and/or evaporator
heat exchangers. Also, the current or power sensors can sense
compressor overload conditions directly.
[0023] Referring now to FIG. 2, an exemplary flow control diagram
is shown to indicate the manner in which the controller 23 may
operate after a line break shutdown has occurred, so as to allow
the compressor 11 to be brought back into operation at an unloaded
state so that at least some, although reduced, cooling can be
accomplished, while the refrigerant system is operating at a
reduced capacity, at a time when the compressor 11 may otherwise be
forced into another line break shutdown resulting in another
prolonged period of non-operation.
[0024] In a block 34, the counter, which counts the number of
shutdowns in sequence, is set to C=0. Periodically, after a certain
time interval expired, in which the compressor 11 was operated in a
loaded mode as shown in a block 36, the system is queried as to
whether a shutdown on a line, break has occurred as shown in a
block 37. If not, the system continues to operate until a shutdown
has occurred in which case, the control steps to a block 38. The
counter then resets to C=C+1, and then the query is made in a block
39, whether C=2 (i.e. whether there have been two line breaks in
sequence). In this regard, it should be understood that in this
particular example, the threshold for implementing the control
method of the present invention has been set at two line break
occurrences. This, of course, can be varied as desired for any
particular application.
[0025] If, in a block 39, C does not equal 2 (i.e. this is not the
second line break in succession), or is less than 2 and equals to
1, in this particular example, then a timer is set at 0 in a block
41, and the refrigerant system operation is initiated in the same
loaded mode, after the line break is returned to its operational
state. If C is found to be equal to 2, then two consecutive
shutdowns have occurred, and the controller 23 steps to a block 40
wherein the system is queried as to whether the time since the last
line break shutdown is greater then t.sub.1, which is a time period
which has been predetermined to be an allowable time interval
between consecutive shutdowns and therefore giving reason for not
implementing the unloading mode of operation, since in that case,
two consecutive shutdowns are unlikely to be caused by the same
factor. Therefore if t has been determined to be greater than
t.sub.1, then the controller 23 steps to a block 42 to reset the
counter back to C=1. Further, as before, the timer is set at t=0 in
the block 41 and the refrigerant system is made to operate in the
same loaded mode as shown in the block 36.
[0026] If t does not exceed t.sub.1, then most likely the same
factor caused two consecutive shutdowns, and the controller 23
steps to a block 43 to reset the timer to t=0, and then to a block
44 where the compressor motor is restarted in next in sequence
unloaded mode of operation. At this point, the particular mode of
operation for the compressor 11 has changed such that it made to
operate in a more unloaded state than the state which caused the
previous line break shutdown. For instance, for the exemplary
refrigerant system shown in FIG. 1, the sequence of operational
modes from the most loaded mode to the least loaded mode would be
as follows: economized, fully loaded mode; non-economized fully
loaded mode; non-economized bypass mode; and non-economized bypass
mode with suction modulation valve.
[0027] Thus, presuming that, when the second line break shutdown
occurred, the system was operating in an economized, fully loaded
mode, then, in a block 44, the compressor may be restarted as
operating in a non-economized, fully loaded mode. If another line
break shutdown then occurs as at a block 46, then the refrigerant
system would proceed to a block 47 so that the loaded mode is reset
to non-economized, fully loaded operation now.
[0028] If a line break shutdown does not occur as shown in the
block 46, then the refrigerant system controller 23 proceeds to a
block 48 and it is queried whether the time interval in the
unloaded mode of operation is greater than t.sub.2, which is a
predetermined sufficiently safe time interval after which the
refrigerant system may try to restart in the loaded mode of
operation. If t is greater than t.sub.2, then the control 23 resets
to the block 34 and the cycle is repeated. lithe time t is less
than t.sub.2, then the system resets to the block 44, and operation
in the unloaded mode continues.
[0029] It should be understood that the above flow diagram is only
one example of the method, with particular values of certain
parameters being used. Thus, the number of line break shutdowns
that occurs prior to the unloading step can be selected as desired,
as can the values t.sub.1 and t.sub.2. Further, rather than
counting on predetermined time intervals t.sub.1 and t.sub.2, the
refrigerant system may be "tested" in a more loaded mode of
operation by relying on the feedback from the sensors positioned
within the refrigerant system and associated environments. These
sensors, such as, for instance, temperature and/or pressure
sensors, and their preferred locations are known in the art.
[0030] Referring now to FIG. 3, there is shown a typical example of
various temperature trends that may occur during operation in more
and less loaded modes. As is common, the ambient temperature
T.sub.amb tends to increase from early morning until late
afternoon. Thus, when operating without the control features as
described hereinabove, the line break temperature in a loaded mode
of operation T.sub.load, may reach the cutoff temperature limit
T.sub.cutoff, as shown. However, if the system is operating with
the control features as discussed hereinabove, then the line break
temperature in an unloaded mode of operation, T.sub.unload, remains
below the cutoff temperature limit T.sub.cutoff in which the
compressor would be shut down. Thus, the refrigerant system
continues to operate and provide conditioned air to a
climate-controlled space.
[0031] It should be noted that the refrigerant system control 23
may operate proactively to potentially prevent any line break
shutdowns by keeping compressor operational parameters within the
predetermined allowable ranges, by sequentially unloading the
compressor 11. In this case, the control 23 would rely on feedback
from the sensors positioned within the refrigerant system and
providing information associated with the critical operational
parameters for the compressor 11. These sensors, such as, for
instance, temperature sensors, pressure sensors, current sensors
and power sensors, and their preferred locations, are known in the
art. Such sensors may directly measure critical operational
parameters for the compressor 11 or provide sufficient data to the
control 23 that could be translated into the critical parameter
values.
[0032] It should also be understood that in the context of the
above embodiments, a compressor can be selected from a variety of
compressor types, including reciprocating, screw, scroll,
centrifugal or axial compressors. Each compressor can be
represented by multiple compressors. For example, a compressor may
consist of several sequential centrifugal compressor stages. Also,
multiple compressors may operate in parallel or tandem arrangement.
Further, this invention can be applied to different refrigerant
system types, including residential or commercial cooling and
heating applications. It can also be used for providing cooling and
refrigeration in supermarkets, truck-trailer and container
applications.
[0033] While certain preferred embodiments of the present invention
have been disclosed in detail, it is to be understood that various
modification in its structure may be adopted without departing from
the spirit and scope of the invention.
* * * * *