U.S. patent application number 11/070987 was filed with the patent office on 2006-09-07 for skipping frequencies for variable speed controls.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20060198744 11/070987 |
Document ID | / |
Family ID | 36944282 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198744 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
September 7, 2006 |
Skipping frequencies for variable speed controls
Abstract
A control for an electric motor is utilized to avoid operation
in or near the resonance frequencies for the electric motor and its
associated system components. The resonance frequencies can be
identified experimentally at the design stage, or during operation
of a component and electric motor. During start-up, shutdown or
frequency adjustment, the control drives the speed through the
resonance frequency zones more rapidly, and also avoids operation
in or near those resonance frequencies during steady state
operation. In disclosed embodiments, the electric motors are
associated with fans, pumps and compressors in a refrigerant
system.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Assignee: |
Carrier Corporation
|
Family ID: |
36944282 |
Appl. No.: |
11/070987 |
Filed: |
March 3, 2005 |
Current U.S.
Class: |
417/423.1 |
Current CPC
Class: |
F04B 2203/0204 20130101;
F25B 2600/0253 20130101; F25B 2600/112 20130101; H02P 23/20
20160201; Y02B 30/741 20130101; Y02B 30/70 20130101; F04B 35/04
20130101; F04B 2201/0806 20130101; Y02B 30/743 20130101; F04B 17/03
20130101; H02P 23/04 20130101; F25B 2500/13 20130101; F04B
2203/0209 20130101; F25B 49/025 20130101 |
Class at
Publication: |
417/423.1 |
International
Class: |
F04B 17/00 20060101
F04B017/00 |
Claims
1. An electric motor and component comprising: an electric motor
for driving an associated component; and a control for said
electric motor, said control being operable to drive said electric
motor through a variable range of operational frequencies, said
control storing at least one undesirable zone of operational
frequency for said electric motor, and said control limiting an
amount of time said electric motor operates in said at least one
undesirable zone of operational frequency.
2. The electric motor and component as set forth in claim 1,
wherein said control moves between frequencies by varying frequency
and monitoring operation of the component, and said control not
moving an operational frequency of said electric motor to said at
least one undesirable zone of operational frequency.
3. The electric motor and component as set forth in claim 1,
wherein said control avoids steady state operation in said at least
one undesirable zone of operational frequency during operation of
said electric motor and said component.
4. The electric motor and component as set forth in claim 1,
wherein said component is included in a refrigerant system.
5. The electric motor and component as set forth in claim 1,
wherein said control being programmed to move rapidly through said
at least one undesirable zone of operational frequency during
start-up of said motor.
6. The electric motor and component as set forth in claim 1,
wherein said control being programmed to move rapidly through said
at least one undesirable zone of operational frequency during
shutdown of said electric motor.
7. A refrigerant system comprising: a compressor, said compressor
being provided with a first electric motor for driving a
compressor; a first heat exchanger downstream of said compressor,
and a first fluid-moving device associated with said first heat
exchanger, said first fluid-moving device being provided with a
second electric motor; an expansion device downstream of said first
heat exchanger, a second heat exchanger downstream of said
expansion device, and a second fluid-moving device associated with
said second heat exchanger, said second fluid-moving device being
provided with a third electric motor; and a variable speed control
for at least one of said first, second and third electric motors,
said control being programmed to store at least one undesirable
operational frequency zone, and said control being programmed to
minimize an amount of time said at least one of said first, second
and third electric motors operate in said undesirable operational
frequency zone.
8. The refrigerant system as set forth in claim 7, wherein at least
one of said first and second fluid-moving devices moves air over
its associated heat exchanger.
9. The refrigerant system as set forth in claim 7, wherein at least
one of said first and second fluid-moving devices moves liquid
through its associated heat exchanger.
10. The refrigerant system as set forth in claim 7, wherein said
control moves between frequencies by varying frequency and
monitoring operation of said refrigerant system, and said control
not moving an operational frequency of said at least one of said
first, second and third electric motors to said undesirable
operational frequency zone.
11. The refrigerant system as set forth in claim 7, wherein said
control avoids steady state operation at said undesirable
operational frequency during operation of said at least one of said
first, second and third electric motors.
12. The refrigerant system as set forth in claim 7, wherein said
control being programmed to move rapidly through said at least one
undesirable zone of operational frequency during start-up of said
motor.
13. The refrigerant system as set forth in claim 7, wherein said
control being programmed to move rapidly through said at least one
undesirable zone of operational frequency during shutdown of said
electric motor.
14. The refrigerant system as set forth in claim 7, wherein said
undesirable operational frequency zones are pre-determined.
15. The refrigerant system as set forth in claim 7, wherein said
undesirable operational frequency zones are determined by placing
transducers on a component or part of the refrigerant system and
monitoring operation of said transducer as an operational frequency
of said at least one of said first, second and third electric
motors changes.
16. The refrigerant system as set forth in claim 15, wherein said
transducers include vibration transducers.
17. The refrigerant system as set forth in claim 15, wherein said
transducers include pressure pulsation sensors.
18. The refrigerant system as set forth in claim 15, wherein said
transducers include sound transducers.
19. The refrigerant system as set forth in claim 7, wherein at
least one of said first, second and third electric motors are
provided with a control programmed to store an undesirable
operational frequency zone, and said controls each being programmed
to minimize the amount of time each of said first, second and third
electric motors operates in said undesirable operational frequency
zone.
20. A method of operating an electric motor comprising the steps
of: (1) providing an electric motor for driving a component, said
electric motor being operable at a varying operational frequency,
and said electric motor being provided with a control, said control
storing at least one zone of operational frequency for said
electric motor; and (2) utilizing said control to drive said
electric motor, and minimize an amount of time said electric motor
spends at said at least one zone of operational frequency.
21. The method as set forth in claim 20, wherein said control
varies an operational frequency, and monitors operation of said
component, and said control not varying the operational frequency
into said at least one zone of operational frequency.
22. The method as set forth in claim 20, wherein said control
further avoids operation at said at least zone of operational
frequency during steady state operation of said electric motor.
23. The method as set forth in claim 20, wherein said control
avoids operation at said at least one zone of operational frequency
during transient operation of said electric motor by quickly
passing through the at least one zone of operational frequency
during the transient operation.
24. The method as set forth in claim 20, wherein said component
being a compressor in a refrigerant system.
25. The method as set forth in claim 20, wherein said component
being a fluid-moving device for moving a fluid over a heat
exchanger in a refrigerant system.
26. The method as set forth in claim 25, wherein said fluid-moving
device is a pump for moving liquid through the heat exchanger.
27. The method as set forth in claim 25, wherein said fluid-moving
device is a fan for moving air over the heat exchanger.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a method of avoiding objectionable
frequencies for equipment driven by a variable speed motor, and in
particular for motors driving equipment utilized in refrigerant
systems.
[0002] Electric motors are utilized in refrigerant systems to drive
the fans, pumps and compressors. As is known, in a basic
refrigerant system, a compressor compresses a refrigerant and
delivers that refrigerant downstream to a first heat exchanger. The
first heat exchanger exchanges heat between the refrigerant and
another heat transfer media such as air, and passes the refrigerant
to an expansion device. From the expansion device, the refrigerant
is delivered to another heat exchanger, and heat is again exchanged
with another heat transfer media. From the second heat exchanger,
refrigerant is returned to the compressor. Fans or pumps are
associated with each of the two heat exchangers, and a motor is
typically associated with each fan or pump. Further, a motor is
provided to drive a compressor unit. Also, refrigerant system
circuits can have other components such as for example fans or
pumps driven by a variable speed motors.
[0003] Variable speed motors are becoming more widely utilized in
refrigerant systems. A variable speed motor provides a designer
with enhanced flexibility in system operation and control. For
instance, the capacity of the refrigerant system can be changed by
varying the speed of the compressor motor. Thus, variable speed
motors and driven equipment can operate across a variety of
operational frequencies. Typically, the variable speed motor starts
from a frequency of zero and is ramped up toward a desired
operational frequency. Thus, the frequency advances from zero
upwardly to an operational frequency, which may be selected to
achieve a desired cooling capacity, etc. Further, at shutdown, the
frequency decreases from that operational frequency back towards
zero.
[0004] A control for the variable speed motor may change the
operational frequency, as conditions or load demands faced by the
refrigerant system change.
[0005] One problem with the above-described systems is that for any
mechanical systems, there are certain frequencies, which have
undesirable aspects, for example, as caused by either acoustic or
mechanical resonances. Such frequencies could cause excessive
vibration and internal pulsations resulting in component damage as
well as undesirable noise potentially leading to customer
discomfort. The above-described systems, with the motor frequencies
starting from zero and advancing upwardly towards the desired
operational frequency, may pass through these resonance frequencies
both at start-up and at shutdown. Also, as the control changes
frequencies during operation to satisfy external load demands, it
may sometimes move the electric motor operation to one of the
resonance frequency zones that should be avoided. The system
resonance frequencies can also be excited by multiples of motor
running speed frequencies, or by the running frequencies (or their
multiples) of the driven equipment itself. It should be pointed out
that the equipment running speed frequency can be different than
that of the motor, if for example the driven equipment is attached
to the motor via a gearbox.
[0006] This is undesirable, as excessive vibration, noise and
pulsations may occur and result in damage of the system
components.
SUMMARY OF THE INVENTION
[0007] In a disclosed embodiment of this invention, the undesirable
frequencies for a particular component associated with an electric
motor are identified. As motor frequency is varied, the control is
programmed to avoid those undesirable frequency zones. In known
control algorithms for an electric motor associated with a
refrigerant system, the frequency is varied, and the resultant
change from the refrigerant system operation is monitored. The
control has a desired system operational feature. That desired
operational feature may be the cooling capacity of the refrigerant
system, as an example. In one well-known control method, the
control does not necessarily determine the required operational
frequency of the motor. Instead, the control varies the operational
frequency and monitors the resultant change on the refrigerant
system until a frequency is found at which the operation of the
system is as desired. Typically, the frequency is varied in
incremental steps. With this invention, the control will vary the
operational frequency of the electric motor, but will skip
operation in zones associated with the undesirable frequencies.
[0008] As mentioned above, the disclosed application for such a
control and method would be for the fans, pumps and compressors
driven by a motor in a refrigerant system. However, other system
components may benefit from-this basic control concept.
[0009] The undesirable frequencies (frequency that would normally
be associated with either acoustical or mechanical resonances) may
be determined experimentally, in a laboratory for a particular type
of equipment, or may be determined by various types of sensors
mounted upon the component. As an example, sensors can be mounted
on a fan housing, and sense one of the vibration characteristics.
The frequency of the motor or the running frequency of the driven
equipment or multiples thereof can be associated with the varying
vibration level, and in this manner, the frequencies most subject
to vibration and exceeding the desired level can be identified, and
then avoided, or associated with a "higher slope" of ramp-up during
the start-up, shutdown and frequency adjustment processes. The same
reasoning would apply to measurement of excessive pulsations, as
for example measured by dynamic pressure transducers installed into
the piping adjacent to the system components.
[0010] Additionally, the system may self-learn during operation by
comparing, for instance, vibration sensor measurements to
acceptable values and the controller may include frequencies to be
avoided to the skip frequency list in a stored database.
[0011] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic view of a refrigerant system
incorporating the present invention.
[0013] FIG. 2 is a graph of one of the vibration characteristics
versus the operational frequency of an electric motor.
[0014] FIG. 3A is a graph of the operational frequency over time in
accordance with an inventive method.
[0015] FIG. 3B is a flowchart of the inventive method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] FIG. 1 shows a refrigerant system 20 incorporating
compressor 22 delivering a compressed refrigerant to a heat
exchanger 24. The heat exchanger 24 is associated with a fan 26 for
driving air over the heat exchanger 24. The fan 26 is associated
with a motor, as known. A variable speed control C and a transducer
T are associated with the fan 26. The variable speed control C
drives the motor for the fan 26, and the transducer T may identify
one of the parameters associated with vibration level at the
fan.
[0017] Refrigerant passes from the heat exchanger 24 downstream to
an expansion device 28, and then to another heat exchanger 30. The
heat exchanger 30 is associated with its own fan 32. A variable
speed motor control C and transducer T are also associated with the
fan 32.
[0018] The refrigerant passes from the heat exchanger 30 back to
the compressor 22. As is known, a motor drives a compressor unit
22, and a variable speed control C and a transducer T are
associated with the compressor 22.
[0019] While refrigerant systems such as are utilized for air
conditioning typically have fans moving air over the heat
exchangers, other refrigerant systems may be utilized with fluids
other than air. As an example, the assignee of the present
invention has recently developed a system wherein a refrigerant
system is utilized to heat water. In such a case, at least one of
the heat exchangers would include a pump moving water over the heat
exchanger, rather than a fan moving air. The present invention
would extend to such systems.
[0020] As shown in FIG. 2, if one were to plot the operational
frequency of a motor versus one of the characteristics associated
with the vibration, pulsation or sound level within a component
associated with the motor, there would be typically one or more
"resonance frequencies" at which the vibration/pulsation/sound
level increases dramatically. As shown in FIG. 2, these frequency
zones are designated as X.sub.1 and X.sub.2. The present invention
seeks to limit the operation of the motors in or near these
frequencies, or to "skip" these frequencies.
[0021] FIG. 3A is a control diagram of the present invention. As
shown, the control may operate by moving through a series of
incremental steps A, B, C, and D. The control moves to one of these
steps, and operates the refrigerant system. The operation of the
refrigerant system is monitored, and if the refrigerant system is
operating as desired, the control will remain at that operational
frequency. However, it is typical that the control must vary the
operational frequency, and over time certainly will often need to
vary the operational frequency when external load demands change or
the indoor space is reaching the desired conditions. As shown in
FIG. 3A, when the operational frequency is varied, it is varied in
steps that avoid the resonance frequency zones. Thus, if the
control starts the refrigerant system 20 operating at the frequency
A, and determines that the operation of the refrigerant system 20
does not correspond to a desired state to satisfy cooling
requirements, it will advance to frequency B. Again, if frequency B
does not provide the desired result, the control will increase
frequency to C. From frequency C, a shorter incremental step to
frequency D may be utilized. This is an overly simplified
explanation of the controls, which may be known in the art (other
than the inventive addition of skipping through the zones X.sub.1
and X.sub.2). Typically, the incremental steps might be smaller,
and/or of different size, and there may be several between each of
the resonance frequency zones. However, the FIG. 3A does provide an
understanding of the operation basics.
[0022] In this manner, while the motor frequency will pass through
both zones X.sub.1 and X.sub.2 during start-up, shutdown or
frequency adjustment, it will only be in those zones for a brief
period of time. Thus, the excessive vibration, noise or pulsation
will not be felt for any undue length of time.
[0023] Moreover, as the control C controls the speed of the motor
during operation, the speed may be varied dependent on operational
conditions. That is, a worker of ordinary skill in the art would
recognize various reasons for which variation in the speed may be
desirable. As one example only, as the desired capacity for the
compressor changes, it would be desirable to vary the motor speed
for the compressor and consequently perhaps fan or pump speed as
well. The controls C for this invention are programmed (as
described below) to avoid operating in the zones X.sub.1 and
X.sub.2, regardless of whether operation in such zones may be
dictated by the operational conditions.
[0024] The zones X.sub.1 and X.sub.2 may be determined in any one
of several manners. In the illustrated embodiment, the transducers
T are utilized to find the undesirable frequencies (as mentioned
earlier the undesirable frequencies may be associated with system
or component resonances but can be "undesirable" for other
considerations as well) by monitoring at least one of vibration,
pulsation, sound or other characteristics on the several system
components. Alternatively, the resonance frequencies can be
determined experimentally for a specific family of components or
type of the equipment and then pre-programmed into the operating
logic of the controllers C.
[0025] Another method would be to utilize a system that will
"self-learn" the frequencies to be avoided. Another method might be
to vary the speed during initial operation to "hunt" for the
resonance frequencies to be avoided and then input these
frequencies into the system controller such that they can be
avoided. Such cases may surface when system natural frequencies are
installation dependant or cannot be generalized for an entire
product line. The `hunt` for these undesirable frequencies may be
repeated on a regular basis to detect whether there has been a
change in these resonance frequencies over time.
[0026] The transducer T can be an accelerometer, and can be mounted
on the fan or compressor housing, on interconnecting pipes, on the
heat exchangers, etc. Other types of transducers such as proximity
sensors, velocity pick-up vibration sensors, etc. can be utilized
as well. Further, pulsation/acoustic measurement transducers such
as a dynamic pressure sensor as well as other types of sound
measurements, which may be remote to the component at issue, can be
utilized. Furthermore, for redundancy purposes, multiple
transducers can be employ to determine undesirable operational
frequency zones.
[0027] FIG. 3B is a flowchart of this invention, and shows the
start-up or shutdown procedure, as well as the continuous operation
while avoiding the "skipped" frequencies.
[0028] Although a preferred embodiment of this invention has been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
* * * * *