U.S. patent application number 16/412787 was filed with the patent office on 2020-11-19 for linear compressor and methods of setpoint control.
The applicant listed for this patent is Haier US Appliance Solutions, Inc.. Invention is credited to Gregory William Hahn, Srujan Kusumba.
Application Number | 20200362842 16/412787 |
Document ID | / |
Family ID | 1000004123867 |
Filed Date | 2020-11-19 |
United States Patent
Application |
20200362842 |
Kind Code |
A1 |
Hahn; Gregory William ; et
al. |
November 19, 2020 |
LINEAR COMPRESSOR AND METHODS OF SETPOINT CONTROL
Abstract
A linear compressor and methods of operation, for example, to
control a setpoint and vary cooling capacity of the linear
compressor, are provided herein. An appliance may include a linear
compressor having a reciprocating piston movable in a negative
axial direction toward a chamber and positive axial direction away
from the chamber. The appliance may further include a motor
operatively coupled to the reciprocating piston, the motor having a
resting setpoint, an inverter configured to supply a variable
frequency waveform to the motor, and a controller configured to
control the variable frequency waveform. The controller may be
configured to direct a positive DC voltage to the motor to shift
the resting setpoint to increase a cooling capacity of the linear
compressor.
Inventors: |
Hahn; Gregory William;
(Louisville, KY) ; Kusumba; Srujan; (Louisville,
KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haier US Appliance Solutions, Inc. |
Wilmington |
DE |
US |
|
|
Family ID: |
1000004123867 |
Appl. No.: |
16/412787 |
Filed: |
May 15, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 2201/0806 20130101;
F04B 2203/04 20130101; F04B 35/04 20130101; F25D 11/022 20130101;
F04B 2201/0206 20130101 |
International
Class: |
F04B 35/04 20060101
F04B035/04; F25D 11/02 20060101 F25D011/02 |
Claims
1. An appliance, comprising: a linear compressor, the linear
compressor having a reciprocating piston movable in a negative
axial direction toward a chamber and positive axial direction away
from the chamber a motor operatively coupled to the reciprocating
piston, the motor having a resting setpoint; an inverter configured
to supply a variable frequency waveform to the motor; and a
controller configured to control the variable frequency waveform,
the controller being further configured to direct a positive DC
voltage to the motor to shift the resting setpoint to increase a
cooling capacity of the linear compressor.
2. The appliance of claim 1, wherein the positive DC voltage is a
constant voltage applied across a plurality of sinusoidal cycles of
the variable frequency waveform.
3. The appliance of claim 1, wherein the controller is further
configured to apply an amplitude skew increasing half-cycle
amplitude in the positive axial direction for a plurality of
sinusoidal cycles of the linear compressor.
4. The appliance of claim 1, wherein the controller is further
configured to apply a phase skew increasing half-cycle wavelength
in the positive axial direction for a plurality of sinusoidal
cycles of the linear compressor.
5. The appliance of claim 1, wherein the controller is further
configured to: determine that additional cooling capacity is
required at the refrigerator; and increase the positive DC voltage
in response to determining that additional cooling capacity is
required.
6. The appliance of claim 5, wherein increasing the positive DC
voltage comprises increasing the positive DC voltage by a
predetermined voltage value.
7. The appliance of claim 6, wherein the predetermined voltage
value is chosen from a predetermined range of voltage values
associated with increased cooling capacities.
8. The appliance of claim 1, further comprising a temperature
sensor configured to signal that a pull-down event is required at
the refrigerator.
9. The appliance of claim 1, further comprising a temperature
selection control configured to select additional cooling capacity
from the linear compressor.
10. The appliance of claim 1, wherein the controller is further
configured to decrease the positive DC voltage to zero volts to
reset the resting setpoint to return to a nominal cooling capacity
of the linear compressor
11. A method for operating a linear compressor of a refrigerator,
the linear compressor comprising a motor and a reciprocating piston
movable in a negative axial direction toward a chamber and positive
axial direction away from the chamber, the method comprising:
supplying a variable frequency waveform to the motor of the linear
compressor to produce a reciprocal motion in the piston at a first
cooling capacity; determining that an increase in cooling capacity
is required; and directing a positive direct current (DC) voltage
to the motor to induce an extension force at the motor in the
positive axial direction during at least a portion of the supplying
step in response to the determining step.
12. The method of claim 11, wherein the positive DC voltage is a
constant voltage applied across a plurality of sinusoidal cycles of
the linear compressor.
13. The method of claim 11, further comprising applying an
amplitude skew increasing half-cycle amplitude in the positive
axial direction for a plurality of sinusoidal cycles of the linear
compressor.
14. The method of claim 11, further comprising applying a phase
skew increasing half-cycle wavelength in the positive axial
direction for a plurality of sinusoidal cycles of the linear
compressor.
15. The method of claim 11, wherein the determining that the
increase in cooling capacity is required comprises determining that
a pull-down event is occurring in the refrigerator.
16. The method of claim 11, wherein the determining that the
increase in cooling capacity is required comprises receiving a
selection to pull-down a temperature of a storage area of the
refrigerator.
17. The method of claim 11, further comprising: determining whether
additional cooling capacity is required after applying the
extension force; and increasing the positive DC voltage in response
to determining that additional cooling capacity is required.
18. The method of claim 17, wherein increasing the positive DC
voltage comprises increasing the positive DC voltage by a
predetermined voltage value.
19. The method of claim 18, wherein the predetermined voltage value
is chosen from a predetermined range of voltage values associated
with increased cooling capacities.
20. The method of claim 11, wherein the extension force is
sufficient to shift a resting setpoint of the linear compressor.
Description
FIELD OF THE INVENTION
[0001] The present subject matter relates generally to linear
compressors, such as linear compressors for refrigerators and other
appliances.
BACKGROUND OF THE INVENTION
[0002] Some refrigerators may include sealed systems for cooling
chilled chambers of the refrigerators. The sealed systems generally
include a compressor that generates compressed refrigerant during
operation of the sealed systems. The compressed refrigerant flows
to an evaporator where heat exchanges from the chilled chambers, to
cool the chilled chambers and food items located therein.
[0003] Certain refrigerators have included linear compressors for
compressing refrigerant. Linear compressors generally include a
piston and a driving coil. The driving coil receives a current that
generates a force for oscillating the piston (i.e., sliding the
piston forward and backward within a chamber having a cylinder
head). An elastic element, such as a spring, may be provided to aid
in such oscillation. During motion of the piston within the
chamber, the piston compresses refrigerant. Generally, the force of
gas compression acts to push the piston away from the chamber and
cylinder head.
[0004] Motion of the piston within the chamber may be controlled
such that the piston does not crash against another component of
the linear compressor during motion of the piston within the
chamber. The overall motion may be proportional to a stroke length,
which may be dependent upon a setpoint of the piston or motor
operating the piston. Furthermore, cooling capacity is proportional
to the stroke length and setpoint. Generally, the setpoint is a
preset physical point determined by the mechanical mounting of the
motor to the linear compressor, and therefore is generally not
adjustable. Moreover, as stated above, increasing stroke length
motion within the chamber may cause undesirable mechanical
crashing.
[0005] Accordingly, it would be useful to provide a linear
compressor and method of operation for addressing one or more of
the above-identified issues. In particular, a linear compressor and
methods of setpoint and cooling capacity control would be
especially advantageous.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Aspects and advantages of the invention will be set forth in
part in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0007] In one example aspect of the present disclosure, an
appliance is provided. The appliance may include a linear
compressor having a reciprocating piston movable in a negative
axial direction toward a chamber and positive axial direction away
from the chamber. The appliance may further include a motor
operatively coupled to linear compressor, the linear motor having a
resting setpoint and stroke, an inverter configured to supply a
variable frequency waveform to the motor, and a controller
configured to control the variable frequency waveform. The
controller may be configured to direct a positive DC voltage to the
motor to shift the resting setpoint to increase a cooling capacity
of the linear compressor.
[0008] In another example aspect of the present disclosure, a
method of operating a linear compressor is provided. The linear
compressor may include a motor and a reciprocating piston movable
in a negative axial direction toward a chamber and positive axial
direction away from the chamber. The method may include supplying a
variable frequency waveform to the motor of the linear compressor
to produce a reciprocal motion in the piston at a first cooling
capacity, determining that an increase in cooling capacity is
required, and directing a positive direct current (DC) voltage to
the motor to induce an extension force at the motor in the positive
axial direction during at least a portion of the supplying step in
response to the determining step.
[0009] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] A full and enabling disclosure of the present invention,
including the best mode thereof, directed to one of ordinary skill
in the art, is set forth in the specification, which makes
reference to the appended figures.
[0011] FIG. 1 is a front elevation view of a refrigerator appliance
according to an example embodiment of the present disclosure.
[0012] FIG. 2 is schematic view of certain components of the
refrigerator appliance of FIG. 1.
[0013] FIG. 3 provides a perspective view of a linear compressor
according to an example embodiment of the present disclosure.
[0014] FIG. 4 provides a side section view of the linear compressor
of FIG. 3.
[0015] FIG. 5 provides an exploded view of the linear compressor of
FIG. 4.
[0016] FIG. 6 provides a plot of cooling capacity and associated
efficiency for a conventional linear compressor compared to the
linear compressor of FIG. 3.
[0017] FIG. 7 provides a method for operating a linear compressor
according to an example embodiment of the present disclosure.
[0018] FIG. 8 provides a flow chart illustrating a method for
operating a linear compressor according to an example embodiment of
the present disclosure.
[0019] FIG. 9 provides a movement plot of a linear compressor
model.
[0020] FIG. 10 provides a plot of a variable frequency waveform
with associated DC voltage for setpoint control, according to an
example embodiment of the present disclosure.
[0021] FIG. 11 provides a plot of a variable frequency waveform
with an applied phase or amplitude skew for setpoint control,
according to an example embodiment of the present disclosure.
DETAILED DESCRIPTION
[0022] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used with
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0023] FIG. 1 depicts a refrigerator appliance 10 that incorporates
a sealed refrigeration system 60 (FIG. 2). It should be appreciated
that the term "refrigerator appliance" is used in a generic sense
herein to encompass any manner of refrigeration appliance, such as
a freezer, refrigerator, refrigerator/freezer combination, and any
style or model of conventional refrigerator. In addition, it should
be understood that the present subject matter is not limited to use
in appliances. Thus, the present subject matter may be used for any
other suitable purpose, such as vapor compression within air
conditioning units or air compression within air compressors. As
illustrated, the refrigerator appliance 10 includes one or more
compartments 14 and 18 for chilling food or other items by manner
of refrigeration as described herein.
[0024] FIG. 2 is a schematic view of certain components of
refrigerator appliance 10, including a sealed refrigeration system
60 of refrigerator appliance 10. A machinery compartment 62
contains components for executing a known vapor compression cycle
for cooling air. The components include a compressor 64, a
condenser 66, an expansion device 68, and an evaporator 70
connected in series and charged with a refrigerant. As will be
understood by those skilled in the art, refrigeration system 60 may
include additional components, e.g., at least one additional
evaporator, compressor, expansion device, and/or condenser. As an
example, refrigeration system 60 may include two evaporators.
[0025] Within refrigeration system 60, refrigerant flows into
compressor 64, which operates to increase the pressure of the
refrigerant. This compression of the refrigerant raises its
temperature, which is lowered by passing the refrigerant through
condenser 66. Within condenser 66, heat exchange with ambient air
takes place so as to cool the refrigerant. A fan 72 is used to pull
air across condenser 66, as illustrated by arrows A.sub.C, so as to
provide forced convection for a more rapid and efficient heat
exchange between the refrigerant within condenser 66 and the
ambient air. Thus, as will be understood by those skilled in the
art, increasing air flow across condenser 66 can, e.g., increase
the efficiency of condenser 66 by improving cooling of the
refrigerant contained therein.
[0026] An expansion device (e.g., a valve, capillary tube, or other
restriction device) 68 receives refrigerant from condenser 66. From
expansion device 68, the refrigerant enters evaporator 70. Upon
exiting expansion device 68 and entering evaporator 70, the
refrigerant drops in pressure. Due to the pressure drop and/or
phase change of the refrigerant, evaporator 70 is cool relative to
compartments 14 and 18 of refrigerator appliance 10. As such,
cooled air is produced and refrigerates compartments 14 and 18 of
refrigerator appliance 10. Thus, evaporator 70 is a type of heat
exchanger which transfers heat from air passing over evaporator 70
to refrigerant flowing through evaporator 70.
[0027] Collectively, the vapor compression cycle components in a
refrigeration circuit, associated fans, and associated compartments
are sometimes referred to as a sealed refrigeration system operable
to force cold air through compartments 14, 18 (FIG. 1). The
refrigeration system 60 depicted in FIG. 2 is provided by way of
example only. Thus, it is within the scope of the present subject
matter for other configurations of the refrigeration system to be
used as well.
[0028] FIG. 3 provides a perspective view of a linear compressor
100 according to an example embodiment of the present disclosure.
FIG. 4 provides a side section view of linear compressor 100. FIG.
5 provides an exploded side section view of linear compressor 100.
As discussed in greater detail below, linear compressor 100 is
operable to increase a pressure of fluid within a chamber 112 of
linear compressor 100. Linear compressor 100 may be used to
compress any suitable fluid, such as refrigerant, a working fluid,
or air. In particular, linear compressor 100 may be used in a
refrigerator appliance, such as refrigerator appliance 10 (FIG. 1)
in which linear compressor 100 may be used as compressor 64 (FIG.
2). As illustrated, linear compressor 100 defines an axial
direction A, a radial direction R, and a circumferential direction
C. Linear compressor 100 may be enclosed within a hermetic or
air-tight shell (not shown). The hermetic shell can, e.g., hinder
or prevent refrigerant from leaking or escaping from refrigeration
system 60.
[0029] Turning now to FIG. 4, linear compressor 100 includes a
casing 110 that extends between a first end portion 102 and a
second end portion 104, e.g., along the axial direction A. Casing
110 includes various static or non-moving structural components of
linear compressor 100. In particular, casing 110 includes a
cylinder assembly 111 that defines a chamber 112. Cylinder assembly
111 is positioned at or adjacent second end portion 104 of casing
110. Chamber 112 extends longitudinally along the axial direction
A. Casing 110 also includes a motor mount mid-section 113 and an
end cap 115 positioned opposite each other about a motor. A stator,
e.g., including an outer back iron 150 and a driving coil 152, of
the motor is mounted or secured to casing 110, e.g., such that the
stator is sandwiched between motor mount mid-section 113 and end
cap 115 of casing 110. Linear compressor 100 also includes valves
(such as a discharge valve assembly 117 at an end of chamber 112)
that permit refrigerant to enter and exit chamber 112 during
operation of linear compressor 100.
[0030] A piston assembly 114 with a piston head 116 is slidably
received within chamber 112 of cylinder assembly 111. In
particular, piston assembly 114 is slidable along a first axis A1
within chamber 112. The first axis A1 may include a negative axial
direction A(-) and a positive axial direction A(+), and may be
substantially parallel to the axial direction A. Thus, piston
assembly 114 may alternately slide or oscillate, e.g., the piston
head 116, in the negative axial direction A(-) and the positive
axial direction A(+). During sliding of piston head 116 within
chamber 112, piston head 116 compresses refrigerant within chamber
112. As an example, from a top dead center position (i.e., top dead
center point), piston head 116 can slide within chamber 112 towards
a bottom dead center position (i.e., bottom dead center point)
along the positive axial direction A(+), i.e., an expansion stroke
of piston head 116. When piston head 116 reaches the bottom dead
center position, piston head 116 changes directions and slides in
chamber 112 along the negative axial direction A(-) back towards
the top dead center position, i.e., a compression stroke of piston
head 116. It should be understood that linear compressor 100 may
include an additional piston head and/or additional chamber at an
opposite end of linear compressor 100. Thus, linear compressor 100
may have multiple piston heads in alternative example
embodiments.
[0031] Linear compressor 100 also includes an inner back iron
assembly 130. Inner back iron assembly 130 is positioned in the
stator of the motor. In particular, outer back iron 150 and/or
driving coil 152 may extend about inner back iron assembly 130,
e.g., along the circumferential direction C. Inner back iron
assembly 130 extends between a first end portion 132 and a second
end portion 134, e.g., along the axial direction A.
[0032] Inner back iron assembly 130 also has an outer surface 137.
At least one driving magnet 140 is mounted to inner back iron
assembly 130, e.g., at outer surface 137 of inner back iron
assembly 130. Driving magnet 140 may face and/or be exposed to
driving coil 152. In particular, driving magnet 140 may be spaced
apart from driving coil 152, e.g., along the radial direction R by
an air gap AG. Thus, the air gap AG may be defined between opposing
surfaces of driving magnet 140 and driving coil 152. Driving magnet
140 may also be mounted or fixed to inner back iron assembly 130
such that an outer surface 142 of driving magnet 140 is
substantially flush with outer surface 137 of inner back iron
assembly 130. Thus, driving magnet 140 may be inset within inner
back iron assembly 130. In such a manner, the magnetic field from
driving coil 152 may have to pass through only a single air gap
(e.g., air gap AG) between outer back iron 150 and inner back iron
assembly 130 during operation of linear compressor 100.
[0033] As may be seen in FIG. 4, driving coil 152 extends about
inner back iron assembly 130, e.g., along the circumferential
direction C. Driving coil 152 is operable to move the inner back
iron assembly 130 along a second axis A2 during operation of
driving coil 152. The second axis A2 may be substantially parallel
to the axial direction A and/or the first axis A1. As an example,
driving coil 152 may receive a current from a current source (not
shown) in order to generate a magnetic field that engages driving
magnet 140 and urges piston assembly 114 to move along the axial
direction A in order to compress refrigerant within chamber 112 as
described above and will be understood by those skilled in the art.
In particular, the magnetic field of driving coil 152 may engage
driving magnet 140 in order to move inner back iron assembly 130
along the second axis A2 and piston head 116 along the first axis
A1 during operation of driving coil 152. Thus, driving coil 152 may
slide piston assembly 114 between the top dead center position and
the bottom dead center position, e.g., by moving inner back iron
assembly 130 along the second axis A2, during operation of driving
coil 152.
[0034] A piston flex mount 160 is mounted to and extends through
inner back iron assembly 130. A coupling 170 extends between piston
flex mount 160 and piston assembly 114, e.g., along the axial
direction A. Thus, coupling 170 connects inner back iron assembly
130 and piston assembly 114 such that motion of inner back iron
assembly 130, e.g., along the axial direction A or the second axis
A2, is transferred to piston assembly 114. Piston flex mount 160
defines an input passage 162 that permits refrigerant to flow
therethrough.
[0035] Linear compressor 100 may include various components for
permitting and/or regulating operation of linear compressor 100. In
particular, linear compressor 100 includes a controller (not shown)
that is configured for regulating operation of linear compressor
100. The controller is in, e.g., operative, communication with the
motor, e.g., driving coil 152 of the motor. Thus, the controller
may selectively activate driving coil 152, e.g., by supplying
current to driving coil 152, in order to compress refrigerant with
piston assembly 114 as described above.
[0036] The controller includes memory and one or more processing
devices such as microprocessors, CPUs or the like, such as general
or special purpose microprocessors operable to execute programming
instructions or micro-control code associated with operation of
linear compressor 100. The memory can represent random access
memory such as DRAM, or read only memory such as ROM or FLASH. The
processor executes programming instructions stored in the memory.
The memory can be a separate component from the processor or can be
included onboard within the processor. Alternatively, the
controller may be constructed without using a microprocessor, e.g.,
using a combination of discrete analog and/or digital logic
circuitry (such as switches, amplifiers, integrators, comparators,
flip-flops, AND gates, field programmable gate arrays (FPGA), and
the like) to perform control functionality instead of relying upon
software.
[0037] Linear compressor 100 also includes a spring assembly 120.
Spring assembly 120 is positioned in inner back iron assembly 130.
In particular, inner back iron assembly 130 may extend about spring
assembly 120, e.g., along the circumferential direction C. Spring
assembly 120 also extends between first and second end portions 102
and 104 of casing 110, e.g., along the axial direction A. Spring
assembly 120 assists with coupling inner back iron assembly 130 to
casing 110, e.g., cylinder assembly 111 of casing 110. In
particular, inner back iron assembly 130 is fixed to spring
assembly 120 at a middle portion 119 of spring assembly 120.
[0038] During operation of driving coil 152, spring assembly 120
supports inner back iron assembly 130. In particular, inner back
iron assembly 130 is suspended by spring assembly 120 within the
stator or the motor of linear compressor 100 such that motion of
inner back iron assembly 130 along the radial direction R is
hindered or limited while motion along the second axis A2 is
relatively unimpeded. Thus, spring assembly 120 may be
substantially stiffer along the radial direction R than along the
axial direction A. In such a manner, spring assembly 120 can assist
with maintaining a uniformity of the air gap AG between driving
magnet 140 and driving coil 152, e.g., along the radial direction
R, during operation of the motor and movement of inner back iron
assembly 130 on the second axis A2. Spring assembly 120 can also
assist with hindering side pull forces of the motor from
transmitting to piston assembly 114 and being reacted in cylinder
assembly 111 as a friction loss.
[0039] FIG. 6 provides a plot of cooling capacity and associated
efficiency for a conventional linear compressor compared to the
linear compressor 100 of FIG. 3. As illustrated, a conventional
linear compressor may operate along curve 604, in a substantially
linear manner. The curve 604 depicts decreased cooling capacity
with decreased stroke length or current amplitude. It follows that
as current and stroke length are increased, cooling capacity also
increases linearly.
[0040] In contrast, the linear compressor 100 may operate along
curve 606. As shown, a basic linear curve portion 608 exists such
that there is a conventionally linear relationship between
increasing current and cooling capacity until approximately
capacity 610. Upon reaching capacity 610, a direct current (DC)
voltage can be injected which offsets a resting setpoint (e.g.,
L.sub.0, described more fully below) of the motor, and therefore
offers increased cooling capacity with a decrease in efficiency.
However, as illustrated, the overall efficiency of the linear
compressor 100 is greater than that of a conventional linear
compressor. For example, because the resting setpoint L.sub.0 of
the linear compressor 100 is decreased as compared to a
conventional compressor at rest, there is reduced friction when
compressing gas, which results in less heating of gases. However,
when the resting setpoint L.sub.0 of the linear compressor 100 is
shifted due to injection of positive DC voltage, cooling capacity
is increased while still retaining overall efficiency much higher
than the conventional compressor cycle curve 604.
[0041] Turning now to FIG. 7, a method 700 is illustrated for
operating a linear compressor according to an example embodiment of
the present disclosure. Method 700 may be used to operate any
suitable linear compressor, such as linear compressor 100 (FIG. 3).
Moreover, it is understood that the entirety (or a portion) of the
method 700 may be utilized as part of, or as an alternative to, any
of the described methods herein. In particular, the method 700 may
be utilized for selectively supplying or directing a DC voltage as
a time varying voltage is supplied to the motor of linear
compressor 100. As described above, the DC voltage may induce a
positive extension force in the motor. Furthermore, the DC voltage
may effectively shift a resting setpoint L.sub.0 of the motor (at
least only during application of the DC voltage).
[0042] As an example, the mechanical dynamic model for linear
compressor 100 may be
F.sub.m=.alpha.i=M{umlaut over (x)}+C{dot over
(x)}+K(x-L.sub.0)-F.sub.gas
[0043] where [0044] M is a moving mass of linear compressor 100;
[0045] .alpha. is a motor force constant; [0046] {umlaut over (x)}
is an acceleration of the motor of linear compressor 100; [0047] C
is a damping coefficient of linear compressor 100; [0048] {dot over
(x)} is a velocity of the motor of linear compressor 100; [0049] K
is a spring stiffness of linear compressor 100; [0050] x is a
position of the moving mass of linear compressor 100; [0051]
L.sub.0 is resting setpoint of linear compressor 100; and [0052]
F.sub.gas is a gas force.
[0053] Accordingly, a different L.sub.0 can be obtained, at least
temporarily, by changing DC voltage. Positive DC Voltage will
increase the stroke length and further increase cooling capacity at
a low clearance. Generally, the control objective of method 700 is
to add V.sub.dc to increase L.sub.0 and stroke length when higher
cooling capacity is needed, required, or selected. For example, a
control signal, temperature sensor, temperature selection
apparatus, or other suitable control signal may be used to signal
that higher cooling capacity is needed.
[0054] With respect to FIG. 7, the DC voltage is indicated as a
variable value at V.sub.dc. The time varying voltage is indicated
at V.sub.ac. A resulting applied voltage function for the combined
DC voltage (V.sub.dc) and time varying voltage (V.sub.ac) is
indicated at V(t), which controls a duty cycle generator to the
motor. An index value for the DC voltage is indicated at
.DELTA.V.sub.dc. An index limit for the combined DC voltage
(V.sub.dc) may be provided in some embodiments. For instance, a
lower index limit, such as 0 (e.g., as shown at FIG. 7) may be
provided. Additionally or alternatively, although not shown in FIG.
7, an upper index limit (e.g., between 2 Volts and 5 Volts) may be
provided. An index rate (e.g., between 0.25 second and 1.5 seconds)
is indicated at T.sub.EC, such that a delay in the combined DC
voltage (V.sub.dc) is indicated at Z.sup.-TEC.
[0055] A determination may be made whether an increase in cooling
capacity is required by signaling a change in DC voltage. If
increased cooling capacity is required, the DC voltage (V.sub.dc)
is indexed higher (e.g., from a starting value of 0). In
particular, the DC voltage (V.sub.dc) is increased by the index
value (.DELTA.V.sub.dc). Moreover, the DC voltage (V.sub.dc) is
combined as a positive value with the time varying voltage
(V.sub.ac) to form the voltage function [V(t)]. Additionally, the
DC voltage (V.sub.dc) may be repeatedly increased by the index
value (.DELTA.V.sub.dc). Moreover, the repeated increases may occur
at the index rate (T.sub.EC) until the DC voltage (V.sub.dc)
exceeds the index limit (e.g., upper index limit) or until
increased cooling capacity is no longer required. If increased
cooling is no longer required, the DC voltage (V.sub.dc) is
decreased by the index value (.DELTA.V.sub.dc) immediately, or as
an indexed value, to zero volts DC.
[0056] FIG. 8 provides a flow chart illustrating a method 800 for
operating a linear compressor 100 according to an example
embodiment of the present disclosure. Generally, the method 800 is
substantially similar to the method 700. For example, the method
800 includes supplying a variable frequency waveform to the motor
of the linear compressor to produce a reciprocal motion in the
piston at a first cooling capacity, at block 802. The waveform may
be the voltage function [V(t)] of FIG. 7.
[0057] Generally, the first cooling capacity may be a base capacity
related to a resting setpoint L.sub.0 of the linear compressor 100.
Other first cooling capacities may be chosen, including those
already having a small offset of the resting setpoint L.sub.0 due
to DC voltage injection or other scenarios.
[0058] Any suitable time varying voltage waveform may be supplied
to the motor of linear compressor 100 at step 802. For example, the
time varying voltage may have at least two frequencies components
at step 802. Thus, the time varying voltage may be
v.sub..alpha.(t)=v.sub.0[sin
(2.pi.f.sub.1t)+sin(2.pi.f.sub.2t)]
[0059] where [0060] v.sub.a is a voltage across the motor of linear
compressor 100; [0061] f.sub.1 is a first frequency; and [0062]
f.sub.2 is a second frequency.
[0063] The first and second frequencies f.sub.1, f.sub.2 may be
about the resonant frequency of linear compressor 100. In
particular, the first and second frequencies f.sub.1, f.sub.2 may
be just greater than and just less than the resonant frequency of
linear compressor 100, respectively. For example, the first
frequency f.sub.1 may be within five percent greater than the
resonant frequency of linear compressor 100, and the second
frequency f.sub.2 may be within five percent less than the resonant
frequency of linear compressor 100. In alternative example
embodiments, the time varying voltage may have a single frequency
at step 802.
[0064] The method 800 further includes determining that an increase
in cooling capacity is required, at block 804. The determining may
include receiving a discreet input indicating that a user has
requested an increase in cooling capacity. The determining may also
include determining that a pull-down event has occurred (such as by
leaving a refrigerator door open, initiating an ice maker, or other
scenarios). The determining may also include receiving indication
from a temperature sensor, a temperature control interface, of
other temperature control apparatuses.
[0065] The method 800 further includes directing a positive direct
current (DC) voltage to the motor to induce an extension force at
the motor in the positive axial direction during at least a portion
of the supplying step in response to the determining step, at block
806. This extension force positively shifts the resting setpoint
L.sub.0, as described below.
[0066] An example of shifting the resting setpoint L.sub.0 is
illustrated generally at FIG. 9. In particular, FIG. 9 illustrates
an example movement plot of a linear compressor model, e.g., taken
during step 806. As may be seen in FIG. 9, the movement or
oscillation of piston assembly 114 may be plotted as a sinusoidal
wave wherein x corresponds to piston assembly 114 position (i.e.,
relative to the chamber 112). Thus, the position at which x=0 is
understood to correspond to the base portion of chamber 112 (e.g.,
a cylinder head). As shown, the sinusoidal wave is defined across
one or more strokes of the piston assembly 114. Thus, the
sinusoidal wave may be formed from one or more sinusoidal cycles
defined by movement (e.g., of piston head 116) from a midpoint to a
top dead center point, to a bottom dead center point, and back to
the midpoint. The position 909 is the actual midpoint of the
sinusoidal wave. In other words, 909 is the midpoint of stroke
length (i.e., .DELTA.x.sub.SL) between bottom dead center (i.e.,
x.sub.BDC) and top dead center (i.e., x.sub.TDC). In a
free-floating or ideal system, piston assembly 114 would naturally
oscillate about its equilibrium point L.sub.0 (i.e.,
x.sub.mid=L.sub.0). However, positive DC voltage effectively moves
L.sub.0 upward in the positive axial direction A(+). In other
words, extension of the piston assembly 114 in the positive axial
direction A(+) is greater than extension in the negative axial
direction A(-). Accordingly, while the physical setpoint of L.sub.0
remains unchanged, the midpoint of oscillation (909, effectively
L.sub.0) is shifted through application of a positive DC
voltage.
[0067] In certain example embodiments, the DC voltage of step 806
may be directed continuously or constantly after the determination
is made at step 804. Thus, the positive DC voltage may be a
constant voltage that is applied during both the positive axial
movement and negative axial movement of the piston assembly 114.
Moreover, the positive DC voltage may be applied across a plurality
of sinusoidal cycles (i.e., strokes) of the piston assembly 114 as
it travels between bottom dead center (x.sub.BDC) and top dead
center (x.sub.mc). Notably, directing a constant DC voltage may
preserve the existing harmonics for the sinusoidal motion within
linear compressor 100.
[0068] FIG. 10 provides a plot of a variable frequency waveform
with associated DC voltage for setpoint control, according to an
example embodiment of the present disclosure. As shown, the
waveform 1000 has a midpoint L0 which has been shifted upwards due
to injection of positive DC voltage constantly over multiple cycles
of the waveform 1000. It is apparent then, that the area under the
sinusoidal curve represented at 1002 is greater than 1004, which
allows for increased cooling capacity on-the-fly, without
physically altering the structure of the linear compressor 100.
[0069] In additional or alternative example embodiments, the DC
voltage of step 806 may be directed intermittently after the
determination is made at step 804.
[0070] The intermittent DC voltage may be applied according to a
set amplitude skew or phase skew. FIG. 11 provides a plot of a
variable frequency waveform with an applied phase or amplitude skew
for setpoint control, according to an example embodiment of the
present disclosure.
[0071] In particular, the amplitude skew may increase the amplitude
of sinusoidal motion for the linear compressor 100 in the positive
axial direction A(+). The amplitude skew is applied across a
plurality of sinusoidal cycles (i.e., strokes) of the piston
assembly 114 as it travels between bottom dead center (x.sub.BDC)
and top dead center (x.sub.TDC). Thus, the amplitude skew may
increase half-cycle amplitude in the positive axial direction A(+),
e.g., such that half-cycle amplitude in the positive axial
direction A(+) 1102 (e.g., amplitude of movement above L.sub.0) is
greater than half-cycle amplitude in the negative axial direction
A(-) 1104 (e.g., amplitude of movement below L.sub.0).
[0072] As another example, the intermittent DC voltage may be
applied according to a set phase skew. In particular, the phase
skew may increase the wavelength of sinusoidal motion for the
linear compressor 100 in the positive axial direction A(+). The
phase skew is applied across a plurality of sinusoidal cycles
(i.e., strokes) of the piston assembly 114 as it travels between
bottom dead center (x.sub.BDC) and top dead center (x.sub.TDC).
Thus, the phase skew may increase half-cycle wavelength in the
positive axial direction A(+), e.g., such that half-cycle
wavelength in the positive axial direction A(+) (e.g., wavelength
or time of movement above L.sub.0) is greater than half-cycle
wavelength in the negative axial direction A(-) (e.g., wavelength
or time of movement below L.sub.0).
[0073] Thus, as described above, methods for controlling a resting
setpoint and cooling capacity of an appliance have been provided.
Technical effects and benefits of the above examples may include
higher operational efficiency at low cooling capacity. This may
result in better energy savings over the life of an appliance
because high cooling capacity is generally used during only a small
percentage of the operational life of an appliance. Additionally,
due to a lower resting physical setpoint L.sub.0, there is lower
friction at low cooling capacity (e.g., friction is reduced by
about 30% because the stroke length is reduced). This may further
increase the longevity of an appliance due to decreased failures
related to mechanical wear at the linear compressor 100. Finally,
lower recompression losses (e.g., gas at low capacity is not
recompressed and therefore the overall cycle is cooler) and higher
peak efficiency (e.g., cooler cylinder and suction gas vs high
capacity) may also be realized.
[0074] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *