U.S. patent application number 09/833556 was filed with the patent office on 2001-11-01 for refrigerator.
Invention is credited to Arakawa, Noriaki, Ishii, Makoto, Kumakura, Hideo, Nakamura, Hideyuki, Takagi, Junichi, Wakatabe, Takeshi, Yoshida, Hideki.
Application Number | 20010035018 09/833556 |
Document ID | / |
Family ID | 27323406 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035018 |
Kind Code |
A1 |
Takagi, Junichi ; et
al. |
November 1, 2001 |
Refrigerator
Abstract
A refrigerator, having a motor for driving a compressor, an
inverter for controlling the operation of the motor, a converter
responsive to AC to perform a boosting function to supply DC of
variable voltage to the inverter, converter control means for
controlling the converter so that a plurality of DC voltages are
outputted thereby and inverter control means for controlling the
inverter in pulse width modulation each of the plurality of
voltages. The lowest voltage among the plurality of voltages being
a voltage which turns off the boosting function of the
converter.
Inventors: |
Takagi, Junichi;
(Tochigi-ken, JP) ; Ishii, Makoto;
(Utsunomiya-shi, JP) ; Arakawa, Noriaki;
(Tochigi-ken, JP) ; Wakatabe, Takeshi; (Sano-shi,
JP) ; Yoshida, Hideki; (Tochigi-ken, JP) ;
Nakamura, Hideyuki; (Utsunomiya-shi, JP) ; Kumakura,
Hideo; (Ashikaga-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
27323406 |
Appl. No.: |
09/833556 |
Filed: |
April 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09833556 |
Apr 13, 2001 |
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09335781 |
Jun 18, 1999 |
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6244061 |
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Current U.S.
Class: |
62/228.4 |
Current CPC
Class: |
F25B 2600/021 20130101;
F25D 2400/30 20130101; F25B 49/025 20130101; Y02B 30/70
20130101 |
Class at
Publication: |
62/228.4 |
International
Class: |
F25B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 1998 |
JP |
10-293318 |
Jun 18, 1998 |
JP |
10-170919 |
Sep 3, 1998 |
JP |
10-249295 |
Claims
What is claimed is:
1. A refrigerator, comprising: motor for driving a compressor; an
inverter for controlling the operation of said motor; a converter
responsive to AC to perform a boosting function to supply DC of
variable voltage to said inverter; converter control means for
controlling said converter so that a plurality of DC voltages are
outputted thereby; and inverter control means for controlling said
inverter in pulse width modulation each of said plurality of
voltages; the lowest voltage among said plurality of voltages being
a voltage which turns off the boosting function of said
converter.
2. A refrigerator, comprising: motor for driving a compressor; an
inverter for controlling the operation of said motor; a converter
having a rectifier circuit for converting AC to DC and a boosting
circuit for boosting a DC voltage and supplying the DC to said
inverter; boosting circuit control means for controlling said
boosting circuit so that said converter can output a plurality of
DC voltages; and inverter control means for controlling said
inverter using pulse width modulation of each of said plurality of
voltages; the lowest voltage among said plurality of voltages being
an output voltage of the rectifier circuit of said converter.
3. A refrigerator, comprising: a rectifier circuit for converting
AC into DC; a boosting chopper for boosting said DC; a reactor
provided between said rectifier circuit and said boosting chopper;
an inverter provided behind said boosting chopper for converting DC
to AC; a motor which is controlled by said inverter and which
drives a compressor; boosting chopper control means for controlling
said boosting chopper so that the DC inputted to said inverter
becomes DC of a plurality of kinds; and inverter control means for
controlling said inverter using the pulse width modulation of each
of the plurality of types of DC voltages; said reactor presenting a
large inductance in a small current range and a small inductance in
a large current range.
4. The refrigerator according to claim 3, wherein said reactor
comprises coils wound around a ringed core having at least one
gap.
5. A refrigerator, comprising: motor for driving a compressor; an
inverter for controlling said motor; a converter having a rectifier
circuit for converting AC to DC and a boosting circuit for boosting
a DC voltage and supplying DC to said inverter; boosting circuit
control means for controlling said boosting circuit so that said
converter can output a plurality of DC voltages; and inverter
control means for controlling said inverter using pulse width
modulation of each of said plurality of voltages; said refrigerator
further comprising; first operating means for operating said motor
in a speed range which is lower than a first rotating speed; second
operating means for driving said motor at a second speed which is
greater than said first rotating speed; wherein said plurality of
DC voltages comprise three stages of voltages representing high,
intermediate and low voltages; said boosting chopper control means
being arranged so that the three stages of high, middle and low
voltages are selected corresponding to the rotating speed of said
motor, said high voltage being selected when said second operating
means is selected.
6. A refrigerator, comprising: a motor for driving a compressor; an
inverter for controlling operation of said motor; a converter
having a rectifier circuit for converting AC to DC and a boosting
circuit for boosting a DC voltage and supplying DC to said
inverter; boosting circuit control means for controlling said
boosting circuit so that said converter can output a plurality of
DC voltages; and inverter control means for controlling said
inverter using pulse width modulation of each of said plurality of
voltages; wherein said plurality of DC voltages are selected based
on a rotating speed command of said motor and an actual speed of
rotation thereof.
7. A refrigerator, comprising: motor for driving a compressor; an
inverter for controlling said motor; a converter responsive to AC
for supplying DC of variable e voltage to said inverter; said
refrigerator further comprising: means for setting the DC voltage
supplied to said inverter at a value higher than the value
converted from AC to DC.
8. A refrigerator, comprising: motor for driving a compressor; an
inverter for controlling said motor; a converter responsive to AC
for supplying DC of variable voltage to said inverter; said
refrigerator further comprising: means for driving said motor at a
voltage which is lower than said DC voltage at the time of starting
of said motor.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of U.S. application Ser.
No. 09/335,781, filed Jun. 18, 1999, the subject matter of which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an inverter refrigerator
which has a power circuit for rectifying alternating current to
output a desired DC voltage and a motor control circuit for driving
a motor.
[0003] Hitherto, a control unit for controlling the speed of a
compressor motor by providing a rectifier circuit for rectifying AC
to convert it into DC and by combining a power circuit, which
suppresses higher harmonics of current and which controls the DC
voltage, with a driving circuit for driving the compressor motor,
has been disclosed in PCTJP 97/13318 (First Document).
[0004] The First Document describes a motor control circuit
comprising a rectifier circuit and a smoothing circuit for
converting AC power to DC, a converter circuit having a chopper
circuit for controlling the DC voltage by utilizing an energy
storage effect caused by switching operations and a reactor
(inductance), a motor driving unit comprising an inverter circuit
and a motor connected to the DC side of the converter circuit, an
inverter control circuit for controlling the speed of the motor by
controlling the switching operations of the inverter circuit, a
speed detecting circuit for computing the speed of the motor by
detecting the position of the rotor of the motor, a speed control
circuit for controlling the speed of the motor via the inverter
control circuit by taking in the computed value of speed and a
value of a speed command, and a DC voltage control circuit for
controlling the DC voltage via the converter control circuit by
taking in an output signal of the speed control circuit and
effecting control in accordance with the output signal.
[0005] The inverter control circuit drives the motor by driving a
switching element of the inverter circuit to apply a rotating
magnetic field to the motor based on a position signal from the
speed detecting circuit and a conduction ratio signal from the
speed control circuit. The speed detecting circuit detects the
induced voltage of the motor to calculate the position of the rotor
and outputs a pulse-like position detection signal. It also
calculates the speed from the calculated position signal and
outputs it to the speed control circuit as a speed detected value.
Then, the speed control circuit calculates the conduction ratio
signal of the PWM pulse of the inverter so that a deviation between
the speed command from the outside and the speed detected value is
zeroed. The speed of the motor is controlled by the inverter
circuit, the motor, the speed detecting circuit, the inverter
control circuit and the speed control circuit described above.
[0006] The converter control circuit drives the switching element
of the chopper circuit in accordance with the signal from the DC
voltage control circuit. The DC voltage control circuit detects the
DC voltage and the output signal of the speed control circuit,
e.g., the conduction ratio signal, and controls the DC voltage so
as to raise the DC voltage by a predetermined width when the
conduction ratio signal reaches a predetermined value, e.g., at the
upper limit within a certain range of the conduction ratio, or
controls the DC voltage so as to drop the DC voltage by a
predetermined width when the conduction ratio signal reaches the
lower limit value. The DC voltage control circuit of the converter
is formed by the converter circuit, the converter control circuit
and the DC voltage control circuit and operates to control the DC
voltage.
[0007] Although the motor control unit described in the First
Document has not been described with regard to possible use for a
refrigerator, one using so-called PAM control means for controlling
a DC voltage as a motor control unit for driving a refrigerator
compressor has been described in JPA-7-260309 (Second Document) and
JP-A-7-218097 (Third Document).
[0008] Although the Second and Third Documents have suggested that
energy may be saved by using the PAM inverter as a controller of a
motor for driving a compressor of a refrigerator, they have
provided so specific proposal for saving energy while performing
those functions required by a refrigerator. The structure described
in the First Document has not been considered for use in a
refrigerator, so that it provides no disclosure concerning energy
saving.
[0009] The power voltage (AC voltage supplied to house-hold plugs)
for driving the motor becomes .+-.7.5% of the reference value when
an allowable variation prescribed by the electric utility law and a
voltage drop within a home are taken into consideration. The
conventional controller of the motor using a voltage doubling
circuit has a difference of voltage in the DC stage of 43 V between
the maximum value and the minimum value of 260 V to 303 V, so that
there is a situation in which the motor is not activated when the
voltage of the DC stage is low.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a
refrigerator which is capable of achieving energy saving while
those functions required of a refrigerator are performed.
[0011] A second object of the present invention is to provide a
refrigerator which allows higher harmonics to be reduced while
achieving an energy saving.
[0012] A third object of the present invention is to provide a
refrigerator whose compressor can be activated even when the
voltage of the power supply fluctuates.
[0013] The above-mentioned objects may be achieved by a
refrigerator comprising a motor for driving a compressor; an
inverter for rotating and controlling the motor; and a converter
for inputting AC to supply DC of variable voltage to the inverter
and having a first operating mode for operating the motor in a
speed range which is less than a first rotating speed and a second
operating mode for operating the motor with a second speed which is
faster than the first rotating speed.
[0014] The second object may be achieved by a refrigerator
comprising a rectifier circuit for converting AC into DC; a
boosting chopper for boosting the DC; a reactor provided between
the rectifier circuit and the boosting chopper; an inverter
provided behind the boosting chopper for converting DC to AC; a
motor which is rotated and controlled by the AC from the inverter
and which drives a compressor; boosting chopper control means for
controlling the boosting choppers so that the DC inputted to the
inverter becomes DC of a plurality of kinds; and inverter control
means for controlling the inverter using pulse width modulation at
each of the plurality of types of DC voltages. The refrigerator is
arranged such that the reactor presents a large inductance in a
small current range and a small inductance in a large current
range.
[0015] The above-mentioned third object may be achieved by a
refrigerator comprising a motor for driving a compressor; an
inverter for rotating and controlling the motor; and a converter
for inputting AC to supply DC of variable voltage to the inverter,
and comprising further means for increasing the DC voltage supplied
to the inverter relative to the value converted from AC to DC in
activating the motor.
[0016] The specific nature of the invention, as well as other
objects, uses and advantages thereof, will clearly appear from the
following description and from the accompanying drawings in which
like numerals refer to like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a block diagram of a controlling for a
refrigerator according to an embodiment of the invention;
[0018] FIG. 2 is a circuit diagram showing the internal structure
of a converter PAM voltage command generator;
[0019] FIG. 3 is a graph showing the characteristics of motor
applied voltage and a conduction ratio versus rotating speed;
[0020] FIG. 4 is a chart showing the time constant change
characteristics of the converter PAM voltage command generator;
[0021] FIG. 5 is a graph showing the characteristics of a reactor
of a converter circuit;
[0022] FIG. 6 is a graph showing the motor efficiency when DC
voltage switching and converter control are turned off;
[0023] FIG. 7 is a waveform chart showing currents when the pulse
width is changed in the course of modulating the pulse width;
[0024] FIG. 8 is a characteristic diagram showing the efficiency of
a control circuit when converter control is turned off and on;
[0025] FIG. 9 is a graph showing the transition of the DC voltage
in activating the motor;
[0026] FIG. 10 is a longitudinal section view schematically
illustrating the structure of the freezer-refrigerator according an
embodiment of the invention;
[0027] FIG. 11 is a flowchart for explaining ice-making control of
the freezer-refrigerator of the embodiment;
[0028] FIG. 12 is a circuit diagram showing the structure of
circuits for switching over between full-wave rectification and
double voltage rectification; and
[0029] FIG. 13 is a characteristic diagram showing the DC voltage
characteristics in switching from the full-wave rectification to
the double voltage rectification.
DETAILED DESCRIPTION OF THE INVENTION
[0030] A refrigerator is required to have a quick freezing
capability for quickly freezing cooked foods for preserving them
and storing them, a quick ice-making capability for making ice in a
short time and an energy-saving capability for keeping the annual
charge for electricity low (reduce annual power consumption)
because the refrigerator is used while being constantly plugged
into the power source in ordinary homes. While the quick freezing
and quick ice-making capabilities may be achieved by increasing the
rotating speed of the compressor to increase the amount of
refrigerant circulating during the freezing cycle, it is necessary
to drive the compressor at low speed to save energy. The following
problems occur in trying to achieve both a driving of the
compressor at high speed and at low speed.
[0031] Presently, a brush-less motor, in which a permanent magnet
is embedded in a rotator and the rotator is rotated by causing a
stator to generate a rotating magnetic field produced by an
inverter, is used often as a motor for operating the compressor of
the typical refrigerator (mainly a reciprocating-type). The
rotating speed of this brush-less motor may be expressed by the
following expression:
N'=(V-IR)/k.phi.
[0032] where, (N) denotes the rotating speed of the motor, (V) is
the motor applied voltage, (I) is the motor current, (R) is the
internal resistance of the motor, (k) is a coefficient, and (.phi.)
is the flux density.
[0033] As it is apparent from the above expression, the greater the
applied voltage V and the smaller the internal resistance R of the
motor, the higher the rotating speed is. While 288 V, which is
twice 144 V (about 250 V when a load is connected), of DC voltage
inputted to the inverter may be obtained by using a voltage
doubling circuit, the internal resistance R of the motor varies
depending on whether the specification of the motor is set at a
high speed or a low speed.
[0034] When the specification is set at a high speed for example,
the value of the internal resistance R is reduced by setting the
number of turns of the stator of the motor at 120 turns, for
example. However, there has been a problem when the specification
of the motor is set at the high speed side in that the efficiency
of the motor drops remarkably in a low speed range.
[0035] Meanwhile, when the number of turns of the coils of the
stator is set at 140 turns, for example, to adjust the
specification of the motor to the low speed range (to enhance the
efficiency in the low speed range), there arose a problem in that
the rotating speed necessary for the quick freezing and quick
ice-making operations cannot be obtained because the motor applied
voltage V is kept constant and the internal resistance R of the
motor increases.
[0036] Thus, according to the present embodiment, the high speed
rotation of the motor has been realized by adjusting the
specification of the motor to the low speed range and by increasing
the inverter inputted voltage in the high speed range. While the
increase of the inverter input voltage, i.e., the DC stage voltage,
may be achieved by providing a boosting chopper (or a PWM
controllable converter) behind a converter for converting AC to DC
and by controlling this boosting chopper in chopping (PAM control),
there has been a problem when the boosting chopper is operated over
the whole operational range of the motor, as described in the First
Document, in that the efficiency of the motor drops in the low
speed range where the voltage applied to the motor is low. That is,
when the inverter control is performed for the refrigerator, the
rotating speed of the compressor motor is driven often at the
present minimum rotating speed. In such a case, there has been a
problem in that the efficiency of the circuit drops due to
switching loss of a power element when an input current is caused
to forcibly flow to boost the voltage by a boosting chopper circuit
within the converter circuit at this time by the switching
operation of the power element and by an energy storage effect of
the reactor.
[0037] Further, even at the minimum rotating speed, the lowest
voltage of the DC voltage must be controlled at 163 V or more
including voltage fluctuation when the switching operation of the
power element is implemented to boost the DC voltage in the
boosting chopper circuit within the converter circuit. Therefore,
there has been a problem in that the compressor motor is designated
for operation at a point where the DC voltage is high, i.e., it is
not designed optimally, thus dropping the efficiency.
[0038] This happens because the value of the DC voltage is about
144 V and the lowest DC voltage obtained by boosting it with the
lowest conduction ratio is about 163 V in case of full-wave
rectification not using a voltage doubling circuit, the pulse width
which is the PWM waveform is thinned, the value of the current
flowing during the ON period of the inverter increases (the maximum
value of the current flowing during the period when a switching
element of a certain phase is ON) and the difference with the
lowest current in a circulating mode (the period during which
current is flowing in a circulating diode in that phase) increases
in trying to reduce the rotating speed. This differential current
is proportional to the pulsating flux density, and the greater then
differential current, the greater the iron loss becomes.
[0039] In order to solve this problem, according to the present
embodiment, the DC voltage is lowered further by turning off the
boosting chopper in the low speed range. The pulse width of the PWM
of the inverter may be widened by lowering the voltage of the DC
stage. The pulsating flux density may be reduced and the iron loss
of the motor may be reduced as a result by thus widening the pulse
width because the difference between the maximum current value and
the minimum current value in one period of the inverter switching
element may be reduced.
[0040] In addition, while a lower voltage has been realized by
turning off the boosting chopper in the low speed range of the
motor to reduce the iron loss of the motor, as described above,
there has arisen a problem in that high order higher harmonics
contained in the input current are increased by turning off the
boosting chopper. Although the current waveform is sinusoidal and
higher harmonic components may be reduced in the range in which the
boosting chopper is operative by controlling the power factor to
almost 1, because the current command is created based on the input
AC voltage, the current waveform is determined by the value of the
inductance L of the reactor of an LC filter provided in the DC
stage between the converter and the inverter in the range in which
the boosting chopper is not operative, and a sharp current whose
peak value is large and whose width is small flows as the value of
L is small and the current waveform becomes sinusoidal as the value
of L is large. Then, although the problem of the higher harmonics
may be solved by increasing the inductance of the reactor, there
arises a problem in that the size of the reactor which allows the
higher harmonics to be reduced increases, and it cannot be easily
housed in an electric component box provided between a back plate
and an inner plate of the refrigerator, for example.
[0041] In order to solve this problem, according to the present
embodiment, an inductance variable reactor whose inductance
increases in the low current range is used. The reactor is
constructed so that a loop magnetic circuit is formed by winding a
coil around an iron or amorphous material and so that an air gap is
provided at part of this magnetic circuit. While the use of a
reactor on the DC side of the inverter having an iron core has been
describe din JP-B-64-2029 and has an effect of reducing higher
harmonics, the greater the current flowing through the reactor, the
smaller the inductance becomes in a reactor merely having an iron
core. It poses a problem in that the necessary inductance value
cannot be obtained over the whole range in which the boosting
chopper is turned off and higher harmonics increase in the low
speed side in that range.
[0042] According to the present embodiment of the invention, the
influence caused by the higher harmonics may be minimized over the
whole operating range of the motor because the reactor is
structured so as to have a gap at a part by forming the iron core
and other parts into a ring, and the constant inductance value L is
maintained even if the current value increases from the start.
Further, as will be described later, while the present embodiment
is arranged so as to operate at one speed (lowest speed) when the
boosting chopper is turned off, the degree of freedom of design is
widened without changing the reactor per machine type within the
range because the approximately constant part exists in the
inductance value of this reactor even when the lowest speed is
different per type of refrigerator.
[0043] One embodiment of the invention described above will be
explained below with reference to the drawings. FIG. 1 is a block
diagram for explaining of the whole structure of the motor
controller comprising the converter circuit using the rectifying
circuit and the boosting chopper circuit, the inverter circuit and
the compressor motor.
[0044] An AC power source 1 is supplied to a plug socket is general
and the refrigerator receives electricity by inserting a plug of
the refrigerator power cord into the plug socket. The received AC
is connected to a converter circuit 2 to be converted into DC. The
converter circuit 2 outputs the current as a DC via diodes 21, 22,
23 and 24 composing a rectifier circuit, a rector 25, a diode 26
and a boosting chopper circuit within the converter circuit 2 is
connected to the output side of the rectifier circuit in the
converter circuit 2 and boosts the voltage by forcibly causing the
input current to flow by the switching operation of the transistor
27 and the energy storage effect of the reactor 25, as described
above. The boosted DC voltage is supplied to a smoothing capacitor
5 so as to be outputted as a stable DC voltage. While the boosting
mechanism is well known, it will be explained briefly. When the
diode 21 side is plus and the switching element 27 is ON, the
current flows from the AC power source 1, to the diode 21, the
reactor 25, the switching element 27, the diode 24 and back to the
AC power source 1, and electromagnetic energy is accumulated in the
reactor 25. When the switching element 27 is turned off at this
time, a current flows through the smoothing capacitor 5 from the
reactor 25 via the diode 26 for preventing a reverse current flow
and the electromagnetic energy is shifted to the capacitor 5, thus
boosting the voltage of the capacitor 5. Thereby, the DC stage
voltage is boosted. It is noted that the resistor 28 within the
converter circuit 2 is a resistor for detecting current.
[0045] An inverter 3 which converts DC to AC and which generates a
rotating magnetic field for rotating the motor 7 is connected to
the capacitor 5. The inverter 3 is connected with the motor 7 for
driving the compressor 4. Although the compressor 4 which is driven
by the motor 7 is not shown in detail in the figure, it is mainly a
reciprocating-type compressor housed in a closed container together
with the motor 7. It may be also a rotary-type compressor.
[0046] The inverter 3 is a three-phase inverter in which IGBT
(Insulated Gate Bipolar Transistor) devices 31a through 32c are
used as switching elements in the present embodiment. Circulating
diodes 33a through 34c are connected to those switching elements in
parallel, respectively. Then, the rotating speed of the motor 7 is
controlled by controlling conduction of the DC supplied from the
capacitor 5 in phases of 120 degrees based on the output of the
rotating position detector of the motor 7 so that a preset rotating
speed is attained and by controlling the conduction ratio (pulse
width control) in the conduction period in each phase.
[0047] It is noted that a resistor 6 is a resistor for detecting
current. The value of this detected current is sent to an
over-current protector 111, which outputs a signal for turning off
all switching elements in the inverter 3, to a driver 110 when the
value of the detected current exceeds a threshold level. Then, the
driver 110 turns off the switching elements. This is provided so as
not to have a current minor loop in the control of the
inverter.
[0048] A comparator 100 compares the freezer compartment present
temperature, which is indicated by a signal from a temperature
obtained from a freezer compartment temperature detector 138 and
outputs the temperature deviation before reaching the maximum speed
command, the speed command becomes constant when the deviation is
greater than that. Meanwhile, the induced voltage of the motor 7 is
inputted to a position detector 102 to compute the position of the
magnet from this induced voltage and a signal representing the
rotating speed of the motor 7 is outputted by a speed calculator
103 based on the position signal. A comparator 104 compares this
detected speed with the above-mentioned speed command (in regard to
this, a speed command limiter 136 and a selecting circuit 137 will
be described later). The deviation of the speed is inputted to an
inverter PWM duty commanding device 105, and a pulse train whose
pulse width is determined so that the speed deviation is zeroed is
generated by proportional-plus-integral computation based on the
speed deviation. The output signal of the position detector 102 is
also inputted to a commutation output device 108 to output a pulse
train which represents a commutation timing of the conduction of
120 degrees of the switching element of each phase (a pulse train
which deviates by 120 degrees per each phase) per each switching
element (the figure shows one switching element). The switching
elements 32a, 32b and 32c composing a lower arm of each phase turn
on during this period of commutation timing and ON/OFF operation of
the switching elements 31a, 31b and 31c composing the upper arm is
controlled via a driver 110 by taking AND logic of the pulse train
representing the commutation timing and the pulse train
representing the previous PWM signal using an AND circuit 109.
[0049] Next, the control of the DC stage voltage of the converter
circuit 2 will be explained. The voltage of the DC stage in the
present embodiment is controlled in three stages of high voltage
(280 V), intermediate voltage (170V) and low voltage (120V). The
high voltage and the intermediate voltage are realized by
controlling ON/OFF operation of the boosting chopper 27. The
boosting chopper 27 is turned off to increase the output pulse
width of the inverter 3 in the low voltage range, thus,
contributing to the energy saving.
[0050] The actual rotating speed of the motor 4 computed by the
speed calculator 103 and the speed command computed by the speed
command generator 101 are inputted to a converter PAM voltage
command generator 106 and a converter operation judging device 107.
The converter PAM voltage command generator 106 generates a high
voltage or intermediate voltage command based on the inputted
actual speed and the speed command. The value of this voltage
command is compared with the DC voltage across the capacitor 5
detected by the Dc voltage detecting circuit 50 to output a command
having a current peak value so that the voltage across the
capacitor 5 becomes the selected high voltage or intermediate
voltage. When it is judged that the DC stage voltage must be
lowered based on the inputted actual speed and the speed command,
the converter operation judging device 107 outputs a chopper off
signal (PAM off signal) which operates to turn off the boosting
chopper (hereinafter the switching element 27 may be referred to as
the boosting chopper 27).
[0051] A multiplier 201 multiplies the command of the current peak
value from the converter PAM voltage command generator 106 with the
voltage (pulsating current) detected by the voltage detector 29 and
full-wave rectified by the diodes 21, 22, 23 and 24 to output an
instantaneous current command. A comparator 202 compares the
instantaneous current command with the actual instantaneous current
detected by the current detecting resistor 28 and inputs the
deviation thereof to a comparator 204 to compare the deviation with
a saw-toothed wave (chopping wave) generated by an oscillator 203
to obtain a pulse width modulated signal. This signal is inputted
to and amplified by a driving circuit 205 to generate a gate signal
of the boosting chopper 27. The phase of the input voltage almost
is equal to that of the current and the power factor approaches 1
by effecting control so that the differences between the
instantaneous current command and the instantaneous current is
eliminated. It is possible to suppress the higher harmonics by
forming the current into a sinusoidal wave. It is noted that when a
low voltage is required, the chopper off signal which is the output
of the converter operation judging device 107, is inputted to the
drive circuit 205 to stop the switching operation of the boosting
chopper 27 by blocking the gate signal thereof.
[0052] Each element surrounded by a dotted line A is packaged in
one integrated circuit. It is noted that the output of the
converter PAM voltage command generator 106 is the intermediate
voltage command during the time when the chopper off signal is
outputted and the chopping signal based on the deviation of the
instantaneous current is outputted to the drive circuit. At this
time, they are formed in the integrated circuit so that the DC
stage voltage rises gradually even if the chopper off signal is
released (not shown).
[0053] Many converter control circuits whose control is
circuit-integrated (IC-ed) and which control a DC voltage by
controlling an analog voltage have been manufactured recently.
[0054] It is noted that, although the voltage command and the value
of the actual speed in the embodiment described above, it may be
determined by the conduction ratio of the pulse width modulation
signal of the inverter.
[0055] Next, details of the converter PAM voltage command generator
106 will be explained with reference to FIG. 2. The high voltage or
the intermediate voltage is selected by processing a program based
on the value of the speed command and the value of the actual speed
and a command is outputted in the form of an analog voltage which
enables the selected voltage to be generated on the converter
control circuit side. That is, a command for changing the DC stage
voltage is changed depending on whether the voltage determined by
the value is changed depending on whether the voltage determined by
the value of a partial potential of the resistors R2 and R3 is
outputted or a voltage determined by the volume of the parallel
resistance of the resistors R3 and R4, which are connected in
parallel, and the value of partial potential of the resistor R2 is
outputted.
[0056] However, because a large change occurs in the DC voltage at
the switching point and the stepwise voltage change causes
ill-effects on the PWM duty of the inverter, the present embodiment
is arranged such that the change gradually proceeds by an analog
circuit even when the voltage command changes by the
above-mentioned program processing. This will be explained
below.
[0057] The DC voltage command outputted by the program processing
changes stepwise. Then, the voltage is caused to increase gradually
by giving a time constant to the signal changing stepwise using the
resistor R1 and a capacitor C. This voltage is compared with a
chopping wave formed in the oscillating circuit. The peak value of
the output waveform of this oscillating circuit is set to a level
below the voltage of the DC voltage command value. Because the
output of the comparator is produced when the output of the time
constant circuit is large, a pulse train whose width is widened
gradually as the output voltage of the time constant circuit
gradually increases is outputted. Then, when the capacitor C is
completely charged, the comparator outputs a signal ON. When the
output of the comparator is ON, the transistor T turns on, so that
voltage produced by the value of the parallel resistance of the
resistors R3 and R4 and the partial potential of the referred to as
the first partial potential) is outputted on the converter control
circuit side (the partial potential (hereinafter referred to as the
second partial potential) of the resistors R2 and R3 when the
transistor T is off). The voltage of the first partial potential
and the second partial potential are outputted alternately. The
voltage period of the first partial potential is prolonged as the
voltage of the time constant circuit rises and the voltage of the
first partial potential is outputted in the end. Thus, a
rectangular wave having a different duty width corresponding to the
time constant is outputted to the converter control circuit side.
Although not shown, an integration circuit is provided on the
converter control circuit side to convert the rectangular wave into
an analog voltage. This output becomes the DC voltage command and
the peak value command of the current is obtained by comparing that
value with the actual DC voltage. These controls allow the
pulsation of the rotating speed of the motor 7 to be suppressed
because changes of the voltage in switching the DC voltage may be
suppressed. FIG. 4 shows the pulsation of the rotating speed when
the time constant of the resistor R1 and the capacitor C is
changed. It can be seen that the pulsation of the rotating speed is
small when the time constant is large.
[0058] It is noted that although the chopping wave is formed and
the time constant circuit is formed by the resistor R1 and the
capacitor C in the present embodiment, a rectangular wave having a
different duty width corresponding to the time constant may be
outputted as the DC voltage command to the program
(software-wise).
[0059] When the voltage of the DC stage changes, e.g., from the
intermediate voltage to the high voltage, the peak value of the
pulse train outputted from the inverter 3 becomes high and the
rotating speed increases sharply as the terminal voltage of the
motor 7 increases as a result.
[0060] While the voltage of the DC stage is determined
software-wise from the value of the speed command and the actual
speed within the converter PAM voltage command generator 106 in
order to suppress this phenomenon as described above, the command
of the DC stage changes stepwise and therefore an analog circuit is
provided to weaken this change.
[0061] When the command changes stepwise, a speed feedback circuit
on the motor control side drops the increased speed to the
commanded speed, so that the pulse is thinned to deal with it.
However, the speed feedback circuit cannot respond instantly to the
quick increase of the motor and the speed of the motor cannot but
be increased. Then, when the stepwise change is weakened so as to
allow the speed feedback circuit to respond to that, it is
undeniable that the actual rotating speed becomes higher than the
command value. Although this is not a big problem, there is a
problem in that abnormal noise is produced as the rotating speed
changes.
[0062] Then, according to the present embodiment, the voltage
command of the DC stage is sent from the converter PAM voltage
command generator 106 to the inverter PWM duty command generator
105. When the voltage of the DC stage changes in the direction of
the increase upon receiving the change of the command, the PWM duty
is narrowed down in a range not becoming 0% and it is increased in
a range not becoming 100% when the voltage changes in the direction
of reduction.
[0063] After that, the speed is controlled so as to follow the
speed command even in the DC stage voltage which gradually changes.
That is, it brings about an effect that the burden on the speed
feedback circuit is reduced because the increase/decrease of the
duty which the speed feedback circuit must implement with respect
to the DC stage voltage changing direction is implemented based on
the increase/decrease of the DC voltage command in advance.
[0064] Next, the control provided for actuating the compressor
(motor) will be explained. The voltage normally transmitted to
homes is allowed to have a fluctuation range based on the
applicable electric utility law. It then has a fluctuation width of
281.+-.7.5% (260 V to 303 V) in the double voltage representation
when a voltage drop due to interior wiring is taken into
consideration. Therefore, there is a case when it becomes difficult
to start the motor as its rotating torque is insufficient when the
voltage is low because the starting torque of the compressor is
also large. Thus, the present embodiment is arranged such that the
DC voltage command is controlled to the high voltage level or the
intermediate voltage level at first to obtain a DC voltage which
fluctuates less and the activation of the motor is started during
eh time when the compressor is stopped or when the starting command
is issued. Thereby, the stable DC voltage of 281.+-.3% is supplied,
thus, starting the motor reliably.
[0065] That is, the converter PAM voltage command generator 106
takes in the actual speed, which is represented by the output of
the speed calculator 103 and the speed command which is represented
by the output of the selecting circuit 137, and when the actual
speed is 0 and the speed command is issued, it judges that the
compressor is to be started and sets the DC voltage command as the
high voltage command. Then, the inverter causes the switching
operation to start the motor under this voltage as shown in FIG. 9.
After that, when the freezer temperature approaches the temperature
present value, the converter PAM voltage command generator 106
commands the low voltage via the intermediate voltage to drive the
motor under the low voltage condition. At this time, the DC voltage
fluctuates due to the fluctuation of the power supply voltage as
described before because switching in the boosting chopper is
stopped. However, even if there is a fluctuation of the power
supply voltage, the motor is controlled so as to follow the speed
command because the induced voltage of the motor has risen, the
speed feedback control has been established and the pulse width of
the PWM for maintaining that speed is attained. It is noted that
when the PAM is turned off to lower the voltage, while the inverter
controls the motor so that the speed command is attained by
increasing the pulse width, the lowest speed is selected such that
the conduction ratio becomes 100% when the voltage is the lowest in
the fluctuation width of the AC power supply voltage.
[0066] Here, a quick freezing operation, a quick ice-making
operation and a save operation will be explained. The home freezing
performance of a household refrigerator makes it possible to
suppress the growth of ice crystals within the cellular structures
during freezing, to suppress the effluence of fluid from food
(juice containing flavors and nutrition) during defrosting due to
the destruction of cells in the food and to freeze with a high
grade by minimizing the time of passing a maximum ice crystal
produced zone (-1.degree. C. to -5.degree. C.) where most of the
moisture in foods is frozen. In order to realize that, a quick
freezing button (quick ice-making button) 134 is provided on a door
of the refrigerator so that the quick freezing button (quick
ice-making) operation is started when the button 134 is pressed.
Beside the one provided on the door of the refrigerator, the quick
freezing button 134 may be a relay contact or an electronic switch
which may be closed by a remote controller.
[0067] When the quick freezing button 134 is pressed, a timer
within a quenching circuit 133 is activated and the quick freezing
operation of two hours at most is conducted until the quick
freezing button 134 is manually released or the timer turns off.
The quenching circuit 133 sends a speed command for setting the
rotating speed of the motor at 4,200 turns/minute (fixed) to a
selecting circuit 137. The selecting circuit 137 selects the speed
command from the quenching circuit 133 and outputs it to a
comparator 104. When the speed command of the motor is fixed, the
deviation of the temperature may become large returning it, so that
a temperature command is set at a value lower than the normal one
by -7.degree. C. Therefore, the temperature command is set by
adding -7.degree. C. to an output from a temperature setting device
130 by an adder 135. The deviation of this temperature and the
actual temperature is outputted from a comparator 100. Taking in
this temperature deviation, the quenching circuit 133 prevents the
refrigerator and vegetable compartments, other than the freezer
compartment, from being overcooled when the freezer temperature
becomes lower than the preset freezer temperature (normally
-18.degree. C.) by 7.degree. C. during the quick freezing operation
by setting the speed command from the fixed value of the motor
4,200 turns/min. to 1 turns/min. When the freezer temperature rises
and exceeds the preset temperature which is lower than the normal
temperature by 7.degree. C. (by having hysteresis), the quenching
circuit 133 issues the speed command of the motor again to start
the quick freezing operation. This action is repeated until the
timer is turned off.
[0068] The quick freezing (ice-making) operation described above
has made it possible to shorten the maximum time of passing the ice
crystal generating zone to 30 minutes or less, thereby to freeze
products with a high quality.
[0069] Energy-saving in a refrigerator has been advocated lately
from governmental demands as a measure for preventing global
warming. In order to respond to this demand, according to the
present embodiment, a save button 132 is provided on the door of
the refrigerator to realize an energy-saving mode.
[0070] When the save button 132 is pressed, the saving operation
circuit 131 is activated. In order to raise the preset temperature
(temperature command) by 1.degree. C., the saving operation circuit
131 outputs a signal for adding 1.degree. C. to the output of the
temperature setting device 130. An adder 135 does the adding and an
output of the adder 135 is set as a temperature command during the
save operation. Saving operation circuit 131 also outputs a signal
to a speed command limiter 136 so that no speed command of 3,000
turns/min. or more is outputted to the rear stage even if the speed
command at the output of the speed command generator 101 exceeds
3,000 turns/min. Thus, the temperature deviation is reduced by
raising the preset temperature. Therefore, the low voltage of the
DC stage voltage of the main circuit is more likely to be selected
and the pulse width of the inverter PWM waveform is increased, the
iron loss of the motor is reduced and the power consumption may be
reduced as described before. Further, because the DC stage voltage
can be controlled, the operable minimum rotating speed may be set
between 1,600 turns/min. to 2,000 turns/min. Therefore, the
rotating speed of the motor will not be increased unnecessarily
even though the temperature deviation is small, so that the power
consumption may be reduced. Still more, the maximum speed is
suppressed to 3,000 turns/min., even when the temperature deviation
is very large, so that the rotating speed will not become high
unnecessarily and the power consumption may be reduced when this
save button 132 has been pressed.
[0071] By the way, saving operation circuit 131 takes in the output
of the freezer temperature detector 138 and releases the save
control by detecting when the temperature of the freezer
compartment exceeds -10.degree. C. When the load is so large that
the intra-freezing temperature rises even if the operation is
continued at the rotating speed of the motor of 3,000 turns/min.,
the saving operation circuit 131 releases the save operation to
return to the normal operation and to cool the compartment to keep
the temperature of the foods stored in the compartment at an
adequate temperature.
[0072] It is noted that because the quick freezing operation is not
compatible with the save operation, the system operates such that
one of the operations is nullified even when the button of one
operation is pressed during the time when the other button of the
other operation is operative.
[0073] Next, the operations for switching the DC voltage and for
turning on/off the converter will be explained by reference to FIG.
3. FIG. 3 is a graph in which the horizontal axis represents the
rotating speed of the compressor motor and the vertical axis
represents voltage applied to the motor and the conduction ratio.
FIG. 3 shows a case when the load is constant.
[0074] A speed command is large and actual speed is also large in a
state in which the refrigerator compartments are not cool even
though the compressor is operative because the temperature
difference is large. While a command is issued for setting the DC
voltage to a high voltage based on the both of them, this signal
initially is 0 V and is outputted to the time constant circuit. The
partial potentials across the resistors R2 and R3 are supplied to
the converter control circuit side and the DC voltage is set at the
high voltage of 280 V, for example. The motor 4 is controlled at
high speed when the DC voltage is 280 V. While a variable width of
the rotating speed is controlled within a range of 2,700 turns to
4,200 turns, the drive signal is created on the inverter control
circuit side based on the conduction ratio signal from the
deviation of the speed as described above to drive the switching
elements, e.g., the transistors, of the inverter 3 to control the
speed of the motor 4. The conduction ratio corresponding to the
variable width of the rotating speed is controlled within a range
of 45% to 95% for example.
[0075] When the compartment of the refrigerator is cooled down and
the temperature thereof approaches the preset temperature, the
rotating speed of the compressor motor 4 drops. When the command of
the rotating speed of the motor 4 is less than 2,700 turns for
example and the actual rotating speed also falls below 2,700 turns
(the conduction ratio is 4.5% or less for example when the value of
command is decided by the conduction ratio to the switching element
of the inverter 3), the output to the time constant circuit is set
to HIGH, and the resistors R3 and R4 are connected in parallel to
change the value of the partial potential and to set the DC voltage
to the intermediate voltage of 170 V (point B). At this time, the
conduction ratio becomes 95% for example.
[0076] Here, since the product of the DC voltage and the conduction
ratio must coincide before and after the switching, it is necessary
to set the conduction ratio at a value not exceeding 100% when the
DC voltage is lowered. The variable width of the rotating speed is
controlled within a range of 1,600 to 2,700 turns and the
conduction ratio is 55% for example when the rotating speed is
1,600 turns.
[0077] When the compartment of the refrigerator is cooled down
further and the temperature thereof approaches the preset
temperature, the rotating speed of the motor 7 is set at the lowest
rotating speed of 1,600 turns for example. When the conduction
ratio to the switching element of the inverter 3 falls below 55%
for example of the command of the rotating speed of the motor 7 is
1,600 turns which is the lowest rotating speed and the actual
rotating speed is also 1,600 turns, the control of the converter
control circuit inside is turned off to set at the low voltage
(point A). This control is made by the converter operation judging
device 107 described above. Here, the conduction ratio must be set
at a value not exceeding 100% when the DC voltage is lowered. It is
noted that the control of the converter control circuit side may be
turned off also when the rotating speed of the compressor motor 7
is not lowest.
[0078] The values of the conduction ratio and the rotating speed
are values for accommodation of explanation. The speed of the motor
may be controlled by lowering the DC voltage as the rotating speed
of the compressor motor 7 decelerates by repeating the
above-mentioned actions.
[0079] Next, a case when the compressor motor 7 is accelerated in
contrast to what is described above will be explained. When the
intra-compartment temperature rises as the door of the refrigerator
is opened or warm foods are put into the compartment when the motor
7 is at the lowest rotating speed, then the rotating speed command
of the motor 7 exceeds the lowest rotating speed for example and
the actual rotating speed also exceeds the lowest rotating speed
(the conduction ratio is 55% or more for example when the DC
voltage command is switched by taking the conduction ratio to the
switching element of the inverter 3 into consideration) in contrast
to what is described above. In such a case, the control of the
converter control circuit side is turned on (point A) to set the DC
voltage at the intermediate voltage of 170 V for example.
[0080] The rotating speed of the motor 7 may be increased further
by setting the DC voltage command given to the time constant
circuit at 0 V to change to the value of the partial potentials of
R2 and R3 and by setting the DC voltage at the high voltage of 280
V for example.
[0081] It is noted that it is necessary to provide hysteresis to
the rotating speed in accelerating and decelerating the motor 7 to
suppress hunting of the rotating speed in switching the DC
voltage.
[0082] Further, although the switching of the DC voltage is
performed in three stages including the control on and off of the
converter in the present embodiment, the number of switching stages
may be increased by proving a plurality of preset voltages in the
DC voltage switching circuit 9.
[0083] FIG. 5 shows the reactor characteristic of the converter
circuit 2. When the compartment of the refrigerator is cooled and
the temperature thereof approaches the preset temperature, the
rotating speed of the motor 4 set at the lowest rotating speed and
the control of the converter control circuit side (boosting chopper
27) is turned off. However, there is a problem in that a value for
restricting the refrigerator cannot be satisfied at this time. The
value of the reactor 25 may be around 1 mH when the DC voltage is
controlled to improve the power factor through the boosting chopper
27 across the whole control range of the rotating speed of the
motor 7 whose guideline on the restriction of the higher harmonics
in the refrigerator is Class D. However, the value of the reactor
25 must be 10 mH or more to satisfy the higher harmonics guideline
by turning off the boosting chopper 27. Therefore, the reactor 25
is arranged to have a characteristic of 10 mH or more during the
low input (low current) when the boosting chopper 27 is turned off
and a characteristic of around 1 mH during the high input (high
current) when the boosting chipper 27 is turned on as described
above. Thereby, the higher harmonics guideline may be satisfied
even when the boosting chopper 27 is turned off.
[0084] FIG. 6 shows the efficiency of the motor in switching the DC
voltage or when the boosting chopper 27 is turned off at the lowest
rotating speed. When the rotating speed of the motor 7 is switched
at 2,700 turns, the DC voltage drops from 280 V to 170 V, so that
the efficiency of the motor improves by about 1 to 2%. It happens
because the DC voltage drops, the conduction ratio of the inverter
3 increases and the iron loss caused by the chopper and lost in the
motor decreases. Further, when the converter control is turned off,
the DC voltage drops from 170 V to 120 V, so that the efficiency of
the motor improves by about 2%. The reason for this will be
explained with reference to FIG. 7. The upper part of FIG. 7 shows
a PWM waveform of the switching element of the inverter 3 when the
DC stage voltage is high. The motor current from the capacitor 5
flows when the switching element is ON. It circulates and
attenuates via the circulating diode when the switching element is
turned off. The peak-to-peak is assumed to be AIM. In the same
manner, the lower part FIG. 7 shows the waveform when the DC stage
voltage is decreased to have the same conduction ratio by which the
same voltage as shown in the upper part in FIG. 7 is applied to the
motor 7. Because the DC stage voltage is low at this time and the
current rising rate is small even when the switching element is
turned on, AIM is small as compared to that shown in the upper part
of FIG. 7. This AIM represents the pulsating flux density of the
motor and means that the smaller the value, the smaller will be the
iron loss of the motor. Accordingly, the greater the conduction
ratio, the better the efficiency of the motor is.
[0085] FIG. 8 is a graph showing the efficiency of the control
circuit when the converter control is turned off and on. When the
input (current) is lowered, the efficiency of the control circuit
is improved by turning off the converter control because the
switching loss of the switching element composing the boosting
chopper is eliminated. Accordingly, the efficiency of the system
may be improved by turning off the control of the converter when
the input at the lowest rotating speed is small similar to the
compressor motor 7.
[0086] While the embodiment described above has been explained with
reference to various numerical values, those numerical values are
just examples and other numerical values may be adopted as long as
they confirm to the concept of the desired control.
[0087] Further, while the embodiment described above has been
explained by reference to a control block diagram to facilitate its
understanding, the comparator 100, the speed command generator 101,
the position detector 102, the speed calculator 103, the comparator
104, the inverter PWM duty command generator 105, the circuit for
computing the voltage command of the converter PAM voltage command
generator 106, the converter operating judging device 107, the
commutation output device 108, the AND circuit 109, the driver, the
over-current protecting circuit 111, saving operation circuit 131,
the quenching circuit 133, the adder 135, the speed command limiter
136 and the selecting circuit 137 may be realized by software. It
is also possible to form these elements into an LSI by adding an
inverter to them.
[0088] The embodiment described above brings about the following
effects. The energy saving factor of the system may be realized by
designing the compressor motor with emphasis on the point where it
is utilized most (at the point of time of the lowest rotating
speed) because the motor can be highly efficient. When the load of
the refrigerator is high, the compressor motor may be operated at
high speed because the DC voltage is increased by the DC voltage
control circuit as described above. Still more, because the DC
voltage drops from 280 V to 170 V when the rotating speed of the
compressor motor 7 is switched to 2,700 turns, the efficiency of
the motor is improved by 1 to 2%. When the converter control is
turned off, the DC voltage drops from 170 V to 120V. Accordingly,
the efficiency of the motor improves by about 2%, thus saving
energy further. Still more, the efficiency of the control circuit
is also improved by turning off the converter control because the
switching loss of the power element may be eliminated.
[0089] Next, an outline of the refrigerator will be explained with
reference to FIG. 10. In the figure, the reference numeral (301)
denotes an automatic ice maker, (302) denotes an ice cube tray,
(303) denotes an ice-making tray temperature detecting sensor,
(304) denotes a water supply unit, (305) denotes a water supply
tank, (306) denotes an ice storage box, (307) denotes a ice
detecting lever for detecting an amount of ice in the ice storage
box 306, (308) denotes an evaporator, (309) denotes a defrosting
heater provided around the evaporator to remove frost adhering on
the evaporator, (310) denotes a intra-compartment cooling air
circulating fan for circulating cooling air within the compartment,
(311) denotes an intra-compartment cooling air circulating fan
motor for driving the intra-compartment cooling air circulating
fan, (312) denotes a controller as shown in FIG. 1, (134) denotes a
quick ice-making (quick freezing) switch as means for starting an
commanding the quick ice-making function (provided in the
controller 312) for quickening ice-making time more than that
during the normal operation, (4) denotes a power compressor
containing the motor which is a rotating driving apparatus, (315)
denotes a refrigerator compartment, (316) denotes an independent
ice-making compartment or an ice-making corner, and (317) denotes a
freezer compartment.
[0090] It is noted that although the above-mentioned quick
ice-making switch 134 is provided within the refrigerator
compartment 315 in FIG. 10 for the purpose of explanation, the
present invention is not confined only to that case, and the switch
may be fixed on the door of the refrigerator or the outer surface
of the main body. It is also noted that the save switch 132 is not
shown in the figure.
[0091] In a refrigerator having the structure as described above,
the quick ice-making function varies the operational rotating speed
of the power compressor 4 and the intra-compartment cooling air
circulating fan motor 311. Thus, it increases the freezing
capability of the freezing cycle and the air amount supplied to the
automatic ice maker 301 temporarily to quicken the ice-making time
within the freezer compartment 317.
[0092] It is noted that according to the present embodiment, the
operational rotating speed of the power compressor 4 is controlled
variably by combining the PWM (pulse width modulation) control in
the inverter circuit and the PAM (pulse amplitude modulation)
control of the converter circuit for example. As a specific method,
the rotating speed of the compressor is controlled by setting the
DC voltage to a low voltage, e.g., 140 V, by the PAM control in the
low speed range which is normally used in the refrigerator and the
specified rotating speed of the compressor is stabilized by the PWM
control of the inverter circuit.
[0093] Then, the DC voltage is set at a high voltage, e.g., 280 V,
by the pulse voltage amplitude control during the quick ice-making
operation and the specified rotating speed of the compressor is
stabilized by the PWM control of the inverter circuit.
[0094] As another method, it is possible to implement the
above-mentioned PWM control of the motor by the PWM and PAM control
in the First Document and just to boost the DC voltage by the pulse
voltage amplitude control to the DC voltage, e.g., 250 V, for
reaching the specified rotating speed of the compressor during
quick ice-making operation. In this case, the PWM control circuit
of the inverter is not implemented because the specified rotating
speed of the compressor is stabilized by the pulse voltage
amplitude control (the inverter outputs one pulse of conduction of
120.degree.).
[0095] FIG. 11 is a flowchart of the control provided for quick
ice-making operation. In the figure, a process of a normal
ice-making operation is carried out in Step 1 at first. Then, it is
judged whether or not the quick ice-making switch 134 is turned on
in Step 2. When it is judged that the quick ice-making switch 134
is turned on (Y) here, the process advances to Step 3 to start the
quick ice-making operation by increasing the rotating speed of the
compressor to more than that of the normal operational rotating
speed of the compressor using the high and low levels of the DC
voltage applied to the power compressor 4, i.e., by the
above-mentioned pulse voltage amplitude control (PAM control). It
is noted that when it is judged that the quick ice-making switch is
not on (N) in Step 2, the process returns to Step 1 again.
[0096] Next, it is monitored whether or not the detected
temperature of the ice cube tray temperature detecting sensor 303
has reached a temperature below a predetermined temperature (which
is set at temperature by which water supplied to the ice cube tray
302 is completely frozen) in Step 4. When it is judged that the
temperature detected by the sensor is below the predetermined
temperature (Y), the process advances to Step 5 and the automatic
ice maker 301 performs an ice separating operation and then a water
supplying operation. Next, it is judged whether or not the quick
ice-making operation mode has been released in Step 6. When it is
judged that the quick ice-making operation mode has been released
(Y), the process returns to Step 1 again. When it is judged that
the quick ice-making operation mode has not been released (N) in
Step 6, the flow returns to Step 4 again. In Step 4, the judging
operation is repeated until it is judged that the detected
temperature of the ice cube tray temperature detecting sensor 303
is below the predetermined temperature.
[0097] As described above, the controller 312 is provided with a
function (pulse voltage amplitude control) for controlling the
operational rotating speed of the power compressor 4 by switching
the DC voltage applied to the compressor motor 7 stepwise so that
the operational rotating speed of the power compressor 4 of the
refrigerator becomes faster than that during normal operation by
turning on the quick ice-making switch 134.
[0098] Thereby, when there is no ice in the ice storage box 306
when ice is necessary or when a large amount of ice is necessary,
the cooling capacity is enhanced by raising the rotating speed of
the power compressor 4 (quick ice-making operation) and the
ice-making time of one time is cut into a half of the time used in
the past (about 0.5 to 1 hour). Because the power compressor 4
operates a predetermined high speed when the quick ice-making
switch 134 is on, the ice-making time of one time is not fluctuated
by the load (outside air temperature, door opening/closing
frequency, amount of load within the compartment) applied normally
to the refrigerator. Therefore, the ice-making capability will not
drop, no enormous amount of time will be necessary and the
fluctuation of ice-making time per one time may be reduced even in
a plurality of ice-making operations. The other functions of the
quick ice-making switch 134 are the same as those which have been
described with reference to FIG. 1.
[0099] Even when it is compared with the case of the PWM control
described above, it is also not necessary to design the motor for
rotating and driving the compressor which is rotated at high speed
in conformity with the high speed range, the efficiency at the low
speed range may be highly maintained and energy saving may be
realized by switching the DC voltage applied to the power
compressor 4 stepwise, i.e., by controlling the operation rotating
speed thereof by pulse voltage amplitude (PAM) control.
[0100] FIG. 12 shows the structure of circuits switching over
full-wave rectification to double voltage rectification and another
method for switching the DC voltage. A power circuit of the
inverter circuit 3 comprises rectifier diodes D1, D2, D3 and D4,
smoothing capacitors C1 and C2 and a switch SW1. The switch SW1 is
controlled by a control circuit 11 composed of a microcomputer and
other elements. The full wave rectifying circuit is formed when the
switch SW1 is OFF and the voltage double rectifying and switching
circuit is formed when it is ON. The DC voltage obtained by
rectifying and smoothing the commercial power source using the full
wave rectifying circuit and the voltage double rectifying and
switching circuit is applied to the switching element of the
inverter circuit 3 to drive the motor 7.
[0101] FIG. 13 shows characteristics of the DC voltage in switching
from the full wave rectification to the double voltage
rectification. The DC voltage characteristics shown here is when
the switch SW1 is set as a relay. Therefore, the time when the DC
voltage rises in switching from the full wave rectifying circuit to
the voltage double rectifying and switching circuit is around 50
ms. During this 50 ms, the control circuit 11 controls the
conduction ratio of the voltage to be applied to the compressor
motor 7 so that the preset rotation speed is attained. The rising
speed of the DC voltage may be varied arbitrarily when the switch
SW1 is a semiconductor by controlling the ON/OFF timing of the
switch for switching from the full wave rectifying circuit to the
voltage doubler rectifying and switching circuit causing the
control circuit 11.
[0102] It is noted that the ripple of the DC voltage shown in FIG.
13 is determined by the capacity of the smoothing capacitors C1 and
C2. Therefore, the ripple voltage may be reduced by increasing the
capacity of the smoothing capacitors C1 and C2.
[0103] As described above, the invention brings about the effects
of reducing the ice-making time considerably and of providing a
refrigerator whose power consumption may be reduced because the
efficiency of the motor is enhanced by an energy saving mode.
[0104] While the preferred embodiments have been described,
variations thereto will occur to those skilled in the art within
the scope of the present inventive concepts which are delineated by
the following claims.
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