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EP 1 318 365 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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04.07.2007 Bulletin 2007/27 |
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Date of filing: 05.12.2001 |
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International Patent Classification (IPC):
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Method of controlling a variable cooling capacity compressor and refrigerator or freezer
controlled by such method
Verfahren zur Regelung eines Kompressors mit variabler Kühlleistung und nach diesem
Verfahren geregelter Kühl- oder Gefrierschrank
Procédé de réglage d'un compresseur à capacité de refroidissement variable et réfrigérateur
ou congélateur contrôlé par ce procédé
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Designated Contracting States: |
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DE ES FR GB IT SE |
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Date of publication of application: |
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11.06.2003 Bulletin 2003/24 |
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Proprietor: WHIRLPOOL CORPORATION |
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Benton Harbor
Michigan 49022 (US) |
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Inventors: |
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- Boer, Alessandro
V.le G. Borghi 27,
21025 Comerio (IT)
- Paganini, Raffaele
V.le G. Borghi 27,
21025 Comerio (IT)
- Contin, Paolo
V.le G. Borghi 27,
21025 Comerio (IT)
- Bonaglia, Alberto
V.le G. Borghi 27,
21025 Comerio (IT)
- Petrigliano, Rocco
V.le G. Borghi 27,
21025 Comerio (IT)
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Representative: Guerci, Alessandro |
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Whirlpool Europe S.r.l.
Patent Department
Viale G. Borghi 27 21025 Comerio (VA) 21025 Comerio (VA) (IT) |
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References cited: :
DE-A- 4 322 366 US-A- 4 918 932 US-A- 5 148 685 US-A- 5 428 965
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US-A- 3 938 017 US-A- 4 934 157 US-A- 5 229 699 US-A- 5 535 593
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- PATENT ABSTRACTS OF JAPAN vol. 1997, no. 11, 28 November 1997 (1997-11-28) & JP 09
196535 A (MATSUSHITA REFRIG CO LTD), 31 July 1997 (1997-07-31)
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The present invention relates to a method of controlling the power output of variable
cooling capacity compressor of a refrigerator/freezer with an electronic controller
that receives a temperature feedback signal from the refrigerator/freezer. With the
term "variable cooling capacity" we mean all kinds of compressors which can vary either
the motor speed (variable speed compressors) or the displacement of the compressor
(linear compressors). In the first case the power output of the compressor is proportional
to the motor speed, which is the feature actually controlled. In the second case the
power output is proportional to the stroke of the piston of the compressor, which
is the feature actually controlled.
[0002] The present invention refers also to a new method of controlling the temperature
of a refrigerator/freezer cell in which the traditional method based on temperature
hysteresis (error proportional part) is replaced by a new and more efficient one.
[0003] The temperature control of a freezer or a refrigerator is usually obtained, in case
of a fixed or variable cooling capacity (VCC) compressor, by cycling the ON/OFF compressor
state, by means of a so-called "hysteresis" or relay control -see, for example, document
US-A-5 428 965. An example of the mentioned control is expressed by the following control process:
if the temperature to be controlled is less than x°C, then the compressor is switched
OFF (because the temperature inside the cell of the refrigerator or freezer is too
low); if temperature is greater than y°C, then the compressor is switched ON (because
the temperature inside the cell is too high). The x and y values are two predetermined
temperatures linked to the set temperature and the difference (y-x) defines the temperature
hysteresis range.
[0004] The effect of the hysteresis or relay control is that the cabinet temperature (refrigerator
or freezer) is forced to oscillate from a minimum to a maximum temperature value and
so the food is never at constant temperature.
[0005] If x value is very close to y value (low hysteresis value), frequent ON/OFF cycles
will be obtained. The consequence is a noise production and an increase of energy
consumption.
[0006] The oscillation amplitude of the cell temperature is not controlled because it depends
on the load amount and type (thermal inertia) and from the external temperature too.
For instance after the compressor has been set to ON (OFF), the temperature continues
to decrease (increase) by inertia. The main consequence of this is a limited control
of the food preservation because of the dependency of the load thermal inertia.
[0007] The ON/OFF temperature control technique, commonly implemented in appliances where
a usual ON/OFF compressor is installed, is also used in cases in which the compressor
has a variable cooling capacity such as variable speed compressors, or linear compressors.
There are several reasons for adopting this ON/OFF temperature hysteresis control
and the main reasons are:
- 1) it is convenient, from the energy point of view, to switch OFF the compressor instead
of running it with the minimum cooling capacity (minimum speed),
- 2) by running the compressor at the minimum cooling capacity the temperature to be
controlled may be cooler than the required so that the compressor OFF state is preferred.
- It is well known that a continuous control is performing better than ON/OFF control:
the peaks of current during the motor-compressor starting phase are eliminated and,
in the refrigeration field, the energy spent to compensate the pressure losses is
reduced as well.
[0008] One of the purposes of the invention is thus to develop a control method and a control
arrangement for a VCC compressor having a lower energy consumption than the controls
known from the state of the art.
[0009] According to the invention, this is done by setting the compressor with the output
signal of the electronic controller that is based on a predetermined on/off band different
from the usual on/off temperature band. If a variable speed compressor is used, the
output signal of the electronic controller is based on a predetermined on/off speed
band. If a linear compressor is used, the output signal of the electronic controller
is based on a predetermined on/off displacement band.
[0010] The applicant has discovered that by using a reference variable in the temperature
control loop which takes into account also other parts of the temperature error, as
the integrative and/or derivative error parts, a surprising reduction in energy consumption
can be obtained, i.e. up to 5% if compared to a traditional temperature hysteresis
control. The effect is that the OFF condition is no longer dependent from a fixed
temperature value but it depends also on the past (integrative) and future (derivative)
parts of the error. Apart from the advantage of a high energy saving, with the method
according to the invention it is possible to have additional benefits in term of a
more stable temperature and noise reduction due to the decrease or elimination of
ON/OFF cycles.
[0011] In the following the invention is described on the basis of the following figures:
- figure 1 shows a known time/temperature diagram used for a typical control strategy
for variable cooling capacity compressors;
- figure 2 is a schematic view of the control loop according to one embodiment of the
invention in which the VCC (Variable Cooling Capacity) compressor is represented by
a variable speed compressor (compressor that changes the cooling capacity according
to an input reference speed) and a so called hybrid controller is composed by a regulator
system (i.e. PID control whose purpose is to set the suitable compressor speed) and
by a cooling capacity adapter block;
- figures 3a and 3b are schematic block diagrams showing the control method according
to the invention;
- figure 4 shows a time/speed diagram according to the control technique of figure 2
based on the speed control variable;
- figure 5 is a diagram showing the control behavior of the known control method for
a freezer according to the control strategy of figure 1, in which different target
temperatures are set; and
- figure 6 is a diagram similar to figure 4 showing the control behavior of the control
method according to the invention.
[0012] In the prior art control method shown in figure 1 the temperature low band T
LB establishes the temperature value for switching OFF the compressor. T
ON determines the ON condition while the T
UB can be used to force the maximum cooling capacity in case of very hot cell or cabinet
temperature condition.
[0013] Between T
LB and T
UB a regulator system (i.e. PID or a "Fuzzy Logic" control in which the temperature
error and/or derivative of the error are used as input signals) can compute the proper
cooling request in a predetermined temperature control band.
[0014] In fig. 5 the temperature control behavior is shown when a method according to figure
1 is adopted and when different target temperatures are set. The temperature hysteresis
value of this example is 0,5 °C. In the diagram the compressor speed S (rpm) is plotted
(upper part) together with the set temperature T or the actual cell temperature A
(lower part of the diagram). From the diagram, every time the actual temperature is
below the target temperature by 0.5°C, the compressor is switched OFF and the Compressor
Speed is set to 0 (zero) rpm.
[0015] In figure 2 a temperature control loop is shown in which the ON/OFF compressor condition
is not determined by the temperature hysteresis control but, according to the present
invention, it is determined by a hybrid control based on a cooling capacity request
hysteresis control.
[0016] To control the cabinet temperature, a regulator system C, PID like, is used. In figure
2 a variable cooling capacity compressor, represented by a variable speed compressor
VSC, is shown together with a refrigerator R and a temperature probe P inside the
cell of the refrigerator.
[0017] The regulator system C sets the proper cooling capacity to the compressor up to reduce
the error temperature close to 0 °C. i.e. actual temperature = target temperature.
[0018] The compressor speed "u" is in the example the output variable of the regulator system
block C. The block K, defined cooling capacity adapter, receives the compressor speed
computed by the regulator system as input and, within it, the speed hysteresis control
is implemented. The output of K block is the compressor state (ON or OFF state) and,
in case of ON state, a compressor speed "u*" within a certain range value. Usually
the compressor speed range is limited: i.e. 4000rpm (maximum) and 2000rpm (minimum).
The low and high limits depend from motor construction (mechanical and electrical
specifications).
[0019] In Fig. 4 the control technique according to the control loop of figure 2 is shown.
The ON/OFF speed band substitutes the ON/OFF temperature band. The OFF speed value
S
PID_OFF ,according to the temperature control loop, is preferably lower than the minimum
compressor speed=2000rpm. The OFF condition is obtained by comparing the regulator's
output parameter, u=S
PID, with a predetermined value: if the S
PID <= Speed_OFF then the adapter K switches OFF the compressor. In the example of figure
4 a hysteresis of 400 rpm is used. The compressor is again switched ON only when the
S
PID becomes higher than a determined value Speed_ON, i.e. 2000 rpm. The above control
technique is also shown in the block diagram of figures 3a and 3b.
[0020] Referring to figure 3a, the first step is to read both the temperature of the sensor
P in the cell and the target temperature fixed by the user. At step 2, an assessment
of the error is made at present time t
0 and at previous times t
1 and t
2. At step 3 the incremental cooling capacity, which is due to the proportional part
of the error, is calculated. At step 4, the incremental cooling capacity, which is
due to the derivative part of the error, is calculated. At step 5, the incremental
cooling capacity, which is due to the integral part of the error, is calculated. At
step 6 the sum of the above three components is calculated. At step 7 the new request
of cooling capacity is calculated by the controller. At step 8 the previous state
of the compressor is stored: OFF_state = compressor switched off, ON_state = compressor
switched on. At step 9, if the new request of cooling capacity is considered too low
(i.e. lower than a predetermined value Speed_OFF), then the compressor is given a
state off (OFF_state). At step 10, if the new request of cooling capacity is higher
than the re-switching threshold speed_on, then the compressor is given a state on
(ON_state). At step 11, if the compressor passes from OFF_state to ON_state, a new
request of cooling capacity is given: Reset_Cooling_Capacity. This is a predetermined
value on which the control system restarts the control loop when the compressor is
switched on. A preferred strategy for further reducing energy consumption is to select
the reset value as the value corresponding to minimum cooling capacity (minimum speed).
[0021] Referring to figure 3b, step 12 corresponds to the limitation of the control action
to the maximum allowed (maximum speed). Step 13 corresponds to the limitation of the
control action to the minimum that is allowed without switching off the compressor.
At step 14 the cooling capacity difference between the new request fixed by the controller
and the present request actually carried out by the compressor is assessed. At step
15 the variable Actual_Cooling_Capacity is given the request change. Step 16 corresponds
to a lower limitation for the cooling capacity; this is due to certain technical limitations
of variable speed compressors that, at very low speed, do not guarantee a proper lubrication.
Step 17 corresponds to an upper limitation of cooling capacity and step 18 is a final
check of the state of the compressor in order to decide if it is switched on or switched
off. Of course at the end of the above control flow a new control cycle starts with
the same flow pattern.
[0022] The u=S
PID is a value which is used for controlling purposes and it may not correspond to the
actual cooling capacity inputted to the compressor u*.
[0023] When the compressor passes from the OFF to the ON state, the u control parameter
of the regulator system is set to a convenient predetermined value: Reset_Cooling
_Capacity. For energy saving purposes and for temperature control stability reasons
the Reset_Cooling _Capacity value is set to the minimum cooling capacity of the compressor.
[0024] Figure 6 shows the advantages of the method according to the invention. One of such
advantages is that temperature oscillation is strongly reduced because the number
of cycles is reduced or even said cycles are eliminated. This is possible since the
compressor speed, determined by the regulator system C (i.e. PID), takes into account
the proportional part of the error as well the derivative and integrative parts. All
these components make the control able to compensate the temperature error by its
present, past and future error state. The u control parameter includes all or some
of the above mentioned information and not only the proportional part as the conventional
control does by switching the compressor OFF when the temperature is below to a threshold
value. The present invention makes use of a hybrid control system able to reduce the
cooling capacity request up to reach the minimum admitted value and set this value
to the compressor. In cases in which the cell or cabinet temperature continues to
decrease the OFF condition is obtained only when the u control parameter is below
a certain threshold vale.
[0025] From a comparison of figures 5 and 6 it is evident that with the control method according
to the invention the OFF conditions occur only when it is strictly necessary (high
target temperature and/or low room temperature), while in all the other conditions
the system has "time" to find a stable cooling capacity (i.e.speed) able to keep the
foods at constant temperature.
1. Method for controlling the cooling capacity of a variable cooling capacity (VCC) compressor,
which is a variable speed compressor (VSC), or a linear compressor, of a refrigerator
or freezer (R) with an electronic controller (C) which receives a temperature feedback
signal, characterized in that the output signal of the electronic controller is a speed signal or a piston stroke
signal based on a predetermined on/off speed band or on a predetermined on/off piston
stroke band respectively.
2. Method according to claim 1, characterized in that the low end of the on/off speed band is lower than or equal to the minimum speed
of the compressor (VSC).
3. Method according to claim 1 or 2, characterized in that the high end of the on/off speed band is higher than or equal to the minimum speed
of the compressor (VSC).
4. Method according to any of the preceding claims, characterized in that the temperature feedback signal is issued by a temperature sensor (P) placed in a
refrigeration cell of the refrigerator or freezer (R).
5. Method according to any of the preceding claims, characterized in that the electronic controller (C) is selected in the group consisting of proportional-integral
(PI) controller, proportional-derivative (PD) controller, proportional-integral-derivative
(PID) controller and any fuzzy logic controller in which the temperature error and/or
derivative of the error are used as input signals.
6. Method according to claim 1, characterized in that when the electronic controller switches on the compressor, it is always switched
on at the minimum speed.
7. Refrigerator or, freezer having a refrigeration cell and a variable cooling capacity
(VCC) compressor which is a variable speed compressor (VSC) or a linear compressor,
with an electronic controtter (C) which receives a temperature feedback signal from
a temperature sensor (P) placed in said cell, characterized in that the electronic controller (C) is able to provide the variable cooling capacity, compressor
(VCC) with a speed signal or a piston stroke signal, that is based on a predetermined
on/off speed band or on a predetermined on/off piston stroke band respectively.
8. Refrigerator or freezer according to claim 7, characterized in that the low end of the on/off speed band is lower than or equal to the minimum speed
of the compressor (VSC).
9. Refrigerator or freezer according to claim 7 or 8, characterized in that the high end of the on/off speed band is higher than or equal to the minimum speed
of the compressor (VSC).
10. Refrigerator or freezer according to any of claims 7 - 9, characterized in that the electronic controller (C) is selected in the group consisting of proportional-integral
(PI) controller, proportional-derivative (PD) controller, proportional-integral-derivative
(PID) controller and fuzzy logic controller.
11. Refrigerator or freezer according to any of claims 7-9, characterized in that when the electronic controller switches on the compressor, it is always switched
on at the minimum speed.
1. Verfahren zum Steuern der Kühlkapazität eines Kompressors variabler Kühlkapazität
(VCC), der ein Kompressor variabler Geschwindigkeit (VSC) oder ein Linearkompressor
ist, eines Kühlschranks oder Gefrierschrank (R) mit einer elektronischen Steuerung
(C), die ein Temperatur-Rückkopplungssignal empfängt, dadurch gekennzeichnet, dass das Ausgabesignal der elektronischen Steuerung ein Geschwindigkeitssignal oder ein
Kolbenhubsignal ist, basierend auf einem vorgegebenen EIN/AUS-Geschwindigkeitsbereich
oder einem vorgegebenen EIN/AUS-Kolbenhubbereich.
2. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, dass das untere Ende des EIN/AUS-Geschwindigkeitsbereichs niedriger oder gleich der Minimalgeschwindigkeit
des Kompressors (VSC)ist .
3. Verfahren gemäß Anspruch 1 oder 2, dadurch gekennzeichnet, dass obere Ende des EIN/AUS-Geschwindigkeitsbereiches größer oder gleich der Minimalgeschwindigkeit
des Kompressors (VSC) ist.
4. Verfahren gemäß einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass das Temperatur-Rückkopplungssignal von einem Temperatursensor (P) gegeben wird, der
in einer Kühlzelle des Kühlschranks oder Gefrierschranks (R) platziert ist.
5. Verfahren gemäß einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die elektronische Steuerung (C) aus der Gruppe ausgewählt ist, die aus einer proportional-integralen
(PI) Steuerung, proportional-ableitenden (PD) Steuerung, proportional-integralableitenden
(PID) Steuerung und jeglicher Fuzzy-Logic-Steuerung besteht, in der der Temperaturfehler
und/oder die Ableitung des Fehlers als Eingangssignale verwendet werden.
6. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, dass, wenn die elektronische Steuerung den Kompressor einschaltet, er immer bei minimaler
Geschwindigkeit eingeschaltet wird.
7. Kühlschrank oder Gefrierschrank mit einer Kühlzelle und einem Kompressor variabler
Kühlkapazität (VCC), der ein Kompressor variabler Geschwindigkeit (VSC) oder ein Linearkompressor
ist, mit einer elektronischen Steuerung (C), die ein Temperatur-Rückkopplungssignal
von einem Temperatursensor (P), der in der Zelle platziert ist, empfängt, dadurch gekennzeichnet, dass die elektronische Steuerung (C) in der Lage ist, dem Kompressor variabler Kühlkapazität
(VCC) ein Geschwindigkeitssignal oder ein Kolbenhubsignal bereitzustellen, das auf
einem vorgegebenen EIN/AUS-Geschwindigkeitsbereich bzw. auf einem vorgegebenen EIN/AUS-Kolbenhubbereich
basiert.
8. Kühlschrank oder Gefrierschrank gemäß Anspruch 7, dadurch gekennzeichnet, dass das untere Ende des EIN/AUS-Geschwindigkeitsbereiches kleiner oder gleich der Minimalgeschwindigkeit
des Kompressors (VSC) ist.
9. Kühlschrank oder Gefrierschrank gemäß Anspruch 7 oder 8, dadurch gekennzeichnet, dass das obere Ende des EIN/AUS-Geschwindigkeitsbereiches größer oder gleich der Minimalgeschwindigkeit
des Kompressors (VSC) ist.
10. Kühlschrank oder Gefrierschrank gemäß einem der Ansprüche 7 bis 9, dadurch gekennzeichnet, dass die elektronische Steuerung ausgewählt ist aus der Gruppe, die aus einer proportional-integralen
(PI) Steuerung, proportional-ableitenden (PD) Steuerung, proportional-integral-ableitenden
(PID) Steuerung und jeglicher Fuzzy-Logic-Steuerung besteht.
11. Kühlschrank oder Gefrierschrank gemäß einem der Ansprüche 7 bis 9, dadurch gekennzeichnet, dass, wenn die elektronische Steuerung den Kompressor einschaltet, er immer bei minimaler
Geschwindigkeit eingeschaltet wird.
1. Procédé de réglage de la capacité de refroidissement d'un compresseur à capacité de
refroidissement variable (VCC), qui est un compresseur à vitesse variable (VSC) ou
un compresseur linéaire, d'un réfrigérateur ou d'un congélateur (R) ayant un contrôleur
électronique (C) qui reçoit un signal de retour de température, caractérisé en ce que le signal de sortie du contrôleur électronique est un signal de vitesse ou un signal
de course de piston basé sur une bande de vitesses d'activation/de désactivation prédéterminée,
ou sur une bande de courses d'activation/de désactivation prédéterminée respectivement.
2. Procédé selon la revendication 1, caractérisé en ce que l'extrémité inférieure de la bande de vitesses d'activation/de désactivation est
inférieure ou égale à la vitesse minimum du compresseur (VSC).
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que l'extrémité supérieure de la bande de vitesses d'activation/de désactivation est
supérieure ou égale à la vitesse minimum du compresseur (VSC).
4. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le signal de retour de température est transmis par un capteur de température (P)
placé dans un compartiment de réfrigération du réfrigérateur ou du congélateur (R).
5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le contrôleur électronique (C) est sélectionné parmi le groupe consistant en un contrôleur
à intégrale proportionnelle (PI), un contrôleur à dérivée proportionnelle (PD), un
contrôleur à intégrale/dérivée proportionnelle (PID) et n'importe quel contrôleur
à logique floue dans lequel l'erreur de température et/ou la dérivée de l'erreur sont
utilisées comme signaux d'entrée.
6. Procédé selon la revendication 1, caractérisé en ce que, lorsque le contrôleur électronique active le compresseur, il est toujours activé
à la vitesse minimum.
7. Réfrigérateur ou congélateur ayant un compartiment de réfrigération et un compresseur
à capacité de refroidissement variable (VCC) qui est un compresseur à vitesse variable
(VSC) ou un compresseur linéaire ayant un contrôleur électronique (C) qui reçoit un
signal de retour de température de la part d'un capteur de température (P) placé dans
ledit compartiment, caractérisé en ce que le contrôleur électronique (C) est capable de fournir au compresseur à capacité de
refroidissement variable (VCC) un signal de vitesse ou un signal de course de piston
qui est basé sur une bande de vitesses d'activation/de désactivation prédéterminée
ou une bande de courses de piston d'activation/de désactivation prédéterminée, respectivement.
8. Réfrigérateur ou congélateur selon la revendication 7, caractérisé en ce que l'extrémité inférieure de la bande de vitesses d'activation/de désactivation est
inférieure ou égale à la vitesse minimum du compresseur (VSC).
9. Réfrigérateur ou congélateur selon la revendication 7 ou 8, caractérisé en ce que l'extrémité supérieure de la bande de vitesses d'activation/de désactivation est
supérieure ou égale à la vitesse minimum du compresseur (VSC).
10. Réfrigérateur ou congélateur selon l'une quelconque des revendications 7 à 9, caractérisé en ce que le contrôleur électronique (C) est sélectionné parmi le groupe consistant en un contrôleur
à intégrale proportionnelle (PI), un contrôleur à dérivée proportionnelle (PD), un
contrôleur à intégrale/dérivée proportionnelle (PID), et un contrôleur à logique floue.
11. Réfrigérateur ou congélateur selon l'une quelconque des revendications 7 à 9, caractérisé en ce que, lorsque le contrôleur électronique active le compresseur, il est toujours activé
à la vitesse minimum.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only.
It does not form part of the European patent document. Even though great care has
been taken in compiling the references, errors or omissions cannot be excluded and
the EPO disclaims all liability in this regard.
Patent documents cited in the description