MXPA06009219A - A refrigerator and a method for controlling variable cooling capacity thereof - Google Patents

Abstract

A refrigerator comprises a compressor and control means for controlling such compressor in response to the temperature inside the refrigerator. The control means are adapted to detect how the temperature changes inside the refrigerator due to the loading of a warm food item, and to adjust the cooling capacity of the compressor accordingly.

Description

A REFRIGERATOR AND A METHOD TO CONTROL VARIABLE COOLING CAPACITY OF THE SAME DESCRIPTION OF THE INVENTION The present invention relates to a refrigerator comprising a compressor having a fixed or variable cooling capacity and control means for controlling such a compressor in response to the temperature inside the refrigerator, as well as to a method for automatically accelerating the cooling time of the food stored in the refrigerator without user interaction and with limited energy consumption. By the term "refrigerator" as used in the description and the appended claims is meant any type of domestic refrigerator and freezer. The term compressor that has variable cooling capacity is understood to mean all types of compressors that have the possibility of changing the output, either by changing the displacement of the compressor (for example, with the so-called free piston compressor) or by change the speed of the compressor (in case of fixed displacement) either continuously or in stages. In general, modern freezers and refrigerators have a feature of fast freezing or rapid cooling. This feature must be activated by the user and consists of keeping the compressor running at its maximum cooling capacity for an appropriate fixed time (ie, 24 hours). Such known technique guarantees the maximum cooling speed and is suitable for rapid cooling of large quantities of food. When the amount of food is not very large, it leads to excess unnecessary cooling of the food and waste of energy. On the other hand, the user often forgets to activate the function or does not consider enough food to manually activate the function. As a consequence, in these cases the cooling process is relatively slow. A refrigerator having the features listed in the appended claims solves the above problem. The present invention provides a control algorithm capable of estimating the amount of hot food inserted in the refrigerator or freezer. Based on this estimate, the algorithm automatically adjusts the response of the compressor to accelerate the cooling process without wasting energy for unnecessary excess cooling. In this way, it is not required that the user activates manually to use the rapid cooling function, and no energy is wasted, because excess cooling is avoided. BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned and other features and objects of the present invention, and the manner of obtaining them, will become more apparent and the invention itself will be better understood by reference to the following description taken together with the accompanying drawings in which Figure 1 shows a typical temperature trend within a known freezer when the user places a quantity of hot food inside the cavity without any "Fast Freeze" function; Figures 2a and 2b show a block diagram describing the logical architecture of the apparatus control algorithm (ACA) according to the present invention in case a variable speed compressor or an on / off compressor is respectively used; Figure 3 shows a typical overdrive test temperature caused by the introduction of hot food; Figure 4 shows the main parameters that can be considered to characterize the shape of the overshoot and to estimate the enthalpy of the hot food; Figure 5 shows a recovery of hot food temperature, with an apparatus control algorithm according to the present invention; Figure 6 shows the automatic fast freezing obtained by estimating enthalpy of hot food just with the base of the temperature peak of the test overshoot; in Figure 6a only one door opening was considered, while in Figure 6b a door opening with 10 kg of hot food load was considered; Figure 7 shows the automatic fast freezing obtained by estimating the enthalpy of hot food with the base of the temperature peak of the test overshoot and in the area of test temperature overshoot; in Figure 7a only one door opening was considered, while in Figure 7b a door opening with 10 kg of hot food load was considered; Figure 8 highlights the faster recovery and decrease obtained by considering the Aover area of overdrive temperature test in addition to the peak temperature Tpeak; Figures 9a and b show a comparison between a decrease in hot food with the known function "Fast Freeze" activated and a recovery according to the present invention respectively, highlighting how the traditional function of rapid freezing can cause excessive "sub-cooling" and unnecessary food (it was considered half load); Figure 10 shows a comparison between the energy consumption against the time obtained with the known function of rapid freezing (in the working condition shown in Figure 9a) and the energy consumption obtained with a refrigerator according to the present invention (in the working condition of Figure 9b); and Figures 11 and 12 show an example of an automatic rapid freezing function obtained by applying the present invention to an apparatus with a variable speed compressor and an on / off compressor respectively. With reference to the drawings, in which experimental data were obtained with a Whirlpool model s25brww20-a / g two-door refrigerator, Figure 1 shows a typical well-known temperature trend inside a freezer when the user places a quantity of hot food inside the cavity. First, the test temperature increases rapidly. When the user closes the door, the temperature begins to fall thanks to the action of traditional temperature control, based on a consequent increase in - the cooling capacity of the compressor (in the example, the speed of the variable speed compressor increases of 1500 rpm at 4000 rpm). The higher the amount of hot food in the freezer, the more the temperature of the test decreases. A further important effect of the introduction of hot food (figure 1) is to heat the "cold packs" ("cold pack" is indicated to the container already stored in the appliance when the hot food is loaded). The present invention relates to a refrigerator and a method for controlling the refrigerator with the triple objective of controlling the activators of the apparatus (compressor, valves, buffer) to: - maximize the temperature decrease of the hot food; - reduce the excess temperature of the "cold pack"; and - minimize energy consumption. Figure 2 shows a block diagram describing the logical architecture of the apparatus control algorithm (AC) according to the present invention. It consists of three main blocks: the thermal load estimator of the hot food (TLE), the test temperature controller (PTC) and the cooling capacity adapter (CCA). The first block (TLE) has the purpose of detecting the hot food introduction event and estimating the quantity of this hot food. With the terms "Thermal load" refer to the enthalpy E of hot food defined as E = (mass of the food) • (specific thermal capacity of the food) • (temperature of the food). The PTC block is intended to control the temperature measured by the traditional sensor by providing an appropriate demand for "cooling capacity" in accordance with the three aforementioned objectives. The CCA cooling capacity adapter converts the cooling capacity demand into an appropriate actuator instruction. Such an actuator can be either the compressor speed if a variable speed compressor is used (figure 2a) or the condition of the compressor (on / off) if a fixed speed compressor is used (figure 2b). In the second case, the CCA block operates according to a hysteresis logic, that is, if the cooling demand u (t) is greater than a predetermined value u (t) on, the compressor will turn off if such a demand for cooling is less than a predetermined value u (t) Dff, the compressor will turn off. Of course, it is possible to use another logic to convert the continuous quantity u (t) to a binary value, for example a PWM (pulse amplitude modulation) technique. The TLE thermal load estimation block and the PTC test temperature controller block are within the main features of the present invention. The TLE block consists of an estimation algorithm based on an accurate analysis of the test temperature signal in order to obtain the hot feed enthalpy E. This is done by processing the test temperature overshoot form (Figure 3) as consequence of the introduction of hot food. With the term form factor, all the factors that characterize the test temperature overshoot, and particularly its derivatives, are described. average temperature value (stable state), peak height, duration of the overshoot, power spectrum or combination thereof. Figure 4 shows the main factors that characterize this form of temperature overshoot and that have been considered to obtain the hot food temperature enthalpy E, according to the present invention. These main factors are summarized here: - the test temperature derivative during the dTr elevation phase (average maximum and minimum) - the test temperature derivative during the decrease (inclination) dTs (average maximum and minimum) - the peak temperature on Tpeak - the overdrive area of the Aover test temperature - the duration of the overshoot? tOVersoot - the power spectrum of the test temperature overshoot.

The way in which the above factors are detected / measured is not described here in detail since this is considered within the normal experience of a refrigerator control designer. Figure 5 shows a recovery of hot food temperature, with an apparatus control algorithm implementing the present invention. By comparing this diagram with the diagram in figure 1 (traditional control) it can be observed how the proposed algorithm performs an appropriate test of "excess cooling". According to the blog diagram in figure 2, the PTC test temperature control blog requires compressor shutdown (demand cooling capacity = 0) when the temperature of the hot food (obtained through the TLE block) is considered sufficiently close to the user's set temperature. It is important to note that the traditional control does not perform any "subcooling" test: when the temperature test reaches the interruption temperature, the compressor shuts down but the food still does not completely cool. On the contrary, the proposed algorithm performs an appropriate "subcooling" of test depending on the estimate of enthalpy of hot feed introduced provided by the TLE block (figure 2). The TLE block recognizes the introduction of the hot feed, processes the test temperature overshoot and provides the PTC block with the enthalpy E of estimated hot feed. The PTC block decides a "subcooling" of an appropriate test temperature sub-pulse. During this phase, the normal control based on the cut-off and cut-off temperature is denied, that is, the compressor is no longer on and off when the temperature inside the refrigerator reaches the cut-off temperature and nominal interruption respectively. During such a phase, the interruption and cutting temperatures are automatically reduced according to the enthalpy of the estimated charged feed and are progressively increased in nominal values in order to provide an efficient energy temperature decrease. This is clearly shown in Figure 5. After the container loaded in the freezer is considered to be sufficiently cooled, the normal method for controlling the compressor is summarized, in which the compressor is turned off when the interruption temperature is reached. With reference to Figure 4, a possible technique for estimating the amount of hot food and for carrying out an appropriate "excess cooling" test is based on the estimate of the AOVer area, ie, the integral of the curve that represents the temperature increase over an average steady state temperature T. If AoVer is the test temperature area caused by the insertion of the hot container, the control algorithm drives the compressor at an appropriate speed to guarantee an area of "excess cooling" that is proportional to the Aunder area, ie, AOVer = 'Aover. The parameter k may depend on the type of device. Furthermore, in the same device, this parameter can be constant or changed with the working conditions (ie, external temperature, temperature set by the user, etc.), and fuzzy logic can be used to intentionally adjust the value k. An alternative technique consists in having an Auder area based on the time derived from the test temperature, that is, with Auner proportional to the derivative either in the temperature rise phase or in the temperature decrease phase: the lower it is the derivative in the phase of decrease, the greater must be Aune, the larger the derivative in the increase phase, the higher must be Auner (derived from the time that is in absolute value). However other parameters (besides the amount of hot food) can affect these parameters (dtr, dTs,? Toershoot and AOVer) And one of these is the external temperature. For this reason, if an external temperature sensor is available in addition to the normal internal temperature sensor, the measurement of the three parameters above can be correlated with the measurement of the external temperature sensor to improve the temperature estimation of the hot food. The same techniques described in the previous paragraphs can also be used to decide an appropriate interval time Dt in which the compressor must be forced to operate at an appropriate level of power (for example at maximum). Of course any combination of the previous techniques can be used. Fuzzy logic and "neural network" techniques can be used for this type of application. For example, a control algorithm based on a set of Fuzzy rules can receive as input all the mentioned parameters shown in Figure 4 and convert them into an estimate of both the mass and temperature of the inserted food or its enthalpy E (like the product of thermal mass by temperature). This estimate can then be passed to a second task which converts it into a compressor cooling capacity demand u (t) and can provide one or more additional parameters such as: area- Even er, sub-cooling test, temperature sff interruption , time interval Dt in which the compressor must be forced to operate at an appropriate power level (if different power levels are available). Alternatively or in addition to the type of technical solution, a temperature control algorithm based on the PID (Proportional-integral-derivative) technique can obtain control. With such an algorithm, the demand for cooling capacity of the compressor u (t) will depend on the error temperature e (t) according to the following formula: u (t) = Kp * ¡í) -f- 1 ** 'faith? (. t) d? t. +, Trrdj *: de. { t) Ti dt Where the temperature error e (t) is defined as: e (t) = Tprobe-Ttarget, Ti is the integral time, Td is the derived time, Ttarget is a temperature reference depending on the set temperature of the user and Kp is a predetermined coefficient. The integral component plays the important role of adapting the cooling capacity to the amount of hot food. In fact it is proportional to the area of the error e (t) along the time axes. During a recovery, this area is significantly affected by the amount of hot food: the larger the amount of hot food, the more "large" the trends e (t) (> 0) with a consequent increase in its area (see Aover area in figure 4). This condition leads to a progressive increase in the cooling capacity of the compressor u (t). In addition, the integrated component guarantees an appropriate "excess cooling" test to compensate for the positive area caused by the insertion of the hot food. To improve this effect, an adaptable PID can be used. A "steady-state PID" will control the temperature of the appliance when there are no disturbances to the system (no door opening, no food introduction). Once door opening and feed introduction events are detected, the "steady state PID" will be disabled and a "decrease PID" algorithm will be used. Such "decrease PID" will provide a fast and efficient temperature decrease of hot food. This can be obtained by adjusting the Ti parameter according to the following criteria: - during the steady state, Ti will be established at its nominal value (Ti = TiN); - once a hot feed introduction is detected and the test temperature overshoot begins, TI is reduced by a factor kl (Ti = TiN / kl, kl > = l). 'This will improve the dependence of the integral part of the PID of the area of overdrive of test temperature which is one of the main factors affected by the enthalpy of the hot food; - at the end of the test temperature overshoot (when e (t) goes from negative to positive) the Ti will be increased by a factor k2: (Ti = TiN * k2, k2 > = l). This will reduce the discharge of the integral part with an excess cooling area of consequent test temperature. Such excess cooling will be proportional to the area of previous temperature overshoot and, consequently, the enthalpy of hot food. The adjustment Ti (and / or other parameters such as Td and Kp) can act together with or replace the well-known "anti-windup" technique in which the integrated part of the temperature error may or may not saturate to a predetermined value. It is important to note the fact that the effectiveness of the invention in providing an appropriate hot food temperature decrease depends on the precision of the enthalpy estimation of the food. The more accurate the estimate, the more precise the decrease will be with respect to the aforementioned triple objective. The quality of the estimate depends mainly on which test temperature overshoot parameters (see Figure 4) will be considered by the TLE block to obtain the enthalpy estimate of the hot feed. In particular, an intuitive solution may suggest estimating the enthalpy of the food only on the basis of the peak Tpeak temperature without any consideration of the shape of the overdrive test temperature. Such a solution type can not get to enable the apparatus control algorithm to correctly recognize the amount of hot food and can provide an erroneous temperature decrease in the sense that it can provide a subcooling of the excessive feed when the amount of hot food is low (with a subsequent waste of energy). Or can provide a rapid decrease not enough in the presence of a large amount of hot food. This fact is highlighted in figures 6a and 6b. These figures show the decrease obtained with an apparatus control that estimates the enthalpy of the food only with the base of the peak test overdrive temperature (Tpeak) and establishes a continuous compressor operating time proportional to the Tpeak. Figure 6a shows the response of such an algorithm type for a 3 minute door opening without feeding introduction. Figure 6b shows the behavior of the same algorithm in response to a door opening with 10 kg of hot feed introduction at the external ambient temperature (20 ° C). In both cases, the peak temperature value (Tpeak) is approximately the same and the algorithm decides during 2 hours of execution of the compressor. After 2 hours, the compressor will turn off according to the normal interruption temperature. It can be seen how the algorithm performs a good recovery of cold pack temperature in the first condition (figure 6a): the compressor shuts off when the temperature of the cold pack returns to the steady state value: any additional subcooling can cause waste of energy. When 10 kg of hot package is introduced (figure 6b) the algorithm decides again during 2 hours of continuous execution of the compress r (the Tpeak value being the same). After 2 hours, the temperature is still above the interruption value; the control algorithm may decide to keep the compressor in a lit condition until the interruption temperature is reached. But in this case, the controller outputs are not optimal. In fact the compressor shuts off when the cold package is still higher than 3 ° C above the steady state value and the hot package is still 5 ° C above the steady state value. Figures 7a and 7b show the behavior of a control apparatus in which the enthalpy estimate of the hot food is based on the peak temperature and the overshoot area. The perturbations considered here are exactly the same as those considered with the previous algorithm (3 minutes of door opening without load introduction, door opening with 10 kg load introduction). In particular, an adaptable PID according to the aforementioned idea was considered here as a control algorithm (with kl = l and k2 = 2, Ti = 3600 seconds). By analyzing Figures 7a and b, it can be seen how the decrease and recovery are performed correctly in both conditions by providing the algorithm's ability to automatically adapt the response of the compressor and the excess cooling of the test temperature to the amount of hot load introduced. In fact in the first case, the compressor was turned off when the cold package was very close to the steady state value (only 0.5 ° C over the steady state value). In the second case (10 kg of introduction of hot charge), again the compressor was turned off when the hot containers reached the stable value and the cold package is only 1 ° C above the steady state temperature and returns to its value of steady state half the time. Furthermore, it can be observed that in both cases, the algorithm does not immediately restore the interruption and cut-off temperatures after the first disconnection but increases them progressively up to the steady-state value. This is done to have a rapid recovery of packaging and decrease avoiding temperatures of excessive cold tests that can cause waste of energy (the colder the test temperature, the colder the temperature of the evaporator and, consequently, the less efficient the thermodynamic cycle). Figure 8 highlights the recovery performed by the two algorithms considered. The main advantages of the present invention are as follows. The algorithm adapts the response of the compressor to the hot thermal mass avoiding any waste of energy due to unnecessary excess cooling. In particular, figure 9a shows the effects of the traditional rapid freeze function manually activated by the user: in this case the amount of "average load" of hot food has been inserted in the freezer. The traditional fast freeze function keeps the compressor working at full capacity for 24 hours with consistent subcooling of the food with a consequent waste of energy. Figure 9b shows the automatic rapid freezing performed by the method according to the present invention in the same working condition of figure 9a: without any user interaction, the same amount of hot food is quickly recovered without "excess cooling" of unnecessary food. Figure 10 shows the comparison between energy consumption in the two previous cases. The method according to the invention is completely automatic, this means that the user is not required to activate any function. So the risk of a slow temperature recovery, when the user forgets to activate the rapid freezing function present in known refrigerators, is avoided. Finally, it is important to emphasize that the present invention can be applied to devices with variable capacity compressor and on / off compressor. According to the block diagram of figure 2, in the case of variable speed compressor, the cooling demand provided by the PTC block will become a demand for speed through an appropriate curve (for example, linear). In the case of a traditional on / off compressor, the cooling demand will be converted into a compressor status instruction according to an appropriate logic (hyssis, PWM). Figures 11 and 12 show an application example according to the invention to a variable speed compressor and to a on / off compressor respectively. Even if the description focuses primarily on an example algorithm applied to a freezer, the same algorithm can also be used in a refrigerator or in a fresh food compartment of an appliance having more than one cooling cavity.

Claims (12)

1. CLAIMS 1. A refrigerator comprising a compressor having control means for controlling it in response to the temperature inside the refrigerator, characterized by the control means being adapted to detect how the temperature inside the refrigerator varies due to the loading of a food or a similar event, and to adjust the cooling capacity of the compressor and / or its state (on / off) accordingly. The refrigerator according to claim 1, characterized in that the control means is adapted to increase the cooling capacity of the compressor and / or the operating time of the compressor proportionally to an estimated enthalpy (E) of the loaded food. 3. Method for controlling the variable cooling capacity in a refrigerator having a compressor of variable cooling capacity, in which the control is based on the temperature signal of a temperature sensor inside the refrigerator, characterized in that the variation of the Temperature due to food loading or a similar event is detected and the cooling capacity of the compressor is adjusted accordingly to have a faster cooling of such food. 4. Method for controlling the condition of an on / off compressor in which the control is based on the temperature signal from a temperature sensor inside the refrigerator, characterized in that the temperature variation due to the loading of a food or a a similar event is detected and the compressor state, together with the operating time of the compressor, is accordingly adjusted to have a faster cooling of such a food. The method according to claim 3 or 4, characterized in that it comprises the following steps: - detecting any variation of the test temperature over a predetermined average temperature value due to the loading of a food inside the refrigerator; - analyzing the form factors of the test temperature variation, preferably factors of form that are selected in the group that consists of the derivative, area, peak, duration of the overshoot, power spectrum or combination thereof; - estimate the enthalpy (E) of the loaded food from the analysis of the test temperature form and the related shape factors; e - increasing the cooling capacity of the variable capacity compressor or compressor operating time of the on / off compressor so that the integral and / or the variation peak of the test temperature below the predetermined average temperature is proportional to the enthalpy of the estimated loaded food. The method according to claim 3 or 4, characterized in that it comprises the following steps: - detecting any variation of the test temperature over a predetermined average temperature value due to the loading of a food inside the refrigerator; - estimate the integral of the test temperature variation against time; and increasing the cooling capacity of the variable capacity compressor or the compressor operating time of the on / off compressor so that the integral and / or peak variation of the test temperature under the predetermined average temperature, due to the Increased cooling capacity of the compressor is proportional to the integral of variation of the temperature over the predetermined value. The method according to claim 3 or 4, characterized in that it comprises the following steps: - detecting any variation of the test temperature over a predetermined average value due to the loading of a food inside the refrigerator; - estimate the derivative of the test temperature against time in the decrease of temperature due to the intervention of the control; and increase the cooling capacity of the variable capacity compressor or the compressor operating time of the on / off compressor so that the integral and / or peak variation of the test temperature under the average predetermined temperature value, due to the increased cooling capacity of the compressor, it is inversely proportional to the temperature derivative. The method according to claim 4, characterized in that the cooling capacity u (t) of the compressor is adjusted with a control algorithm based on a PID technique according to the following formula: where the temperature error e ( t) is defined as: e (t) = Tprobe-Ttarget, Ti is the integral time, Td is the derived time, and Kp is a constant coefficient. 9. The method according to claim 8, characterized by the parameters Ti, Td, Kp are adjusted according to a door opening of the refrigerator or from a sudden detection of temperature rise to be able to accelerate the cooling time of the food . The method according to claim 5 or 6, characterized by parameters such as the areas and derivatives of the measured temperatures are processed using flexible calculation techniques such as fuzzy logic and neural networks to provide an estimate of the enthalpy of the inserted food and to adapt the 'response of the compressor accordingly. 11. The method according to the claim 4, characterized in that the demand for cooling capacity is converted from a continuous quantity to a discrete quantity for controlling an on / off compressor. 12. The method in accordance with the claim 5, characterized in that in which the compressor is turned on and off when the temperature inside the refrigerator reaches nominal cutting and interruption temperature respectively, characterized in that such interruption and cutting temperatures are reduced according to the enthalpy of the estimated loaded food and Increase progressively in nominal values to provide an efficient energy temperature decrease.