JP2009074779A - Cooling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling apparatus capable of accurately controlling an internal temperature to a target temperature more quickly. <P>SOLUTION: The cooling apparatus R is provided with a controller C bringing the present temperature closer to the target temperature by carrying out PID control of a rotational frequency of a compressor motor 26M of a compressor 26 composing a refrigerating cycle, on the basis of a deviation e between the target temperature and the present temperature. The controller C changes a PID coefficient, for example, a proportional coefficient Kp, an integral coefficient Ki, a differential coefficient Kd, and a fixed value Df for carrying out the PID control in response to the deviation e. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cooling device installed in a low-temperature showcase, a low-temperature storage, an air conditioner, and the like, and more particularly to a cooling device that performs PID control of the rotation speed of a compressor motor based on a deviation e between a target temperature and a current temperature. is there.

Conventionally, for example, a cooling device employed in a low temperature showcase has a predetermined refrigerant circuit formed by connecting a compressor, a condenser, a pressure reducing device, an evaporator, and the like sequentially in a ring shape by piping, and the refrigerant circuit Is filled with a predetermined amount of refrigerant. When the compressor is operated, the refrigerant is compressed into a high-temperature and high-pressure gas state and flows into the condenser. In the condenser, the refrigerant dissipates heat and is condensed and liquefied, and then decompressed by a decompression device and supplied to the evaporator. In the evaporator, the liquid refrigerant after being depressurized evaporates, and at that time, it absorbs heat from the surroundings and exhibits a cooling action (for example, see Patent Document 1).
2004-232994

  Incidentally, the rotational speed of the compressor is normally controlled between the minimum rotational speed and the maximum rotational speed by the control device. That is, when the temperature in the cabinet, which is the space to be cooled in the showcase, reaches the upper limit temperature, the control device starts the compressor. And a control device controls the rotation speed of a compressor within the range of the minimum rotation speed and the maximum rotation speed which were preset based on the output of the various sensors etc. for detecting the temperature of a refrigerant | coolant, and internal temperature. Then, the compressor is stopped when the inside temperature of the showcase is lowered to the lower limit temperature. Thereby, the inside of the showcase was maintained at a predetermined cooling temperature.

  Here, the maximum number of revolutions and the minimum number of revolutions of the compressor are set in advance as described above, and the maximum number of revolutions is high in order to obtain a necessary cooling capacity at the time of pull-down when the power is turned on or after the defrosting operation is completed. As a result, the cooling efficiency during pull-down was improved.

  However, during normal operation other than pull-down, the compressor is frequently turned on and off due to the maximum rotational speed set high, increasing power consumption and maintaining the internal temperature at the target temperature with high accuracy. There was a problem that made it difficult to do.

Therefore, the compressor motor is controlled by the inverter device so that the operating frequency is PID-controlled and the internal temperature is more smoothly brought close to the target temperature with high accuracy. The PID control is executed by a PID arithmetic processing unit provided inside the control device. Specifically, the proportional (P), integral (I), and differential (D) calculations are executed from the deviation e between the target temperature and the actual internal temperature, and are reduced in proportion to the deviation e. Proportional operation for calculating the control amount in the direction, integration operation for calculating the control amount in the direction to reduce the integral value of the deviation e (the value obtained by integrating the deviation e with the target temperature in the time axis direction), and the change in the deviation e A differential operation for calculating a control amount in the direction of decreasing the inclination (differential value) is performed, and the operating frequency of the compressor motor is determined from the control amount obtained by adding these control amounts. An arithmetic expression is shown below.
Arithmetic operation amount = proportional amount + integral amount + derivative amount + fixed amount proportional amount = (current temperature-target temperature) x Kp
Integral amount = ((previous temperature−target temperature) + (current temperature−target temperature)) × Ki
Differential amount = (current temperature−previous temperature) × Kd
Fixed amount = Df
Conventionally, as described above, the proportional coefficient Kp used for calculating the proportional quantity, the integral coefficient Ki used for calculating the integral quantity, the differential coefficient Kd used for calculating the differential quantity, and the fixed quantity Df are mounted with the cooling device. It was determined for each model such as showcase, and it was possible to change the setting. However, once set, PID control is performed using the same PID coefficient at the time of pull-down such as when the power is turned on or after the completion of the defrosting operation or during normal operation.

  Therefore, when controlled with a PID coefficient suitable for normal operation (small PID coefficient), a comparatively gentle temperature is obtained even during pull-down that requires a large cooling capacity as shown by the one-dot chain line in FIG. There is a problem that the time required to approach the target temperature is increased due to a change (decrease), and it takes time to perform cooling at an appropriate temperature. On the other hand, when the control is performed with a PID coefficient suitable for the initial stage of pull-down (a large PID coefficient), as shown by the broken line in FIG. 6, the gradient of the temperature drop becomes large and is lower than the target temperature. There is a problem that a shoot occurs.

  Therefore, the present invention has been made to solve the conventional technical problem, and provides a cooling device that can accurately control the internal temperature to the target temperature at an earlier stage.

  The cooling device of the present invention includes a control device that brings the current temperature closer to the target temperature by PID-controlling the rotational speed of the compressor constituting the refrigeration cycle based on the deviation e between the target temperature and the current temperature. The control device is characterized by changing a coefficient for performing PID control in accordance with the deviation e.

  The cooling device according to a second aspect of the present invention is characterized in that, in the above invention, the control device increases the coefficient as the deviation e increases, and decreases the coefficient as the deviation e decreases.

  According to a third aspect of the present invention, there is provided the cooling device according to any one of the above-mentioned inventions, wherein the control device has a plurality of threshold values for changing the coefficient with respect to the target temperature.

  According to the present invention, in the cooling device including the control device that brings the current temperature closer to the target temperature by PID-controlling the rotational speed of the compressor constituting the refrigeration cycle based on the deviation e between the target temperature and the current temperature. The control device changes the coefficient for performing the PID control in accordance with the deviation e. For example, as the deviation e is larger, the coefficient is increased, and the coefficient is decreased as the deviation e is smaller. By doing so, it becomes possible to PID-control the rotation speed of the compressor using an appropriate coefficient according to the deviation e between the target temperature and the current temperature.

  Therefore, at the time of pull-down such as when the power supply is large or the defrosting operation is finished with a large deviation e between the target temperature and the current temperature, the amount of change in the compressor frequency is increased by performing PID control using a large coefficient, It becomes possible to cool the inside of the cabinet. On the other hand, during normal cooling operation where the deviation e between the target temperature and the current temperature is small, PID control is performed using a small coefficient to reduce the amount of change in the compressor frequency, thereby suppressing undershoot and the target temperature. It is possible to perform control close to

  As a result, it is possible to control the internal temperature to the target temperature with low power consumption and high accuracy in a short time.

  According to the invention of claim 3, in each of the above-mentioned inventions, the control device has a plurality of threshold values for changing the coefficient with respect to the target temperature, so that it can withstand a pull-down or a sudden internal temperature change. Thus, it is possible to appropriately PID-control the rotation speed of the compressor by the coefficient corresponding to each threshold value.

  Therefore, it is possible to bring the internal temperature close to the target temperature at an early stage while effectively suppressing undershoot, and reduction of power consumption can be realized.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a low-temperature showcase 1 according to an embodiment having a cooling device R of the present invention, and FIG. 2 is a vertical side view of the low-temperature showcase 1 of FIG. The low temperature showcase 1 of an Example is an open showcase which has an opening in the front surface installed in stores, such as a convenience store and a supermarket.

  The main body 2 is constituted by a heat insulating wall 3 having a substantially U-shaped cross section that opens to the front surface of the showcase 1 and side plates 4 and 4 attached to both sides thereof. A back panel 6 and a top panel 7 are disposed on the back and top surfaces of the inside of the heat insulating wall 3 with a space therebetween, and the back panel 6 and the top panel 7 and the heat insulating wall 3 are spaced from the back. A rear duct 9 extending upward is formed.

  In addition, a deck pan 10 extending forward is provided at the lower end of the back panel 6, and a display chamber 11 is formed inside the back panel 6, the top panel 7, and the deck pan 10. A plurality of shelves 12 are installed in the display chamber 11, and in this embodiment, four shelves are installed vertically. A lower duct 14 communicating with the rear duct 9 and constituting a part thereof is formed below the deck pan 10.

  The upper end of the rear duct 9 communicates with the cool air discharge port 16 located at the upper edge of the front opening of the display chamber 11, and the front end of the lower duct 14 is located at the lower edge of the front opening of the display chamber 11 and is made of a plurality of slits. It communicates with the suction port 17. Further, a cool air circulation blower 19 is disposed in the lower duct 14 below the deck pan 10, and an evaporation constituting a refrigeration cycle together with a compressor 26 and a condenser 27 described later in the rear duct 9 behind the display chamber 11. A container 15 is provided vertically.

  On the other hand, a machine room 25 is formed below the heat insulating wall 3, and a compressor 26, a condenser 27, a condenser blower 28, and the like are installed in the machine room 25, as well as a power source and a control. An electrical box (not shown) that houses the substrate is also provided.

  Here, the refrigerant circuit 40 which comprises the cooling device R in a present Example is demonstrated with reference to the refrigerant circuit figure of FIG. A condenser 27 is connected to the piping 42 on the discharge side of the compressor 26. An expansion valve 44 as a pressure reducing device is connected to the outlet side of the condenser 27 via a pipe 43. The expansion valve 44 is connected to the evaporator 15, and the outlet side of the evaporator 15 is connected to the compressor 26 to constitute an annular refrigeration cycle.

  A back plate 29 made of a steel plate is attached to the back of the heat insulating wall 3 with a predetermined distance from the back surface of the heat insulating wall 3, and an exhaust duct is provided between the back plate 29 and the heat insulating wall 3. 30 is configured. The lower end of the exhaust duct 30 opens and communicates with the rear portion of the machine room 25, and the upper end is open above the showcase 1. Therefore, when the condenser blower 28 is operated, the outside air sucked into the machine room 25 passes through the condenser 27 and exchanges heat, and is then blown to the compressor 26 to cool the compressor 26 by air. Then, it is discharged to the outside through the exhaust duct 30.

  A panel 31 closes the front surface of the machine room 25 so that it can be opened and closed. Reference numeral 32 denotes an evaporating dish provided in the lower part of the machine room 25, and drain water (dewed water, defrosted water, etc.) from the evaporator 15 flows in through a drain hose (not shown) and is stored.

  Next, the control device C in the present embodiment will be described with reference to FIG. The control device C is composed of a general-purpose microcomputer and controls the cooling device R, and includes a timer 50, a PID arithmetic processing unit 56, and a storage unit 57 as time limit means. Further, a control panel 47 having various setting switches and a display unit is connected. The various setting switches also include an LCD panel (setting means) 8 that can arbitrarily set the set temperature in the display chamber 11 as will be described in detail later. Further, on the input side of the control device C, an internal temperature sensor 48 for detecting the internal temperature, a refrigerant inlet side temperature sensor 54 for detecting the refrigerant temperature on the refrigerant inlet side of the evaporator 15, and the evaporator 15. A refrigerant outlet side temperature sensor 55 and the like for detecting the refrigerant temperature on the refrigerant outlet side are connected. Here, the in-compartment temperature sensor 48 is provided, for example, on the ceiling in the display room 11 of the showcase 1 and detects the in-compartment temperature that is the temperature in the display room 11.

  On the other hand, on the output side of the control device C, a compressor motor (DC motor) 26M that drives the compressor 26, a blower motor 19M that drives the blower 19 for circulating cold air, a blower motor 28M that drives the blower 28 for condenser, An expansion valve 44 and the like are connected. Here, the compressor motor 26M is connected via the inverter device 41, and thereby the frequency of the power source is changed, and the rotational speed of the compressor motor 26M is changed to thereby compress the refrigerant in the compressor 26. Can be changed. The blower motors 19M and 28M are connected via drive circuits 52 and 53 such as a chopper circuit, respectively, so that the rotational speed can be arbitrarily changed. And based on each output mentioned above, the control apparatus C controls the opening degree of the expansion valve 44, and controls the rotation speed of each motor 26M, 19M, and 28M.

Here, the control device C in the present embodiment performs PID control on the operation frequency of the compressor motor 26M. This PID control is executed by a PID calculation processing unit 56 provided inside the control device C. The PID calculation processing unit 56 is a temperature detected by the internal temperature sensor 48 (a space to be cooled). From the deviation e between the temperature in the display chamber 11 (hereinafter referred to as the current temperature) and the cooling target temperature set by the LCD panel 8 of the control panel 47, the proportional (P), integral (I), and differential (D) The operation is executed. Specifically, the PID arithmetic processing unit 56 calculates the control amount in a direction to decrease the current e and the target temperature in proportion to the deviation e, and the integral value of the deviation e (deviation e from the cooling target temperature e (The value obtained by integrating in the time axis direction) an integral operation for calculating a control amount in a direction to reduce, and a differential operation for calculating a control amount in a direction to reduce the slope (differential amount) of change in deviation e. The operating frequency of the motor 26M of the compressor 26 is determined from the control amount obtained by adding. An arithmetic expression is shown below.
Calculation formula Control amount = Proportional amount + Integral amount + Derivative amount + Fixed amount Proportional amount = (Current temperature-Target temperature) x Kp
Integral amount = ((previous temperature−target temperature) + (current temperature−target temperature)) × Ki
Differential amount = (current temperature−previous temperature) × Kd
Fixed amount = Df
Based on the calculated control amount, the inverter device 41 controls the operating frequency of the compressor motor 26M. Here, Kp in the above equation is a proportional coefficient used for calculating the proportional quantity, Ki is an integral coefficient used for calculating the integral quantity, Kd is a differential coefficient used for calculating the differential quantity, and Df is It is a fixed amount.

  Here, the storage unit 57 of the control device C stores a plurality of current temperature threshold values for each target temperature, in the present embodiment, a first threshold value, a second threshold value, and a third threshold value. Here, the difference between the first threshold value and the target temperature is smaller than the difference between the second threshold value and the target temperature, and the difference between the second threshold value and the target temperature is the difference between the third threshold value and the target temperature. The difference is smaller than the difference (third threshold> second threshold> first threshold). The storage unit 57 stores a PID coefficient corresponding to each threshold, specifically, the proportional coefficient Kp, the integral coefficient Ki, the differential coefficient Kd, and the fixed amount Df.

  For example, the PID coefficient 3 for the third threshold is a proportional coefficient Kp3, an integral coefficient Ki3, a differential coefficient Kd3, and a fixed amount Df3, and the PID coefficient 2 for the second threshold is a proportional coefficient Kp2, an integral coefficient Ki2, a differential coefficient Kd2, fixed amount Df2, and PID coefficient 1 for the first threshold value is proportional coefficient Kp1, integral coefficient Ki1, differential coefficient Kd1, and fixed amount Df1. Here, each proportional coefficient is set to a large coefficient in the order of Kp3, Kp2, and Kp1 (Kp3> Kp2> Kp1), and each integral coefficient is set to a large coefficient in the order of Ki3, Ki2, and Ki1 (Ki3> Ki2> Ki1). Each differential coefficient is a large coefficient in the order of Kd3, Kd2, and Kd1 (Kd3> Kd2> Kd1), and each fixed amount is a large coefficient in the order of Df3, Df2, and Df1 (Df3> Df2> Df1). .

  The cooling control of the showcase 1 with the above configuration will be described. The control device C detects the temperature in the display room (cooled space) 11, that is, the current temperature by the internal temperature sensor 48, and executes the cooling operation based on the current temperature and a preset target temperature. That is, when the operation of the compressor 26 is started, the high-temperature and high-pressure gas refrigerant discharged from the piping 42 on the discharge side of the compressor 26 flows out to the condenser 27. Here, since the expansion valve 44 is controlled to be opened and closed by the control device C, the sufficiently condensed and liquefied refrigerant is decompressed by the expansion valve 44 and then flows into the evaporator 15. Then, the refrigerant flowing into the evaporator 15 disposed in the back duct 9 evaporates, takes heat from the surroundings and exhibits a cooling action, and then returns to the compressor 26.

  The cool air exchanged with the evaporator 15 is discharged from the cool air discharge port 16 by a cool air circulation blower 19 disposed in the lower duct 14 communicating with the rear duct 9, and the cool air circulates in the display chamber 11. After cooling to a predetermined cooling temperature, it returns to the lower duct 14 via the cold air inlet 17 located at the lower edge of the front opening of the display chamber 11. Thereby, an air curtain by cold air is formed in the front opening of the display chamber 11, and cold air leakage and outside air intrusion in the display chamber 11 are suppressed.

  Here, specific frequency control of the compressor motor 26M will be described in detail. First, a PID coefficient used when performing PID control on the frequency of the compressor motor 26M is determined. Specifically, as shown in the flowchart of FIG. 5, the control device C has the current internal temperature, that is, the current temperature larger than the third threshold value stored in the storage unit 57 of the control device C in step S <b> 1. Determine whether or not. Usually, at the start of pull-down such as when the power is turned on in the cooling operation or after the defrosting operation is completed, the difference (deviation e) between the target temperature and the current temperature is the largest, and the current temperature is stored in the storage unit 57. It is higher (larger) than the third threshold.

  Thus, when the current temperature is higher than the third threshold value, the process proceeds to step S2, and the PID coefficient used for the PID control is set to the PID coefficient 3, specifically, the proportional coefficient Kp3, the integral coefficient Ki3, the differential coefficient Kd3, The fixed amount Df3 is set, and the process proceeds to S3, and the compressor motor 26M performs PID control of the power supply frequency using the PID coefficient 3.

  In this case, by performing PID control of the frequency of the compressor motor 26M using the largest PID coefficient 3 stored in the storage unit 57 of the control device C, PID control is performed such that the amount of change is increased by the large coefficient. As shown in the graph showing the change in temperature and the change in the rotational speed of the compressor in FIG. 6, the internal temperature can be drastically lowered.

  Thereafter, the control device C detects the current temperature by the internal temperature sensor 48 every predetermined time, and determines whether or not the current temperature is higher than the third threshold value in step S1. When it is determined that the current temperature is gradually decreased and is equal to or lower than the third threshold value due to the cooling operation, the control device C proceeds to step S4 and determines whether the current temperature is higher than the second threshold value. Judge whether or not.

  Here, when the current temperature is equal to or lower than the third threshold value and higher than the second threshold value, the control device C proceeds to step S5, and changes the PID coefficient used for PID control from the previous PID coefficient 3. Specifically, the proportional coefficient Kp2, the integral coefficient Ki2, the differential coefficient Kd2, and the fixed amount Df2 are set, and the process proceeds to S3, and the compressor motor 26M is set to the power frequency using the PID coefficient 2. PID control.

  With this cooling operation, the current temperature further decreases, and when the control device C determines that the current temperature is equal to or lower than the second threshold value, the process proceeds to step S6, where the current temperature is lower than the first threshold value. Judge whether it is large or not.

  Here, when the current temperature is equal to or lower than the second threshold value and higher than the first threshold value, the control device C proceeds to step S7, and changes the PID coefficient used for PID control from the previous PID coefficient 2. The PID coefficient is changed to 1. Specifically, the proportional coefficient Kp1, the integral coefficient Ki1, the differential coefficient Kd1, and the fixed amount Df1 are set, the process proceeds to S3, and the compressor motor 26M is set to the power frequency using the PID coefficient 1. PID control.

  When the current temperature is equal to or lower than the first threshold value, the control device C proceeds to step S8, changes the PID coefficient used for PID control to PID coefficient 0, specifically, from the proportional coefficient Kp1. The compressor motor 26M is PID controlled with Kp0 being smaller, Ki0 being smaller than the integral coefficient Ki1, Kd0 being smaller than the differential coefficient Kd1, and Df0 being smaller than the fixed amount Df1.

  In this way, a plurality of threshold values are set for the target temperature, and the rotational speed of the compressor motor 26M is set to PID using the PID coefficient set corresponding to the threshold value until the current temperature reaches any threshold value. By controlling, until the current temperature reaches the third threshold value where the deviation e between the target temperature and the current temperature is the largest, the largest PID coefficient 3 (Kp3, Ki3, Kd3, Df3) makes it possible to increase and control the amount of change in the rotational speed of the compressor motor 26M, and to cool the interior rapidly.

  On the other hand, at the time of pull-down, the interior is gradually cooled, and after the current temperature reaches the second threshold value that is the second largest next to the third threshold value where the deviation e between the target temperature and the current temperature is the largest, Is controlled by the PID coefficient 2 (corresponding to the PID coefficient 3 which is the second largest coefficient, Kp2, Ki2, Kd2, Df2) set to correspond to the threshold value of the compressor motor 26M. It becomes possible to do. Thereby, when the deviation e is smaller than the difference between the third threshold value and the target temperature, the compressor motor 26M is used by using a smaller PID coefficient (specifically, a PID coefficient 2 smaller than the PID coefficient 3). Since PID control can be performed, it is possible to perform control that suppresses undershoot and approaches the target temperature in a shorter time.

  After the interior is further cooled and the current temperature reaches the first threshold value where the deviation e between the target temperature and the current temperature is the smallest, the PID coefficient set corresponding to the first threshold value 1 (coefficient smaller than the PID coefficient 2; Kp1, Ki1, Kd1, Df1) makes it possible to control the amount of change in the rotational speed of the compressor motor 26M to be smaller. Thereby, when the deviation e is smaller than the difference between the second threshold value and the target temperature, the compressor motor 26M is used by using a smaller PID coefficient (specifically, a PID coefficient 1 smaller than the PID coefficient 2). Since it is possible to perform PID control, it is possible to perform control that further suppresses undershoot and approaches the target temperature in a shorter time.

  After the internal temperature (current temperature) reaches the target temperature by the cooling control, normal cooling control, specifically, the smallest threshold value corresponding to the target temperature is set as in the above. If it is lower, the PID coefficient 0 (Kp0, Ki0, Kd0, Df0) smaller than the PID coefficient is used for PID control of the rotational speed of the compressor motor 26M with a small change amount.

  Therefore, the control device C uses a larger PID coefficient 3 as the deviation e is larger as a coefficient (PID coefficient) for performing PID control in accordance with the deviation e. PID-controls the rotational speed of the compressor motor 26M using the PID coefficient 1). As a result, at the time of pull-down such as when the power supply is large or the defrosting operation is finished with a large deviation e between the target temperature and the current temperature, the amount of change in the compressor frequency is increased by PID control using a large coefficient, It becomes possible to cool the inside of the cabinet rapidly. On the other hand, during normal cooling operation where the deviation e between the target temperature and the current temperature is small, PID control is performed using a small coefficient to reduce the amount of change in the compressor frequency, thereby suppressing undershoot and the target temperature. It is possible to perform control close to

  As a result, it is possible to control the internal temperature to the target temperature with low power consumption and high accuracy in a short time.

  Further, in the present embodiment, as described above, the control device C has a plurality of threshold values for changing the PID coefficient with respect to the target temperature, in this case, three, so that the temperature change at the time of pulling down or abrupt On the other hand, the rotational speed of the compressor motor 26M can be appropriately PID controlled by the PID coefficient corresponding to each threshold value.

  Therefore, it is possible to bring the internal temperature (current temperature) closer to the target temperature at an early stage while suppressing undershoot more effectively, and reduction in power consumption can be realized.

  In the above description, the example in which three threshold values are set is described. However, the threshold value may be one, two, or four or more. However, more precise temperature control can be realized by finely setting the threshold value.

  In addition, the above threshold values may be the same regardless of the target temperature to be set. In addition to this, a ratio change according to the target temperature to which the difference between the threshold values is set can be used. It may be arbitrarily changeable.

  Furthermore, in this embodiment, the PID coefficient used for the PID control is changed depending on whether the actual current temperature has changed to a predetermined threshold value. However, the present invention is not limited to this. Even if the deviation e is calculated and the PID coefficient used for PID control is changed depending on whether the deviation e has changed to a predetermined threshold value, the same effect can be obtained. In this case, when the deviation e is larger than the largest threshold value, the rotational speed of the compressor motor 26M is PID controlled using the largest PID coefficient set corresponding to the threshold value, and the deviation e is equal to or less than the threshold value. If the value is larger than the next largest threshold value, the rotational speed of the compressor motor 26M is PID controlled using the next largest PID coefficient set corresponding to the threshold value. Similarly, the PID coefficient is changed according to the threshold value set as the deviation e, and the rotational speed of the compressor motor 26M is PID-controlled.

  As a result, when the current temperature is far from the target temperature, PID control with a large amount of change can be performed using a large PID coefficient, and when the current temperature approaches the target temperature, a small PID can be performed. PID control with a small amount of change can be performed using the coefficient.

  Therefore, it is possible to bring the internal temperature (current temperature) closer to the target temperature at an early stage while suppressing undershoot more effectively, and reduction in power consumption can be realized.

  In addition, although the present Example demonstrates the case where the said cooling device R is applied to the low temperature showcase 1, it is not limited to this, Cooling provided with compressors, such as a cooling storage and an air conditioner. It may have a device.

It is a perspective view of the low-temperature showcase of the Example provided with the cooling device of this invention. It is a vertical side surface of the low-temperature showcase of FIG. It is a refrigerant circuit diagram. It is an electrical block diagram of a control apparatus. It is a flowchart of the determination of a PID coefficient. It is a figure which shows the change of internal temperature and compressor rotation speed.

Explanation of symbols

R Cooling device C Control device 1 Low temperature showcase 8 LCD panel (setting means)
DESCRIPTION OF SYMBOLS 11 Display chamber 15 Evaporator 16 Cold air discharge port 17 Cold air suction port 19 Air blower for cold air 19M Blower motor 25 Machine room 26 Compressor 26M Compressor motor 27 Condenser 28 Condenser blower 28M Blower motor 41 Inverter device 44 Expansion valve 47 Control Panel 48 Internal temperature sensor 56 PID calculation processing unit 57 Storage unit

Claims (3)

In a cooling device including a control device that brings the current temperature closer to the set temperature by PID-controlling the rotational speed of the compressor that constitutes the refrigeration cycle based on the deviation e between the set temperature and the current temperature.
The said control apparatus changes the coefficient for performing the said PID control according to the said deviation e, The cooling device characterized by the above-mentioned.   The cooling device according to claim 1, wherein the controller increases the coefficient as the deviation e increases, and decreases the coefficient as the deviation e decreases.   The cooling device according to claim 1, wherein the control device has a plurality of threshold values for changing the coefficient with respect to the set temperature.

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