Abstract:
A refrigerator and a safety control method thereof, which is capable of ensuring protection from a high voltage applied to a shelf on which food is placed in order to improve food preservation. The safety control method of a refrigerator having a storage chamber which stores food, the method includes sensing a chamber temperature of the storage chamber, comparing the sensed chamber temperature with a predetermined setting temperature and generating a high voltage when the chamber temperature is less than the predetermined setting temperature, supplying the generated high voltage to the inside of the storage chamber to preserve the food, determining whether a high voltage cutoff condition occurs while the high voltage is supplied to the inside of the storage chamber, and cutting off the high voltage supplied to the inside of the storage chamber when the high voltage cutoff condition occurs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0090298, filed on Sep. 18, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a refrigerator which is capable of improving food preservation by applying a high voltage to a shelf on which food is placed. More particularly, to a refrigerator which can ensure protection from a high voltage applied to a shelf and a safety control method thereof. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a conventional refrigerator employs a general cooling system, which enables refrigerant to circulate in the refrigerator so as to provide a food storage chamber with cooling air generated by absorbing surrounding heat when the liquid refrigerant evaporates, thereby freshly storing food for a long time. Recently, in accordance with various lifestyles of a user or variation of favorite food, a function for storing meat, fish, vegetables or kimchi is differentiated from the existing freezing and cooling functions. In addition, the food is desired to be stored in an original form. 
         [0006]    As a refrigerator for storing food (for example, fresh meat or fish and shellfish) in an original form, there is provided a refrigerator having a high voltage processing function disclosed in Japanese Patent Application No. 06-323721. 
         [0007]    In the refrigerator disclosed in the above publication, an electric field processing chamber is formed in a part or all of a freezing chamber and a high voltage is applied to a shelf on which food is placed, such that the food stored in the electric field processing chamber is prevented from rotting to improve storage quality and thawing quality of meat or fish and shellfish. 
         [0008]    At this time, since the high voltage is applied to the shelf on which the food is placed, an electric shock may occur when a person contacts the shelf applied with the high voltage. Accordingly, in a conventional refrigerator, as a safety device for preventing the electric shock, a door switch is provided, which senses the opening and closing state of a door of the electric field processing chamber such that the high voltage is cut off when the door is opened and the high voltage is applied when the door is closed. 
         [0009]    However, in the conventional safety device of the refrigerator, when a person voluntarily operates the door switch in a state where the door is opened, the person may be exposed to the high voltage. Furthermore, when the door switch fails, the person may be exposed to the high voltage. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, it is an aspect of the present invention to provide a refrigerator and a safety control method thereof, which is capable of ensuring safety by cutting off a high voltage when a door switch fails or a person contacts with a shelf of the refrigerator. 
         [0011]    It is another aspect of the present invention to provide a refrigerator and a safety control method thereof, which is capable of ensuring safety by sensing an actual chamber temperature as well as an opening and closing state of a door, and applying a high voltage only when the chamber temperature falls to less than or equal to a predetermined temperature. 
         [0012]    It is yet another aspect of the present invention to provide a refrigerator and a safety control method thereof, which is capable of ensuring safety by cutting off a high voltage when insulation between food which is placed on a shelf applied with the high voltage and an inner wall of a storage chamber is broken down, and thus, current having at least a setting value is detected. 
         [0013]    It is yet another aspect of the invention to provide a refrigerator and a safety control method thereof, which is capable of displaying an operation state of the refrigerator due to cutoff of a high voltage. 
         [0014]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
         [0015]    These and/or other aspects of the present invention are achieved by providing a safety control method of a refrigerator which preserves food by supplying a high voltage to an inside of a storage chamber storing the food, the method including detecting a value of current supplied to the inside of the storage chamber, and comparing the detected current value with a predetermined setting value and cutting off the high voltage supplied to the inside of the storage chamber when the current value is greater than or equal to the setting value. 
         [0016]    It is another aspect of the present invention to provide a safety control method of a refrigerator which preserves food by supplying a high voltage to an inside of a storage chamber storing the food, the method including detecting whether a door of the storage chamber is opened; and cutting off the high voltage supplied to the inside of the storage chamber when the door of the storage chamber is opened. 
         [0017]    It is another aspect of the present invention to provide a safety control method of a refrigerator which preserves food by supplying a high voltage to an inside of a storage chamber storing the food, the method including sensing a chamber temperature of the storage chamber, and comparing the sensed chamber temperature with a predetermined setting temperature and cutting off the high voltage supplied to the inside of the storage chamber when the chamber temperature is greater than or equal to a total sum of the predetermined setting temperature and a predetermined temperature. 
         [0018]    It is another aspect of the present invention to provide a safety control method of a refrigerator which preserves food by supplying a high voltage to an inside of a storage chamber storing the food, the method including determining whether a person approaches the inside of the storage chamber, and cutting off the high voltage supplied to the inside of the storage chamber when the person approaches the inside of the storage chamber. 
         [0019]    The method further includes displaying an operation state of the refrigerator due to the cutoff of the high voltage supplied to the inside of the storage chamber. 
         [0020]    According to an aspect of the present invention, the inside of the storage chamber is a shelf on which the food is placed. 
         [0021]    It is another aspect of the present invention to provide a safety control method of a refrigerator having a storage chamber which stores food, the method including sensing a chamber temperature of the storage chamber, comparing the sensed chamber temperature with a predetermined setting temperature and generating a high voltage when the chamber temperature is less than the predetermined setting temperature, supplying the generated high voltage to an inside of the storage chamber to preserve the food, determining whether a high voltage cutoff condition occurs while the high voltage is supplied to the inside of the storage chamber, and cutting off the high voltage supplied to the inside of the storage chamber when the high voltage cutoff condition occurs. 
         [0022]    The high voltage cutoff condition includes at least one of a condition that a value of current supplied to the inside of the storage chamber is greater than or equal to a predetermined setting value, a condition that a door of the storage chamber is opened, a condition that a chamber temperature is greater than or equal to a total sum of the predetermined setting temperature and a predetermined temperature, and a condition that a person approaches the inside of the storage chamber. 
         [0023]    It is another aspect of the present invention to provide a refrigerator including a storage which stores food, a high voltage generator generating a high voltage supplied to an inside of the storage chamber, a power supply switch switching a power supply to drive the high voltage generator, a temperature sensor sensing a chamber temperature of the storage chamber, and a control unit comparing the sensed chamber temperature with a predetermined setting temperature, controlling the power supply switch to supply the high voltage generated at the high voltage generator to the inside of the storage chamber when the chamber temperature is less than the predetermined setting temperature. 
         [0024]    The control unit controls the power supply switch to turn off the power supply to drive the high voltage generator, when the chamber temperature rises to greater than or equal to a total sum of the predetermined setting temperature and a predetermined temperature while the high voltage is supplied to the inside of the storage chamber. 
         [0025]    The refrigerator further includes a current detecting unit detecting a value of current supplied to the inside of the storage chamber, wherein the control unit compares the detected current value with a predetermined setting value and controls the power supply switch to turn off the power supply to drive the high voltage generator, when the detected current value is greater than or equal to the predetermined setting value. 
         [0026]    The refrigerator further includes a door switch detecting whether a door of the storage chamber is opened or closed, and the control unit controls the power supply switch to turn off the power supply to drive the high voltage generator when the door switch detects that the door is opened. 
         [0027]    The refrigerator further includes a sensor sensing whether a person approaches the inside of the storage chamber, and the control unit controls the power supply switch to turn off the power supply to drive the high voltage generator when the sensor senses that the person approaches the inside of the storage chamber. 
         [0028]    According to an aspect of the present invention, the sensor includes at least one of a contact sensor, a proximity sensor, an infrared ray sensor and a touch sensor. 
         [0029]    The refrigerator further includes a display unit displaying an operation state of the refrigerator due to the turn-off of the power supply for driving the high voltage generator. 
         [0030]    The control unit determines whether a high voltage cutoff condition occurs while the high voltage is supplied to the inside of the storage chamber and cut off the high voltage supplied to the inside of the storage chamber when the high voltage cutoff condition occurs. 
         [0031]    The high voltage cutoff condition includes at least one of a condition that a value of current supplied to the inside of the storage chamber is greater than or equal to a predetermined setting value, a condition that a door of the storage chamber is opened, a condition that a chamber temperature is greater than or equal to a total sum of the predetermined setting temperature and a predetermined temperature, and a condition that a person approaches the inside of the storage chamber. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0033]      FIG. 1  is a front view of a refrigerator according to an embodiment of the present invention; 
           [0034]      FIG. 2  is a partial perspective view of  FIG. 1 ; 
           [0035]      FIG. 3  is a block diagram illustrating a safety control device of the refrigerator according to a first embodiment of the present invention; 
           [0036]      FIG. 4  is a block diagram illustrating a safety control device of the refrigerator according to a second embodiment of the present invention; and 
           [0037]      FIGS. 5A and 5B  are flowcharts illustrating a safety control method of a refrigerator according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0039]      FIG. 1  is a front view illustrating a refrigerator according to an embodiment of the present invention and  FIG. 2  is a partial perspective view of  FIG. 1 . 
         [0040]    In  FIG. 1 , the refrigerator according to this embodiment of the present invention comprises a main body  10  having a storage chamber  12  capable of improving food preservation using a high voltage and a door  14  which opens and closes a front surface of the storage chamber  12 . A door switch  16 , which detects the opening and closing state of the door, is provided at an inside of the storage chamber  12  which is in contact with the door  14 . 
         [0041]    A mechanical chamber  18 , which forms a separate space, is provided above the main body  10 , and a high voltage generator  20 , which generates a high voltage, is provided in the mechanical chamber  18 . 
         [0042]    The storage chamber  12  is divided by a plurality of shelves  22  such that food is placed on each shelf  22 , and a temperature sensor  24  to sense a chamber temperature is provided on a wall surface of the storage chamber  12 . 
         [0043]    The shelf  22  is in contact with a power supply line  26  provided on the rear side of the storage chamber  12  and connected to the high voltage generator  20 . The high voltage generated at the high voltage generator  20  is applied to the shelf  22 . The shelf  22  is made of a conductive material to which the high voltage is easily applied. A cover made of an insulating material is provided on an outer surface of the power supply line  26 , to prevent the power supply line  26  from directly contacting the main body  10 . 
         [0044]    Since the high voltage is applied to the shelf  22 , a contact sensor  28  is provided so as to prevent an accident from occurring due to the contact of a person. Accordingly, even when the door switch  16  fails or a person voluntarily operates the door switch  16 , that is, the person contacts the shelf  22 , it is possible to ensure the safety of the person from the high voltage applied to the shelf  22 . 
         [0045]    Although the contact sensor  28 , which senses whether a person contacts the shelf  22 , is provided according to an embodiment of the present invention, the present invention is not limited thereto. That is, it may be sensed whether the person contacts or approaches the shelf  22  using a proximity sensor, an infrared ray sensor or a touch sensor, for example. According to an embodiment of the present invention, the contact sensor  28  is integrally combined with the shelf  22 , as shown in  FIG. 2 , however, the contact sensor  28  is not limited thereto, the position thereof may vary, as necessary. 
         [0046]    In addition, as shown in  FIG. 2 , the shelf  22  is received in the storage chamber  12  to be spaced apart from the inner wall  12   a  of the storage chamber  12 . Supporting members  30 , which support four corners of the shelf  22 , are provided on the main body  10  at the inner wall  12   a  of the storage chamber  12 , and an insulating member  32  which prevents the high voltage generated at the high voltage generator  20  from being applied to the main body  10  through the supporting member  30 , is provided between the supporting member  30  and the shelf  22  supported by the supporting member  30 . 
         [0047]    Although not shown in figure, a compressor, a condenser, an expansion valve and an evaporator are provided in a general cooling system which enables refrigerant to circulate in the refrigerator so as to provide the storage chamber  12  with cooling air generated by absorbing surrounding heat when the liquid refrigerant evaporates, thereby freshly storing food for a long time. 
         [0048]      FIG. 3  is a block diagram illustrating a safety control device of the refrigerator according to a first embodiment of the present invention. The safety control device comprises a fuse  52  connected with a commercial power supply  50 , the high voltage generator  20 , a current detecting unit  56 , a signal converting unit  58 , a control unit  60 , a power supply driving unit  62 , a power supply switch  64 , a display unit  66 , and an input unit  68 , in addition to the components of  FIGS. 1 and 2 . 
         [0049]    The fuse  52  is an overload protection circuit which blows to prevent abnormal current from flowing in an electric circuit when current having at least a predetermined value flows in the power supply line through the commercial power supply  50 . 
         [0050]    The high voltage generator  20  is a high voltage transformer which boosts an alternating current voltage supplied through the commercial power supply  50  to generate the high voltage (approximately 1 to 10 kV). The generated high voltage is supplied to the shelf  22  in the storage chamber  12  through the power supply line  26 , and a resistor  54  is connected with a secondary side of the high voltage generator  20  to restrict a current component of the high voltage supplied to the shelf  22 . 
         [0051]    The current detecting unit  56  is a CT sensor, for example, which is connected with a secondary side of the high voltage generator  20  and detects the current inputted to the shelf  22 . When the value of the detected current is greater than or equal to the setting value due to insulation breakdown between the food put on the shelf  22  applied with the high voltage and the inner wall  12   a  of the storage chamber  12 , the high voltage generator  20  is prevented from generating the high voltage. 
         [0052]    The signal converting unit  58  is a circuit which converts an AC component of input current detected by the current detecting unit  56  into direct current (DC) and inputs the direct current to the control unit  60 . 
         [0053]    The control unit  60  is a microcomputer which controls an entire operation of the refrigerator, receives signals of the door switch  16 , the temperature sensor  24 , the contact sensor  34  and the current detecting unit  56 , and controls the power supplied to the high voltage generator  20 . 
         [0054]    More specifically, the control unit  60  controls the power supply connected with the high voltage generator  20  according to the opening-and-closing sensing signal of the door switch  16 , such that the high voltage is cut off when the door  14  is opened and the high voltage is applied to the shelf  22  when the door  14  is closed. 
         [0055]    The control unit  60  also enables the temperature sensor  23  to sense an actual chamber temperature, in addition to the sensing of the opening and closing state of the door  14 , and controls the power supply connected to the high voltage generator  20  such that the high voltage is applied only when the chamber temperature falls to less than or equal to a user setting temperature. 
         [0056]    The control unit  60  controls the power supply connected with the high voltage generator  20  such that the high voltage is cut off when the contact sensor  34  detects that a person contacts the shelf  22 , for example, when the door switch  16  fails or the person voluntarily operates the door switch  16 . 
         [0057]    The control unit  60  controls the power supply connected with the high voltage generator  20  such that the high voltage is cut off when the food, which is placed on the shelf  22  applied with the high voltage, is in contact with the inner wall  12   a  of the storage chamber  12  to break down insulation and the value of the current detected by the current detecting unit  56  is greater than or equal to the setting value. 
         [0058]    The power supply driving unit  62  is a driving circuit which applies the power to a primary side of the high voltage generator  20  according to a control signal of the control unit  60  and the power supply switch  64  turns on/off the commercial power source  50  connected with the high voltage generator  20  according to the drive of the power supply driving unit  62  and is formed of a semiconductor device i.e., a power relay or a TRIAC, for example. 
         [0059]    The display unit  66  displays an operation state of the high voltage generator  20  due to the voltage cutoff to a user, by the control signal of the control unit  60 . 
         [0060]    The input unit  69  inputs a user control instruction to the control unit  60  and comprises a start button which starts temperature control and preservation control after the food is placed on the storage chamber  12  and a plurality of buttons, for example, a temperature setting button to set the temperature of the food. 
         [0061]      FIG. 4  is a block diagram illustrating a safety control device of the refrigerator according to a second embodiment of the present invention. The safety control device shown in  FIG. 4  is similar to that shown in  FIG. 3 , except that a ground line connected with the secondary side of the high voltage generator  20  connected with the current detecting unit  56  is inserted into a module of the high voltage generator  20 , independent of a ground line of the storage chamber  12 . Even when the ground line connected with the secondary side of the high voltage generator  20  is inserted into the module, the same object and effect as those of  FIG. 3  can be accomplished. 
         [0062]    Hereinafter, the operation and the effect of the refrigerator and the safety control method thereof will be described. 
         [0063]      FIGS. 5A and 5B  are flowcharts of the safety control method of the refrigerator according to an embodiment of the present invention. 
         [0064]    First, in operation  100 , a user places food, which is desired to be stored, on the shelf  22  of the storage chamber  12 , and from operation  100 , the process moves to operation  102 , where the user operates the temperature setting button provided in the input unit  68  to input a setting temperature Ts of the food. 
         [0065]    When the setting temperature Ts is input in operation  102 , the process moves to operation  104 , where the control unit  60  determines whether a cooling start signal is input through a start button provided in the input unit  68 . When the start button is pressed in operation  104 , the process moves to operation  106  where the control unit  60  starts the temperature control which allows the food placed on the shelf  22 , to be stored at the setting temperature Ts by operating the cooling system which enables refrigerant to circulate in the refrigerator so as to provide the storage chamber  12  with cooling air. 
         [0066]    Next, under the control of the control unit  60 , in operation  108 , the temperature sensor  24  senses the chamber temperature Tc of the storage chamber  12  which varies depending on the drive of the cooling system and from operation  108 , the process moves to operation  110 , where the control unit  60  compares the sensed chamber temperature Tc with the setting temperature Ts. 
         [0067]    As the result of comparison, when the chamber temperature Tc is greater than the setting temperature Ts in operation  110 , the process returns to operation  106 , where the temperature control is continuously performed until the chamber temperature Tc falls to less than or equal to the setting temperature Ts and, when the chamber temperature Tc is less than or equal to the setting temperature Ts in operation  110 , high voltage control for storing the food for a long time (experimental result: about a month) in an original state starts in operation  112 . 
         [0068]    In operation  112 , under the control of the control unit  60 , the power supply switch  64  is turned on by the power supply driving unit  62 , and the commercial power supply  50  supplies the power to the primary side of the high voltage generator  20 . 
         [0069]    When the commercial power supply  50  supplies the power to the primary side of the high voltage generator  20 , the high voltage of approximately 1 to 10 kV is generated at the secondary side of the high voltage generator  20  and from operation  112 , the process moves to operation  114 , where the high voltage generated at the secondary side of the high voltage generator  20  is applied to the shelf  22  through the power supply line  26  provided on the rear side of the storage chamber  12  to perform the high voltage control of the food. 
         [0070]    The preservation of the food using the high voltage is described in a refrigerator having a high voltage processing function, which is disclosed in Japanese Patent Application Publication No. 06-323721, and thus their detailed description will be omitted. Hereinafter, the technical characteristics of the present invention which ensures protection from the high voltage applied to the shelf  22  will be described in detail. 
         [0071]    First, from operation  114 , the process moves to operation  116 , where when the high voltage is applied to the shelf  22 , the current Ic inputted to the shelf  22  is detected by the current detecting unit  56 . The AC component of the detected input current Ic is converted into the direct current (DC) by the signal converting unit  58  and inputted to the control unit  60 . 
         [0072]    Now, referring to  FIG. 5B , from operation  116 , the process moves to operation  118 , where the control unit  60  determines whether the value of the detected current Ic is greater than or equal to a setting value Is. When the value of the detected current Ic is less than the setting value Is in operation  118 , the process moves to operation  120  where the control unit  60  determines that the insulation between the shelf  22  applied with the high voltage and the inner wall  12   a  of the storage chamber  12  has not broken down. Accordingly, the high voltage is continuously generated. 
         [0073]    Meanwhile, when the value of the detected current Ic is greater than or equal to the setting value Is in operation  118 , the process moves to operation  126 , where the control unit  60  determines that the food placed on the shelf  22  applied with the high voltage, contacts the inner wall  12   a  of the storage chamber  12  to break down the insulation and controls the power supply driving unit  62  to turn off the power supply switch  64 , and accordingly the commercial power supply  50  does not supply the power to the high voltage generator  20  to prevent the high voltage from being generated. Therefore, when the insulation between the shelf  22  and the inner wall  12   a  of the storage chamber  12  has broken down and thus the value of the current Ic detected by the current detecting unit  56  is greater than or equal to the setting value Is, it is possible to ensure protection from the high voltage applied to the shelf  22 . 
         [0074]    In operation  120 , the control unit  60  determines whether the door  14  is opened, using the door switch  16 . When it is determined that the door  14  is not opened in operation  120 , the high voltage is continuously generated and, when it is determined that the door  14  is opened in operation  120 , the process moves to operation  126 , where the control unit  60  controls the power supply driving unit  62  to turn off the power supply switch  64 , and accordingly the commercial power supply  50  does not supply the power to the high voltage generator  20  to prevent the high voltage from being generated. Therefore, when the door  14  is opened, it is possible to ensure protection from the high voltage applied to the shelf  22  by preventing the high voltage from being generated. 
         [0075]    In addition to the current detection due to insulation breakdown and the sensing of the opening and closing state of the door  14 , when it is determined in operation  120  that the door is opened, the process moves to operation  122 , where the control unit  60  determines whether the actual chamber temperature Tc detected by the temperature sensor  24  is greater than or equal to a total sum of the setting temperature Ts and a predetermined temperature R (approximately 2 to 3° C.). When the chamber temperature Tc is less than the total sum of the setting temperature Ts and the predetermined temperature R in operation  122 , the high voltage is continuously generated. 
         [0076]    Meanwhile, when the chamber temperature Tc is greater than or equal to the total sum of the setting temperature Ts and the predetermined temperature R, the process moves to operation  126 , where the control unit  60  controls the power supply driving unit  62  to turn off the power supply switch  64 , and accordingly the commercial power supply  50  does not supply the power to the high voltage generator  20  to prevent the high voltage from being generated. Therefore, in consideration that the door switch  16  fails or the user voluntarily operates the door switch  16 , it is possible to check the variation of the chamber temperature Tc to ensure the safety. 
         [0077]    When it is determined in operation  122  that the chamber temperature Tc less than the total sum of the setting temperature Ts and the predetermined temperature R, the process moves to operation  124 , where the control unit  60  determines whether a person contacts the shelf, using the contact sensor  28 . When the person does not contact the shelf, the process returns to operation  114  shown in  FIG. 5A . 
         [0078]    Meanwhile, when it is determined that the person contacts the shelf in operation  124 , the process moves to operation  126 , where the control unit  60  controls the power supply driving unit  62  to turn off the power supply switch  64 , and accordingly the commercial power supply  50  does not supply the power to the high voltage generator  20  to prevent the high voltage from being generated. Therefore, in addition to the case where the door switch  16  fails or the user voluntarily operates the door switch  16 , even when the variation of the actual chamber temperature Tc is too minute to be checked, it is possible to ensure the safety. 
         [0079]    When at least one of the condition that the value of the current Ic detected by the current detecting unit  56  is greater than or equal to the setting value Is due to the insulation breakdown between the shelf  22  and the inner wall  12   a  of the storage chamber  12 , the condition that the door  14  is opened, the condition that the actual chamber temperature Tc is greater than or equal to the setting temperature Ts plus the predetermined temperature, and the condition that the person contacts the shelf  22  is satisfied, the control unit  60  prevents the commercial power supply  50  from supplying the power to the high voltage generator  20  in order to ensure protection from the high voltage applied to the shelf  22 . 
         [0080]    Subsequently, under the control of the control unit  60 , the display unit  68  displays the operation state of the refrigerator due to the cutoff of the high voltage in operation  128 . 
         [0081]    As described above, in a refrigerator and a safety control method thereof according to the present invention, it is possible to ensure protection from a high voltage when a door switch fails or a person contacts a shelf. 
         [0082]    According to the present invention, the opening and closing state of a door is detected and an actual chamber temperature is sensed. Only when the actual chamber temperature is less than a predetermined temperature, the high voltage is applied. When the value of the detected current is greater than or equal to the setting value due to the insulation breakdown between food, which is put on a shelf applied with the high voltage, and an inner wall of a storage chamber, it is possible to cut off the high voltage to ensure safety. 
         [0083]    According to the present invention, it is possible to display the operation state due to the cutoff of the high voltage to a user. 
         [0084]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.