Abstract:
The invention provides a refrigerator having a compressor, the refrigerator including: a motor driving the compressor; a motor driver supplying power to the motor; and a controller outputting a control signal corresponding to a second command speed to the motor driver, and outputting a control signal corresponding to a first command speed which is higher than the second command speed to the motor driver when a driving on/off ratio of the motor driver is maintained below a given reference driving on/off ratio for a given reference period. Accordingly, it is an aspect of the present invention to provide a refrigerator to operate a compressor stably and easily under overload or low voltage conditions, and a method for controlling the same.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Korean Patent Application No. 2005-0111786, filed on Nov. 22, 2005, 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 and a method for controlling the same, and more particularly, to a refrigerator in which an operation state of a compressor is changed in accordance with external conditions.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, a refrigerator includes a compressor which compresses or expands a refrigerant by using a piston connected to a motor. The speed of the motor driving the compressor is controlled depending on an ambient environment.  
         [0006]     When ambient temperature of the refrigerator is relatively high or when the refrigerator that has been in the state of being turned off for a long period of time is turned on, the motor speed is rapidly increased compared with a normal speed in order to overcome load torque that resists operation of the motor.  
         [0007]     However, it is difficult for the motor speed to reach a given command speed mostly due to the load torque. Thus, the motor is driven at a command speed lower than the initially given command speed in order to reduce generation of noise and vibration.  
         [0008]     However, the motor is driven at such a lower speed than normal, even in case that the operation state of the motor of the refrigerator is improved so that the motor can be driven at the initial command speed. Driving the motor at the lower speed may cause decrease of a cooling speed of the refrigerator, thereby decreasing refrigeration efficiency.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is an aspect of the present invention to provide a refrigerator that operates a compressor stably and easily under overload or low voltage conditions, and a method for controlling the same.  
         [0010]     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.  
         [0011]     The foregoing and/or other aspects of the present invention can be achieved by providing a refrigerator having a compressor, the refrigerator including: a motor driving the compressor; a motor driver supplying power to the motor; and a controller outputting a control signal corresponding to a second command speed to the motor driver, and outputting a control signal corresponding to a first command speed which is higher than the second command speed to the motor driver when a driving on/off ratio of the motor driver is maintained below a given reference driving on/off ratio for a given reference period.  
         [0012]     According to an aspect of the present invention, the speed of the motor increases as the driving on/off ratio increases.  
         [0013]     According to an aspect of the present invention, the controller outputs a control signal corresponding to a command speed lower than a given command speed to the motor driver when the speed of the motor does not reach the given command speed even though the driving on/off ratio is maximized.  
         [0014]     According to an aspect of the present invention, when the speed of the motor reaches the first command speed, the controller increases the reference driving on/off ratio.  
         [0015]     According to an aspect of the present invention, when the speed of the motor reaches the first command speed, the controller reduces the reference period.  
         [0016]     According to an aspect of the present invention, when the speed of the motor does not reach the first command speed, the controller reduces the reference driving on/off ratio.  
         [0017]     According to an aspect of the present invention, when the speed of the motor does not reach the first command speed, the controller increases the reference period.  
         [0018]     According to an aspect of the present invention, the motor driver includes an inverter having a switching element, and the driving on/off ratio can be replaced with a duty ratio of the switching element.  
         [0019]     The foregoing and/or other aspects of the present invention can be achieved by providing a method for controlling a refrigerator having a motor and a motor driver driving the motor, the method including: outputting a control signal corresponding to a second command speed to the motor driver; determining whether a driving on/off ratio of the motor driver is maintained below a given reference driving on/off ratio for a given reference period; and outputting a control signal corresponding to a first command speed which is higher than the second command speed when it is determined that the driving on/off ratio is maintained for the given reference period.  
         [0020]     According to an aspect of the present invention, the method further includes increasing the reference driving on/off ratio when the speed of the motor reaches the first command speed.  
         [0021]     According to an aspect of the present invention, the method further includes decreasing the reference period when the speed of the motor reaches the first command speed.  
         [0022]     According to an aspect of the present invention, the above method further includes reducing the reference driving on/off ratio when the speed of the motor does not reach the first command speed.  
         [0023]     According to an aspect of the present invention, the above method further includes increasing the reference period when the speed of the motor does not reach the first command speed.  
         [0024]     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The above and/or other aspects and advantages of the prevent invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompany drawings, in which:  
         [0026]      FIG. 1  is a control block diagram of a refrigerator according to an embodiment of the present invention.  
         [0027]      FIG. 2  is a control flowchart showing a method for controlling the refrigerator according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     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 like elements throughout. The embodiments are described below so as to explain the present invention by referring to the figure.  
         [0029]      FIG. 1  is a control block diagram of a refrigerator according to an embodiment of the present invention.  
         [0030]     As shown in  FIG. 1 , a refrigerator  1  includes a compressor  10 , a motor  20  driving the compressor  10 , a motor driver  30  supplying power to the motor  20 , and a controller  40  controlling the motor driver  30 .  
         [0031]     The compressor  10  of the refrigerator  1  compresses a refrigerant with a high temperature and a high pressure. The compressor  10  includes a piston connected to the motor  20 , and the refrigerant is repeatedly compressed and expanded by iterative linear motion of the piston according to rotation of the motor  20 .  
         [0032]     The motor  20  may be provided as a brushless direct current (DC) motor. The motor  20  drives the compressor  10  using power supplied from the motor driver  30 . The speed of the motor  20  is determined by the controller  40  and the motor driver  30 , and may vary depending on ambient environment of the refrigerator.  
         [0033]     For example, the speed of the motor  20  varies depending on ambient temperature of the refrigerator, a current temperature in the refrigerator, and a preset temperature. Also a residual pressure in the motor  20  also may cause variation of the motor speed. For example, the compressor  10  may be driven at a high speed in order to increase a cooling speed when the ambient temperature of the refrigerator is relatively high or a difference between temperature in the refrigerator and a preset temperature is not within a predetermined allowable range, whereas the compressor  10  is driven at a low speed in order to maintain the cooling speed properly when the ambient temperature of the refrigerator is relatively low or the difference between the temperature in the refrigerator and the set temperature is within the predetermined allowable range.  
         [0034]     Meanwhile, it consumes a lot of power to decrease the temperature in the refrigerator when the temperature in the refrigerator is significantly high or the refrigerator that has been turned off for a long period time is turned on. When the compressor  10  is driven under such an overloaded refrigeration cycle, a pressure difference between a delivery unit (outlet) and a suction unit (inlet) of the compressor  10  significantly increases thereby causing high torque load of the motor  20  driving the compressor  10 . Such high torque load causes the speed of the motor  20  to be increased.  
         [0035]     The motor driver  30  supplies power to the motor  20  for driving the motor  20 , and the controller  40  controls a driving on/off ratio. The motor driver  30  includes a converter (not shown) and an inverter inverting a direct current power output from the converter to an alternate current power input to the motor  20 .  
         [0036]     The converter converts the alternate current power to the direct current power and the direct current power is switched in accordance with a given control signal by the inverter.  
         [0037]     The inverter includes a plurality of switching elements, each of which is repeatedly turned on/off according to a pulse width modulation (PWM) control signal output from the controller  40 . The driving on/off ratio is understood as the ratio of an on-period of the switching element to an off-period of the switching element. That is, more power is supplied to the motor  20  as the driving on/off ratio increases, thereby increasing the speed of the motor  20 . A reference value for the on-period can be changed as long as such a relationship between the driving on/off ratio and the speed of the motor  20  is satisfied.  
         [0038]     Therefore, the driving on/off ratio according to the embodiment of the present invention can be replaced with a duty ratio of the switching element of the inverter, which represents the ratio of the on-period to one on/off cycle of the switching element. The power supplied to the motor  20  increases as the duty ratio of the switching element increases, thereby increasing the speed of the motor  20 .  
         [0039]     The controller  40  detects the state of the refrigerator  1  and the speed of the motor  20  to control the speed on the motor  20  in accordance with the state of the refrigerator  1  and outputs a control signal corresponding to a given speed command to the motor driver  30  based on the state of the refrigerator  1  and the speed of the motor  20 . The control signal output from the controller  40  includes a PWM control signal for controlling the switching element of the inverter.  
         [0040]     As described above, when the refrigeration cycle is driven under overload and thus load torque of the motor  20  increases, a voltage higher than a rated voltage should be supplied to the motor  20 . Thus, the controller  40  outputs a control signal corresponding to the command speed higher than the speed of the motor  20  that has been driven at the rated voltage. Hereinafter, the speed of the motor  20  to overcome the load torque is referred to as a first command speed.  
         [0041]     When the controller  40  outputs a control signal corresponding to the first command speed to the motor driver  30 , the motor driver  30  switches the switching element of the inverter. However, when the speed of the motor  20  does not reach the first command speed due to the load torque even though the driving on/off ratio is maximized, in other words, the duty ratio of the switching element is 100%, the controller  40  outputs a control signal corresponding to a second command speed which is lower than the first command speed. As a result, noise that can be generated from the refrigerator is reduced and occurrence of a defect due to overdriving the motor  20  can be prevented.  
         [0042]     After the control signal corresponding to the second command speed is output, the controller  40  determines whether the driving on/off ratio of the motor driver  30  can be maintained at a lower value than a given reference driving on/off ratio for a given reference period. In more detail, it can be implied that the motor  20  can be fully driven at the second command speed when the driving on/off ratio is maintained at the given reference driving on/off ratio rather than at 100%, for example, below 80% for the reference period.  
         [0043]     When the motor  20  has been driven at the second command speed, which is lower than the first command speed, for a period longer than the reference period, the controller  40  determines that the load torque of the motor  20  is reduced and outputs a control signal corresponding to the first command speed.  
         [0044]     When the speed of the motor  20  does not reach the second command speed even though the speed of the motor  20  is reduced to the second command speed and the power is fully supplied to the motor  20 , the controller  40  outputs a control signal corresponding to the speed lower than the second command speed and the above-described process is repeatedly performed.  
         [0045]     According to the prior art, the control signal corresponding to the second command speed lower than the first command speed is output and the speed of the motor  20  is maintained at the second command speed, and as a result, a cooling speed of the refrigerator is decreased. However, according to the present invention, the speed of the motor  20  can be restored to the first command speed depending on the state of the motor  20 .  
         [0046]     When the speed of the motor  20  reaches the first command speed by the control signal corresponding to the first command speed, the controller  40  increases the reference driving on/off ratio or decreases the reference period. Variations of such a driving condition for the motor  20  are for preventing noise that can be generated when the speed of the motor  20  is changed and for stably driving the motor  20  when the speed of the motor  20  is repeatedly changed.  
         [0047]     That is, the speed of the motor  20  that has been reached the first command speed can be reduced to the second command speed. In order to avoid the iterative changes in the motor speed and stably drive the motor  20 , the reference driving on/off ratio is increased to 90% from 80% when the speed of the motor  20  is reduced from the first command speed to the second command speed. In addition, the speed of the motor  20  can be promptly changed from the second command speed to the first command speed by reducing the reference period of the second command speed.  
         [0048]     When the speed of the motor  20  does not reach the first command speed, the controller  40  can reduce the reference driving on/off ratio to 70% from 80% or increase the reference period. The speed of the motor  20  does not reach the first command speed even though the control signal corresponding to the first command speed is output to the motor driver when the reference driving on/off ratio is set relatively too high or a residual load torque of the motor is relatively high. Therefore, the controller  40  may reduce the reference driving on/off ratio to alleviate a condition that causes the speed of the motor  20  to be consistently maintained at the second command speed, or increase the reference period until the load torque of the motor  20  is significantly reduced.  
         [0049]     Such an additional control of the controller  40  can prevent the motor  20  from being driven abnormally between the first command speed and the second command speed and reduce noise and vibration that can be generated when the speed of the motor  20  is changed.  
         [0050]     The controller  40  is activated when load torque exists in the motor  20  and when an initial power voltage input to the refrigerator is lower than as normal and thus the motor  20  is driven at relatively high speed.  
         [0051]     In terms of functional aspects, the controller  40  determines the state of the refrigeration and controls the motor driver  30  according to the embodiment of the present invention. However, there can be provided two controllers for controlling the overall state of the refrigerator by sensing temperature of the refrigerator and for controlling the motor driver  30  respectively and the motor  20  can be controlled by communication between the two controllers.  
         [0052]      FIG. 2  is a control flowchart showing a method for controlling a refrigerator according to the embodiment of the present invention. The method for controlling the refrigerator will now be described with reference to  FIG. 2 .  
         [0053]     When the refrigerator is in the state of being overloaded or a power voltage is respectively low, a control signal corresponding to a first command speed is output (S 10 ). At this time, the first command speed is higher than a normal speed of the motor  20 . After a given period, it is determined whether a driving on/off ratio of the motor driver  30  is maximized (S 20 ).  
         [0054]     When the driving on/off ratio is not maximized, it can be understood that the motor  20  is driven at the first command speed.  
         [0055]     When the driving on/off ratio is determined to be maximized, it is determined whether or not the speed of the motor  20  reaches the first command speed (S 30 ). When the speed of the motor  20  does not reach the first command speed even though the driving on/off ratio is maximized, the controller  40  outputs a control signal corresponding to a second command speed which is lower than the first command speed in order to prevent noise and vibration from being generated from the motor  20  and reduce load on the motor  20  (S 40 ).  
         [0056]     Subsequently, it is determined whether the driving on/off ratio of the motor driver  30  is maintained below a reference driving on/off ratio for a reference period (S 50 ). When it is maintained for the reference period, the controller  40  outputs the control signal corresponding to the first command speed again (S 60 ). This means that the motor  20  is in the state of being able to reach the first command speed.  
         [0057]     After outputting the control signal corresponding to the first command speed, the controller  40  determines whether the speed of the motor  20  reaches the first command speed (S 70 ).  
         [0058]     When it is determined that the speed of the motor  20  does not reach the first command speed, the driving on/off ratio is reduced so that the speed of the motor  20  can easily reach the first command speed or the reference period of the second command speed is increased so that load torque of the motor  20  can be significantly reduced (S 80 ).  
         [0059]     However, when the speed of the motor  20  reaches the first command speed, the driving on/off ratio is increased in order to prevent repetitive operation of the motor between the first command speed and the second command speed or the reference period of the second command speed is reduced when the load torque of the motor  20  is determined to be significantly reduced (S 90 ).  
         [0060]     As described above, a refrigerator and a method for controlling the refrigerator according to the present invention can drive a compressor stably and easily even under overload or low voltage conditions.  
         [0061]     Although a few exemplary embodiments of the present invention have been shown and described, it will 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 appended claims and their equivalents.