Abstract:
An apparatus and method of controlling a linear compressor. The apparatus includes a current detection unit to detect current, a control unit to determine whether a collision between a piston and a valve occurs, and controlling a stroke of the linear compressor, and a compressor drive unit to perform adjustment of the stroke of the linear compressor. The method includes presetting a maximum stroke and a collision point according to a load, selectively increasing and reducing a stroke of the linear compressor according to a variation in the load, and controlling the stroke.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 02-11025, filed Feb. 28, 2002, in the Korean Industrial 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 generally to an apparatus and method of controlling a linear compressor, and more particularly to an apparatus and method of controlling a linear compressor, which is capable of preventing collisions between the piston and valve of the linear compressor, thereby improving the operational efficiency of the linear compressor.  
           [0004]    2. Description of the Prior Art  
           [0005]    As depicted in FIG. 1, a linear compressor  1  is comprised of a drive unit  2 , a resonance spring  3 , a displacement restricting unit  4 , a valve  5 , a cylinder head  6 , a piston  7  and a cylinder block  8 .  
           [0006]    A conventional apparatus to control the operation of a linear compressor is described below.  
           [0007]    Referring to FIG. 2, the conventional control apparatus is comprised of a core  10 , first and second coils  12  and  13 , a signal processing unit  20  and a microcomputer  30 . The core  10  is made of a magnetic substance and moved in conjunction with a part (that is, a piston) whose position is desired to be detected, the first and second coils  12  and  13  are symmetrically wound around the core  10 , and the signal processing unit  20  detects and outputs variations in position of the core  10  using voltages induced to the first and second coils  12  and  13 .  
           [0008]    The signal processing unit  20  is comprised of a first full-wave rectification unit  21 , a second full-wave rectification unit  22 , a differential amplification unit  23 , a filter unit  24 , and a peak detection unit  25 . The first full-wave rectification unit  21  full-wave rectifies the voltage induced to the first coil  12 , the second full-wave rectification unit  22  full-wave rectifies the voltage induced to the second coil  13 , the differential amplification unit  23  amplifies a difference between the voltages full-wave rectified by the first and second full-wave rectification units  21  and  22 , the filter unit  24  eliminates a high-frequency component from a signal outputted from the differential amplification unit  23 , and the peak detection unit  25  detects the maximum and minimum values of a signal outputted from the filter unit  24 , and transmits the detected values to a microcomputer  30 .  
           [0009]    The operation of the conventional linear compressor is described below.  
           [0010]    If the position of the core  10  is varied by a variation in position of a part (for example, the piston) whose position is desired to be detected while alternating current (AC), having a frequency of several KHz, is applied to the first and second coils  12  and  13  from the outside, voltages in proportion to the variation in position of the core  10  are induced to the first and second coils  12  and  13 . The voltages induced to the first and second coils  12  and  13  are full-wave rectified by the first and second full-wave rectification units  21  and  22 , and the full-wave rectified voltages are inputted to input terminals of the differential amplification unit  23 . The differential amplification unit  23  amplifies a difference between the voltages full-wave rectified by the first and second full-wave rectification units  21  and  22 , and outputs the amplified difference to the filter unit  24 . The filter unit  24  eliminates a high-frequency component from the signal outputted from the differential amplification unit  23 , and outputs the filtered signal to the peak detection unit  25 . The peak detection unit  25  full-wave rectifies the signal outputted from the filter unit  24 , and outputs the rectified signal to the microcomputer  30 . The microcomputer  30  controls the stroke of the linear compressor  1  according to the signal rectified by and outputted from the filter unit.  
           [0011]    The conventional linear compressor control apparatus controls only a stroke detected by a sensor, etc., so the stroke of the linear compressor can be controlled to be constant. However, in the linear compressor the center position of whose piston is varied according to load, a top clearance cannot be kept constant with respect to the top dead center of the piston. As a result, there occurs a problem that the piston of the linear compressor is brought into collision with the valve of the linear compressor.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, it is an object of the present invention to provide an apparatus and method of controlling a linear compressor, which is capable of controlling a top clearance for the top dead center of the piston of the linear compressor, thus preventing the collision between the piston and valve of the linear compressor and improving the operational efficiency of the linear compressor.  
           [0013]    Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
           [0014]    The foregoing and other objects of the present invention are achieved by providing an apparatus to control a linear compressor, comprising: a current detection unit to detect current supplied to the linear compressor; a control unit to determine whether a collision between a piston and a valve of the linear compressor occurs by using an output signal from the current detection unit, and controlling a stroke of the linear compressor if the collision occurs; and a compressor drive unit to perform adjustment of the stroke of the linear compressor in response to control of the control unit.  
           [0015]    In addition, the present invention provides a method of controlling a linear compressor, comprising: presetting a maximum stroke and a collision point according to a load; selectively increasing and reducing a stroke of the linear compressor according to a variation in the load; and controlling the stroke according to a variation in current supplied to the linear compressor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These and other objects 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:  
         [0017]    [0017]FIG. 1 is a longitudinal section of a conventional linear compressor;  
         [0018]    [0018]FIG. 2 is a block diagram of a conventional apparatus to control the linear compressor of FIG. 1;  
         [0019]    [0019]FIG. 3 is a block diagram illustrating an apparatus to control a linear compressor in accordance with an embodiment of the present invention;  
         [0020]    [0020]FIG. 4 is a graph illustrating current waveforms in accordance with the operation of the linear compressor;  
         [0021]    [0021]FIG. 5 is a graph illustrating the displacements of a displacement unit and a resonance spring in accordance with the present invention;  
         [0022]    [0022]FIG. 6 is a graph illustrating the recognition of a maximum stroke and a collision point using decreases in current; and  
         [0023]    [0023]FIG. 7 is a flowchart illustrating a method of controlling the linear compressor in accordance with the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    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 in order to explain the present invention by referring to the figures.  
         [0025]    [0025]FIG. 3 is a block diagram illustrating an apparatus to control a linear compressor in accordance with an embodiment of the present invention.  
         [0026]    Referring to FIG. 3, the linear compressor control apparatus of the present invention comprises a control unit  330  and a compressor drive unit  200 . The control unit  330  controls the entire operation of the linear compressor  100 , while the compressor drive unit  200  operates the linear compressor  100  in response to the control of the control unit  330 . The linear compressor control apparatus of the present invention further comprises a first storage unit  341  and a second storage unit  342 . The first storage unit  341  stores preset data including preset conduction angle data in response to input voltage, while the second storage unit  342  stores reset data. Additionally, in the linear compressor control apparatus of the present invention, a voltage detection unit  310  and a current detection unit  320  are connected to the control unit  330 . The voltage detection unit  310  detects the voltage of the power supplied to the linear compressor  100 , while the current detection unit  330  detects the current of the power supplied to the linear compressor  100 .  
         [0027]    [0027]FIG. 4 is a graph illustrating current waveforms in accordance with the operation of the linear compressor of the present invention. Referring to this figure, “A” represents a reference current waveform. “B” represents a current waveform at a maximum stroke point. “C” represents a current waveform at a collision point. “D” represents a first reference variation that is preset to recognize a maximum stroke. “E” represents a second reference variation that is preset to recognize a collision between the piston and valve of the linear compressor  100 . Accordingly, if current is varied by “E”, it is recognized that the piston is in collision with the valve.  
         [0028]    [0028]FIG. 5 is a graph illustrating the displacements of a displacement restricting unit and a resonance spring (refer to FIG. 1) in accordance with an embodiment of the present invention. In FIG. 5, “a” represents the displacement of the displacement restricting unit, while “b” represents the displacement of the resonance spring. P1 represents a point where the displacement restricting unit and the resonance spring are brought into tight contact with each other at a rated displacement point. P2 represents a point where the displacement restricting unit and the resonance spring are brought into tight contact with each other at a maximum stroke point. P3 represents a point where the displacement restricting unit and the resonance spring are brought into tight contact with each other at a collision point. Referring to FIG. 5, a maximum stroke is greater than a stroke at a rated displacement point, and a stroke at a collision point is greater than the maximum stroke.  
         [0029]    [0029]FIG. 6 is a graph illustrating the recognition of a maximum stroke and a collision point using decreases in current. In this drawing, “α” represents the trace of maximum stroke values according to a decrease in current and load, while “β” represents the trace of collision points according to a decrease in current and load.  
         [0030]    A method of controlling the linear compressor in accordance with the present invention is described below.  
         [0031]    [0031]FIG. 7 is a flowchart illustrating the linear compressor control method of the present invention.  
         [0032]    Referring to FIG. 7, the control unit  330  sets a maximum stroke and a collision point of the piston at operation S 10 . In this case, the amount of load is generally set depending on the opening/closing of a door of a refrigerator, the amount of food in a refrigerator, the set temperature of an interior of a refrigerator, the temperature of outside air, etc.  
         [0033]    If the present load is heavy at operation S 10 , the maximum stroke is set to a first stroke value α1, and the collision point is set to a first collision point β1. If the present load is moderate at operation S 10 , the maximum stroke is set to a second stroke value α2, and the collision point is set to a second collision point β2. If the present load is light at operation S 10 , the maximum stroke is set to a third stroke value α3, and the collision point is set to a third collision point β3. These stroke values and collision points are preset to fulfill relations of α1 &lt;α2&lt;3, β1&lt;β2&lt;β3, α1≦β1, α2≦β2 and α3≦β3.  
         [0034]    After the setting of the maximum stroke and the collision point is completed, the control unit  330  determines whether the load is varied at operation S 20 . In this case, the variation of the load is generally dependent on the opening/closing of a door of a refrigerator, the amount of food in a refrigerator and the set temperature of an interior of a refrigerator. If the load is varied at operation S 20 , the control unit  330  determines whether the load is increased at operation S 30 . On the other hand, if the load is not varied at operation S 20 , the process returns to operation S 10 .  
         [0035]    If the load is increased at operation S 30 , the control unit  330  controls the compressor drive unit  200  so that the stroke of the piston of the linear compressor  100  is increased at operation S 40 . On the other hand, if the load is not increased at operation S 30 , the load is considered as being decreased, so the control unit  330  controls the compressor drive unit  200  to allow the stroke of the piston of the linear compressor  100  to be decreased at step S 31 .  
         [0036]    The control unit  330  detects current supplied to the linear compressor  100  through the current detection unit  320  and calculates a corresponding current variation at operation S 50 . The control unit  330  determines whether the calculated current variation is greater than a first preset reference variation at operation S 60 .  
         [0037]    If the calculated current variation is greater than the first preset reference variation at operation S 60 , the control unit  330  determines whether the calculated current variation is equal to or greater than a second preset reference variation at operation S 70 .  
         [0038]    If the calculated current variation is equal to or greater than the second preset reference variation at operation S 70 , the control unit  330  sets a collision conduction angle, a maximum conduction angle and sets a rated conduction angle at operation S 80 , thereby recognizing a collision point. Additionally, the control unit  330  sets a decrease in the stroke of the piston of the linear compressor  100  to prevent collisions between the piston and the valve at operation S 90 , and controls the compressor drive unit  200  so that the linear compressor  100  performs a reduced stroke operation at operation S 100 . Otherwise, if the calculated current variation is not equal to or greater than the second preset reference variation at operation S 70 , the control unit  330  sets the stroke of the piston and then reduces the stroke operation.  
         [0039]    If the calculated current variation is not greater than the first preset reference variation at operation S 60 , the control unit  330  determines whether a calculated current variation is equal to the first preset reference variation at operation S 61 . If the calculated current variation is equal to the first preset reference variation at operation S 61 , the control unit  330  sets a maximum conduction angle and a rated conduction angle to determine a maximum stroke at operation S 62 . Accordingly, the control unit  330  controls the compressor drive unit  200  so that the linear compressor  100  performs a maximum stroke operation at operation S 63 . Thereafter, the process returns to operation S 10 .  
         [0040]    On the other hand, if the calculated current variation is not equal to the first preset reference variation at operation S 61 , the control unit  330  controls the compressor drive unit  200  so that the linear compressor  100  maintains a current stroke operation (that is, performs a normal operation) at operation S 64 .  
         [0041]    As described above, the present invention provides an apparatus and method of controlling a linear compressor, which is capable of securing a top clearance to correspond to the load without using an additional sensor, thereby minimizing collisions between the piston and the valve and, accordingly, maintaining a highly efficient operation.  
         [0042]    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.