Patent Publication Number: US-8109736-B2

Title: Apparatus and method for controlling operation of a linear compressor using a phase difference inflection point detecting unit

Description:
This application is a 371 national stage filing of International Application No. PCT/KR2006/005841, filed Dec. 28, 2006 and claims priority to Korean Application No. 10-2006-0004619, filed Jan. 16, 2006, each of which are incorporated by reference in their entireties, as if fully set forth herein. 
     TECHNICAL FIELD 
     The present invention relates to a compressor, and more particularly, to an apparatus and method for controlling an operation of a linear compressor by detecting a phase difference inflection point at a time point when a phase difference between a current and a stroke is placed within a certain region, and by recognizing the phase difference infection point as a top dead center (TDC)=0. 
     BACKGROUND ART 
     Generally, a reciprocating compressor sucks, compressed, and then discharges refrigerant gas by linearly reciprocating a piston in a cylinder. The compressor is divided into a reciprocating compressor and a linear compressor according to a driving method of the piston. 
     In the reciprocating compressor, a crankshaft is coupled to a rotary motor and a piston is coupled to the crankshaft, thereby converting a rotation force of the rotary motor into a reciprocation force. 
     In the linear compressor, a piston connected to a mover of a linear motor is linearly moved. 
     The linear compressor is not provided with a crank shaft for converting a rotation motion into a linear motion thus not to have a frictional loss due to the crank shaft, thereby having a higher compression efficiency than a general compressor. 
     When the linear compressor is applied to a refrigerator or an air conditioner, a compression ratio of the linear compressor is varied by varying a voltage applied to a motor inside the linear compressor. Accordingly, a cooling capacity of the refrigerator or the air conditioner is controlled. 
     When the linear compressor is applied to a refrigerator or an air conditioner, a compression ratio of the linear compressor is varied by varying a stroke voltage applied to the linear compressor. Accordingly, a cooling capacity of the refrigerator or the air conditioner is controlled. Herein, the stroke denotes a distance between an upper dead point of the piston and a lower dead point of the piston. 
     The related art linear compressor will be explained with reference to  FIG. 1 . 
       FIG. 1  is a block diagram showing a driving controlling apparatus for a linear compressor in accordance with the related art. 
     As shown in  FIG. 1 , the related art driving controlling apparatus for a linear compressor comprises a current detecting unit  4  for detecting a current applied to a motor (not shown) of the linear compressor  6 ; a voltage detecting unit  3  for detecting a voltage applied to the motor of the linear compressor  6 ; a stroke calculating unit  5  for calculating a stroke estimation value of the linear compressor based on the detected current, the detected voltage, and a parameter of the motor; a comparing unit  1  for comparing the calculated stroke estimation value with a preset stroke command value, and outputting a difference value therebetween; and a stroke controlling unit  2  for controlling a turn-on period of a triac (not shown) serially connected to the motor based on the difference value so as to vary a voltage applied to the motor, and thereby controlling a stroke of the linear compressor  6 . 
     Hereinafter, an operation of the driving controlling apparatus for a linear compressor will be explained with reference to  FIG. 1 . 
     The current detecting unit  4  detects a current applied to a motor (not shown) of the linear compressor  6 , and outputs the detected current to the stroke calculating unit  5 . 
     The voltage detecting unit  3  detects a voltage applied to the motor of the linear compressor  6 , and outputs the detected voltage to the stroke calculating unit  5 . 
     The stroke calculating unit  5  calculates a stroke estimation value (X) of the linear compressor by substituting the detected current, the detected voltage, and a parameter of the motor into a following equation 1. Then, the stroke calculating unit  5  applies the calculated stroke estimation value (X) to the comparing unit  1 . 
     
       
         
           
             
               
                 
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     The R denotes a resistance of the motor, the L denotes an inductance of the motor, the α denotes a constant of the motor, the V M  denotes a voltage applied to the motor, the i denotes a current applied to the motor, and the ī denotes a variation ratio of the current applied to the motor according to time. That is, the ī is a differential value of the i (di/dt). 
     The comparing unit  1  compares the stroke estimation value with the stroke command value, and applies a difference value therebetween to the stroke controlling unit  2 . 
     The stroke controlling unit  2  varies a voltage applied to the motor of the linear compressor  6  based on the difference value, thereby controlling the stroke of the linear compressor  6 . 
       FIG. 2  is a flowchart showing a method for controlling an operation of a linear compressor in accordance with the related art. 
     Referring to  FIG. 2 , a stroke estimation value obtained by the stroke calculating unit  5  is applied to the comparing unit  1  (S 1 ). Then, the comparing unit  1  compares the stroke estimation value with a preset stroke command value (S 2 ), and outputs a difference value therebetween to the stroke controlling unit  2 . 
     When the stroke estimation value is smaller than the stroke command value, the stroke controlling unit  2  increases a voltage applied to the motor so as to control a stroke of the linear compressor (S 3 ). On the contrary, when the stroke estimation value is larger than the stroke command value, the stroke controlling unit  2  decreases the voltage applied to the motor (S 4 ). 
     Herein, the voltage applied to the motor is increased or decreased by controlling a turn-on period of a triac (not shown) electrically connected to the motor. 
     The stroke command value is varied according to a size of a load of the linear compressor. More concretely, when the load is large, the stroke command value is increased thus to increase the stroke of the piston, thereby preventing decrease of a cooling capacity. 
     On the contrary, when the load is small, the stroke command value is decreased thus to decrease the stroke of the piston, thereby preventing increase of the cooling capacity and preventing a collision between the piston and the cylinder due to an over stroke. 
     In the related art method for controlling an operation of a linear compressor, a stroke estimation value of the linear compressor is calculated based on a parameter of a motor, a resistance and a reactance. Then, a stroke control is performed based on the stroke estimation value. 
     However, when the stroke estimation value is calculated, an error occurs according to a deviation of the parameter and each component thus not to precisely perform the stroke control. Accordingly, the piston is not placed to TDC=0, thereby degrading a reliability of the apparatus. 
     DISCLOSURE OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an apparatus and method for controlling an operation of a linear compressor by detecting a phase difference inflection point at a time point when a phase difference between a current and a stroke is placed within a certain region, and by recognizing the phase difference infection point as a top dead center (TDC)=0. 
     To achieve these objects, there is provided an apparatus for controlling an operation of a linear compressor, comprising: a controlling unit for detecting a phase difference between a current and a stroke, and outputting a frequency varying signal or a phase difference inflection point detecting signal based on the detected phase difference; a phase difference inflection point detecting unit for judging whether to detect a phase difference inflection point or not by the phase difference inflection point detecting signal, and outputting a stroke command value controlling signal based on a result of the judgement; and a stroke command value determining unit for determining a stroke command value based on the stroke command value controlling signal. 
     To achieve these objects, there is also provided a method for controlling an operation of a linear compressor, comprising: driving a linear compressor with a capacity corresponding to a certain stroke command value; detecting a voltage and a current applied to a motor, and calculating a stroke based on the voltage and current; detecting a phase difference between the stroke and the current; comparing the detected phase difference with a preset value, and detecting a phase difference inflection point based on a result of the comparison; and detecting a TDC according to whether the phase difference inflection point has been detected, and then varying a stroke command value according to a load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a method for operating a linear compressor in accordance with the conventional art; 
         FIG. 2  is a flowchart showing a method for operating a linear compressor in accordance with the conventional art; 
         FIG. 3  is a block diagram showing a configuration of an apparatus for operating a linear compressor according to the present invention; and 
         FIG. 4  is a flowchart showing a method for operating a linear compressor according to the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     Hereinafter, with reference to  FIGS. 3 and 4 , will be explained an apparatus and method for controlling an operation of a linear compressor by detecting a phase difference inflection point at a time point when a phase difference between a current and a stroke is placed within a certain region, and by recognizing the phase difference infection point as a top dead center (TDC)=0. 
     In the present invention, a maximum driving efficiency is implemented when the phase difference between a current and a stroke is placed within a certain region and the phase difference infection point is regarded as a top dead center (TDC)=0. 
     The TDC represents a ‘Top Dead Center’ point of the piston of the linear compressor, and denotes a position of the piston when a compression process of the piston is completed. 
     Since the linear compressor has the most excellent efficiency when the TDC is 0, the piston is controlled so as to be positioned at a point of TDC=0. 
       FIG. 3  is a block diagram showing a configuration of an apparatus for operating a linear compressor according to the present invention. 
     As shown, the apparatus for controlling an operation of a linear compressor according to the present invention comprises a stroke command value determining unit  100 , a comparing unit  200 , a PWM signal generating unit  300 , an inverter  400 , a current detecting unit  500 , a voltage detecting unit  600 , a stroke detecting unit  700 , a controlling unit  800 , and a phase difference inflection point detecting unit  900 . 
     The current detecting unit  500  detects a current applied to a motor of a linear compressor, and the voltage detecting unit  600  detects a voltage applied to the motor of the linear compressor. 
     The stroke detecting unit  700  calculates a stroke by using the detected current and the detected voltage. 
     The controlling unit  800  detects a phase difference between the detected current and the stroke, and outputs a frequency varying signal or a phase difference inflection point detecting signal based on the detected phase difference. 
     That is, when the detected phase difference is within a preset range, the controlling unit  800  outputs a phase difference inflection point detecting signal. On the contrary, when the detected phase difference is not within the preset range, the controlling unit  800  outputs a frequency varying signal. 
     As another embodiment, the controlling unit  800  calculates a speed of a stroke by the stroke detecting unit  700 , and calculates a phase difference between the speed and the current. Then, the controlling unit  800  compares the detected phased difference with a reference phase difference, thereby outputting a frequency varying signal or a phase difference inflection point detecting signal. That is, when the detected phase difference is within a preset range, the controlling unit  800  outputs a phase difference inflection point detecting signal. On the contrary, when the detected phase difference is not within the preset range, the controlling unit  800  outputs a frequency varying signal. 
     The PWM signal generating unit  300  generates a PWM signal for varying a frequency of a voltage applied to a motor based on the frequency varying signal, and the inverter  400  varies a voltage and a frequency applied to the motor of the linear compressor based on the PWM signal. 
     The PWM signal generating unit  300  analyzes the frequency varying signal. When the phase difference is more than a preset value, the PWM signal generating unit  300  generates a PWM signal to increase a frequency. However, when the phase difference is less than the preset value, the PWM signal generating unit  300  generates a PWM signal to decrease a frequency. 
     The phase difference inflection point detecting unit  900  judges whether to detect a phase difference inflection point according to the phase difference inflection point detecting signal outputted from the controlling unit  800 , and outputs a stroke command value controlling signal based on a result of the judgement. 
     When a phase difference inflection point is detected by the phase difference inflection point detecting signal, the phase difference inflection point detecting unit  900  outputs a control signal to maintain a present stroke command value. On the contrary, when the phase difference inflection point is not detected by the phase difference inflection point detecting signal, the phase difference inflection point detecting unit  900  outputs a control signal to increase a present stroke command value. 
     When the phase difference is more than a minimum value within a preset range, the phase difference inflection point detecting unit  900  detects the time point as a phase difference inflection point. 
     The stroke command value determining unit  100  determines a stroke command value based on the stroke command value controlling signal. 
     An operation of the apparatus for controlling an operation of a linear compressor according to the present invention will be explained with reference to  FIG. 4 . 
     The linear compressor is operated with a certain stroke command value (SP 11 ). 
     Then, the current detecting unit  500  detects a current of a motor of the linear compressor, and the voltage detecting unit  600  detects a voltage of the motor of the linear compressor (SP 12 ). 
     Then, the stroke detecting unit  700  calculates a stroke by using the detected current and the detected voltage (SP 13 ). 
     Then, the comparing unit  200  calculates a difference value between the stroke command value and the stroke. The PWM signal generating unit  300  generates a PWM signal corresponding to the difference value thus to apply it to the inverter  400 . Then, the inverter  400  varies a frequency and a voltage according to the PWM signal, and applies them to a motor of the linear compressor (SP 14  to SP 16 ). 
     The controlling unit  800  detects a phase difference between the detected current and the stroke (SP 17 ), and outputs a frequency varying signal or a phase difference inflection point detecting signal based on the detected phase difference. 
     As another embodiment, the controlling unit  800  calculates a speed of a stroke, and detects a phase difference between the speed and the current. Then, the controlling unit  800  outputs a frequency varying signal or a phase difference inflection point detecting signal based on the detected phase difference. 
     Then, the controlling unit  800  compares the phase difference between the stroke and the current with a preset phase difference (a value within an approximate range of 80°˜100°). When the detected phase difference is within a preset range, the controlling unit  800  outputs a phase difference inflection point detecting signal. 
     Then, the phase difference inflection point detecting unit  900  judges whether a phase difference inflection point has occurred by the phase difference inflection point detecting signal. If it is judged that the phase difference inflection point has occurred (SP 21 ), the phase difference inflection point detecting unit  900  judges a present stroke to be placed at a point of ‘TDC=0’ thus to maintain the present stroke command value (SP 22 ). On the contrary, if it is judged that the phase difference inflection point has not occurred, the phase difference inflection point detecting unit  900  judges the present stroke as a stroke less than the ‘TDC=0’ (SP 23 ) thus to increase the present stroke command value (SP 24 ). 
     When the phase difference between the stroke and the current is more than a preset range, the controlling unit  800  increases a frequency by increasing a duty ratio of the PWM signal (SP 20 ). On the contrary, when the phase difference between the stroke and the current is less than the preset range, the controlling unit  800  decreases a frequency by decreasing a duty ratio of the PWM signal (SP 19 ). 
     That is, in the present invention, a frequency is varied so that a phase difference between a current and a stroke may be placed within a certain region. If the phase difference between the current and the stroke is within a certain region, a phase difference inflection point is detected thus to be recognized as a ‘TDC=0’. 
     The present invention has the following effects. 
     First, a phase difference between a current and a pulse width modulation (PWM) voltage is calculated, a phase delay value to compensate the phase difference is calculated, and a reference current is delayed by the calculated phase delay value thus to remove a distortion phenomenon of a current. Accordingly, a driving efficiency of the compressor is enhanced, and a TDC is precisely controlled. 
     It will also be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.