Compressor digital control failure shutdown algorithm

Abstract

A method of controlling the loading and unloading of a compressor includes selectively loading and unloading a compressor by engaging and disengaging, respectively, compressor members with the controller in response to system load data, monitoring at least one of the discharge pressure and the suction pressure at a predetermined time interval for a continuous time period, storing values based on the at least one of the discharge pressure and the suction pressure during the continuous time period, and determining a predetermined value indicative of compressor operation in which the compressor members are engaged. The method further includes comparing at least one of the stored values with the predetermined value and providing a signal to cease operation of the compressor when the comparison fails to indicate compressor operation in which the compressor members are engaged.

1 . A method of controlling the loading and unloading of a compressor, the method comprising:
 selectively loading and unloading a compressor by engaging and disengaging, respectively, compressor members with the controller in response to system load data:   loading the compressor to increase a fluid pressure from a suction pressure to a discharge pressure when the compressor members are engaged;   unloading the compressor when the compressor members are disengaged;   monitoring at least one of the discharge pressure and the suction pressure at a predetermined time interval for a continuous time period;   storing values based on the at least one of the discharge pressure and the suction pressure during the continuous time period;   determining a predetermined value indicative of compressor operation in which the compressor members are engaged;   comparing at least one of the stored values with the predetermined value;   providing a signal to cease operation of the compressor when the comparison fails to indicate compressor operation in which the compressor members are engaged.   
     
     
         2 . The method of  claim 1 , further including the step of providing a signal to restart the compressor after waiting for a second predetermined time interval and if fewer than a predetermined number of signals to cease operation of the compressor have occurred during the second predetermined time interval. 
     
     
         3 . The method of  claim 1 , wherein storing values based on the at least one of the discharge pressure and the suction pressure during the continuous time period means storing the maximum and minimum values of one of the discharge pressure and the suction pressure during the continuous time period, the method further including
 calculating a difference between a stored maximum value of the one of the discharge pressure and the suction pressure and a stored minimum value of the one of the discharge pressure and the suction pressure,   and wherein comparing at least one of the stored values with the predetermined value means comparing the difference with the predetermined value.   
     
     
         4 . The method of  claim 3 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged when the difference is not equal to or greater than the predetermined value at any time during the continuous time period. 
     
     
         5 . The method of  claim 3 , wherein the difference represents an increase in discharge pressure. 
     
     
         6 . The method of  claim 3 , wherein the difference represents a decrease in suction pressure. 
     
     
         7 . The method of  claim 1 , further including calculating a direction of the slope of the at least one of the discharge pressure and the suction pressure for the continuous time period, and wherein comparing at least one of the stored values with the predetermined value means comparing the direction with the predetermined value. 
     
     
         8 . The method of  claim 7 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged when the direction of the slope does not change during the continuous time period. 
     
     
         9 . The method of  claim 7 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged if the direction of the slope of the discharge pressure does not change from negative to positive during the continuous period. 
     
     
         10 . The method of  claim 7 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged if the direction of the slope of the suction pressure does not change from positive to negative during the continuous period. 
     
     
         11 . The method of  claim 1 , further including determining a maximum pressure differential between the discharge pressure and the suction pressure at each time interval and determining a minimum pressure differential between the discharge pressure and the suction pressure at each time interval, and further including calculating a difference between the determined maximum pressure differential and the determined minimum pressure differential, and wherein comparing at least one of the stored values with the predetermined value means comparing the difference with the predetermined value. 
     
     
         12 . The method of  claim 11 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged when the difference did not rise by the predetermined value during the continuous time period. 
     
     
         13 . The method of  claim 1 , further including calculating the ratio of the discharge pressure to the suction pressure over the continuous time period, and wherein comparing at least one of the stored values with the predetermined value means comparing the calculated ratio with the predetermined value. 
     
     
         14 . The method of  claim 13 , wherein the comparison fails to indicate compressor operation in which the compressor members are engaged when the calculated ratio drops below the predetermined value. 
     
     
         15 . The method of  claim 14 , wherein the predetermined value is approximately 1.4 
     
     
         16 . The method of  claim 1 , wherein the compressor is a scroll compressor.