Compressor motor control

Abstract

A compressor, which is susceptible to protective shutdowns when certain operating conditions are sensed, includes a control feature wherein, when the compressor is restarted after a period of time, it may be caused to operate in an unloaded mode such that a reoccurrence of the shutdowns is less likely.

1 . A control for operating a refrigerant system of the type having a motor-driven compressor which is subject to variable load conditions,
 An identification mechanism identifying a condition indicative of an excessive compressor load when operating the compressor in a first loaded mode; and   an unloading mechanism for responsively reducing the compressor load to prevent compressor shutdown.   
     
     
         2 . A control as set forth in  claim 1  wherein said identification mechanism comprises at least one sensor. 
     
     
         3 . A control as set forth in  claim 1  wherein said compressor load is associated with a compressor motor load. 
     
     
         4 . A control as set forth in  claim 2  wherein said at least one sensor includes a compressor motor current sensor. 
     
     
         5 . A control as set forth in  claim 2  wherein said at least one sensor includes a sensor for sensing the temperature of the compressor drive motor. 
     
     
         6 . A control as set forth in  claim 2  wherein said at least one sensor includes both a compressor motor current sensor and a compressor motor temperature sensor. 
     
     
         7 . A control as set forth in  claim 2  wherein said at least one sensor includes at least one of a temperature sensor and a pressure sensor sensing operating conditions within the refrigerant system. 
     
     
         8 . A control as set forth in  claim 1  wherein said unloading mechanism automatically reduces the load on the compressor motor by switching to one of the following modes of operation: non-economized and bypass to suction. 
     
     
         9 . A control as set forth in  claim 1  wherein said unloading mechanism automatically reduces the load on the compressor motor by at least one of the following means: a suction modulation valve, a suction pulse width modulation valve, a variable speed drive for the compressor motor, a multi-speed drive for the compressor motor, permanent disengagement of at least some of the compression elements, engagement-disengagement of compression elements in the pulse width modulation manner, variable air management system and a variable number of active heat exchangers in the refrigerant system. 
     
     
         10 . A control as set forth in  claim 1  and including a compressor drive motor overload protection which is adapted to shut down the operation of the compressor. 
     
     
         11 . A control as set forth in  claim 10  wherein said motor overload protection comprises a line break shutdown apparatus. 
     
     
         12 . A control as set forth in  claim 7  wherein said motor overload protection comprises an overload sensor. 
     
     
         13 . A control as set forth in  claim 10  and including a counter for counting the number of consecutive shutdowns by the compressor drive motor overload protection and a timer for recording the time from an initial shutdown of the compressor by the line break apparatus to the time of a subsequent shutdown of the compressor by the line break apparatus. 
     
     
         14 . A control as set forth in  claim 13  and including a tinier for recording the time from an initial shutdown of the compressor to the time of a subsequent shutdown of the compressor. 
     
     
         15 . A control as set forth in  claim 14  wherein said unloading mechanism reduces the load on the compressor drive motor only when the counter has recorded a predetermined number of shut offs within a predetermined period of time. 
     
     
         16 . A control as set forth in  claim 1  and including a loading mechanism for selectively and automatically increasing, the load on the compressor when certain predetermined conditions are met. 
     
     
         17 . A control as set forth in  claim 16  and including a timer for recording the time from the last shutdown of the compressor by the line break apparatus. 
     
     
         18 . A control as set forth in  claim 17  wherein a loading mechanism increases load on the compressor drive motor when a predetermined period of time from the last shutdown has expired. 
     
     
         19 . A method of controlling a refrigeration system of the type having a motor driven compressor which is subject to variable load conditions comprising the steps of:
 sensing a condition indicative of an excessive compressor load when operating the compressor in a first loaded mode; and   responsively reducing the compressor load to prevent compressor shutdown   
     
     
         20 . A method as set forth in  claim 19  wherein said sensed condition indicative of an excessive compressor load is one indicative of an excessive compressor motor load. 
     
     
         21 . A method as set forth in  claim 19  wherein said reducing step is initiated prior to an anticipated overload shutdown. 
     
     
         22 . A method as set forth in  claim 19  wherein said recovery step is initiated after the occurrence of an overload shutdown and prior to restarting the compressor drive motor after a period if time. 
     
     
         23 . A method as set forth in  claim 19  wherein said sensing step comprises the step of sensing the compressor motor current. 
     
     
         24 . A method as set forth in  claim 19  wherein said sensing step is that of sensing the temperature of the compressor drive motor. 
     
     
         25 . A method as set forth in  claim 19  wherein said sensing step involves the sensing of both the compressor motor current and the compressor motor temperature. 
     
     
         26 . A method as set forth in  claim 19  wherein said compressor load reducing step automatically reduces the load on the compressor motor by switching to one of the following modes of operation: a non-economized and bypass to suction. 
     
     
         27 . A method as set forth in  claim 19  wherein said load reducing step automatically reduces the load on the compressor motor by at least one of the following means: a suction modulation valve, a suction pulse width modulation valve, a variable speed drive for the compressor motor, a multi-speed drive for the compressor motor, permanent disengagement of at least some of the compression elements, engagement-disengagement of compression elements in the pulse width modulation manner, variable air management system and a variable number of active heat exchangers in the refrigerant system. 
     
     
         28 . A method as set forth in  claim 19  and including the step of counting the number of consecutive shut offs by the line break apparatus and recording the time from initial shutting off of the compressor by a line break apparatus to the time for a subsequent shutting off of the compressor a line break. 
     
     
         29 . A method as set forth in  claim 28  wherein said load reducing step involves reducing the load capacity mode of operation only when the counter has recorded a predetermined number of shut offs within a predetermined period of time. 
     
     
         30 . A method as set forth in  claim 19  and including the step of selectively increasing the load capacity mode of operation under certain predetermined conditions.