Compressor motor preheat control

Abstract

A method of controlling a vapor cycle system having first and second compressors includes operating the first compressor to compress refrigerant while the second compressor is idle, sensing a motor temperature of the second compressor, activating a preheating mode in which the motor of the second compressor is powered to generate heat when the motor temperature of the second compressor is below a lower temperature threshold, turning off the preheating mode when the sensed motor temperature of the second compressor is above an upper temperature threshold, and limiting the maximum duration of the preheating mode to a preheating time period, such that the preheating mode is turned off after being activated for the preheating time period.

1 . A method of controlling a vapor cycle system having first and second compressors, the method comprising:
 operating the first compressor to compress refrigerant while the second compressor is idle;   sensing a motor temperature of the second compressor;   activating a preheating mode in which the motor of the second compressor is powered to generate heat when the motor temperature of the second compressor is below a lower temperature threshold;   turning off the preheating mode when the sensed motor temperature of the second compressor is above an upper temperature threshold; and   limiting the maximum duration of the preheating mode to a preheating time period, such that the preheating mode is turned off after being activated for the preheating time period.   
     
     
         2 . The method of  claim 1 , wherein the lower temperature threshold is approximately 48.9° C. (120° F.), and wherein the upper temperature threshold is approximately 54.4° C. (130° F.). 
     
     
         3 . The method of  claim 1 , wherein the motor temperature of the second compressor is sensed by sensing resistance with a thermistor. 
     
     
         4 . The method of  claim 1 , wherein the preheating time period is approximately 14 minutes. 
     
     
         5 . The method of  claim 1  and further comprising:
 maintaining the second compressor preheat mode in an off condition for a delay period; and 
 reactivating the preheating mode for the second compressor for the preheating time period following the delay period. 
 
     
     
         6 . The method of  claim 5 , wherein the delay period is approximately 30 minutes. 
     
     
         7 . The method of  claim 1  and further comprising:
 starting the second compressor to compress refrigerant after the preheat mode is turned off. 
 
     
     
         8 . A vapor cycle system comprising:
 a first compressor having an electric motor, a motor temperature sensor, and a motor controller;   a second compressor having an electric motor, a motor temperature sensor, and a motor controller;   a refrigerant circuit, wherein the first compressor and the second compressor are connected in fluid communication with the refrigerant circuit in parallel; and   a control module operatively connected to the motor controller of each of the first and second compressors, wherein the control module is configured to command the motor controllers of each of the first and second compressors to operate only one of the first and second compressors to compress refrigerant and to operate the other, idle one of the first and second compressors in a preheat mode, wherein the preheat mode is activated to generate heat with the motor of the idle one of the first and second compressors to a preheat temperature range, and wherein the control module is further configured to limit a duration of the preheat mode to a preheating time period.   
     
     
         9 . The vapor cycle system of  claim 8 , wherein the preheat temperature range is approximately 48.9° C. (120° F.) to approximately 54.4° C. (130° F.). 
     
     
         10 . The vapor cycle system of  claim 8 , wherein the motor temperature sensors of each of the first and second compressors is a thermistor. 
     
     
         11 . The vapor cycle system of  claim 8 , wherein the control module is further configured to maintain the preheat mode of the idle one of the first and second compressors in an off condition for a delay period and then reactivate the preheating mode for the idle one of the first and second compressors for the preheating time period following the delay period. 
     
     
         12 . The vapor cycle system of  claim 11 , wherein the preheating time period is approximately 14 minutes, and wherein the delay period is approximately 30 minutes. 
     
     
         13 . A method of operating a dual compressor vapor cycle system, the method comprising:
 operating a first compressor to compress refrigerant;   selectively activating a preheating mode of a second compressor connected in parallel with the first compressor to reduce migration of refrigerant, lubricant or a combination thereof from the first compressor to the second compressor, wherein the preheating mode comprises supplying power to an electric motor of the second compressor to generate heat, wherein the preheating mode is activated when the second compressor is idle;   controlling the preheating mode of the second compressor according to sensed motor temperature by default; and   limiting a duration of the preheating mode of the second compressor to a preheating time period to provide failsafe protection against overheating.   
     
     
         14 . The method of  claim 13 , wherein the preheating mode is controlled to maintain a sensed motor temperature within a range of approximately 48.9° C. (120° F.) to approximately 54.4° C. (130° F.). 
     
     
         15 . The method of  claim 13  and further comprising:
 maintaining the second compressor preheat mode in an off condition for a delay period; and 
 reactivating the preheating mode for the second compressor for the preheating time period following the delay period. 
 
     
     
         16 . The method of  claim 15 , wherein the preheating time period is approximately 14 minutes, and wherein the delay period is approximately 30 minutes. 
     
     
         17 . A method of operating a vapor cycle system having a compressor with an electric motor, the method comprising:
 sensing a motor temperature of the electric motor when the compressor idle;   determining if the motor temperature is below a lower temperature threshold;   when the motor temperature is below the lower temperature threshold, supplying current to the electric motor to generate heat while the compressor remains idle; and   ceasing to generate heat with the electric motor when the sensed motor temperature is above an upper temperature threshold.   
     
     
         18 . The method of  claim 17  and further comprising:
 activating the compressor when the motor temperature is above the lower temperature threshold and after ceasing to generate heat with the electric motor. 
 
     
     
         19 . The method of  claim 17 , wherein the lower temperature threshold is approximately 29.4° C. (85° F.), and wherein the upper temperature threshold is approximately 32.2° C. (90° F.). 
     
     
         20 . The method of  claim 17 , wherein the motor temperature is sensed by sensing resistance with a thermistor.