Expansion Valve Position Control Systems And Methods

Abstract

A system includes a load module, a comparison module and a control module. The load module is configured to determine a current load of a compressor. The comparison module is configured to compare the current load to a previous load of the compressor to generate a comparison signal based on the comparison. The control module is configured to generate (i) a first control signal based on a superheat value of the compressor, and (ii) a second control signal based on the current load and the previous load. The control module is configured to, based on the comparison signal, control a position of an expansion valve according to either the first control signal or the second control signal.

What is claimed is: 
     
         1 . A system comprising:
 a load module configured to determine a current load of a compressor;   a comparison module configured to compare the current load to a previous load of the compressor to generate a comparison signal based on the comparison; and   a control module configured to generate (i) a first control signal based on a superheat value of the compressor, and (ii) a second control signal based on the current load and the previous load,   wherein the control module is configured to, based on the comparison signal, control a position of an expansion valve according to either the first control signal or the second control signal.   
     
     
         2 . The system of  claim 1 , wherein the control module is configured to control the position of the expansion valve according to the second control signal in response to the comparison signal being greater than a predetermined threshold. 
     
     
         3 . The system of  claim 2 , wherein the control module is configured to control the position of the expansion valve according to the first control signal in response to the comparison signal being less than or equal to the predetermined threshold. 
     
     
         4 . The system of  claim 2 , further comprising a timer module configured to compare a value of a timer to a predetermined time, wherein the control module is configured to (i) determine the previous load and then start the timer, and (ii) determine the current load when the timer value is equal to the predetermined time. 
     
     
         5 . The system of  claim 1 , wherein the control module is configured to default to controlling the position of the expansion valve according to the first control signal and controls the position of the expansion valve according to the second control signal when the change in the load is greater than a predetermined threshold. 
     
     
         6 . The system of  claim 1 , wherein the first control signal is at least one of a proportional, integral, and derivative control signal. 
     
     
         7 . The system of  claim 1 , wherein the control module is configured to generate the first control signal based on a superheat setpoint,
 wherein the control module is configured to determine the superheat value based on (i) a suction temperature of the compressor, and (ii) a suction pressure of the compressor.   
     
     
         8 . The system of  claim 1 , wherein the control module is configured to generate the second control signal based on a ratio between the current load and the previous load. 
     
     
         9 . The system of  claim 1 , wherein the control module is configured to generate the second control signal based on a previous version of the second control signal. 
     
     
         10 . The system of  claim 9 , wherein the control module is configured to generate the second control signal based on a first input constant, a ratio of the current load and the previous load, and a second input constant. 
     
     
         11 . A system comprising:
 a load module configured to detect a change in a load of a compressor; and   a control module configured to generate (i) a proportional, integral, derivative (PID) control signal based on a superheat value of the compressor, and (ii) an expansion valve control signal based on the change in the load,   wherein the control module is configured to, in response to the change in the load, transition from controlling a position of an expansion valve according to the PID control signal to controlling the position of the expansion valve according to the expansion valve control signal.   
     
     
         12 . The system of  claim 11 , wherein the control module is configured to default to controlling the position of the expansion valve according to the PID control signal and controls the position of the expansion valve according to the expansion valve control signal when the change in the load is greater than a predetermined threshold. 
     
     
         13 . The system of  claim 11 , wherein the control module is configured to generate the expansion valve control signal based on a ratio between the load and a previous load of the compressor. 
     
     
         14 . The system of  claim 11 , wherein the control module is configured to generate the expansion valve control signal based on a previous version of the expansion valve control signal. 
     
     
         15 . The system of  claim 14 , wherein the control module is configured to generate the expansion valve control signal based on multiplication of (i) a first input constant, (ii) the previous version of the expansion valve control signal, and (iii) a ratio of the load and a previous load to an exponential input constant. 
     
     
         16 . A method comprising:
 determining a current load of a compressor;   comparing the current load to a previous load of the compressor;   generating a comparison signal based on the comparison; and   based on the comparison signal, either
 generating a first control signal based on a superheat value of the compressor and controlling a position of an expansion valve according to the first control signal, or 
 generating a second control signal based on the current load and the previous load and controlling the position of the expansion valve according to the second control signal. 
   
     
     
         17 . The method of  claim 16 , further comprising controlling the position of the expansion valve according to:
 the second control signal in response to the comparison signal being greater than a predetermined threshold; and   the first control signal in response to the comparison signal being less than or equal to the predetermined threshold.   
     
     
         18 . The method of  claim 16 , further comprising:
 controlling the position of the expansion valve according to the first control signal and not the second control signal when the change in the load is less than or equal to a predetermined threshold; and   controlling the position of the expansion valve according to the second control signal and not the first control signal when the change in the load is greater than the predetermined threshold.   
     
     
         19 . The method of  claim 16 , further comprising generating the second control signal based on:
 a ratio between the current load and the previous load of the compressor; and   a previous version of the second control signal.   
     
     
         20 . The method of  claim 16 , further comprising:
 generating the first control signal based on a superheat setpoint;   determining the superheat value based on (i) a suction temperature of the compressor, and (ii) a suction pressure of the compressor; and   generating the second control signal based on a previous position of the expansion valve and a ratio of the current load and the previous load.