System and method for map-interpolation based control of ejectors in an ejector refrigeration circuit

Abstract

A system for map-interpolation based control of ejectors in an ejector refrigeration circuit includes a controller coupled to each of the ejectors and adapted to generate maps based on predefined conditions. The controller identifies a first map associated with a first temperature of a heat rejecting heat exchanger and a second map associated with a second temperature of the heat rejecting heat exchanger. The controller predicts an opening percentage of the first ejector from at least one of opening percentages indicated in the first map and opening percentages indicated in the second map. Finally, the controller adjusts the opening percentage of the first ejector based on the predicted opening percentage.

We claim: 
     
         1 . A system for map-interpolation based control of a plurality of ejectors in an ejector refrigeration circuit, the system comprising:
 a plurality of ejectors, each of the plurality of ejectors having a primary high pressure input port, a secondary low pressure input port, and an output port; and   a controller coupled to each of the plurality of ejectors, the controller adapted to:
 generate a plurality of maps based on a set of predefined conditions, each of the plurality of maps associated with a corresponding temperature of a heat rejecting heat exchanger; 
 identify a first map from the plurality of maps associated with a first temperature of the heat rejecting heat exchanger and an input signal indicative of a flow rate of a refrigerant fluid through the first ejector; 
 identify a second map from the plurality of maps associated with a second temperature of the heat rejecting heat exchanger; 
 predict an opening percentage of the first ejector from at least one of a plurality of opening percentages indicated in the first map and a plurality of opening percentages indicated in the second map; and 
 adjust the opening percentage of the first ejector based on the predicted opening percentage. 
   
     
     
         2 . The system according to  claim 1 , wherein predicting the opening percentage comprises:
 identifying a first opening percentage from the plurality of opening percentages indicated in the first map and a second opening percentage from the plurality of opening percentages indicated in the second map;   performing a linear interpolation to fit a line between the identified first opening percentage and the identified second opening percentage;   identifying a slope of the line as a rate-of-change of the flow rate of the refrigerant fluid through the first ejector; and   predicting the opening percentage at which the first ejector is to be maintained based on interpolation of the identified slope when the heat rejecting heat exchanger is at an intermediate temperature between the first temperature and the second temperature.   
     
     
         3 . The system according to  claim 1 , wherein each of the plurality of maps indicates a rate of change of the flow rate of the refrigerant fluid through each of the plurality of ejectors based on a change in the opening percentage of each of the plurality of ejectors during the corresponding temperature of the heat rejecting heat exchanger. 
     
     
         4 . The system according to  claim 1 , wherein each of the plurality of maps comprises a plurality of stages and the opening percentage of at least the first ejector from the plurality of ejectors is greater than zero in each of the plurality of stages. 
     
     
         5 . The system according to  claim 4 , wherein the plurality of stages comprises at least:
 a first stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector equals zero;   a second stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector and a second ejector equals zero; and   a third stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector, the second ejector, and a third ejector equals zero.   
     
     
         6 . The system according to  claim 5 , wherein when transitioning between the plurality of stages of a first map, the controller is further configured to:
 perform an extrapolation to fit a line to the plurality of opening percentages lying within a predefined hysteresis band indicated in the first map;   identify a slope of the line as a rate-of-change of the flow rate of the refrigerant fluid through the first ejector; and   predict the opening percentage at which the plurality of ejectors is to be maintained based on interpolation of the identified slope.   
     
     
         7 . The system according to  claim 1 , wherein the set of predefined conditions comprises:
 the opening percentages of the plurality of ejectors increase within a stage;   when switching between the plurality of stages of each of the plurality of maps, the opening percentages of the plurality of ejectors are adjusted to keep the flow rate of the refrigerant fluid constant;   when switching between the plurality of stages of each of the plurality of maps, the opening percentages of the plurality of ejectors are greater than zero; and   a flow rate of the refrigerant fluid through the secondary low pressure input port of each of the plurality of ejectors is greater than zero.   
     
     
         8 . The system according to  claim 1 , wherein the plurality of ejectors are controllable variable ejectors connected in a parallel configuration. 
     
     
         9 . The system according to  claim 1 , wherein the ejector refrigeration circuit comprises:
 a high pressure ejector circuit comprising in a direction of flow of a circulating refrigerant:
 the heat rejecting heat exchanger having an inlet side and an outlet side; 
 the plurality of ejectors, each of the plurality of ejectors having the primary high pressure input port, the secondary low pressure input port, and the output port, wherein the primary high pressure input port is in fluid communication with the outlet side of the heat rejecting heat exchanger; 
 a receiver, having an inlet, a liquid outlet, and a gas outlet, the inlet in fluid communication with the output port of each of the plurality of ejectors; 
 at least one compressor having an inlet side and an outlet side, the inlet side of the at least one compressor in fluid communication with the gas outlet of the receiver and the outlet side of the at least one compressor in fluid communication with the inlet side of the heat rejecting heat exchanger; and 
   a refrigerating evaporator flow path comprising in the direction of flow of the circulating refrigerant:
 a liquid pump having an inlet side and an outlet side, the inlet side in fluid communication with the liquid outlet of the receiver; 
 at least one refrigeration expansion device having an inlet side and an outlet side, the inlet side of the at least one refrigeration expansion device in fluid communication with the outlet side of the liquid pump; and 
 at least one refrigeration evaporator having an inlet side and an outlet side, the inlet side in fluid communication with the outlet side of the at least one refrigeration expansion device and the outlet side in fluid communication with the secondary low pressure input port of each of the plurality of ejectors. 
   
     
     
         10 . The system according to  claim 9 , wherein the liquid pump comprises a bypass-line having a switchable bypass valve for allowing refrigerant to selectively bypass the liquid pump by opening the switchable bypass valve. 
     
     
         11 . A method for map-interpolation based control of a plurality of ejectors in an ejector refrigeration circuit, the method comprising:
 generating, via a controller, a plurality of maps based on a set of predefined conditions, each of the plurality of maps associated with a corresponding temperature of a heat rejecting heat exchanger;   identifying, via the controller, a first map from the plurality of maps associated with a first temperature of the heat rejecting heat exchanger and an input signal indicative of a flow rate of a refrigerant fluid through the first ejector; and   identifying, via the controller, a second map from the plurality of maps associated with a second temperature of the heat rejecting heat exchanger;   predicting, via the controller, an opening percentage of the first ejector from at least one of a plurality of opening percentages indicated in the first map and a plurality of opening percentages indicated in the second map; and   adjusting, via the controller, the opening percentage of the first ejector based on the predicted opening percentage.   
     
     
         12 . The method according to  claim 11 , wherein predicting the opening percentage comprises:
 identifying a first opening percentage from the plurality of opening percentages indicated in the first map and a second opening percentage from the plurality of opening percentages indicated in the second map;   performing a linear interpolation to fit a line between the identified first opening percentage and the identified second opening percentage;   identifying a slope of the line as a rate-of-change of the flow rate of the refrigerant fluid through the first ejector; and   predicting the opening percentage at which the first ejector is to be maintained based on interpolation of the identified slope when the heat rejecting heat exchanger is at an intermediate temperature between the first temperature and the second temperature.   
     
     
         13 . The method according to  claim 11 , wherein each of the plurality of maps indicates a rate of change of the flow rate of the refrigerant fluid through each of the plurality of ejectors based on a change in the opening percentage of each of the plurality of ejectors during the corresponding temperature of the heat rejecting heat exchanger. 
     
     
         14 . The method according to  claim 13 , wherein each of the plurality of maps comprises a plurality of stages and the opening percentage of at least the first ejector from the plurality of ejectors is greater than zero in each of the plurality of stages. 
     
     
         15 . The method according to  claim 13 , wherein the plurality of stages comprises at least:
 a first stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector equals zero;   a second stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector and a second ejector equals zero; and   a third stage, wherein the opening percentage of the plurality of ejectors excluding the first ejector, the second ejector, and a third ejector equals zero.   
     
     
         16 . The method according to  claim 15 , wherein when transitioning between the plurality of stages of a first map, the controller is further configured to:
 perform an extrapolation to fit a line to the plurality of opening percentages lying within a predefined hysteresis band indicated in the first map;   identify a slope of the line as a rate-of-change of the flow rate of the refrigerant fluid through the first ejector; and   predict the opening percentage at which the plurality of ejectors is to be maintained based on interpolation of the identified slope.   
     
     
         17 . The method according to  claim 11 , wherein the set of predefined conditions comprise:
 the opening percentages of the plurality of ejectors increase within a stage;   when switching between the plurality of stages of each of the plurality of maps, the opening percentages of the plurality of ejectors are adjusted to keep the flow rate of the refrigerant fluid constant;   when switching between the plurality of stages of each of the plurality of maps, the opening percentages of the plurality of ejectors are greater than zero; and   a flow rate of the refrigerant fluid through a secondary low pressure input port of each of the plurality of ejectors is greater than zero.   
     
     
         18 . The method according to  claim 11 , wherein each of the plurality of ejectors comprise a primary high pressure input port, a secondary low pressure input port, and an output port. 
     
     
         19 . The method according to  claim 11 , wherein the ejector refrigeration circuit comprises:
 a high pressure ejector circuit comprising in the direction of flow of a circulating refrigerant:
 the heat rejecting heat exchanger having an inlet side and an outlet side; 
 the plurality of ejectors, each of the plurality of ejectors having the primary high pressure input port, the secondary low pressure input port, and the output port, wherein the primary high pressure input port is in fluid communication with the outlet side of the heat rejecting heat exchanger; 
 a receiver, having an inlet, a liquid outlet, and a gas outlet, the inlet in fluid communication with the output port of each of the plurality of ejectors; 
 at least one compressor having an inlet side and an outlet side, the inlet side of the at least one compressor in fluid communication with the gas outlet of the receiver and the outlet side of the at least one compressor in fluid communication with the inlet side of the heat rejecting heat exchanger; and 
   a refrigerating evaporator flow path comprising in the direction of flow of the circulating refrigerant:
 a liquid pump having an inlet side and an outlet side, the inlet side in fluid communication with the liquid outlet of the receiver; 
 at least one refrigeration expansion device having an inlet side and an outlet side, the inlet side of the at least one refrigeration expansion device in fluid communication with the outlet side of the liquid pump; and 
 at least one refrigeration evaporator having an inlet side and an outlet side, the inlet side in fluid communication with the outlet side of the at least one refrigeration expansion device and the outlet side in fluid communication with the secondary low pressure input port of each of the plurality of ejectors. 
   
     
     
         20 . The method according to  claim 19 , wherein the liquid pump comprises a bypass-line including a switchable bypass valve allowing refrigerant to selectively bypass the liquid pump by opening the switchable bypass valve.