Method for controlling a vapour compression system connected to a smart grid

Abstract

A method for controlling operation of a vapour compression system ( 1 ) is provided, the vapour compression system ( 1 ) comprising two or more refrigeration entities, such as display cases. A signal representing a reference power consumption is received and compared to an actual power consumption of the vapour compression system ( 1 ). Based on the comparison, local controllers ( 3 ) calculate a setpoint temperature for a corresponding refrigeration entity, in order to obtain a power consumption which is equal to the reference power consumption. Each refrigeration entity is controlled in accordance with the calculated setpoint temperatures.

What is claimed is: 
     
         1 - 8 . (canceled) 
     
     
         9 . A method for controlling operation of a vapour compression system, the vapour compression system comprising one or more compressors, a heat rejecting heat exchanger unit, a central controller, and two or more refrigeration entities, each refrigeration entity comprising an expansion device, an evaporator, a refrigerated volume arranged at the evaporator and a local controller arranged to control operation of the refrigeration entity in order to maintain a setpoint temperature in the refrigerated volume, each local controller being arranged to communicate with the central controller, the method comprising the steps of:
 for each refrigeration entity, defining an upper temperature limit, T max , and a lower temperature limit, T min , where T min <T max ,   the central controller receiving a signal representing a reference power consumption of the vapour compression system,   the central controller comparing the reference power consumption to an actual power consumption of the vapour compression system,   the central controller communicating the result of said comparison to each of the local controllers,   each local controller calculating a setpoint temperature for the corresponding refrigerated volume, based on the result of the comparison, and in order to obtain a power consumption of the vapour compression system which is equal to the reference power consumption, the calculated setpoint temperature being limited to be within the interval T min  to T max , and   controlling operation of each refrigeration entity in accordance with the calculated setpoint temperatures.   
     
     
         10 . The method according to  claim 9 , wherein the step of comparing the reference power consumption to an actual power consumption of the vapour compression system comprises obtaining an error signal, e, and wherein the step of communicating the result of the comparison to each of the local controllers comprises communicating the error signal, e, to each of the local controllers. 
     
     
         11 . The method according to  claim 9 , wherein the step of calculating a setpoint temperature comprises calculating a setpoint adjustment, ΔT, and adding said setpoint adjustment, ΔT, to a nominal setpoint temperature, T 0 , thereby obtaining a calculated setpoint temperature, T ref =T 0 +ΔT. 
     
     
         12 . The method according to  claim 9 , wherein the step of calculating a setpoint temperature comprises decreasing a previous setpoint temperature in the case that the reference power consumption is higher than the actual power consumption of the vapour compression system, and increasing a previous setpoint temperature in the case that the reference power consumption is lower than the actual power consumption of the vapour compression system. 
     
     
         13 . The method according to  claim 9 , wherein the step of limiting the calculated setpoint temperature is performed using a saturation filter. 
     
     
         14 . The method according to  claim 9 , wherein the step of defining an upper temperature limit, T max , and a lower temperature limit, T min , comprises the steps of:
 obtaining a measure for a temperature of goods being stored in the refrigerated volume, and   calculating the upper temperature limit, T max , and the lower temperature limit, T min , on the basis of the obtained measure for a temperature of goods being stored in the refrigerated volume.   
     
     
         15 . The method according to  claim 9 , further comprising the steps of, for each refrigeration entity:
 calculating an error signal, e s , reflecting a difference between a calculated setpoint temperature and a limited setpoint temperature,   supplying the calculated error signal, e s , to the local controller, and   the local controller modifying the calculated setpoint temperature based on the calculated error signal, e s .   
     
     
         16 . The method according to  claim 10 , wherein the step of calculating a setpoint temperature comprises calculating a setpoint adjustment, ΔT, and adding said setpoint adjustment, ΔT, to a nominal setpoint temperature, T 0 , thereby obtaining a calculated setpoint temperature, T ref =T 0 +ΔT. 
     
     
         17 . The method according to  claim 10 , wherein the step of calculating a setpoint temperature comprises decreasing a previous setpoint temperature in the case that the reference power consumption is higher than the actual power consumption of the vapour compression system, and increasing a previous setpoint temperature in the case that the reference power consumption is lower than the actual power consumption of the vapour compression system. 
     
     
         18 . The method according to  claim 11 , wherein the step of calculating a setpoint temperature comprises decreasing a previous setpoint temperature in the case that the reference power consumption is higher than the actual power consumption of the vapour compression system, and increasing a previous setpoint temperature in the case that the reference power consumption is lower than the actual power consumption of the vapour compression system. 
     
     
         19 . The method according to  claim 10 , wherein the step of limiting the calculated setpoint temperature is performed using a saturation filter. 
     
     
         20 . The method according to  claim 11 , wherein the step of limiting the calculated setpoint temperature is performed using a saturation filter. 
     
     
         21 . The method according to  claim 12 , wherein the step of limiting the calculated setpoint temperature is performed using a saturation filter. 
     
     
         22 . The method according to  claim 10 , wherein the step of defining an upper temperature limit, T max , and a lower temperature limit, T min , comprises the steps of:
 obtaining a measure for a temperature of goods being stored in the refrigerated volume, and   calculating the upper temperature limit, T max , and the lower temperature limit, T min , on the basis of the obtained measure for a temperature of goods being stored in the refrigerated volume.   
     
     
         23 . The method according to  claim 11 , wherein the step of defining an upper temperature limit, T max , and a lower temperature limit, T min , comprises the steps of:
 obtaining a measure for a temperature of goods being stored in the refrigerated volume, and   calculating the upper temperature limit, T max , and the lower temperature limit, T min , on the basis of the obtained measure for a temperature of goods being stored in the refrigerated volume.   
     
     
         24 . The method according to  claim 12 , wherein the step of defining an upper temperature limit, T max , and a lower temperature limit, T min , comprises the steps of:
 obtaining a measure for a temperature of goods being stored in the refrigerated volume, and   calculating the upper temperature limit, T max , and the lower temperature limit, T min , on the basis of the obtained measure for a temperature of goods being stored in the refrigerated volume.   
     
     
         25 . The method according to  claim 13 , wherein the step of defining an upper temperature limit, T max , and a lower temperature limit, T min , comprises the steps of:
 obtaining a measure for a temperature of goods being stored in the refrigerated volume, and   calculating the upper temperature limit, T max , and the lower temperature limit, T min , on the basis of the obtained measure for a temperature of goods being stored in the refrigerated volume.   
     
     
         26 . The method according to  claim 10 , further comprising the steps of, for each refrigeration entity:
 calculating an error signal, e s , reflecting a difference between a calculated setpoint temperature and a limited setpoint temperature,   supplying the calculated error signal, e s , to the local controller, and   the local controller modifying the calculated setpoint temperature based on the calculated error signal, e s .   
     
     
         27 . The method according to  claim 11 , further comprising the steps of, for each refrigeration entity:
 calculating an error signal, e s , reflecting a difference between a calculated setpoint temperature and a limited setpoint temperature,   supplying the calculated error signal, e s , to the local controller, and   the local controller modifying the calculated setpoint temperature based on the calculated error signal, e s .   
     
     
         28 . The method according to  claim 12 , further comprising the steps of, for each refrigeration entity:
 calculating an error signal, e s , reflecting a difference between a calculated setpoint temperature and a limited setpoint temperature,   supplying the calculated error signal, e s , to the local controller, and   the local controller modifying the calculated setpoint temperature based on the calculated error signal, e s .