Enthalpy based control for a refrigeration appliance

1. A method of operating a refrigerator appliance comprising a variable speed compressor, the steps comprising:

receiving a set point temperature T i-sp for a component of the appliance;

measuring the temperature T i of the component;

calculating an excess enthalpy H i of the component from the steps of receiving and measuring;

determining an instantaneous cooling capacity required C ap to reduce the excess enthalpy H i to zero within a selected time period T s ; and

calculating a compressor speed that delivers at least the instantaneous cooling capacity required C ap while minimizing power consumption of the compressor;

operating the variable speed compressor at the determined compressor speed.

2. A method of operating a refrigerator appliance as in claim 1 , wherein:

the step of receiving further comprises receiving the set point temperatures T i-SP for multiple components of the appliance;

the step of measuring further comprises measuring the temperatures T i for multiple components of the appliance;

the step of calculating an excess enthalpy H i further comprises calculating the excess enthalpy H i for each of the multiple components of the appliance; and wherein the method of operating a refrigerator appliance further comprises

calculating the total excess enthalpy H of the appliance from the excess enthalpy H i determined for the multiple components of the appliance.

3. A method of operating a refrigerator appliance as in claim 1 , wherein the multiple components of the appliance comprise a fresh food compartment and a freezer compartment.

4. A method of operating a refrigerator appliance as in claim 3 , wherein the excess enthalpies H i for the freezer compartment and fresh food compartment are calculated based on a mass of air in the freezer compartment and a mass of air in the fresh food compartment.

5. A method of operating a refrigerator appliance as in claim 1 , wherein the step of calculating a compressor speed further comprises applying a regression analysis of the compressor cooling capacity to calculate the compressor speed.

6. A method of operating a refrigerator appliance as in claim 1 , wherein the step of determining comprises using a proportional-integral controller that is based on a linear model of the refrigerator appliance.

7. A method of operating a refrigerator appliance as in claim 6 , wherein the step of determining further comprises:

receiving a desired settling time; and

using a proportional-integral controller that calculates a proportional constant k p and an integral constant k i using the following relationship:

ω

n

=

4

ζ

⁢

⁢

t

s

where

ω n is a natural frequency,

ζ is a damping ratio, and

t s is the desired settling time.

8. A method of operating a refrigerator appliance as in claim 7 , wherein the step of determining further comprises using the proportional-integral controller in which the proportional constant k p is determined using the following relationship:

k p =2ζω n

9. A method of operating a refrigerator appliance as in claim 8 , wherein the step of determining further comprises using the proportional integral controller in which the integral constant k i is determined using the following relationship:

k i =k p 2 +2(1−ζ) 2 ω n 2

10. A method of operating a refrigerator appliance as in claim 9 , wherein the desired settling time t s is in the range of about 0.5 hours to about 2 hours.

11. A method of operating a refrigerator appliance as in claim 7 , wherein the desired settling time t s is in the range of about 1 hour to about 2 hours.

12. A method of operating a refrigerator appliance as in claim 1 , further comprising the step of setting the speed of the compressor based on results from the step of calculating a compressor speed.

13. A refrigerator appliance, comprising:

at least one component that is configured for cooling during operation of the appliance;

a refrigeration loop configured for providing cooling to the component during operation of the appliance, the refrigeration loop comprising

one or more evaporators;

one or more condensers;

a variable speed compressor;

one or more expansion devices;

at least one temperature sensor configured for providing temperature measurement of the component;

one or more controllers configured for

receiving at least one temperature measurement from the temperature sensor;

calculating an excess enthalpy of the component using the at least one temperature measurement and a temperature set point;

determining an instantaneous cooling capacity required Cap to reduce the excess enthalpy to a predetermined minimum value H PMV within a predetermined time period t s ; and

ascertaining a compressor speed S c that delivers at least the instantaneous cooling capacity required Cap while reducing the power consumption of the compressor,

operating the variable speed compressor substantially at compressor speed S c .

14. A refrigerator appliance as in claim 13 , wherein predetermined value H PMV is zero.

15. A refrigerator appliance as in claim 13 , wherein said at least one component comprises a compartment of the appliance, and wherein the excess enthalpy for the compartment is calculated based on a mass of air in the compartment.

16. A refrigerator appliance as in claim 13 , wherein said one or more controllers are further configured to apply a regression analysis of cooling capacity of the compressor in ascertaining the compressor speed.

17. A refrigerator appliance as in claim 13 , wherein said one or more controllers comprise a proportional-integral controller that is configured with a linear model of the refrigerator appliance.

18. A refrigerator appliance as in claim 17 , wherein the proportional integral controller is further configured to apply a proportional constant k p and an integral constant k i that are determined using the following relationship:

ω

n

=

4

ζ

⁢

⁢

ts

where

ω n is a natural frequency,

ζ is a damping ratio, and

t s is the predetermined time period.

19. A refrigerator appliance as in claim 18 , wherein the proportional constant k p is determined using the following relationship:

k p =2ζω n

20. A refrigerator appliance as in claim 19 , wherein the integral constant k i is determined using the following relationship:

k i =k p 2 +2(1−ζ) 2 ω n 2 .