Fuzzy logic based controller for cooling and refrigerating systems

• US 5,440,891 A
• Filed: 01/26/1994
• Issued: 08/15/1995
• Est. Priority Date: 01/26/1994
• Status: Expired due to Term

• Current Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Original Assignee: James O. Hindmon Jr, Phillip G. Hindmon Sr
• Inventors: Hindmon, Phillip G. Sr., Hindmon, James O. Jr.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US08/187,448
• Time in Patent Office: 566 Days
• Field of Search: 62/175, 62/117, 62/229, 62/228.3, 62/213, 236/78 D
• US Class Current: 62/117
• CPC Class Codes: F25B 2400/075 with parallel compressors
• CPC Class Codes: F25B 2400/22 Refrigeration systems for supermarkets
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: F25B 2600/23 Time delays
• CPC Class Codes: F25B 49/022 Compressor control arrangements
• CPC Class Codes: F25B 5/02 arranged in parallel
• CPC Class Codes: F25B 6/04 arranged in series
• CPC Class Codes: F25D 21/008 by timer
• CPC Class Codes: G05B 13/0275 using fuzzy logic only
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A control system for controlling a plurality of compressors by means of fuzzy logic. Control is provided by selecting a combination of available compressors, which may include one or more fixed speed compressors and a variable speed compressor. The controller output signals are responsive to inputs monitoring either the pressures in the system'"'"'s refrigerant suctions lines, the temperatures of the refrigerated spaces, or where a plurality of evaporators are connected to a set of compressors, the temperature of the coldest refrigerated case, or a combination of the desired suction pressure and temperature of the refrigerated space. The output capacity of the system is chosen based on the degree of membership of each input variable as compared to the total for all inputs.

Claims

1. A refrigeration system control device using fuzzy logic for controlling a plurality of refrigeration compressors such that the closest capacity is selected to match the load to each of a plurality of evaporators comprising:

a control having an input adapted to be connected to a means to sense the temperature in the controlled space wherein a control signal is indicative of the maximum refrigeration load of the controlled space;

a means for determining whether the primary control variable in said space is above or below a single predetermined desired target;

a pressure sensing means connected to the refrigeration system in a manner which allows generating a signal responsive to the suction pressure of the refrigeration system;

a means for generating a signal indicative that the temperature in said space is above a predetermined high alarm setpoint or below a low alarm setpoint, said signal causing disconnect of said temperature control signal from the control device and allowing the control to use a signal from the pressure sensing means as the control signal;

a signal means to indicate that said controlled space is in defrost, such means causing disconnect of said temperature control signal from the control device and allowing the control to use a signal from the pressure sensing means as the control signal;

a timer having an adjustable timing interval based upon the error in the control signal of the device and the single predetermined desired target for that control signal and the rate of change of the control signal;

a selection means consisting of fuzzy logic rules and membership functions for determining, after said timer interval has elapsed, the closest combination of available compressors which will match the load;

an output being an electric signal adapted to selectively energize or de-energize said combination of the plurality of refrigeration compressors.

2. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity,

wherein applying said control algorithm comprises the steps of determining a first degree of membership for said measured temperature signal, determining a second degree of membership for said measured suction pressure signal, applying a plurality of operational rules to said first and second degrees of membership, and combining the output of said operational rules in a predetermined manner to obtain said output signals.

3. A method for controlling a refrigeration system as recited in claim 2, wherein said compressors comprise a plurality of fixed speed compressors, and wherein said output signals are operative for energizing a combination of said fixed speed compressors.

4. A method for controlling a refrigeration system as recited in claim 3, wherein said combination of said fixed speed compressors comprises the minimum closest capacity required to match the thermal load on said refrigeration system.

5. A method for controlling a refrigeration system as recited in claim 2, wherein said compressors comprise at least one fixed speed compressor and a variable speed compressor, and said output signals are operative for energizing and de-energizing said at least one fixed speed compressor, and for varying the speed of said variable speed compressor.

6. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

determining if said cooled space is in a defrost mode;

selecting said second operating mode if said cooled space is in said defrost mode;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity.

7. A method for controlling a refrigeration system as recited in claim 6, further comprising the steps of:

determining when said defrost mode is terminated; and

continuing to operate in said second operating mode until a predetermined period of time subsequent to the termination of said defrost mode has elapsed.

8. A method for controlling a refrigeration system as recited in claim 7, further comprising the step of selecting said fist operating mode after said predetermined period of time has elapsed.

9. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

establishing an upper temperature boundary and a lower temperature boundary;

determining if said measured temperature signal is within a range defined by said upper and lower temperature boundaries;

selecting said first operating mode if said measured temperature signal is within said range;

selecting said second operating mode if said measured temperature signal is not within said range;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity.

10. A method for controlling a refrigeration system as recited in claim 9, further comprising the steps of:

continuing to operate in said second operating mode until a predetermined period of time has elapsed; and

determining, at the end of said predetermined time period, whether said measured temperature signal is within said range.

11. A method for controlling a refrigeration system as recited in claim 10, further comprising the step of selecting said first operating mode if said measured temperature signal is within said range.

12. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a rate of change of said temperature and providing a rate of change signal to said controller;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal, said measured suction pressure signal, and said rate of change signal; and

providing output signals for operating said compressors at said desired capacity.

13. A method for controlling a refrigeration system as recited in claim 12, further comprising the step of determining an adjustable timing interval based on said rate of change signal and the difference between said measured temperature and said target temperature, and wherein said desired capacity is determined subsequent to the expiration of said timing interval.

14. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a rate of change of said suction pressure and providing a rate of change signal to said controller;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal, said measured suction pressure signal, and said rate of change signal; and

providing output signals for operating said compressors at said desired capacity.

15. A method for controlling a refrigeration system as recited in claim 14, further comprising the step of determining an adjustable timing interval based on said rate of change signal and the difference between said measured suction pressure and said target suction pressure, and wherein said desired capacity is determined subsequent to the expiration of said timing interval.

16. A refrigeration system controller for controlling a refrigeration system, said refrigeration system comprising a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising:

a temperature sensor for measuring the temperature of said cooled space and for providing a corresponding measured temperature signal to said controller;

a suction pressure sensor for measuring the suction pressure of said compressors and for providing a corresponding measured suction pressure signal to said controller; and

a control unit operative for

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a desired capacity of said compressors by applying a control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity,

wherein said control algorithm comprises the steps of determining a first degree of membership for said measured temperature signal, determining a second degree of membership for said measured suction pressure signal, applying a plurality of operational rules to said first and second degrees of membership, and combining the output of said operational rules in a predetermined manner to obtain said output signals.

17. A refrigeration system controller as recited in claim 16, wherein said compressors comprise a plurality of fixed speed compressors, and wherein said output signals are operative for energizing a combination of said fixed speed compressors.

18. A refrigeration system controller as recited in claim 17, wherein said combination of said fixed speed compressors comprises the minimum closest capacity required to match the thermal load on said refrigeration system.

19. A refrigeration system controller as recited in claim 16, wherein said compressors comprise at least one fixed speed compressor and a variable speed compressor, and said output signals are operative for energizing or de-energizing said at least one fixed speed compressor, and for varying the speed of said variable speed compressor.

20. A refrigeration system controller for controlling a refrigeration system, said refrigeration system comprising a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising:

a temperature sensor for measuring the temperature of said cooled space and for providing a corresponding measured temperature signal to said controller;

a suction pressure sensor for measuring the suction pressure of said compressors and for providing a corresponding measured suction pressure signal to said controller; and

a control unit operative for

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

determining if said cooled space is in a defrost mode;

selecting said second operating mode if said cooled space is in said defrost mode

determining a desired capacity of said compressors by applying a control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity.

21. A refrigeration system controller as recited in claim 20, wherein selecting said first or second operating mode further comprises the steps of:

determining when said defrost mode is terminated;

continuing to operate in said second operating mode until a predetermined period of time subsequent to the termination of said defrost mode has elapsed; and

selecting said fist operating mode after said predetermined period of time has elapsed.

22. A refrigeration system controller for controlling a refrigeration system, said refrigeration system comprising a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising:

a temperature sensor for measuring the temperature of said cooled space and for providing a corresponding measured temperature signal to said controller;

a suction pressure sensor for measuring the suction pressure of said compressors and for providing a corresponding measured suction pressure signal to said controller; and

a control unit operative for

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

establishing an upper temperature boundary and a lower temperature boundary;

determining if said measured temperature signal is within a range defined by said upper and lower temperature boundaries;

selecting said first operating mode if said measured temperature signal is within said range; and

selecting said second operating mode if said measured temperature signal is not within said range.

determining a desired capacity of said compressors by applying a control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity.

23. A refrigeration system controller as recited in claim 22, wherein selecting said first or second operative mode further comprises the steps of:

continuing to operate in said second operating mode until a predetermined period of time has elapsed;

determining, at the end of said predetermined time period, whether said measured temperature signal is within said range; and

selecting said first operating mode if said measured temperature signal is within said range.

24. A refrigeration system controller for controlling a refrigeration system, said refrigeration system comprising a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising:

a temperature sensor for measuring the temperature of said cooled space and for providing a corresponding measured temperature signal to said controller;

a suction pressure sensor for measuring the suction pressure of said compressors and for providing a corresponding measured suction pressure signal to said controller; and

a control unit operative for

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a rate of change of said temperature and providing a rate of change signal to said controller;

determining a desired capacity of said compressors by applying a control algorithm to said measured temperature signal, said measured suction pressure signal, and said rate of change signal; and

providing output signals for operating said compressors at said desired capacity.

25. A refrigeration system controller as recited in claim 24, wherein said control unit is further operative for determining an adjustable timing interval based on said rate of change signal and the difference between said measured temperature and said target temperature, and wherein said desired capacity is determined subsequent to the expiration of said timing interval.

26. A refrigeration system controller for controlling a refrigeration system, said refrigeration system comprising a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising:

a temperature sensor for measuring the temperature of said cooled space and for providing a corresponding measured temperature signal to said controller;

a suction pressure sensor for measuring the suction pressure of said compressors and for providing a corresponding measured suction pressure signal to said controller; and

a control unit operative for

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

determining a rate of change of said suction pressure and providing a rate of change signal to said controller;

determining a desired capacity of said compressors by applying a control algorithm to said measured temperature signal, said measured suction pressure signal, and said rate of change signal; and

providing output signals for operating said compressors at said desired capacity.

27. A refrigeration system controller as recited in claim 26, wherein said control unit is further operative for determining an adjustable timing interval based on said rate of change signal and the difference between said measured suction pressure and said target suction pressure, and wherein said desired capacity is determined subsequent to the expiration of said timing interval.

28. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

determining if said cooled space is in a defrost mode;

selecting said first operating mode if said cooled space is in said defrost mode;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal; and

providing output signals for operating said compressors at said desired capacity.

29. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

providing a temperature error by determining the difference between said measured temperature signal and said target temperature;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal, wherein the relationship between said desired capacity and said temperature error is non-linear; and

providing output signals for operating said compressors at said desired capacity.

30. A method for controlling a refrigeration system, said refrigeration system comprising a controller for implementing a control algorithm, a cooled space, an evaporator associated with said cooled space, and a plurality of compressors operatively connected to said evaporator, comprising the steps of:

measuring the temperature of said cooled space and providing a corresponding measured temperature signal to said controller;

measuring the suction pressure of said compressors and providing a corresponding measured suction pressure signal to said controller;

defining a first operating mode in which said controller attempts to maintain a target temperature in said cooled space by varying the cooling capacity of said compressors;

defining a second operating mode in which said controller attempts to maintain a target suction pressure by varying the cooling capacity of said compressors;

selecting said first operating mode or said second operating mode;

providing a suction pressure error by determining the difference between said measured suction pressure signal and said target suction pressure;

determining a desired capacity of said compressors by applying said control algorithm to said measured temperature signal and said measured suction pressure signal, wherein the relationship between said desired capacity and said suction pressure error is non-linear; and

providing output signals for operating said compressors at said desired capacity.

31. A refrigeration system control device using fuzzy logic for controlling a plurality of refrigeration compressors such that the closest capacity is selected to match the load to each of a plurality of evaporators comprising:

a control having an input adapted to be connected to a pressure sensing means to sense the suction pressure in a refrigeration system wherein a control signal is indicative of the refrigeration load of the controlled space;

a pressure sensing means connected to the refrigeration system in a manner which allows generating a signal responsive to the suction pressure of the refrigeration system;

a means for determining whether the suction pressure in said refrigeration system is above or below a single predetermined desired target;

a timer having an adjustable timing interval based upon the error in the said control signal of the device and the single predetermined desired target for that control signal and the rate of change of the control signal;

a selection means consisting of fuzzy logic rules and membership functions for determining, after said timer interval has elapsed, the closest combination of available compressors which will match the load;

an output being an electric signal adapted to selectively energize or deenergize said combination of the plurality of refrigeration compressors.

32. A refrigeration system control device using fuzzy logic for controlling a plurality of refrigeration compressors and one or more variable speed compressors such that the minimum closest capacity is selected to match the load to each of a plurality of evaporators comprising and an output means to vary the speed of the variable speed compressor until the load is precisely matched:

a control having an input adapted to be connected to a means to sense the temperature in the controlled space wherein a control signal is indicative of the maximum refrigeration load of the controlled space;

a means for determining whether the primary control variable in said space is above or below a single predetermined desired target;

a pressure sensing means connected to the refrigeration system in a manner which allows generating a signal responsive to the suction pressure of the refrigeration system;

a means for generating a signal indicative that the temperature in said space is above a predetermined high alarm setpoint or below a low alarm setpoint, said signal causing disconnect of said temperature control signal from the control device and allowing the control to use a signal from the pressure sensing means as the control signal;

a signal means to indicate that said controlled space is in defrost, such means causing disconnect of said temperature control signal from the control device and allowing the control to use a signal from the pressure sensing means as the control signal;

a timer having an adjustable timing interval based upon the error in the control signal of the device and the single predetermined desired target for that control signal and the rate of change of the control signal;

a selection means consisting of fuzzy logic rules and membership functions for determining, after said timer interval has elapsed, the minimum capacity combination of available compressors which will match the load;

a means for generating a signal indicative of the required speed of said variable speed compressor;

an output being an electric signal adapted to selectively energize or deenergize said combination of the plurality of refrigeration compressors;

an output being an electric signal adapted to control the speed through an external means of said variable speed compressor.

33. A refrigeration system control device using fuzzy logic for controlling a plurality of refrigeration compressors and one or more variable speed compressors such that the minimum closest capacity is selected to match the load to each of a plurality of evaporators comprising and an output means to vary the speed of the variable speed compressor until the load is precisely matched:

a control having an input adapted to be connected to a pressure sensing means to sense the suction pressure in a refrigeration system wherein a control signal is indicative of the refrigeration load of the controlled space;

a pressure sensing means connected to the refrigeration system in a manner which allows generating a signal responsive to the suction pressure of the refrigeration system;

a means for determining whether the suction pressure in said refrigeration system is above or below a single predetermined desired target;

a timer having an adjustable timing interval based upon the error in the said control signal of the device and the single predetermined desired target for that control signal and the rate of change of the control signal;

a timer having an adjustable timing interval based upon the error in the control signal of the device and the single predetermined desired target for that control signal and the rate of change of the control signal;

a selection means consisting of fuzzy logic rules and membership functions for determining, after said timer interval has elapsed, the minimum capacity combination of available compressors which will match the load;

a means for generating a signal indicative of the required speed of said variable speed compressor;

an output being an electric signal adapted to selectively energize or deenergize said combination of the plurality of refrigeration compressors;

an output being an electric signal adapted to control the speed through an external means of said variable speed compressor.