Adaptive control for a refrigeration system using pulse width modulated duty cycle scroll compressor

• US 6,047,557 A
• Filed: 09/29/1997
• Issued: 04/11/2000
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Emerson Climate Technologies Incorporated (Emerson Electric Company)
• Original Assignee: Copeland Corporation LLC (Emerson Electric Company)
• Inventors: Pham, Hung M., Caillat, Jean-Luc M., Singh, Abtar, Bass, Mark
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US08/939,779
• Time in Patent Office: 925 Days
• Field of Search: 62/228.5, 62/126, 62/127, 62/129, 62/196.1, 62/196.2, 62/196.3, 62/203, 62/204, 62/228.3, 62/229, 236/1 EA
• US Class Current: 62/228.5
• CPC Class Codes: A47F 3/04 air-conditioned, refrigerated refrigerators F25D; heating arrangements specially adapted for transparent or reflecting areas H05B3/84
• CPC Class Codes: F04C 18/0215 where only one member is moving
• CPC Class Codes: F04C 2270/015 Controlled or regulated
• CPC Class Codes: F04C 2270/86 Detection
• CPC Class Codes: F04C 23/008 Hermetic pumps
• CPC Class Codes: F04C 27/005 Axial sealings for working fluid
• CPC Class Codes: F04C 28/00 Control of, monitoring of, or safety arrangements for, pumps or pumping installations specially adapted for elastic fluids
• CPC Class Codes: F04C 28/02 specially adapted for several pumps connected in series or in parallel
• CPC Class Codes: F04C 28/06 specially adapted for stopping, starting, idling or no-load operation
• CPC Class Codes: F04C 28/08 characterised by varying the rotational speed
• CPC Class Codes: F04C 28/22 by changing the eccentricity between cooperating members
• CPC Class Codes: F04C 28/265 being obtained by displacing a lateral sealing face
• CPC Class Codes: F04C 28/28 Safety arrangements; Monitoring
• CPC Class Codes: F25B 1/04 with compressor of rotary type F25B1/005, F25B1/10 take precedence
• CPC Class Codes: F25B 2400/22 Refrigeration systems for supermarkets
• CPC Class Codes: F25B 2600/0261 external to the compressor
• CPC Class Codes: F25B 2700/193 of the compressor
• CPC Class Codes: F25B 2700/1933 Suction pressures
• CPC Class Codes: F25B 2700/2106 of fresh outdoor air
• CPC Class Codes: F25B 2700/2117 of an evaporator
• CPC Class Codes: F25B 2700/21174 : of the refrigerant at the inlet of the evaporator
• CPC Class Codes: F25B 2700/21175 : of the refrigerant at the outlet of the evaporator
• CPC Class Codes: F25B 41/22 : between evaporator and compressor
• CPC Class Codes: F25B 41/35 : by rotary motors, e.g. by stepping motors
• CPC Class Codes: F25B 49/005 : of safety devices F25B49/02 and F25B49/04 take precedence
• CPC Class Codes: F25B 49/022 : Compressor control arrangements
• CPC Class Codes: F25B 5/02 : arranged in parallel
• CPC Class Codes: G05D 23/1909 : whose output amplitude can only take two discrete values
• CPC Class Codes: Y02B 30/70 : Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A control for a refrigeration system serviced by a special pulse width modulated compressor coupled to a condenser and evaporator. The system can be of the distributed type wherein the condenser and compressor may be coupled to service a group of adjacent refrigeration cases, wherein each case would have its own evaporator. A controller is coupled to a load sensor for producing a variable duty cycle control signal in which the duty cycle is a function of demand for cooling. Moreover, fuzzy logic techniques may be utilized in order to provide self adaptive tuning control for the system.

Claims

1. A compressor control system, comprising:

a compressor that is selectively operable while energized in at least two states, said compressor comprising a pair of fluid compressing members and including a first state corresponding to a first capacity wherein said pair of fluid compressing members are separated by a seal and a second state corresponding to a second capacity lower than said first capacity wherein said seal between said pair of fluid compressing members is broken;

a load sensor for sensing a property indicative of demand for cooling;

a controller coupled to said load sensor for producing a variable duty cycle control signal in which the duty cycle is a function of demand for cooling;

said controller being coupled to said compressor for causing said compressor to selectively alternate between said first and second states in response to said variable duty cycle control signal, thereby adjusting the capacity of said compressor to the demand for cooling while said compressor is energized.

2. The control system of claim 1 wherein said compressor pumps a refrigerant under pressure and wherein said controller produces said variable duty cycle control signal with a variable cycle time that is a function of fluctuations in refrigerant pressure.

3. The control system of claim 1 wherein said load sensor is a temperature sensor.

4. The control system of claim 1 further comprising pressure sensor coupled to said controller.

5. The control system of claim 1 wherein said load sensor is a temperature sensor and further comprising pressure sensor coupled to said controller.

6. The control system of claim 1 wherein said load sensor senses a property having a first rate of change and wherein said control system further comprising second load sensor that senses a second property having a second rate of change, said second rate of change being substantially greater than said first rate of change.

7. The control system of claim 6 wherein said load sensor senses changes in temperature and wherein said second load sensor senses changes in pressure.

8. The control system of claim 1 wherein said compressor includes fluid compressing members and mechanism for selectively rendering said compressing members effective and ineffective to thereby assume said first state and said second state, respectively.

9. The control system of claim 1 wherein said compressor includes an electric motor and wherein said compressor is configured such that said electric motor remains energized in said first and second states.

10. The control system of claim 1 wherein said compressor has two mechanical elements separated by a seal, said mechanical elements being movable relative to one another to develop fluid pressure and wherein said compressor includes mechanism to selectively break said seal in response to said control signal to thereby alter said fluid pressure developed while allowing said mechanical elements to maintain substantially constant relative movement with one another.

11. The control system of claim 1 wherein said compressor is a scroll compressor.

12. The control system of claim 10 wherein said compressor is a scroll compressor and said two mechanical elements are scroll members.

13. The compressor control system of claim 1 wherein controller provides said variable duty cycle control signal that cycles at a cycle time shorter than the time constant of the load.

14. The compressor control system of claim 1 wherein said first state is substantially at one hundred percent capacity and wherein said second state is substantially at zero percent capacity.

15. The compressor control system of claim 1 further comprising:

a diagnostic module coupled to said controller for monitoring and comparing said duty cycle with at least one predetermined fault value indicative of a system fault condition; and

an alert module responsive to said diagnostic module for issuing an alert signal when said duty cycle bears a predetermined relationship to said fault value.

16. A refrigeration system comprising,

a refrigeration case;

an evaporator disposed in said case;

a condenser and compressor coupled in fluid communication with said evaporator;

said condenser being disposed on said case and having means for transferring heat to ambient;

said compressor comprising a pulse width modulated variable capacity compressor;

a load sensor disposed in said case;

a controller responsive to said load sensor and coupled to said compressor for providing a variable duty cycle control signal to said compressor for modulating said compressor between a sealed state and an unsealed state to thereby adjust the operating capacity of the refrigeration system to its thermal load.

17. The refrigeration system of claim 16 further comprising a second refrigeration case having a second evaporator disposed therein, said second evaporator being coupled in fluid communication with said condenser.

18. The refrigeration system of claim 16 further comprising a second refrigeration case having a second evaporator disposed therein, said second evaporator being coupled in fluid communication with said compressor.

19. The refrigeration system of claim 16 wherein said load sensor is a temperature sensor.

20. The refrigeration system of claim 16 wherein said controller produces said variable duty cycle control signal with a variable cycle time that is a function of fluctuations in pressure.

21. The refrigeration system of claim 16 further comprising pressure sensor coupled to said controller.

22. The refrigeration system of claim 16 further comprising refrigerant regulator valve coupled in fluid communication with said evaporator and being electrically controlled by said variable duty cycle control signal to further adjust the capacity of said refrigeration system.

23. The refrigeration system of claim 22 wherein said valve includes a stepper motor.

24. The compressor control system of claim 16 wherein controller provides said variable duty cycle control signal that cycles at a cycle time shorter than the time constant of the load.

25. The compressor control system of claim 16 wherein said first state is substantially at one hundred percent capacity and wherein said second state is substantially at zero percent capacity.

26. A cooling system comprising,

a housing;

an evaporator disposed in said housing;

a condenser and compressor coupled in fluid communication with said evaporator;

said condenser being disposed on said housing and having means for transferring heat to ambient;

said compressor comprising a pulse width modulated variable capacity compressor;

a load sensor disposed in said case;

a controller responsive to said load sensor and coupled to said compressor for providing a variable duty cycle control signal to said compressor for modulating said compressor between a sealed state and an unsealed state to thereby adjust the operating capacity of the cooling system to its thermal load.

27. The cooling system of claim 26 further comprising a second housing having a second evaporator disposed therein, said second evaporator being coupled in fluid communication with said condenser.

28. The cooling system of claim 26 further comprising a second housing having a second evaporator disposed therein, said second evaporator being coupled in fluid communication with said compressor.

29. The cooling system of claim 26 wherein said load sensor is a temperature sensor.

30. The cooling system of claim 26 wherein said controller produces said variable duty cycle control signal with a variable cycle time that is a function of fluctuations in pressure.

31. The cooling system of claim 26 further comprising pressure sensor coupled to said controller.

32. The cooling system of claim 26 further comprising refrigerant regulator valve coupled in fluid communication with said evaporator and being electrically controlled by said variable duty cycle control signal to further adjust the capacity of said refrigeration system.

33. The compressor control system of claim 26 wherein said first state is substantially at one hundred percent capacity and wherein said second state is substantially at zero percent capacity.

34. A compressor control system, comprising:

a compressor that is selectively operable in at least two states, said compressor comprising a pair of fluid compressing members and including a first state corresponding to a first capacity wherein said pair of fluid compressing members are separated by a seal and a second state corresponding to a second capacity lower than said first capacity wherein said seal between said pair of fluid compressing members is broken;

a load sensor for sensing a property indicative of demand for cooling;

a controller coupled to said load sensor for producing a control signal that cycles based on said sensed property and at a cycle time shorter than the time constant of the load;

said controller being coupled to said compressor for causing said compressor to selectively alternate between said first and second states in response to said control signal such that the cumulative effect of said selective alternation adjusts the capacity of said compressor to the demand for cooling.

35. The control system of claim 34 wherein said control signal is a variable duty cycle control signal and wherein said duty cycle is varied in response to said sensed property.

36. The control system of claim 34 wherein said compressor pumps a refrigerant under pressure and wherein said controller produces said control signal with a variable cycle time that is a function of fluctuations in refrigerant pressure.

37. The control system of claim 34 wherein said load sensor is a temperature sensor.

38. The control system of claim 34 further comprising pressure sensor coupled to said controller.

39. The control system of claim 34 wherein said load sensor is a temperature sensor and further comprising pressure sensor coupled to said controller.

40. The control system of claim 34 wherein said load sensor senses a property having a first rate of change and wherein said control system further comprising second load sensor that senses a second property having a second rate of change, said second rate of change being substantially greater than said first rate of change.

41. The control system of claim 40 wherein said load sensor senses changes in temperature and wherein said second load sensor senses changes in pressure.

42. The control system of claim 34 wherein said compressor includes fluid compressing members and mechanism for selectively rendering said compressing members effective and ineffective to thereby assume said first state and said second state, respectively.

43. The control system of claim 34 wherein said compressor includes an electric motor and wherein said compressor is configured such that said electric motor remains energized in said first and second states.

44. The control system of claim 34 wherein said compressor has two mechanical elements separated by a seal, said mechanical elements being movable relative to one another to develop fluid pressure and wherein said compressor includes mechanism to selectively break said seal in response to said control signal to thereby alter said fluid pressure developed while allowing said mechanical elements to maintain substantially constant relative movement with one another.

45. The control system of claim 34 wherein said compressor is a scroll compressor.

46. The control system of claim 44 wherein said compressor is a scroll compressor and said two mechanical elements are scroll members.

47. The control system of claim 34 wherein said controller is coupled to said compressor such that said compressor selectively alternates between said first and second states at said cycle time.

48. The control system of claim 34 wherein said controller produces a control signal that cycles at a cycle time at least four times shorter than the time constant of the load.