System and method of preventing a surge condition in a vane-type compressor

• US 5,873,257 A
• Filed: 09/11/1997
• Issued: 02/23/1999
• Est. Priority Date: 08/01/1996
• Status: Expired due to Term

• Current Assignee: Smart Power Systems Incorporated
• Original Assignee: Smart Power Systems Incorporated
• Inventors: Peterson, Gregory E.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US08/927,174
• Time in Patent Office: 530 Days
• Field of Search: 62/228.1, 62/228.4, 62/228.5, 62/126, 62/129, 62/209, 62/228.3, 62/181, 62/180, 62/183, 62/184
• US Class Current: 62/180
• CPC Class Codes: F04D 27/0261 by varying driving speed
• CPC Class Codes: F25B 1/053 of turbine type
• CPC Class Codes: F25B 49/022 Compressor control arrangements
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A method of preventing compressor surge in an air conditioning system comprises: 1) determining the refrigerant flow rate at the compressor; 2) determining the input pressure and output pressure at the compressor; 3) determining the pressure ratio (output pressure/input pressure) at the compressor; 4) defining a surge limit based upon the pressure ratio and the refrigerant flow rate; 5) processing system operational inputs including motor speeds and air conditioning pressures; and 6) sending control signals to the air conditioning system to control the refrigerant flow rate and the pressure ratio in a manner to prevent compressor operation at the defined surge limit and to maximize compressor efficiency during transitional periods. An air conditioning system is also provided, as well as an article of manufacture for use with the system for preventing compressor surge.

Claims

1. A method of preventing compressor surge in an air conditioning system, including a centrifugal compressor having an impeller with fixed inlet vanes, the compressor operating at a pressure ratio (P_O /P_I) defined by an output pressure (P_O) divided by an input pressure (P_I) and having a refrigerant flow rate (M), and operating at a compressor motor speed;

a condenser in fluid communication with the compressor, the condenser having a condenser fan;

an expansion device in fluid communication with the condenser; and

an evaporator in fluid communication with the expansion device and including an evaporator fan;

the method comprising;

determining the refrigerant flow rate (M);

determining the input pressure (P_I) and output pressure (P_O);

determining the pressure ratio (P_O /P_I);

defining a surge limit (SL) based upon the pressure ratio (P_O /P_I) and the refrigerant flow rate (M) and

sending control signals to adjust the compressor motor speed and condenser fan speed to control the refrigerant flow rate (M) and the pressure ratio to prevent compressor operation at the defined surge limit.

2. The method of claim 1, further comprising the steps of:

defining a control path for the refrigerant flow rate and pressure ratio to prevent compressor operation at the surge limit; and

sending control signals to the compressor and condenser fan to operate the system in accordance with the defined control path.

3. The method of claim 2, wherein said step of defining a surge limit comprises defining a normal surge limit (SL_norm) suitable for limiting compressor operation during relatively small evaporator load changes.

4. The method of claim 2, wherein said step of defining a surge limit comprises defining a maximum surge limit (SL_max) suitable for limiting compressor operation during relatively large evaporator load changes.

5. The method of claim 2, wherein said step of defining a control path further comprises:

maintaining a constant compressor pressure ratio (P_O /P_I); and

varying the compressor speed while the compressor pressure ratio (P_O /P_I) remains constant in a manner to define a control path.

6. The method of claim 2, wherein said step of defining a control path comprises:

maintaining a constant compressor speed; and

varying the pressure ratio and the refrigerant flow rate in a manner to define a control path, said varying step being achieved by said sending of control signals to adjust the condenser fan speed.

7. The method of claim 2, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio and refrigerant flow rate in a manner to define a control path, said varying step being achieved by said sending of control signals to adjust the compressor motor speed and condenser fan speed.

8. The method of claim 2, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio and refrigerant flow rate in a linear fashion to define a control path resulting in peak compressor adiabatic efficiency throughout the flow rate change, said varying step being achieved by said sending of control signals to adjust the compressor motor speed and condenser fan speed.

9. The method of claim 2, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio, and refrigerant flow rate in a non-linear fashion to define a control path maximizing transition time at peak compressor adiabatic efficiency while maintaining peak compressor adiabatic efficiency throughout the flow rate change, said varying step being achieved by said sending of control signals to adjust the compressor motor speed and condenser fan speed.

10. An air conditioning system, comprising:

a centrifugal compressor having an impeller with fixed vanes, said compressor operating at a pressure ratio (P_O /P_I) defined by an output pressure (P_O) divided by an input pressure (P_I) and having a refrigerant flow rate (M), and operating at a compressor motor speed;

a condenser in fluid communication with said compressor, said condenser having a condenser fan operating at a condenser fan speed;

an expansion device in fluid communication with said condenser;

an evaporator in fluid communication with said expansion device; and

a processor in electrical communication with said compressor, said expansion device, said condenser fan and said impeller, said processor being operative to limit compressor operation to predefined limits by sending control signals to adjust the compressor motor speed and condenser fan speed to prevent compressor surge and to define control paths during refrigerant flow rate changes.

11. The air conditioning system of claim 10, wherein the processor is further operative to:

determine the refrigerant flow rate;

determine the input pressure (P_I) and output pressure (P_O);

determine the pressure ratio (P_O /P_I)

define a surge limit (SL) based upon the pressure ratio (P_O /P_I) and the refrigerant flow rate (M); and

send control signals to the compressor and condenser fan to control the refrigerant flow rate (M) and the pressure ratio to prevent compressor operation at the defined surge limit.

12. The air conditioning system of claim 11, wherein the processor is further operative to:

define a control path for the refrigerant flow rate and pressure ratio to prevent compressor operation at the surge limit; and

send control signals to the compressor and condenser fan to operate the system in accordance with the defined control path.

13. The air conditioning system of claim 12, wherein the processor is further operative to define a normal surge limit (SL_norm) suitable for limiting compressor operation during relatively small evaporator load changes.

14. The air conditioning system of claim 12, wherein the processor is further operative to define a surge limit (SL_max) suitable for limiting compressor operation during relatively large evaporator load changes.

15. The air conditioning system of claim 12, wherein the processor is further operative to:

maintain a constant compressor pressure ratio (P_O /P_I); and

vary the compressor speed while the compressor pressure ratio (P_O /P_I) remains constant in a manner to define a control path.

16. The air conditioning system of claim 12, wherein the processor is further operative to:

maintain a constant compressor speed; and

vary the pressure ratio and the refrigerant flow rate by sending said control signals to adjust the condenser fan speed in a manner to define a control path.

17. The air conditioning system of claim 12, wherein the processor is further operative to vary the compressor speed, pressure ratio and refrigerant flow rate in a manner to define a control path by sending said control signals to adjust the compressor motor speed and condenser fan speed.

18. The air conditioning system of claim 12, wherein the processor is further operative to vary the compressor speed, pressure ratio and refrigerant flow rate by sending said control signals to adjust the compressor motor speed and condenser fan speed to define a linear control path resulting in peak compressor adiabatic efficiency throughout the flow rate change.

19. The air conditioning system of claim 12, wherein the processor is further operative to vary the compressor speed, pressure ratio, and refrigerant flow rate by sending said control signals to adjust the compressor motor speed and condenser fan speed to define a non-linear control path maximizing transition time at peak compressor adiabatic efficiency while maintaining peak compressor adiabatic efficiency throughout the flow rate change.

20. An article of manufacture used to direct a computer or other like programmable apparatus to control operation of an air conditioning system, including a compressor having an impeller with fixed vanes, said compressor operating at a pressure ratio (P_O /P_I) defined by an output pressure (P_O) divided by an input pressure (P_I) and having a refrigerant flow rate (M), and operating at a compressor motor speed;

a condenser in fluid communication with said compressor, said condenser having a condenser fan;

an expansion device in communication with said condenser; and

an evaporator in fluid communication with said expansion device;

the article of manufacture comprising;

a computer-readable storage medium; and

a computer program represented as computer-readable data on the computer-readable storage medium, the computer program directing the computer to perform the steps of;

determining the refrigerant flow rate (M);

determining the input pressure (P_I) and output pressure (P_O);

determining the pressure ratio (P_O /P_I);

defining a surge limit (SL) based upon the pressure ratio (P_O /P_I) and the refrigerant flow rate (M); and

sending control signals to adjust the compressor motor speed and condenser fan speed to control the refrigerant flow rate (M) and the pressure ratio to prevent compressor operation at the defined surge limit.

21. The article of manufacture of claim 20, wherein the computer program directs the computer to perform the further steps of:

defining a control path for the refrigerant flow rate and pressure ratio to prevent compressor operation at the surge limit; and

sending control signals to the compressor and condenser fan to operate the system in accordance with the defined control path.

22. The article of manufacture of claim 21, wherein the step of defining a surge limit comprises defining a normal surge limit (SL_norm) suitable for limiting compressor operation during relatively small evaporator load changes.

23. The article of manufacture of claim 21, wherein the step of defining a surge limit comprises defining a maximum surge limit (SL_max) suitable for limiting compressor operation during relatively large evaporator load changes.

24. The article of manufacture of claim 21, wherein the step of defining a control path further comprises:

maintaining a constant compressor pressure ratio (P_O /P_I); and

varying the compressor speed while the compressor pressure ratio (P_O /P_I) remains constant in a manner to define a control path.

25. The article of manufacture of claim 21, wherein the step of defining a control path comprises:

maintaining a constant compressor speed; and

varying the pressure ratio and the refrigerant flow rate by sending said control signals to adjust the condenser fan speed in a manner to define a control path.

26. The article of manufacture of claim 21, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio and refrigerant flow rate by sending said control signals to adjust the compressor motor speed and condenser fan speed in a manner to define a control path.

27. The article of manufacture of claim 21, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio and refrigerant flow rate by sending said control signals to adjust the compressor motor speed and condenser fan speed to define a linear control path resulting in peak compressor adiabatic efficiency throughout the flow rate change.

28. The article of manufacture of claim 21, wherein said step of defining a control path comprises:

varying the compressor speed, pressure ratio, and refrigerant flow rate by sending said control signals to adjust the compressor motor speed and condenser fan speed to define a non-linear control path maximizing transition time at peak compressor adiabatic efficiency while maintaining peak compressor adiabatic efficiency throughout the flow rate change.