Method and apparatus for detecting surge in centrifugal compressors driven by electric motors

• US 4,581,900 A
• Filed: 12/24/1984
• Issued: 04/15/1986
• Est. Priority Date: 12/24/1984
• Status: Expired due to Term

• Current Assignee: York International Corporation (Johnson Controls International plc)
• Original Assignee: BorgWarner Incorporated
• Inventors: Hagerman, Robert T., Lowe, Madeleine M.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US06/685,686
• Time in Patent Office: 477 Days
• Field of Search: 62/129, 62/126, 62/203, 62/204, 62/208, 62/209, 62/210, 62/215, 62/217, 62/226, 62/228.1, 62/228.3, 62/228.4, 62/228.5, 62/230, 415/17, 415/27, 415/28, 417/19, 417/20, 417/26, 417/43, 417/45
• US Class Current: 62/228.1
• CPC Class Codes: F04D 27/001 Testing thereof; Determination or simulation of flow characteristics; Stall or surge detection, e.g. condition monitoring
• CPC Class Codes: F04D 27/0284 Conjoint control of two or more different functions
• CPC Class Codes: F25B 1/053 of turbine type
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities
• CPC Class Codes: H02H 7/0854 responsive to rate of change of current, couple or speed, e.g. anti-kickback protection H02H7/0851 takes precedence

Abstract

A surge detection apparatus for use in a refrigeration system having a centrifugal compressor driven by an electric motor includes a first pressure transducer for sensing a condenser pressure and a second pressure transducer for sensing an evaporator pressure. A first bandpass digital filter responsive to the condenser pressure and the evaporator pressure is provided for generating a first signal representative of the rate of change of the pressure developed across the compressor. A current transformer is used to sense a current in the electric motor driving the compressor. A second bandpass digital filter responsive to the motor current is provided for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor. A third signal representative of a differential pressure threshold and a fourth signal representative of a first motor current threshold and a second motor current threshold are provided. A computing device responsive to the first through fourth signals indicates when a valid surge is occurring in the compressor.

Claims

1. A surge detection apparatus for use in a refrigeration system having a centrifugal compressor driven by an electric motor comprising:

means for sensing a condenser pressure;

means for sensing an evaporator pressure;

means responsive to said condenser pressure and said evaporator pressure for generating a first signal representative of the rate of change of the pressure developed across the compressor;

means for sensing a current in the electric motor driving the compressor;

means responsive to said motor current for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor;

means for generating a third signal representative of a differential pressure threshold;

means for generating a fourth signal representative of a first motor current threshold and a second motor current threshold; and

computing means responsive to said first through fourth signals for indicating when a valid surge is occurring in the compressor.

2. A surge detection apparatus as claimed in claim 1, wherein said condenser pressure sensing means comprises a first pressure transducer.

3. A surge detection apparatus as claimed in claim 1, wherein said evaporator pressure sensing means comprises a second pressure transducer.

4. A surge detection apparatus as claimed in claim 1, wherein said means for generating the first signal comprises a low-pass filter coupled to said condenser pressure sensing means to produce a condenser pressure signal, a second low-pass filter coupled to said evaporator pressure sensing means to produce an evaporator pressure signal, means for subtracting the evaporator pressure signal from the condenser pressure signal and a bandpass digital filter coupled to said subtracting means for generating the first signal.

5. A surge detection apparatus as claimed in claim 1, wherein said current sensing means comprises a current transformer.

6. A surge detection apparatus as claimed in claim 1, wherein said means for generating the second signal comprises a third low-pass filter coupled to said current sensing means to produce a motor current signal and a second bandpass digital filter responsive to said motor current signal for generating said second signal.

7. A surge detection apparatus as claimed in claim 1, wherein the third signal representative of the differential pressure threshold is varied dependent upon the compressor load.

8. A surge detection apparatus as claimed in claim 1, wherein the fourth signal representative of the first motor current threshold and the second motor current threshold is varied dependent upon the compressor load.

9. A surge detection apparatus as claimed in claim 1, wherein said computing means includes means for comparing said first signal representative of the rate of change of the pressure developed across the compressor against said third signal representative of the differential pressure threshold and for comparing said second signal representative of the rate of change of the RMS motor current against the fourth signal representative of the first motor current threshold and the second motor current threshold, said computing means indicating that a valid surge is occurring when the differential pressure threshold and the first motor current threshold are both exceeded and the second motor current threshold is exceeded within a pre-selected time interval.

10. A surge detection apparatus for use in a refrigeration system having a centrifugal compressor driven by an electric motor comprising:

means for sensing a condenser pressure;

means for sensing an evaporator pressure;

a first bandpass digital filter responsive to said condenser pressure and said evaporator pressure for generating a first signal representative of the rate of change of the pressure developed across the compressor;

means for sensing a current in the electric motor driving the compressor;

a second bandpass digital filter responsive to said motor current for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor;

means for generating a third signal representative of a differential pressure threshold;

means for generating a fourth signal representative of a first motor current threshold and a second motor current threshold; and

computing means responsive to said first through fourth signals for indicating when a valid surge is occurring in the compressor.

11. A surge detection apparatus as claimed in claim 10, wherein said condenser pressure sensing means comprises a first pressure transducer.

12. A surge detection apparatus as claimed in claim 10, wherein said evaporator pressure sensing means comprises a second pressure transducer.

13. A surge detection apparatus as claimed in claim 10, wherein said current sensing means comprises a current transformer.

14. A surge detection apparatus as claimed in claim 10, wherein said computing means includes means for comparing said first signal representative of the rate of change of the pressure developed across the compressor against the third signal representative of the differential pressure threshold and for comparing said second signal representative of the rate of change of the RMS motor current against said fourth signal representative of the first motor current threshold and the second motor current threshold, said computing means indicating that a valid surge is occurring when both the differential pressure threshold and the first motor current threshold are exceeded and the second motor current threshold is exceeded within a pre-determined time interval.

15. A method for detecting surge in a refrigeration system having a centrifugal compressor driven by an electric motor comprising the steps of:

sensing a condenser pressure;

sensing an evaporator pressure;

generating a first signal representative of the rate of change of the pressure developed across the compressor in response to the condenser pressure and the evaporator pressure;

sensing a current in the electric motor driving the compressor;

generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor in response to the motor current;

generating a third signal representative of a differential pressure threshold;

generating a fourth signal representative of a first motor current threshold and a second motor current threshold; and

indicating when a valid surge is occurring in the compressor in response to the first through fourth signals.

16. A method for detecting surge as claimed in claim 15, further comprising the step of varying the differential pressure threshold dependent upon the compressor load.

17. A method for detecting surge as claimed in claim 15, further comprising the step of varying the first motor threshold and the second motor threshold dependent upon the compressor load.

18. A method for detecting surge as claimed in claim 15, wherein the step of generating the first signal includes a first bandpass digital filter.

19. A method for detecting surge as claimed in claim 15, wherein the step of generating the second signal includes a second bandpass digital filter.

20. A method for detecting surge as claimed in claim 15, further comprising the steps of comparing the first signal representative of the rate of change of the pressure developed across the compressor against the third signal representative of the differential pressure threshold, comparing the second signal representative of the rate of the RMS motor current against the fourth signal representative of the first motor current threshold and the second motor current threshold, and indicating that a valid surge is occurring when both the differential pressure threshold and the first motor current threshold are exceeded and the second motor current threshold is exceeded within a pre-determined time interval.

21. A surge detection apparatus for detecting surge in a compressor of a compressor-driven system comprising:

means for generating a first signal representative of the rate of change of the pressure developed across the compressor;

means for sensing a current in an electric motor driving the compressor;

means responsive to said motor current for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor;

means for generating a third signal representative of a differential pressure threshold;

means for generating a fourth signal representative of a first motor current threshold and a second motor current threshold; and

means responsive to said first through fourth signals for indicating when a valid surge is occurring in the compressor.