Compressor protection and grid fault detection device

• US 8,045,302 B2
• Filed: 02/19/2009
• Issued: 10/25/2011
• Est. Priority Date: 02/20/2008
• Status: Active Grant

• Current Assignee: Copeland Corporation LLC (Emerson Electric Company)
• Original Assignee: Emerson Climate Technologies Incorporated (Emerson Electric Company)
• Inventors: Ramayya, George, Jayanth, Nagaraj
• Primary Examiner(s): Leykin; Rita
• Application Number:
  US12/388,972
• Publication Number:
  US 20090225479A1
• Time in Patent Office: 978 Days
• Field of Search: 318/432, 318/434, 324/500, 324/511, 324/512, 324/522, 361/22, 361/30, 361/93.1, 361/31, 361/93.5, 361/93.6, 361/93.9, 361/93.8
• US Class Current: 361/30
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 2600/0251 with on-off operation
• CPC Class Codes: F25B 2700/13 Mass flow of refrigerants
• CPC Class Codes: F25B 2700/151 of the compressor motor
• CPC Class Codes: F25B 2700/2115 of a compressor or the drive means therefor
• CPC Class Codes: F25B 49/022 Compressor control arrangements
• CPC Class Codes: G01R 19/10 Measuring sum, difference or ratio
• CPC Class Codes: G01R 19/16538 in AC or DC supplies G01R19/16519 and G01R19/16528 take precedence
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: H02H 7/08 for dynamo-electric motors
• CPC Class Codes: H02H 7/09 against over-voltage; against reduction of voltage; against phase interruption
• CPC Class Codes: H02H 7/20 for electronic equipment for converters H02H7/10; for electric measuring instruments G01R1/36; for dc voltage or current semiconductor regulators G05F1/569; for amplifiers H03F1/52; for electronic switching circuits H03K17/08
• CPC Class Codes: H02P 29/0241 the fault being an overvoltage

Abstract

A compressor monitoring system includes current and voltage monitors, current and voltage averaging modules, a control module, and a switch. The current monitor measures a current drawn by a motor of a compressor. The current averaging module generates first and second average current values based on the current measured by the current monitor. The voltage monitor measures a utility power voltage. The voltage averaging module generates first and second average voltage values based on the voltage measured by the voltage monitor. The control module selectively generates a fault signal when a first ratio is greater than a first predetermined threshold and a second ratio is less than a second predetermined threshold. The first ratio is based on the first and second average current values. The second ratio is based on the first and second average voltage values. The switch deactivates the motor when the fault signal is generated.

Claims

1. A compressor monitoring system comprising:

a current monitor that measures a current drawn by a motor of a compressor;

a current averaging module that generates first and second average current values based on the current measured by the current monitor;

a voltage monitor that measures a utility power voltage;

a voltage averaging module that generates first and second average voltage values based on the voltage measured by the voltage monitor; and

a control module that selectively generates a fault signal when a first ratio is greater than a first predetermined threshold and a second ratio is less than a second predetermined threshold, wherein the first ratio is based on the first and second average current values, and wherein the second ratio is based on the first and second average voltage values.

2. The compressor monitoring system of claim 1 wherein the first ratio is based on the second average current value divided by the first average current value, wherein the second ratio is based on the second average voltage value divided by the first average voltage value, and wherein the second average current and voltage values are generated after the first average current and voltage values.

3. The compressor monitoring system of claim 2 wherein the first predetermined threshold is approximately 2 and wherein the second predetermined threshold is approximately 0.8.

4. The compressor monitoring system of claim 1 wherein the current averaging module generates each of the first and second average current values by averaging M contiguous current values from the current monitor, wherein the voltage averaging module generates each of the first and second average voltage values by averaging N contiguous voltage values from the voltage monitor, wherein M and N are integers greater than one.

5. The compressor monitoring system of claim 4 wherein M and N are equal to eight.

6. The compressor monitoring system of claim 4 wherein each of the current values from the current monitor corresponds to a period of a periodic input power signal, wherein each of the voltage values from the voltage monitor corresponds to the period of the periodic input power signal, wherein the second average current and voltage values are generated P periods after the first average current and voltage values, and wherein P is equal to one of M and N.

7. The compressor monitoring system of claim 1 wherein the control module determines an operating current threshold and generates the fault signal when current values from the current monitor exceed the operating current threshold for a predetermined length of time.

8. The compressor monitoring system of claim 7 wherein the control module sets the operating current threshold based on a peak startup current.

9. The compressor monitoring system of claim 8 wherein the control module determines the peak startup current based on a maximum one of the current values during a startup period of time after the motor starts, wherein the startup period of time is approximately 200 ms, and wherein the predetermined length of time is approximately 800 ms.

10. The compressor monitoring system of claim 9 wherein the control module generates the fault signal when the current value at an end of the startup period of time exceeds the operating current threshold.

11. The compressor monitoring system of claim 8 wherein the control module determines the operating current threshold based on a product of the peak startup current and approximately 0.4.

24. The compressor monitoring system of claim 1 further comprising a switch that deactivates the motor when the fault signal is generated.

12. A method performed by a compressor monitoring system, comprising:

measuring a current drawn by a motor of a compressor;

generating first and second average current values based on the measured current;

measuring a utility power voltage;

generating first and second average voltage values based on the measured voltage;

determining a first ratio based on the first and second average current values;

determining a second ratio based on the first and second average voltage values; and

selectively generating a fault signal when the first ratio is greater than a first predetermined threshold and the second ratio is less than a second predetermined threshold.

13. The method of claim 12 further comprising:

determining the first ratio based on the second average current value divided by the first average current value; and

determining the second ratio based on the second average voltage value divided by the first average voltage value, wherein the second average current and voltage values are generated after the first average current and voltage values.

14. The method of claim 13 wherein the first predetermined threshold is approximately 2 and wherein the second predetermined threshold is approximately 0.8.

15. The method of claim 12 further comprising:

generating each of the first and second average current values by averaging M contiguous current values; and

generating each of the first and second average voltage values by averaging N contiguous voltage values, wherein M and N are integers greater than one.

16. The method of claim 15 wherein M and N are equal to eight.

17. The method of claim 15 wherein each of the current values corresponds to a period of a periodic input power signal, wherein the first and second voltage values correspond to the period of the periodic input power signal, wherein the second average current and voltage values are generated P periods after the first average current and voltage values, and wherein P is equal to one of M and N.

18. The method of claim 12 further comprising:

determining an operating current threshold; and

generating the fault signal when the measured current values exceed the operating current threshold for a predetermined length of time.

19. The method of claim 18 further comprising setting the operating current threshold based on a peak startup current.

20. The method of claim 19 further comprising determining the peak startup current based on a maximum one of the current values during a startup period of time after the motor starts, wherein the startup period of time is approximately 200 ms, and wherein the predetermined length of time is approximately 800 ms.

21. The method of claim 20 further comprising generating the fault signal when the measured current value at an end of the startup period of time exceeds the operating current threshold.

22. The method of claim 19 further comprising determining the operating current threshold based on a product of the peak startup current and approximately 0.4.

25. The method of claim 12 further comprising deactivating the motor when the fault signal is generated.

23. A compressor monitoring system comprising:

a current monitor that measures a current drawn by a motor of a compressor;

a voltage monitor that measures a voltage of the motor;

a power factor monitor that calculates a power factor of the motor based on the measured current and the measured voltage and generates power factor values;

an averaging module that generates a first average power factor value based on the power factor values and that later generates a second average power factor value based on the power factor values; and

a control module that selectively generates a fault signal when a ratio is less than a predetermined threshold, wherein the control module calculates the ratio based on the second average power factor value divided by the first average power factor value.