System and method for detecting phase loss and diagnosing DC link capacitor health in an adjustable speed drive

1. A system for detecting input phase loss in an adjustable speed drive (ASD) comprising:

an input unit to detect operating data from the ASD, wherein the operating data comprises a DC link current of the ASD;

a state observer adapted to receive the operating data from the input unit and extract a DC link capacitor current of the ASD using the DC link current; and

a controller programmed to:

compare the extracted DC link capacitor current to a predetermined fault range; and

generate a fault indication of an input phase loss if the extracted DC link capacitor current is within the predefined fault range.

2. The system of claim 1 wherein the state observer is further adapted to extract at least one harmonic component of the DC link capacitor current; and

wherein the controller is further programmed to:

compare the at least one harmonic component to the predefined fault range; and

generate the fault indication based on the comparison.

3. The system of claim 2 wherein the controller is further programmed to:

compare at least one of an amplitude of a second harmonic component of the DC link capacitor current and an amplitude of a sixth harmonic component of the DC link capacitor current to the predefined fault range; and

generate the fault indication if at least one of the amplitude of the second harmonic component and the amplitude of the sixth harmonic component is within the predefined fault range.

4. The system of claim 1 wherein the input unit comprises:

a sensor configured to measure current of a shunt resistor of the ASD; and

a processor programmed to calculate the DC link current using the measured current.

5. The system of claim 1 wherein the input unit comprises at least one of a voltage sensor and a current sensor coupled to the ASD; and

wherein the input unit is configured to determine the DC link current based on signals from at least one of the voltage sensor and the current sensor.

6. The system of claim 1 further comprising a fault alert system configured to issue at least one of an audible warning and a visual warning if the fault indication is generated.

7. The system of claim 1 wherein the controller is further programmed to shutdown the ASD if the fault indication is generated.

8. The system of claim 1 further comprising:

at least one backup DC link capacitor positioned within the ASD such that the at least one backup DC link capacitor is selectively operable in parallel with the DC link capacitor; and

wherein the controller is further programmed to activate the at least one backup DC link capacitor such that the at least one backup DC link capacitor operates in parallel with the DC link capacitor if the fault indication is generated.

9. The system of claim 1 wherein the controller is further programmed to:

calculate an estimated lifespan of the DC link capacitor based on the estimated DC link capacitor current; and

output the estimated lifespan to an operator.

10. The system of claim 9 wherein the processor is configured to calculate the estimated lifespan of the DC link capacitor using a capacitor power loss, a capacitor hot spot temperature, a capacitor ambient temperature, and a capacitor thermal resistance.

11. A method for detecting a phase loss in an adjustable speed AC drive comprising:

identifying a DC link current of the adjustable speed AC drive;

providing a state observer having a state space model representation of the adjustable speed AC drive;

inputting the identified DC link current into the state observer;

extracting a DC link capacitor current of the adjustable speed AC drive using the state observer;

comparing at least one component of the DC link capacitor current to a predefined fault range; and

outputting a phase loss indicator if the at least one component of the DC link capacitor current is within the predefined fault range.

12. The method of claim 11 wherein identifying the DC link current comprises one of:

determining the DC link current based on signals received from at least one of a voltage sensor and a current sensor operatively coupled to the adjustable speed AC drive; and

measuring current of a shunt resistor of the adjustable speed AC drive using a shunt sensor operatively coupled to the adjustable speed AC drive.

13. The method of claim 11 further comprising:

comparing a second harmonic component of the DC link capacitor current to the predetermined fault range; and

outputting the phase loss indicator if the second harmonic component of the DC link capacitor current is within the predefined fault range.

14. The method of claim 11 further comprising:

comparing a sixth harmonic component of the DC link capacitor current to the predetermined fault range; and

outputting the phase loss indicator if the sixth harmonic component of the DC link capacitor current is within the predefined fault range.

15. The method of claim 11 further comprising calculating an estimated lifespan of the DC link capacitor using the extracted DC link capacitor current.

16. The method of claim 11 wherein outputting the phase loss indicator further comprises generating at least one of an audible alarm and a visual alarm.

17. A non-transitory computer readable storage medium having stored thereon a computer program comprising instructions which, when executed by at least one processor, cause the at least one processor to:

acquire a DC link current of an adjustable speed drive (ASD);

transmit the DC link current to a state observer formulated to represent the ASD;

extract at least one component of a DC link capacitor current of the ASD from the state observer using the DC link current, wherein extracting the at least one component comprises extracting at least one of a second harmonic component of the DC link capacitor current and a sixth harmonic component of the DC link capacitor current;

compare the amplitude of the at least one extracted component of the DC link capacitor current to a fault range; and

if the amplitude of the at least one extracted component of the DC link capacitor current is within the fault range, generate an indication of a phase loss.

18. The computer readable storage medium of claim 17 wherein the instructions further cause the at least one processor to calculate a predicted lifespan of a DC link capacitor using the at least one extracted component of the DC link capacitor current.

19. The computer readable storage medium of claim 17 wherein the instructions further cause the at least one processor to shutdown the ASD if the amplitude of the at least one extracted component of the DC link capacitor current is within the fault range.

20. The computer readable storage medium of claim 17 wherein the instructions further cause the at least one processor to activate at least one backup DC link capacitor if the amplitude of the at least one extracted component of the DC link capacitor current is within the fault range.