CAVITATION DETECTION DEVICE AND METHOD

• US 20070017284A1
• Filed: 07/25/2005
• Published: 01/25/2007
• Est. Priority Date: 07/25/2005
• Status: Active Grant

• Current Assignee: Nidec Motor Corporation (Nidec Corporation)
• Original Assignee: Emerson Electric Company
• Inventors: Sadasivam, Vinodkumar
• Granted Patent: US 7,637,723 B2
• Time in Patent Office: Days
• US Class Current: 73/168
• CPC Class Codes: F04D 15/0088 Testing machines
• CPC Class Codes: F04D 29/669 especially adapted for liquid pumps F04D29/18 takes precedence

Abstract

Cavitation detection systems and methods include generating a signal representing the power factor of a motor driving a pump, analyzing the power factor signal and determining the presence of cavitation based on the analysis of the power factor signal. The power factor may be estimated using various estimation schemes. Analyzing the signal includes filtering the power factor signal.

Claims

1. A method for sensing cavitation in a pump driven by a motor, comprising:

generating a power factor signal;

analyzing the power factor signal; and

determining the presence of cavitation based on the analysis of the power factor signal.

2. The method of claim 1, further comprising determining the severity of the cavitation based on the analysis of the power factor signal.

3. The method of claim 1, wherein determining the presence of cavitation includes filtering the power factor signal.

4. The method of claim 1, wherein determining the presence of cavitation includes determining the presence of noise in the power factor signal.

5. The method of claim 1, wherein determining the presence of cavitation includes compensating for a loss of flow.

6. The method of claim 1, wherein generating a power factor signal includes estimating the power factor signal.

7. The method of claim 6, wherein estimating the power factor signal includes:

sensing a zero-cross angle of a current waveform applied to phase windings of the motor;

computing the difference between the sensed current zero-cross angle and a predetermined demand voltage angle.

8. The method of claim 7 wherein sensing the zero-cross angle of the current waveform applied to the phase windings comprises sensing the zero-cross angle of the current waveform applied to one of a plurality of phase windings.

9. The method of claim 6, wherein estimating the power factor signal includes:

applying desired voltage amplitude and frequency signals to the motor;

receiving an indication of current applied to phase windings of the motor;

estimating the voltage applied the phase windings of the motor; and

wherein the power factor is estimated based on the phase winding current, the estimated voltage applied to the phase windings and the voltage amplitude and frequency signals.

10. A pump system, comprising:

a motor including a stator, a rotor situated relative to the stator to rotate relative to the stator, and a plurality of phase windings situated within the stator;

a power source connected to the windings to output AC power thereto; and

a controller connected to the power source, the controller programmed to detect cavitation by analyzing a power factor signal.

11. The pump system of claim 10, wherein the motor is an induction motor.

12. The pump system of claim 10, wherein the power factor signal represents an estimated power factor value.

13. The pump system of claim 11, wherein the power factor value is estimated based on the AC power output to the windings.

14. The pump system of claim 13, wherein the power source includes an inverter having a DC bus with positive and negative lines and a plurality of inverter legs connected between the positive and negative lines corresponding to the phase windings, and wherein the voltage applied to each of the phase windings is estimated further in response to the DC bus voltage and the inverter leg current for the corresponding phase winding.

15. The pump system of claim 14, further comprising:

each inverter leg including first and second switching devices connected between the positive and negative lines of the DC bus;

a resistor connected between one of the first and second switching devices and one line of the DC bus; and

a current zero-cross detection circuit connected to receive a signal from the resistor and output an indication of the current zero-crossing to the controller.

16. The pump system of claim 10, wherein the controller comprises a DSP.

17. A cavitation detection system, comprising:

a controller providing control signals to a power source for selectively energizing phase windings of a motor driving a pump;

the controller analyzing a power factor signal and detecting cavitation in response thereto.

18. The cavitation detection system of claim 17, wherein the power factor signal represents an estimated power factor value.

19. The cavitation detection system of claim 18, wherein the controller estimates the power factor value based on the AC power output to the windings.

20. The cavitation detection system of claim 19, wherein the power source includes an inverter having a DC bus with positive and negative lines and a plurality of inverter legs connected between the positive and negative lines corresponding to the phase windings, and wherein the voltage applied to each of the phase windings is estimated further in response to the DC bus voltage and the inverter leg current for the corresponding phase winding.

21. The cavitation detection system of claim 17, wherein the controller comprises a DSP.