Three-phase detection module

1. A method comprising:

receiving N power signals, each having a different one of N phases, over N power supply lines that supply power to a motor, wherein N is an integer greater than two;

using a first isolator, selectively activating a first switch to allow a first current to flow from a first one of the N power supply lines to a second one of the N power supply lines;

using a second isolator, generating a signal based on the first current; and

selectively generating a phase failure signal when the signal is less than a predetermined threshold,

wherein the first isolator includes a first optocoupler,

wherein activating the first switch using the first isolator includes supplying current to a light emitter of the first optocoupler,

wherein the second isolator includes a second optocoupler, and

wherein generating the signal includes supplying a total current including the first current to a light emitter of the second optocoupler.

2. The method of claim 1 further comprising controlling the motor based on the phase failure signal.

3. The method of claim 2 further comprising halting operation of the motor in response to the phase failure signal being generated.

4. The method of claim 1 further comprising activating the first switch for a predetermined period of time based on a duration of one cycle of one of the N power signals.

5. The method of claim 1 further comprising:

selectively activating a second switch to allow a second current to flow from the second one of the N power supply lines to a third one of the N power supply lines; and

selectively activating a third switch to allow a third current to flow from the third one of the N power supply lines to the first one of the N power supply lines.

6. The method of claim 5 wherein:

the second switch includes a third optocoupler;

the third switch includes a fourth optocoupler;

activating the second switch includes supplying current to a light emitter of the third optocoupler; and

activating the third switch includes supplying current to a light emitter of the fourth optocoupler.

7. The method of claim 6 wherein the total current includes the first current, the second current, and the third current.

8. The method of claim 5 further comprising, in response to activating one of the first, second, and third switches, deactivating remaining ones of the switches.

9. The method of claim 8 further comprising sequentially activating the first, second, and third switches.

10. The method of claim 5 further comprising generating the signal based on the first, second, and third currents.

11. The method of claim 10 wherein the signal is proportional to a sum of the first, second, and third currents.

12. The method of claim 5 wherein the first, second, and third currents are zero when the first, second, and third switches, respectively, are deactivated.

13. The method of claim 5 further comprising generating the phase failure signal in response to a peak value of the signal being less than a predetermined threshold at a time when one of the first, second, and third switches is activated.

14. The method of claim 13 further comprising generating the phase failure signal in response to the peak value of the signal over a predetermined period being less than the predetermined threshold.

15. The method of claim 5 further comprising:

determining a first peak value of the signal when the first switch is activated;

determining a second peak value of the signal when the second switch is activated;

determining a third peak value of the signal when the third switch is activated; and

generating a phase imbalance signal in response to a difference between any of the first, second, and third peak values being greater than a predetermined limit.

16. A method comprising:

receiving N power signals, each having a different one of N phases, over N power supply lines, wherein N is an integer greater than two;

selectively activating a first switch to allow a first current to flow from a first one of the N power supply lines to a second one of the N power supply lines;

generating a signal based on the first current;

selectively generating a phase failure signal when the signal is less than a predetermined threshold; and

activating the first switch for a predetermined period of time based on a duration of one cycle of one of the N power signals,

wherein the predetermined period is equal to the duration plus a predetermined value.

17. A method comprising:

receiving N power signals, each having a different one of N phases, over N power supply lines, wherein N is an integer greater than two;

selectively activating a first switch to allow a first current to flow from a first one of the N power supply lines to a second one of the N power supply lines;

generating a signal based on the first current;

selectively generating a phase failure signal when the signal is less than a predetermined threshold;

selectively activating a second switch to allow a second current to flow from the second one of the N power supply lines to a third one of the N power supply lines;

selectively activating a third switch to allow a third current to flow from the third one of the N power supply lines to the first one of the N power supply lines;

activating the first switch;

comparing the signal to a second predetermined threshold while the first switch is activated;

after the signal exceeds the second predetermined threshold, alternately activating the second switch and the third switch;

comparing the signal to the second predetermined threshold while the second switch is activated;

comparing the signal to the second predetermined threshold while the third switch is activated; and

generating a phase reversal signal in response to detecting the signal exceeding the second predetermined threshold while the third switch is activated prior to detecting the signal exceeding the second predetermined threshold while the second switch is activated.

18. A method comprising:

receiving N power signals, each having a different one of N phases, over N power supply lines, wherein N is an integer greater than two;

selectively activating a first switch to allow a first current to flow from a first one of the N power supply lines to a second one of the N power supply lines;

generating a signal based on the first current;

selectively generating a phase failure signal when the signal is less than a predetermined threshold;

selectively activating a second switch to allow a second current to flow from the second one of the N power supply lines to a third one of the N power supply lines;

selectively activating a third switch to allow a third current to flow from the third one of the N power supply lines to the first one of the N power supply lines;

activating the first switch;

comparing the signal to a second predetermined threshold while the first switch is activated;

after the signal exceeds the second predetermined threshold, alternately activating the second switch and the third switch;

determining a first time at which the signal exceeds the second predetermined threshold while the second switch is activated;

determining a second time at which the signal exceeds the second predetermined threshold while the third switch is activated; and

generating a phase reversal signal in response to the first time being later than the second time.